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Practical Navigation for the Modern Boat Owner
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1. Chart Scale Charts vary according to the area that they cover and hence the detail they contain The scale of a chart is given as a ratio one unit of length on the chart represents very many units of length on the Earth s surface So a chart scale of 1 1 000000 means that 1 inch or 1 centimetre on the chart represents 1000000 inches or centimetres on the Earth s surface The scale chosen for use in any particular circumstance depends on the detail required You could not enter a harbour using a 1 1 000000 scale chart you would probably use a chart with a scale of 1 10000 or 1 5000 e A small scale chart covers a large area and has a high scale number say 1 1 000000 one divided by one million is a small number e A large scale chart covers a small area and has a low scale number say 1 5000 one divided by five thousand is a larger number and therefore larger scale Chart scale 24 Our Address on the Earth s Surface Chapter 2 Ideally you would have a small scale chart of your cruising area and large scale charts containing more detail for the harbours and anchorages In fact you may need charts of an intermediate scale as well personally don t buy charts by scale look at individual charts and their detail and buy what want to suit my needs Measuring Latitude and Longitude There will be a grid of latitude and longitude superimposed on the chart This grid will be in degrees and minutes as a
2. Speed over the Ground Speed Through the Water Measuring Speed Through the Water Log Errors 29 30 30 3 3 3 33 35 36 38 38 39 39 50 52 57 I 58 58 58 Contents 7 Depth Sounders 61 How They Work 62 Depth Units 62 Calibration 62 Depth Alarms 63 False Echoes 63 Fishfinders 63 8 Finding Position 65 GPS 65 Other Methods 66 Position Lines 67 Fixing Your Position Using Position Lines 69 Errors in Position Lines 70 How Far Can You See 7 When All Else Fails 72 Chartplotters 73 9 Passage Planning 77 Overview 78 Detailed Plan 79 Just Prior to Departure 80 Passage Planning Procedure 81 Preplan 8 For the Planned Day of Departure 8 Passage Making 81 Passage Grid 86 Approach Spider s Web 86 Compass Rose as a Waypoint 87 Unmarked Danger as a Waypoint 88 Clearing Bearing 88 10 Pilotage 89 Who Does the Piloting 90 Means of Pilotage 90 International System of Buoyage 90 Vil International Buoyage All Areas Planning The Basics of Preparing a Pilot Plan Making a Pilotage Plan Working as a Team Automatic Identification System What is Automatic Identification System How Does AIS Work Class A AIS Class B AIS AIS Displays The AIS Display on a Chartplotter AIS Class B Transceiver 12 Radar How Radar Works Navigation Using Radar Pilotage Using Radar Radar Overlay on a Chart Plotter Setting up Your Radar Radar Used for Collision Avoidance 13 Autopilot
3. Practical Navigation for the Modern Boat Owner PAT MANLEY WILEY 6 NAUTICAL John Wiley amp Sons Ltd Practical Navigation for the Modern Boat Owner Practical Navigation for the Modern Boat Owner PAT MANLEY WILEY 6 NAUTICAL John Wiley amp Sons Ltd Copyright 2008 John Wiley amp Sons Ltd The Atrium Southern Gate Chichester West Sussex PO19 8SQ England Telephone 44 1243 779777 Email for orders and customer service enquiries cs books wiley co uk Visit our Home Page on www wiley com All Rights Reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording scanning or otherwise except under the terms of the Copyright Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd 90 Tottenham Court Road London WIT ALP UK without the permission in writing of the Publisher Requests to the Publisher should be addressed to the Permissions Department John Wiley amp Sons Ltd The Atrium Southern Gate Chichester West Sussex PO19 8SQ England or emailed to permreq wiley co uk or faxed to 44 1243 770620 Designations used by companies to distinguish their products are often claimed as trademarks All brand names and product names used in this book are trade names service marks trademarks or registered trademarks of their respective own
4. the tide is A graphical solution is used to calculate the height of tide at any given time which takes into account any differences in time taken for the tide to rise compared with how long it takes to fall the skew of the tidal curve but doesn t allow for any bumps This method is easy but accurate only for smooth curves see Appendix 3 for full details Secondary Ports The UKHO tidal curves make it very easy to adapt the curve for the standard port into the curve for the secondary port using a graphical solution With practice the procedure is quick and easy although to be honest many yachtsmen are put off using it maybe because they are striving after unnecessary accuracy The French SHOM method allows calculation of tidal heights for secondary ports Most of the others require mental gymnastics if you need to know tidal heights at times other than high or low water For detailed instructions see Appendix 3 Calculating the Depth of Water The principal reason for using tidal height data is to check if the water is deep enough for your boat or that there s sufficient clearance to pass under a bridge or cable You can use electronic tidal curves if you have them that s the easiest way or you ll need to do it all on paper Depth in Which to Anchor It s a good idea to consult the chart for the general depths and to see if there are any rocks or shallow bits but you won t be using chart datum or s
5. 050 true Align grid with latitude or longitude and with green arrows pointing north Measuring direction with a course plotter Outer protractor Parallel Rule Inner protractor Ke aligned with true To use a parallel rule easily there needs to be a compass nea rose on the chart A compass rose is a protractor aligned with true north printed on the chart An inner concentric eo i S protractor aligned with magnetic north may also be shown E j A 4 3 The amount of variation and the year of its validity at that i P Variation with its date point are shown together with the annual change and its of validity and the the annual rate of change direction of change x There are likely to be several compass roses on each chart The variation at each rose may be different Compass rose e Place the edge of the parallel rule along the direction to be measured e Open up the parallel rule until the other edge passes through the centre of the nearest compass rose e If it wouldn t reach far enough walk the rule across the chart until it reaches the centre of the compass rose being careful that its direction isn t altered Align parallel rule A T Magnetic or True Direction with direction anda A gt open it up so that 2 A All paper charts give direction in degrees 1t passes through ore pass rose true You can convert these directions walking it if to magnetic if you w
6. 10 53 BST on 4th July e Look up the times and heights of HW and LW for Portsmouth on 4th July e Apply any correction for local time in this case add 1 hour for BST and write the time of HW in the HW box at the bottom of the curve EEE CE CT all i i PET aa FE tibi a 1 u E a iiir ii ia zi Li i PELE ESSER F275 FREE FEET 7 tees tebe ae sk CEEC EEE HELE 292 FREE gEEE 7 EG EE ECEE RERE EEEE ir a e Fill in the other time boxes along the bottom of the curve e Mark the height of HW on the top tidal HW 1353 UT Ht 4 5metres LW 1917 UT Ht 1 1 metres height scale Tidal data for 4th July Portsmouth Mark the height of LW on the bottom tidal PERSEE height scale LW 0656 uT Ht 0 9 metres Range 3 4 metres e Join these two points with a straight line Se ee Portsmouth e The heights of HW and LW can be ppt fn ttn Ten compared with the heights of MHWS CLELLIVL LE COO and MHWN and of MLWS and MLWN JESSE Sees to see what part of the curve needs tobe F used where there are differences between spring and neap tides ee ee pe Re SS TH Dal iiiikiiiafitai kiii 3 LW a b t i 1 af sil Haw al d a z t LAW Her Coe Fes OS TSE NSF et p353 asy PT eS 757 1855 e Draw a vertical line from the time required on the bottom of the curve 10 53 which equals 3 hours before high Using the tidal curve water until it touches the tidal curve Height of ti
7. I I I i i i i I I J i i i Ha i i sl TENER j K A d i f k ps i i j be p i i O Na K a s f f E E i Se ge l 4 9 j GY gs t p E a s 7 A a a 4 a gt i 1 a Pe Diy A E SON 2 7 i a eT a a a es ee ie ie a e a a a 30 7 age Our Address on the Earth s Surface The Equator Distance and Direction Latitude Direction Greenwich Meridian The Flat Earth Longitude The Spherical Earth and Map Data Our Address Chart Errors Chart Scal International Date Line ah sae Measuring Latitude and Longitude Measurement of Latitude and Longitude Chart Symbols i f you need to find someone you need their address To do this on planet Earth an invisible theoretical grid has been overlaid on the Earth s surface by geographers This grid of Latitude and Longitude allows us to define any point on the Earth s surface with as much accuracy as we wish The Equator The Earth spins on an axis through the North and the South Poles Any circle running around the Earth s maximum circumference is known as a great circle The Equator is a great circle at right angles to the spin axis and equidistant between the poles Latitude Latitude is defined as the angle in degrees between the Equator the centre of the Earth and a point on the Earth s surface If the point is between the Equator and the North Pole it s
8. Mark off the distance travelled through the water in 1 hour from the end of the tidal vector to the ground track line The distance travelled in 1 hour 151 e You now have a vector triangle one side of which has the tidal effect for a given period 1 hour or half an hour the boat speed effect for the same time interval and therefore the third side must represent the distance travelled over the ground for that same time interval e The direction of the boat speed vector from the end of the tide C to where it cuts the ground track at D is the course to steer if there is no leeway Course to steer 165 T 168 M Measure course to Steer When calculating course to steer we will have to steer into wind to make good the course we wish to steer through the water Leeway CTS e If there is any leeway you must steer info wind by the estimated leeway to ensure that the path through the water is in the direction C to D Ground Speed e Measure the length of the ground speed side of the triangle A D This is the distance travelled over the ground in the time interval of the triangle If it s a 1 hour triangle then this is the ground speed If it s a half an hour triangle then this is the distance travelled in half an hour so double it to get the ground speed e Using this ground speed and the distance from your starting point to your destination A B you can work out your estimated ti
9. consider motoring instead of sailing especially if you are short handed and in unfamiliar waters e If the next course is towards a buoy or marker make sure that it s identified properly Pointing in its general direction won t do especially as you will be looking at it from a different perspective Note a feature on the horizon say a tree and relate the position of the buoy with the tree It s three hand width s to the left of that tree sticking above all the others If there s no feature stand behind Keep the buoy aligned with something the helmsman and point to it with your outstretched NAE BAOREN arm over his shoulder to give the same perspective The buoy has moved to port turn to port e At night this is even more important as most of the time the buoy will be invisible Firstly the pilot needs to identify it himself Before you get to the end of this leg use the hand bearing compass on the expected bearing to find the light defining the next leg and then identify its light sequence Now point over the helmsman s shoulder towards the buoy and as the light flashes announce each flash Flash Flash Flash in time with the light This will ensure that the helmsman is seeing the same light as you are e If there s a cross tide asking the helmsman to steer for that buoy is a recipe for disaster Tell the helmsman which way the tide is flowing If it s from port to starboard tell h
10. s likely the light will be visible for only about 10 of the time for 90 of the time it will be invisible Unlit aids to navigation will not be visible at all so IALA System A Starboard hand marks H It Lights any rythm except FI 2 1 G only lit transits are of any use at night Whereas busy commercial ports lend themselves to easy pilotage at night estuaries and havens used mostly by leisure sailors may be difficult or impossible to enter at night International System of Buoyage The International Association of Lighthouse Authorities IALA has standardised the system of buoyage used internationally Owing to a small disagreement there are two systems as follows IALA System A IALA A used throughout most of the world IALA System B IALA B used in the United States of America and those countries which have a close association with the United States of America The difference is the colour of the lateral buoys those marking the edges of a channel 90 IF lit Lights any rythm except Fij2 1 R Fort hand marks IALA System B Starboard hand marks If lit Lights any rythm except FIl2 1 R Port hand marks If Vit Lights any rythm except Fl2 1 G Ce Ce TT Timing Rythm Fl Flashing The number is the number of flashes 0 FI 2 G 5s two green flashes every 5 seconds lf no colour is given colour is white IALA lateral buoyage Pilotage Chapter 10 IALA System
11. CPA and TCPA may be displayed As far as collision avoidance is concerned the important information is CPA and TCPA displayed in the AIS information box From this you can judge what action if any you should take It s worth stating here that your actions Your boat When the cursor is hovered over target a pop up box will appear The target is 2 839 miles from us and the CPA is only 0 64 mile which is uncomfortably close with all the sea room available AlS target information box Target ship a a 2 COG This in not where 5 TA you will meet as this a depends on the 4 speed of each boat With only this information the target could pass ahead collide with you or pass astern are dictated by the International Regulations In this instance the faster ship wiil pass ahead of you for Prevention of Collisions at Sea Colregs 106 Basic AIS display Automatic Identification System Chapter 11 The action to be taken differs if you can or can t see the target visually but as the rules were written long before AIS was conceived Y i i Ta NAME SIMULE it s unclear if rule 19 applies to vessels seen 1 MMSI 100000028 only by AIS rather than only by radar a A e i Normally you can enter a value of CPA oo 086 T at which you would be uncomfortable If a target is predicted to get this close or closer to you the triangle will
12. ES SS SS SSS SS ES SS SS SSS SE eS SSS a ow 30 Autopilots Types of Autopilot Using the Autopilot A n autopilot can reduce the workload on the helmsman and navigator For longer short handed passages it can allow proper time for navigation and pilotage 13 1 Types of Autopilot There are two basic types of autopilots e A simple autopilot which maintains a set compass heading This may have no heading display and will take up the heading the boat is on when the autopilot is switched on Heading is altered with left and right keys and the heading will be monitored using the steering compass 125 Some will have a heading display will again take up the heading at switch on have left and right keys but the heading can now be monitored on the autopilot display and checked against the steering compass e An autopilot linked to the navigation instruments which can automatically take you to a waypoint or even follow a complete route This type will have a remote flux gate compass a heading display and keys and displays allowing a route to be followed Personally do not advocate coupling the autopilot to the navigation system to automatically follow a route for the following reasons e With the autopilot making constant alterations of heading to maintain the cross track error to a minimum the navigator has absolutely no idea of the compass course being followed and ca
13. East We use the format Latitude dd mm mmm Longitude ddd mm mmm The maximum number of degrees latitude is 90 and the maximum number of degrees longitude is 180 Distance and Direction In order to navigate anywhere we need to determine both the distance and the direction to our destination Distance Most of us are used to miles or kilometres but these are not the measurements used at sea or in the air The problem is that these measurements are not related to the geometry of the Earth and so the user has to have a scale of distance to use whenever the distance must be measured The Nautical Mile The nautical mile is directly related to the circumference of the Earth One degree 60 minutes of latitude is equal to 60 nautical miles Thus a gt aA Lire Fi 60 degrees latitude equals S x 60 600 mvo miles 2 ie TTT E aes m mhi j a y i Tai vi Our Address on the Earth s Surface Chapter 2 a i 5 f d m ht l b Y r nas C IP Use latitude scale at same latitude as distance to be measured e One nautical mile equals one minute of latitude Distance can be measured directly from the latitude graticule of the chart The distance from the Equator to 60 degrees North is 60 x 60 3600 nautical miles If you look carefully at a chart you will see that the latitude graticule doesn t have constant spacing This is especially true on a Mercator projection where
14. Guernsey 9O mil The easiest way to illustrate how to go EIA Gunny L640 appro about navigation when applied to passage making is to have a look ata En route tide Yarmouth to Guernsey 1st July 2007 8 real trip This is my method and others may do things a bit differently but I ll tell why do things my way as we proceed from Salcombe in Devon to Poole Harbour in Dorset Before We Start This is a trip of over 100 miles so at a cruising speed of around 6 knots it ll take around 17 hours so here in the English Channel where tides can be quite strong we will have to endure going against the tide for some of the time use Seapro chart plotting software which allows me to investigate the best time to leave taking account of the tidal flow Doing it manually you ll need to take a look at the tidal atlas and decide the best time of departure to make best use of the tides With a forecast wind of northerly Fati te Mannie Novis T Albena nace Plian ince G ariy Total Dute Kemod tor Grornesey Plannee exiting speed Eilina Tw tx tolh Aala he eat ed Walem Fee foe Aea Gd ov Caio fiain dane Aliwal deleat Cherbourg avilable of all gita of Toe and ix all weather Aldooey Ok but mat not be wept pasied by Tae Uhtianable in iiag NE wind Outline plan force 4 hope that we should cruise at about 6 2 knots and Seapro tells me a good time to leave Salcombe is 03 00 BST taking around 16 hours and 40 mi
15. PEF a SS E i 7 ji e Moor your boat in fairly shallow water 7s ae S preferably with a seabed that is firm and of constant depth e Lower a weighted line over the side until the weight just touches the bottom Seabed the line just goes slightly slack Depth sounder calibration 62 Depth Sounders Chapter 7 e Note the point on the line where it enters the surface of the water if you re quick in hauling the line back up you ll see where the line becomes wet e Measure the wet length of the line Adjust the depth sounder offset so that the unit displays the actual depth of water e If you prefer to have depth below the keel set the offset so that the unit displays the actual depth minus the draft of the boat Depth Alarms Many depth sounders allow you to set up one or more audio alarms to warn you that the water is getting shallower or deeper than you would like so that you can take appropriate action False Echoes Reflections from turbulence may cause a false shallow depth to be indicated or the signal may be lost altogether causing the display to flash on and off Wake from a large vessel or from turbulence over rocks Seabed False echo Fishfinders Fishfinders use these false echoes to indicate the presence of fish and expert fishermen can even identify the type of fish on very sensitive units CUDA 28 Fishfinder display 63 30 2 T
16. RAM It does an excellent job but wouldn t run the latest version of my software which does need more computing power but a P4 processor and 256 megabytes of RAM should be fine Check with the software vendor If you really need to use the fantastic 3D capabilities then a high spec machine with a separate graphics card is essential There s much to be said for a computer that is never connected to the Internet as it then wouldn t suffer from a virus What Make of Chart Plotting Software This depends very much on personal choice the depth of your pocket and what you intend to use it for You need to consider what features you require e Some software is pretty basic allowing a route to be constructed but not planned using tidal stream data Others allow full tidal planning and weather routing constructing sailing polar diagrams using lay lines when tacking and more Most software is somewhere in between e There are two types of electronic charts raster and vector Their capabilities are very different and some software will not be compatible with vector charts e Automatic Identification System AIS can be shown on some systems 130 a specific radar system GPS or chartplotter and then transferred to your chartplotter What Type of Electronic Charts Personal Computers Chapter 14 A radar overlay is possible with some systems though this will normally be restricted to Some systems allow waypoint and r
17. This is perfectly normal GPS performance GPS Blackout Solar flares can cause a complete GPS signal blackout on the sunlit side of the Earth s surface In 2006 flares on the 5th and 6th of December caused profound and severe effects to GPS receivers causing a large number of them to stop tracking satellites Professor Dale Gary of the New Jersey Institute of Technology said This solar radio burst occurred during a solar minimum yet produced as much as 10 times more radio noise than the previous record at its peak the burst produced 20000 times more radio emission than i Solar fl u ignificant GPS the entire rest of the Sun This was enough to el Nares can a ae swamp GPS receivers over the entire sunlit side of the Earth The Solar flare cycle covers a period of 11 years Deliberate Interference The strength of the radio signals carrying the GPS data is very low and can easily be interfered with Enemies can deliberately try to disrupt signals in a relatively small local area and military agencies regularly deliberately interfere with the signals to judge the results These tests are promulgated in advance GPS Is Line of Sight A GPS receiver must be able to see a satellite in order to receive its signal If buildings cliffs or trees a yi obstruct that line of site the signal from that satellite kange rings at 25 metres spacing will not be received and the accuracy of the fix may GPS errors with se
18. and their echoes disappeared B R G T This simple mnemonic should help e B adjust the brightness to suit the lighting conditions around you On an LCD display you ll need to adjust the Contrast instead This is not adjusting the signal just making the screen readable e R now select an intermediate range about 4 to 6 miles is good as long as there are targets within range Some authors suggest setting gain before setting range but ideally you need to set the gain at an intermediate range so why not set the range first e G adjust the gain to give good strong returns but don t overdo it As a rule of thumb on a CRT set adjust until there are speckles noise on the screen and then reduce the gain until they are only just visible On a LCD screen adjust the gain until you have speckles and then reduce the gain until there are just no speckles visible If you are not confident about this set the gain to automatic but you will loose a bit of performance e T now adjust the tuning Ideally the set will have a tuning meter you adjust the tuning up and down until you have the maximum number of bars visible Some modern sets don t have this facility and adjusting tuning manually may be difficult for the inexperienced in which case you d better leave it set to automatic The tuning control adjusts the receiver frequency so that it s the same as the transmitter frequency The transmitter magnetron changes freque
19. blink on and off and oN on you ll get an audible alarm The AIS information box A receiver only AIS on your boat will allow Saga Rose is at anchor you to monitor commercial shipping as an but AIS indicates that she is aid to making collision avoidance decisions under way using engine Because of some unreliability of data especially heading it must not be taken as an absolute indication of the situation but in conjunction with radar it is an exceptionally good situational awareness tool reer pees EEE ai Advantages of AIS Fd k i e t can see around corners such as headlands or bends unlike radar which i eee a M can t Whitstar which has just refuelled Saga Rose is under way using engine but her AIS indicates e t can give you the name and MMSI of a that she is still moored ship which you may wish to call Erroneous AIS indications e It can give you the closest point of approach of the target vessel Disadvantages of AIS e Only commercial vessels bigger than 300 GRT are required to fit it you can see only vessels which have it fitted e t can transmit erroneous information AIS Class B Transceiver If we fit a class B AIS transceiver transmitter receiver we must be aware of its limitations e There is absolutely no guarantee that any commercial vessel will see our class B transmissions either because of lack of output power because our set cannot find a 107 free slot or because
20. called north latitude and if between the Equator and the South Pole it s called south latitude A circle can be drawn through all points of the same latitude this circle being a small circle as its circumference is less than the Earth s and it is parallel to the Equator There are an infinite number of points on the Earth s surface with the same latitude so latitude by itself cannot define our address Greenwich Meridian A half great circle joining the North and the South Poles and running through Greenwich Observatory in London England is called the Greenwich Meridian This forms the datum from which the other half of our address is obtained Longitude The angle in degrees between the Greenwich Meridian where it crosses the Equator the centre of the Earth and another point on the Equator is called the longitude It is 12 Our Address on the Earth s Surface Chapter 2 120 degrees Wast 180 degrees East Longitude called west longitude if it s west of the Greenwich Meridian and east longitude if it s east of the Greenwich Meridian All points on the Earth s surface having the same longitude lie on a great circle running through both poles and is known as a meridian of longitude Our Address The combination of the latitude and the longitude of the point provides a unique address on the Earth s surface We can now tell someone else where we are and also find the address of a place we may wish to vis
21. designated a code known as a map datum This is printed on the chart For example in the United Kingdom the map datum is referred to as OSGB36 which stands for Ordnance Survey of Great Britain 1936 the year in which it was devised In the United States of America it s NAD27 but this is then split into versions for different areas and in Australia it s Aus Geo 66 Having different map data mattered not one jot Although the same latitude and longitude may have given positions several hundred metres from their proper position the accuracy of position fixing was such that these errors were undetectable Not so now where even amateur yachtsmen can fix their position to within 15 metres most of the time This difficulty was realised when GPS was being designed and a new international datum was produced which although very complex allowed for the true shape of the Earth everywhere This datum is known as WGS84 World Geodetic System 1984 Paper Charts Only very recently have paper charts been drawn using WGS84 as the datum The majority of paper charts use their local datum so if the GPS receiver is set to give position in WGS84 format which it will by default the position when plotted on the paper chart will be in error by as much as a couple of hundred metres 600 feet This is of significance only if you are trying to use your GPS for close quarters navigation which you should never Madam gt do in isolation
22. detailed in Chapter 4 you must inspect the route thoroughly after you have constructed it Allow You to Follow a Route Having constructed your route you can follow the progress of the boat along the route to get you where you wish to go This can be done in several ways e Steer the boat to keep as close as possible to the route as drawn on the chart e Allow the autopilot to follow the route automatically although don t approve of this method Although this is the normal practise on airliners there are several dangers on small craft The navigator is never really aware of the compass course followed and sO compass errors can pass undetected The helmsman navigator is removed from the close control of the boat and becomes less involved in its safe operation e Use one of several other displays available on the chartplotter to keep on track such as the highway or compass Allow You to Go Direct to Any Geographical Point Chartplotters normally have a GO TO function If the cursor is placed over the point that you wish to go to and the you press the GO TO key a single leg route is set up giving you near instantaneous instructions of how to get there Place the cu rsor on your destination Select CURSOR in the pop up window 74 Finding Position Chapter 8 O Papp mni HESH ao kay Pop up window will show distance and bearing to new destination i Select HIGHWAY soft key to Turn boat t
23. for the tide and wind passing the target at the required distance off Your radar is set up and you re now ready to follow the plan Each piloting situation is different so you ll need to consider how the radar can be used It will depend on how accurately the shoreline or other targets will show up on the screen cliffs showing up very well while low lying beachy shorelines may be very indistinct In some situations radar will be of little use in avoiding underwater dangers because there s no suitable radar target to line up on 120 The floated VARVEBL is just touching the fort The normal VAM is set to the same distance and is Wheeled along the parallel index formed by the floated EBL Parallel indexing See ee Steep coastline Flat coastline Weak radar echo Good radar echo Effect of different types of coastline Radar Overlay on a Chart Plotter The latest trend in full sized chartplotters is to combine them with the radar display It is possible to split the screen so that the chartplotter display uses one half the screen and the radar the other It s also possible on many to overlay the radar display on the chartplotter display so that the two are superimposed To do this requires a high speed electronic fluxgate compass find that for collision avoidance purposes Chartplotter with radar overlay the overlaid screen is too cluttered and prefer a separate radar display However for
24. g rei p U M E E E A AS SR SS ee eee anes lt SSS ee E re m Bll Pilotage WW rereas navigation implies that you are fixing your position by plotting on a chart pilotage means that you are controlling your boat so that it follows a prescribed safe path by visual means This doesn t mean that you can t use electronic aids but as we have 89 seen these can sometimes be highly inaccurate and often pilotage requires us to position our boat accurately to within 10 to 20 metres Pilotage occurs at each end of a passage so pilotage plans need to be included in your passage planning The basic aids to pilotage are the human eye the hand bearing compass and a properly calibrated depth sounder speed log steering compass and a plan Electronic aids can add to your armoury Who Does the Piloting Ideally the pilot should not have any other duties You often see the skipper of a leisure boat helming and piloting as well This isn t desirable If you haven t sufficient crew use the autopilot if you have one when pilotage is demanding Means of Pilotage Day or Night It would seem obvious that night is different from day However there is a fundamental difference that becomes apparent only when you are looking for a lighthouse or lit navigation aid A flashing light is visible only when the light is on As the majority of marine lights have a short flash and a long period of darkness it
25. hati clay Log Salida Time of high water 11 58 Height of high water Height of T tide at 15 05 2 6 metres Tidal curve from PC based navigation software seaPro A5 All chartplotters have tidal curves these days as do many of the PC navigation software packages There are several tidal programmes available for hand held computers and some ordinary GPS receivers are able to display tidal curves In these having selected the day in question you only need to scroll the curser along the time line of the curve for the predicted tidal height to be displayed Many can be programmed with the draft of your boat to give an instant reading of the clearance under your keel You will need to consult your instruction book to see how to do this with any particular system Paper Tidal Curves Standard Ports Different authorities present their data in different ways Although the curves will be similar the method of extracting the actual heights for times other than high or low water will differ and may not be obvious to someone used to a different method The Rule of Twelfths High water LELLU In the open sea and along coasts which do not alter a OE the natural shape of the tidal curve a sine wave very oe bh eS much a good rule of thumb that needs nothing except a A A 4 the heights of high and low water is the rule of twelfths E sI TICL C though you may find
26. in any case Paper charts printed subsequently to the introduction of GPS should be annotated with the datum used and any correction to be applied This correction will be correct only for this chart an adjacent chart may have a different correction Always check both the datum and the correction for any chart you use Modern paper charts always state the correction to be i applied when plotting using a WGS84 position An alternative method is to reset the GPS receiver to present the latitude and longitude to the datum used by the chart If you do this you need to remember to reset it if you change the chart If you re plotting on paper it should make little difference using the 134 metres incorrect datum unless you are navigating solely by GPS in gt os a close quarter s situation Remember errors due to using the eS incorrect datum could exceed 200 metres 600 feet so that 138 metres nee if your approach channel is only 100 metres 300 feet wide Gatum errar distances you could end up on the rocks 21 Electronic Charts Electronic charts are copies of paper charts There are two types of electronic charts e Raster charts which are faithful reproductions of paper charts that have been scanned to produce the electronic copies These will have the same datum as the paper chart scanned e Vector charts which are based on paper charts but enhanced to give added value and if necessary have their datum changed so th
27. is of sine waveform the rule of twelfths as discussed in Chapter 5 will serve well If however the curve is skewed that is not symmetrical or even worse and has deformities then better methods are required if an accurate prediction is required It s essential to reiterate though that these are only predictions The atmospheric pressure and wind can make significant differences and the navigator needs to exercise caution when using calculated height of tide Atmospheric Pressure Corrections e A pressure of 10 millibars hPa above 1013 millibars will depress the tide level by 10 centimetres 4 inches e A pressure of 10 millibars below 1013 millibars will raise the tide level by 10 centimetres 4 inches Tide Tables Tide tables are published for most major ports These give the times and heights of high and low water for every day of the year Where there s no commercial pressure to publish tables tables of differences may be available so that the results obtained from the major port standard ports can be modified to allow calculations to be made for these secondary ports ENGLAND PORTSMOUTH THES AND HEIGHTS OF HIGH AND LOW WATERS JUNE JULY Standard port PORTSMOUTH Tare m Tire m Tina Tame m Times Height metres 46 k q u ia 4q i a it i Hagh wabar Low wnio MH MLV mid ar phat a fore ar Wa ar AT iu wW mui u TT as E oe ar acot osig osta 1100 38 1 6 E au aa neag u uta sie 1200 1800 i
28. meteorological conditions to change the predicted tide level by as much as 0 5 metre and sometimes considerably more It could be argued then that the pursuit of super accuracy in tidal calculations is not appropriate for most situations However in calm conditions access across a shallow sandbar may be made using carefully calculated height of tide at low speed with little clearance under the keel preferably on a rising tide in case you get it wrong Secondary Ports It is uneconomical to have tidal curves and full data for all harbours and anchorages These other harbours are known as secondary ports and are listed with tables of differences from a standard port Using these differences the times of high and low water and their heights can be calculated from the tide times of the standard port and its tidal curve 44 Chapter 5 Secondary port differences Electronic Tidal Curves Without any doubt these are the easiest and quickest ways to obtain tidal height information Because each provider may use data from different authorities there may be apparent discrepancies between different products The differences may seem large at first glance with times of high water sometimes differing by as much as half an hour but when you look at the heights involved these show that they are less than 0 05 metre less than 2 inches apart at the same time so in reality there is a little difference between them hae airy ie
29. narrow and directionally accurate that you can use them to stay in the correct side of the channel No Formal Aids to Pilotage If there s no charted marks transits etc then you have to make up your own You have basically four choices e Try and find charted features that can be aligned to give a safe transit With natural transits you need to be aware that buildings may have been demolished or had something built in front of them Even natural transits in pilot books may have been painted in a different colour trees may have grown or been chopped down You always need a fallback e Mark bearings on your chart from easily visible landmarks natural or man made and use a hand bearing compass to stay on the bearing Initial approach to river Yealm It will be difficult to find your way along this channel in poor visibility or at night so note the directions is and distances A natural transit of the two headlands in line on 069 degrees magnetic In case you can t define the actual headlands you ll need a fallback plan Channel with few buoys A natural transit 73 Choosing your own natural transit e Mark bearings on your chart that will keep you clear of hazards These are known as clearing bearings e Use your calibrated depth sounder to follow depth contours If you approach from outside the 20 metres depth contour keeping the bearing of the church tower not more than 039 degree
30. of deficiencies of their AIS display Even if they can see us with only 30 second updating at best our intentions may not be clear e A recent paper by Andy Norris in the Journal of Navigation published by the Royal Institute of Navigation summed it up thus Any confidence that the potential user of class B equipment has in expecting own vessel s presence to be highlighted to all surrounding SOLAS vessels is misplaced e If we wish to maximise the chances of our vessel being seen by commercial vessels our best chance is to ensure that our boat will appear on their radar screen The best way of achieving this is probably to fit an active radar reflector such as See Me rather than rely on many of the so called radar reflectors currently on the market Some commonly seen have such poor radar reflectivity as to be almost useless 108 ee a i i L J ri i I I il I i I I H i he majority of boat owners buy radar for collision avoidance for which proper training is required However radar is a very powerful navigation and pilotage tool as well 109 How Radar Works The radar scanner rotates at approximately 24 revolutions per minute and while it does this it transmits pulses of microwave energy The time interval between each pulse is long enough to allow a pulse to travel out to the maximum range of the radar and back to the scanner This means that the radar is listening for about 99 9 of
31. on 14th July at 15 06 French Summer Time SHOM definitions Durs of tida LW bo HW a Tiel range a at pion ee an ee ee i J Time of interest mt baleni Mm LW weve meee Tavs rahiraa biitit d ar i 81 meters July 14th HW 1146 UT 1 6 05 meters yee range priv LW 1823 UT 1 1 45 meters Neap range 2 5 millimeters We want the height of tide at 1506 UT 2 Duration of tide HW to LW 6 hours 43 minutes Time after HW 1246 1506 2 hours 20 minutes Range for day 6 05 1 45 4 6 metres Height below HW 1 15 metres Height of tide is HW 6 05 1 15 4 9 metres at 1506 French Summer Time SHOM graphical sulution e Note the times and heights of HW and LW for Cherbourg e Calculate the time after HW that you want to know the height of tide this can also be done relative to LW 2 hour 20 minutes Point A 160 Tidal Heights and Tidal Streams Appendix C Calculate the duration from HW to LW 6 hour 43 minutes Point B Calculate the range of the tide HW ht minus LW ht 4 6 m Point C e Point D shows the height of tide at 15 06 below the height of HW e If you use the time interval before LW the answer will be the height of tide above LW Differences at Secondary Port The method is almost identical to that used by UKHO Remember to correct for local time after you ve done all the other calculations HEURES AU PORT PRINCIPAL HAUTEURS AU PORT PRINCIPAL DE REFERENCE DE REFERENCE ME
32. on the other side of the bulkhead in the cabin and only a few inches from the compass Removing the speaker removed the deviation On another occasion the boat builder had mounted the windscreen wiper motor only 300 mm one foot away from the steering compass As it wasn t practicable to move either the large deviation had to be accepted and allowed for Fluxgate Compasses Autopilots and radars need a compass input This comes No magnetic material warning sign from a fluxgate compass which consists of coils that es clr Asi measure the Earth s magnetic field electronically There s no magnet in this unit which is mounted remotely in a suitable position and the output is sent to any unit or display needing magnetic heading information Positioning of the Fluxgate Compass There are two basic requirements e a position of minimum motion due to pitch heave and roll e a position on minimum magnetic deviation Fluxgate compass Often these two requirements are in conflict The first condition is usually achieved by fitting the fluxgate in the after third of the hull s length The next best is the middle third and the least desirable is the forward third However this latter position is often found to be the area of least deviation Compromise is required Note The detector must be mounted athwart ship and Magnetic Steer Steer may need to be mounted either on the forward or aft side of lee eee Autapliot th
33. oroe E E Soar EEE F dazre ot EEE rroo g e TT beoeo t TE EA POP poroa or f ET tororo fE T Eeoarraot CETE oe T E I _ amp ak dml BaO rrr rr rr rn ee rr O rr re re A au ow ao Finding Position A GPS receiver will give us our present position in the form of Latitude and Longitude so that we won t know where we are until we plot this on a chart 65 Active Route Bearing to waypoint Distance to waypoint Cross track error XTE If we have constructed and activated a route or used the Go To or MOB functions our GPS set will give us distance and bearing to the next waypoint and also any cross i aes iw track error The cross track error 1 Cee 2 ie a is how far left or right we 4 cae me a is ie a i are from the direct line between the position that we activated the route or pressed the GO To or MOB keys and the next waypoint or place we want to go to or MOB _ The distance to go bearing Bearing and distance to waypoint and cross track error to waypoint and cross track error can all be used as position lines to plot on a chart to make fixing our position easier Remember though these three types of position line are GPS based and if that is in error our position lines are inaccurate and could be dangerous As usual we should always use as many different navigation tools as possible Other Methods In the age of satellite navigation it might see
34. p l L L B i l l I iT ee I l I E i l E i L i L L E T n iiiiiMiIiMiiIiMiiIiMii iMii iM lt E Tr ZT 23 ae LS a i aia Toso Personal Computers 129 I ve been using a personal computer PC for some navigation activities on my boat since about 1999 It isn t essential by any means but it s very useful and enjoy using it Only users who have never experienced a computer crash would ever dream of using a PC as their sole means of navigation What Type of PC With the advent of on board entertainment PCs there s a temptation to use a desktop or miniaturised desktop computer for the job That s fine when you are running on mains or generator power but running off an inverter can cause unwanted shutdowns and wouldn t recommend it when you are using it for navigation believe that a laptop PC is a better bet It can be run from a smaller inverter or a 12 volts adaptor but should always be able to fall back on its internal battery if the external power fails The hard drive in a laptop will be more robust that a desktop version and the cost of a ruggedised laptop is prohibitive Unless you want to make use of the three dimensional 3D capabilities of some chart plotting software a powerful PC is not required My boat PC runs Windows 98 and has a 475 megahertz CPU and only 64 megabytes of random access memory
35. paper with hourly progress marks and label the ETA at each point e Moving from one tidal atlas diagram to the next estimate the tidal current at each point Tide at 15 30 Tie at 17 30 166 Tidal Planning and Plotting Appendix D e Mark in the tidal vectors at the start point on the passage chart e Measure the estimated passage time from the last tidal vector to where it cuts the ground track Mark off water distance covered in ten haurs e This is the single course to steer Where will the Tide Take You It seems common sense to enquire where the boat will travel on its way to its destination Indeed how can you monitor the boat s progress if you don t know where it s supposed to be This is easily accomplished by plotting estimated positions along the way before you even start This has the added advantage that should you have to resort to plotting EPs it s already been done at your leisure So how do you accomplish that e Draw your direct track on your passage chart e Mark hourly progress points on the chart e Draw lines perpendicular to the direct track long enough to accommodate the maximum tidal effect e Draw a track grid parallel to direct track with lines at 1 nautical mile spacing Theoretically this grid should be parallel to the Draw lines for the expected progress each hour 167 CTS but in reality it s easier to use the direct track whi
36. planning a passage Wind Against Tide Where a wind driven surface current is running counter to the tidal current a significant change in wave shape will occur This effect is known as wind against tide and can make a relatively calm sea change abruptly as the tide turns Where the tidal current is large and the wind strong conditions can change from uncomfortable to dangerous very rapidly Currents in the Open Oceans and Inland Seas Because the difference in water level due to the tide is usually very small generally there s no significant tidal flow However this doesn t mean that there are no currents Currents may be seasonal such as the North Atlantic s Gulf Stream in which case they can be predicted long term or wind driven in which case they change from day to day COLIN CARNIS AAD BEA E Even though the difference in tidal heights is small a restriction to the flow by such things as islands can cause acceleration to the small tidal current to a much larger value that needs to be taken into account Amongst other places this effect can be seen in parts of the Mediterranean Sea Finding the Value of the Tidal Flow Various hydrographic departments will have built up a database of tidal flow at specific points during the tidal cycle for neap and spring tides 52 Chapter 5 Tidal Diamonds These specific points are shown on charts as a diamond with a letter of the alphabet inside the diamond These a
37. spring tides will be 25 greater than the mean range and neap tides will be 25 less than the mean range The Tidal Day As the Earth spins on its axis once every ere 24 hours one might expect that the tidal day would also span 24 hours In other words there would be two high waters in 24 hours each being 12 hours apart In fact successive high waters are about 12 hours and 25 minutes apart so why is this Each second high water occurs when that meridian faces the Moon ignoring inertia effects As the Earth moves along its orbit around the Sun and the Moon moves in its orbit around the Earth Cee maai this takes longer than 24 hours The average extra X time between each second high water is around E 50 minutes but varies between 29 minutes and 1 lt hour and 26 minutes because the angular rotation 1 day of the Earth around the Sun is not constant Therefore on an average each high water is 12 hours and 25 minutes later than the last Earth s orbit around Sun Moon s orbit around Earth Tidal day is longer than 24 hours High Water Time For any given location the time of day when high water springs occurs is roughly constant Likewise the time of the local high water neaps is also roughly constant Look at your local tide tables to see what these times are for your home port and you then have a valuable planning tool For instance in the UK s Solent high water spri
38. the time and transmitting for less than 0 1 Although each pulse may be 2 or 4 kilowatts the average power is only 2 to 4 watts Measuring Range If one of these pulses strikes a solid object the pulse is reflected back to the scanner and the time taken for the return journey is used to calculate the distance of the target from your boat Range is determined by measuring the time take for a single radar pulse to travel from the radar antenna to the target and back Measuring range Measuring Bearing At the time a returning echo is received the radar measures the angle of the scanner from the bows of the boat Because the pulse travels at the speed of light this is effectively the bearing of the target from the bows The radar knows nothing about compass Direction is measurec from the bows of the boat in a clockwise direction Measuring of direction 110 Chapter 12 direction so unless it is supplied with direction from an external electronic fluxgate compass or a GPS it can give direction only in degrees relative If a GPS heading input is used radar can measure magnetic direction only when the boat is moving The Reflectivity of a Target The reflectivity of the target depends on its angle to the radar beam its size its surface texture and what it s made of The diagrams here give some idea of how the angle and the texture affect how much signal is returned to the radar scan
39. to an isolated danger Don t get too close to these as the danger may extend well from the mark so have a look at the chart This is the only buoy with a light characteristic of flashing 2 white Cardinal buoyage system IALA A amp E Special Mark These are non navigational in nature and are used as yacht racing marks to show the boundaries of danger areas and to indicate water skiing areas elc If lit the lights are yellow Emergency Wreck Marking Buoy Introduce in 2007 these buoys can be quickly placed around a new wreck prior to normal buoys being laid if required Where several buoys are used to mark the same wreck the flashing lights are synchronised These diagrams show how the IALA buoys may be used In order to use the cardinal system reference must be Top mark if fitted RED ball If lit Iso or White light Oc or LFI 10s or Mol What this means is much more light than is usual for a buoy IALA sale water mark the tairway buoy Top mark Two BLACK balls If lit White light This is the ony Fi 2 anywhere H you see this keep clear IALA isolated danger mark Top mark if fitted a yellow cross If lit Fl Y Yellow light X IALA Special marks il_ Emergency wreck marking buoy Narrow Channel Marked by Buoys or Beacons at Frequent Intervals This is the easiest form of pilotage just keep in the channel At night it s des
40. to allow this J Distance is measured by measuring the U TU L time taken for the GPS signal to travel Slide signal sideways to obtain match to measure time difference from the satellite to the receiver As the Measuring the time taken for the GPS signal to reach the GPS receiver time taken is only 0 06 second for a satellite immediately overhead an error of one thousandth of a second would give an error of 200 miles Each satellite has an onboard Atomic Clock which is super accurate but for each receiver to be similarly equipped GPS would not be a practical proposition Satellites transmit a semi random signal which the receiver matches with its own semi random signal The distance the receiver has to move its own signal to get a match is a measure of the time difference and a range can then be calculated It s a bit like matching continually repeated barcodes in reality This is accurate enough to get a first guess at the distance Fixing Position with GPS If the distance to the satellite is calculated by the receiver it can be plotted as a position line where any place on the Earth s surface is the same distance from the satellite The receiver must lie somewhere on that position line If the distances from two more satellites are calculated and plotted the receiver must lie on all three lines Normally this can occur at only one point on the Earth s surface and so that must indicate the position of the receiver Beca
41. to plan to steer one continuous heading allowing for the tide along the complete leg to use the tide to best advantage see Appendix D Seapro draws the planned track over the seabed for me so that can monitor our progress show how to do this manually in Appendix D Provided that we are keeping reasonably close to our planned ground track with no large errors induced by tide and speed different from planned or compass error don t alter heading until the halfway point provided that it s safe to do so At that stage alter heading to get me back on track at the next waypoint do this again at 84 Date jasa 2007 From MEME Ss co ee ee EN oe fe GA ICA rl e a i ARA SARENE r ra mai pe al id mee AS a E amp 3 a gt JE iy i E i RHBBBHHSBHHBBBEN zl elals el 3 3 3 313 3 F Bot VEY EM EY ESS E HE 3 nl Ca Passage Planning Chapter 9 AAE O OAT EO O din os 2 ATA eee Faw as pars ae ree A on 26 ar i ess dart Fe tnd seit Fat apar abad AIE a aA od a E fojereranre Ep perae E jl sone eed ar ane if E tr ati inet te sal any a hew m TIET 2 a r ep LAG ENG Sep te ees ee Pa ae RT TRY PE anime we OAT ade ll a i call E aE Wai laa ae oc hl io qpe a PF ar tan E aEE SREBRBRRRERARREEREE RG He RES CCNE OGM MSS hme m im ali err M a a i a CS O Passage log jo half the remaining dis
42. which allows for tide and leeway The electronic chart is supplied on a data card that is plugged into a card slot in the chartplotter The electronic cartography may be provided by the chartplotter s manufacturer or by a third party provider Ensuring accurate and up to date cartography is a large undertaking and some may consider that a large well funded specialist provider may be more accurate than a smaller provider s wares Most chartplotter manufacturers stick with one provider but some allow the use of several 73 What Can a Chartplotter Do Tell You Where You Are The first and most obvious thing is to display the boat s position on the chart so that you know where the boat is at any time There are caveats here See GPS errors in Chapter 1 and chart errors in Chapter 2 There are no source diagrams on electronic charts although they may refer to the cartography on which they are based or at least the date of the source chart That gives no idea at all of the date of the surveys which may well have been in the 19th century Allow You to Construct a Route You can construct a route that you would like the boat to follow Here there s another warning Unlike a car s satnav which is supposed to know where the roads are and will confine the route to known roads there are no roads at sea Ask the chartplotter to plan a route between two points which have land or rocks in the way it will direct you to run aground As
43. writing Garmin GPS and chartplotters wouldn t accept route transfers in NMEA It s possible to send individual waypoints but you will have to string these together yourself in the Garmin GPS chartplotter There seems to be no problem in Garin slows only NMEA waypoints ba Dee chartplotters which use third party cartography such as Garmin translar C Map and Navionics AIS on a PC Some PC chart plotting software is able to display AIS information All received AIS targets are displayed in real time on the chart with their tracks course over ground and with some software a vector based on its rate of turn F J m os a mE om tz OO x D a m r i Hy pas pt Se at IH With AIS switched on all received vessels are displayed Data boxes show vital information AIS display 1 If the closest point of approach CPA becomes less gt than the user defined value the target blinks an audio irl tet it Hi ram DREA bappa ha amie Dea egy Deen D Cty LF Hofer fates Sete mest Faar Lo oS ei lt 7 All targets can be displayed and then individual targets selected to display all its transmitted data AIS display 2 warning sounds and the display includes the value of glee the CPA and the elapsed time until the CPA A list of all the targets can be displayed on the a cel screen al
44. yy es Swe eee An aR Ch a oe a i gorreet ged Thi j we ae BEGERDOSS DeAAee The grib file weather can be displayed If the grib file is for a forecast period of 60 hours the wind direction and other data if available can be shown for varous time Intervals Midnight GRIB breng Fe i a E aa fn o fo mn C Lee i PUT it ag i ay Personal Computers Chapter 14 GRidded Binary format and the files cover a specific forecast time period giving say the conditions every 4 hours for the following 72 hours GRIB files are available from various sources Some are free and have minimal but sufficient data and some are by subscription Subscription data will be on a much smaller grid basis and contain added data such as wave heights temperature cloud cover and more en ee es a ne a ee ee ee a alee T a ir x FF f pr P eg SEN paesan ea PERION M i aa T F T pir d TIELET pennae sprig f paee 1h bd 4 ssa ph Pedro ooo ga ham OO Op open a taea TRO pa TT T fas s eala p a s aked ETET tae A OGereeg aguas apres Wobgh gp ertdanact oy By stftafeans A OAE DELET T iiaia l i H wre ket pgs eee Opie tia 2 5 ae oor yh e i Sas rem dus s k i3 Daa tk fn sates coos of Lh a a aH ap we fei a ka EJ i oF W i T ee poe CE apagu055a BORA The wind pattern for 24 hours later Tih weird atten For 43 hours la
45. 10m tim 1ir PA FFAA FFI EEF 3 3 3 3 EY 3 _ E HEE EE itt PRCEC CECE i ae FE EE aaa haber T RE RR ES A A eo ewer TT TET COCA SSC inno ll i oe eee eee TY ete T TTT TTT HEEE JSrSHserOnetaeretserataeee i l i LELEL A ees TT r TTT toitte T ELS E aaa 2 eee eee eee PEASE ERE EREE RREN TE 4h 3h 2h ih o im 2m Im 4m Sm 6m Time of interest before or after LW en OR Time of interest before or after HW Height below HW SHOM graphical method of calculating height of tide SHOM differences from standard ports 176 Tidal Planning and Plotting Appendix D Copyright SHOM 2002 An extract from the SHOM table of coefficients 177 _ _ 3 00 I I I I I J l J I J l I i i i i I i i i i I i i i 1 a 05 55 UK Hydrographic Office source diagram 178 r ey ree nam Tidal Planning and Plotting Appendix D d equinoxe coef 120 E S ee EE een are Mean high water springs de vive eau coef 95 PLEINE MER PE ER i Mean high waterneaps de mort eau coef 45 Se eter cee ca aces ecto recacre tense en sees NT MOYEN Mean sea level i ee BASSE MER tonni at ete aie ate arn Mean low waterneaps ISTPAUIZER e a eon d Chart Datum des cartes coef 120 Approximate SHOM definitions __ UKHO equivalents SHOM definitions 179 TIME ZONE UT ENGLAND POR
46. 17 transit To do this the radar must be used in north up mode Let us follow the same route into Portsmouth Harbour as before but this time we ll use the fort and the northeastern shores to guide us in There are a number of ways that we could set up the radar but using the radar simulator we ll follow through a suitable procedure I ve removed all the buoys from the display so that we can just concentrate on the things we are going to use e Mark on the approach chart into Portsmouth the centrelines of the Swashway and the small boat channel e Measure the direction of the Swashway and the distance off that it passes from the fort Note also the point before which you want to be established on the centreline e Measure the direction of the small boat channel and the distance off the shore that it cuts the Swashway VAMEBL 1 is set to a BAG of 229 T and a ANG of 0 31 mile VAMEBL 2 is set to a BAG of 049 T and a ANG of 0 31 mile VAM EBL 1 is floated so that the bearing passes along the VAMEBL 1 is now floated to coincide with EBL 2 NW side of the fort and the and the VAM is centred onthe shoreline This forms the centreline of the Swashway that you are VAMEBL is floated so that its EBL touches he VAM 1 to going to use for radar pilotage become the centreline of the Swashway Radar preparation 1 Radar preparation 2 e Set up a VRM EBL to the reciprocal direction of the Swashway and the distance off from the fort e Flo
47. 700 2300 47 ar a mu 18 47 a 9 ae Differences BEMBRIDGE HARBOUR AT T is i Pee as bhi T s0020 0o00 smon 0020 m amg T hima ii Ti aE T aa ar mii ii iii as mii T FORELAND LE Slip 5005 inaia 0005 amit an bili i ea di 4 iil 18 bhi T 3 itil i 18 irti s 3 ith T VENTNOR io a ii Bi mi i Wo a PE ahi t 0135 000 0035 Tiea iiai tph ti Thig T SANDOWN mes ern ia ue aJ E on O00 Hos 860010 19 I t 4 wa Li 19 ITE aa 4 BBI CT ti TH a bs S is z tr rE ibd zi Lis 7 ap m 5 m 3 5 Dred 1 p3 al HE Es EEE z E UKHO Tidal Predictions In many parts of the United Kingdom the tidal curve is skewed and along parts of England s south coast the curve is far from smooth especially due to the flow up and down the channel and the influence of the Isle of Wight Tidal curve for Portsmouth 156 Tidal Heights and Tidal Streams Appendix C The UKHO has developed a graphical method of finding the height of tide at any time on any day of the year This allows for the different shapes of the tidal curve which may apply to spring and neap tides The easiest way to describe the use of the UKHO method is by following an example which will entail the use of the curve for a standard port applying the differences for a secondary port and then using the curve to find the height of tide at a particular time Get Today s Information We will find the height of tide at Portsmouth at a eens
48. A has the green buoys on the starboard ee Preferred chanel to Por right hand side of the channel when entering a port Bifurcation marks eH ig whereas IALA System B has the red buoys on the starboard side of the channel when entering a port For those used Preferred chanel to Starboard to IALA System A remembering the rhyme Red Right F2 1R Returning when in IALA System B waters is useful Where a channel splits into two both navigable but where it is preferable to use one a preferred channel buoy ima systems icici Sassi ahi is used The main body of the buoy is coloured as if it were sivreation marks Oe ain in the preferred channel whilst the colour of the band tells e you which way to turn The chart will show the general direction of buoyage where there is any doubt It s essential for the pilot to ALA Systema Understand that when proceeding i aia in the direction of buoyage the starboard hand buoys are passed on the starboard side of the boat that is leave the green buoys to ALA Systema starboard for IALA A and leave the red buoys to starboard for IALA B O When proceeding in the opposite direction the red buoys are left to starboard IALA A and the green buoys are left to starboard IALA B This applies to the preferred channel marks as well This means that when travelling in the opposite direction the preferred channel to starboard buoy means turn left Some people find this concept diffi
49. A set will listen for other transmissions to find a vacant slot and then reserves this slot for its own regular transmissions If all the slots are busy it looks for a much weaker signal indicating a greater range and takes this slot This is known as self organising In very busy areas the range at which contacts can be seen slowly deteriorates Class A AIS This is the compulsory system fitted by commercial shipping worldwide It transmits a great deal of data much of which such as destination etc is entered manually by the bridge crew and the rest such as GPS position is wired directly from the ship s equipment The heading information from the compass system has often been found unreliable as has the data that has been manually entered The dynamic information is updated every 10 seconds for vessels up to 14 knots and every 2 seconds for vessels travelling at more than 23 knots and the transmitting power is 12 5 watts Class B AIS This is a simpler and cheaper system designed for voluntary fit vessels and transmits at only l or 2 watts It has a built in GPS and the dynamic data consists of only position COG a and SOG although heading may be added nomad identification System Data is transmitted at only 30 second intervals 3 and the set cannot reserve slots ahead Instead it has to listen for an unused slot or a slot with 104 Automatic Identification System Chapter 11 a much weaker
50. Devonport Tidal stream atlas for western English Channel Tidal Diamonds Versus Tidal Atlases Which should you use diamonds or atlases If you need to know the information for a particular point such as when diving use the diamond For planning or general navigation it s normally easier to use an atlas Tidal Speeds and Directions Generally there will be two values for the tidal speed one for spring tides and one for neap tides Often these are shown without a decimal point so 23 is not twenty three knots but two point three Where two figures are shown the greater is for spring tides the lesser for neaps and a mental interpolation is sufficiently accurate in other words a good guess 54 Chapter 5 The direction of the tidal arrow is the direction of the flow Tides unlike winds flow toa compass point so a north westerly tide is flowing towards the north west On many tidal atlases the boldness of the arrow signifies its speed Each chart will be named for a specific hour before or after high water at the reference port The currents shown are the average for that particular hour and apply from half an hour before until half an hour after the nominal time Tidal Reference Port The reference port for tidal atlases need not be for any port particularly close or even within the charted area What matters is that high water times and tidal range are readily available and that ideally it s in the same time zon
51. E f is largest As the Earth spins within the bulge the sea level rises as the bulge approaches reaches a maximum and then falls to a minimum about 6 hours later The difference between the height of the high water and the height of Spring tides occur at New and Full moon low water the range is a maximum and this is known as i iS Spring tides a spring tide and occurs twice a month 40 Chapter 5 Because of inertia effects spring tides happen a couple of days after the time when the Sun Moon and Earth are in line Spring tides occur then a couple of days after the New Moon or the Full Moon are seen Neap Tides When the line joining the Earth and Moon is at right angles b to that joining the Earth and Sun the gravitational force on the Earth and oceans is minimum and so the gravitational bulge is a minimum also The tidal range at this time is minimum and these lower tides are called neap tides Neap tides are associated with Half Moon but inertia also affects this so neap tides occur around 2 days after the first and second Half Moon Tides change from spring tides to neap tides and back to spring tides over a 14 day period The heights of a spring Neap tides and neap tides vary throughout the year the highest springs being associated approximately with the equinoxes in the spring and autumn hence the term spring tides The lowest neaps are associated approximately with the solstices th
52. ERRE O SEA EUG eee With ihe emor emaoved our position is comect The saw tooth red track line shows where deliberate errors of 300 600 and 1000 metres were introduced The correct picture z gt ne E SE oo oo eee fa al vil j iH H fj jtoljele i tij Kagh PA Heading 40 radar range 0 75 mile The magenta lines show where I have rotated the radar image through 9 degrees to align it with the directions of the shorelines This error could be due to compass deviation the radar not being aligned with the boat s centreline or one set of data being based on magnetic and the other true Compass error 140 Radar superimposed on chart North up heading 230 radar range set at 2 miles Software has matched the radar range to the scale of the chart and converted the radar image to North up Superimposed radar Superimposed radar with split screen Heading 170 radar range 2 miles There is some evidence of a compass error as the retum for the NW and NE shores appear to be misaligned by about 6 degrees Superimposed radar and split screen Personal Computers Chapter 14 on the radar at low water Also superimposition sometimes makes it clearer which are boats rather than navigation marks PC Radar for Pilotage The usefulness of superimposed radar for pilotage can t be understated except for one problem the screen must be in the view of the pilot who should be in ful
53. MARPA Wheeling nicely along the Swashway and watching the depth sounder carefully 115 TARGETS Still maintaining the correct distance off Approaching the northeastern shore so resetting VAM1 to 0 28 nM the distance off that we being our turn onto a heading of 325 T Still watching the depth carefully Tumed onto a heading of 355 T EBL 325T is nearly pointing at southern point of entrance so maintaining heading 355 of 355 for a little longer Ar HT wS T EBL now on southern point of entrance and heading 325 0 240m F a 116 Just reaching 0 28 mile off the northeastern shore s0 starting the turn onto 325 T The cross check here is that the depth is now increasing to greater then 5 metres len ms Changed range to 0 75 mile come port 10 degrees onto a heading 345 T as EBL2 is now very nearly on the southem point of the entrance Depth now is between five and ten metres Nicely established in small channel setto 0 5 mile 337 T a Inside entrance range set at 0 125 mile and heading 337 T PFET Through entrance range set at 0 25 mile heading 290 Now on a heading of 217 T range set at 0 125 mile turning onto a heading of 217 T to destination proceeding down channel to destination each of these which can be used to find the direction and bearing of targets In the case of pilotage we can pre set these to help us follow our plan
54. Professional sets allow what is called parallel indexing an excellent aid to pilotage but we are able to use VRMs instead and if your radar is able to float your EBL VRM pair you have a direct equivalent of parallel indexing In order to describe the method of using the radar for pilotage have set up an approach to Portsmouth Harbour using Lightmaster Software s radar simulator Having made our plan we start our approach from the Solent and aim for the shallow water Swashway We then maintain the desired distance off the northwestern coast to remain in the channel turn for the entrance when the distance off the northeastern shore is correct and follow the bearing into the entrance remaining in the small boat channel just outside the main deepwater channel In a real situation you will be monitoring the depth sounder as well The following sequence of diagrams shows the process Floating EBL VRM Some radar sets allow the VRM EBL origin to be offset or floated This allows pilotage where there s not a long straight piece of land with a good radar echo Because the floated EBL and VRM are anchored to a static radar target or indeed a static position anywhere on the radar screen we can define a route to be followed just as we would follow a visual Radar pilotage plan into Portsmouth Harbour entrance using the Swashway and small boat channel Chart of entrance to Portsmouth Pilotage plan details 1
55. Should you wish to do any long distance sailing you ll need to study this topic further Mercator Projection Let us imagine a translucent Earth with a powerful light source at its centre If we were to wrap a cylinder of paper around the globe the outline of the land would be projected onto the inner surface of the cylinder of paper If we now trace the outline onto the paper and unfurl it we would have a chart drawn using the Mercator projection We can immediately see that instead of the parallels of latitude being equally spaced they get further apart as we go towards the poles This is the projection that makes Greenland 2 172000 square kilometres look hugely bigger than the slightly larger Algeria 2382000 square kilometres The meridians which should meet at the poles are parallel Mercator charts are useful for some types of navigation but we need to be aware of the changing scale of the chart as we move north or south of the Equator The direction of north is always vertical towards the top of the chart It is impossible to show the polar regions Conical Projections Again we need to imagine a translucent Earth with a light at the centre This time we wrap the paper in the shape of a cone which touches the Earth somewhere north or south of the Equator The area that we re mapping influences where we make the tangent to the surface We can see that the parallels of latitude are parallel but curved and
56. TSMOUTH For summai Tine add ONE Times and heights of high and low waters Hour in nen shaded areas PORTSMOUTH Mean spring and meap cumes Mean ranges heaps LT Tidal curve for Portsmouth 180 Tidal Planning and Plotting Appendix D Sourced Google Maps mapping service SE Ie OCEAN CURRENTS AMD SEA ICE a fae Mani E C a E aE a NM T E dili MN H ii i Wick a apd we A a fn we Ma M aa imac fp q ean ag gt wo yo re ihn i s Tt i T ii E i 1 3 z Po p F j f J 4 f s i m ao a EE m me ee ea oe es eee ee E 181 Height Underwater rock over which the depth is unknown but which is considered dangerous to surface navigation 182 LM Lifeboats Flat calm or force 10 always wear one Whether they re training or out on a shout RNLI crew members always wear lifejackets It s a rule informed by years of experience They know that whatever the weather the sea s extremely unpredictable and can turn at a moment s notice They see people caught out all the time People who ve risked or even lost their lives as a result The fact is a lifejacket will buy you vital time in the water and could even save your life But only if you re wearing it For advice on choosing a lifejacket and how to wear it correctly call us on 0800 328 0600 UK or 1800 789 589 Rol or visit our website rnli org uk seasafety lifej
57. a calculator handy l E UE EA This assumes that in the first hour after high water the HHA 8 level falls by one twelfth of that tide s range from high a pee 9 water after the second hour it has fallen by three twelfths i Se after the third hour by six twelfths the fourth hour by nine 2 TT TTR twelfths and the fifth hour by eleven twelfths niin oS Poet This is the principle used by clocks and watches that Multiply the age he Ante eso indicate the state of tide It follows that these work only if to get the fall from high water the tidal curve is close to normal in shape eiod i ii a a Mean ranges UKHO Method JE REET Tidal curves for ports around the United Kingdom are often far from symmetrical and don t lend themselves to rule of thumb methods of calculation The EAE V2 OM UI UKHO has developed an excellent and z simple method of obtaining the height ee aug SE oe of tide at any time For full details of this method see Appendix 3 UKHO style tidal curve for port somewhere 46 Chapter 5 The French SHOM Method The French take a very different approach which works well for smooth curves but doesn t take account of lumpy curves as does the UK method To allow for neaps and springs each tide is given a factor with 100 representing the equinoctial tides above and below mean water level whose factor is zero This gives an immediate idea of how springy or neapy
58. aPro chart plotting software This can be edited manually and on some versions of the software may be automatically updated as you sail It is the performance data from these polars that is used with the forecast winds to produce the weather routing sail plans Allowing for the Forecast Wind Some chart plotting software allows you to insert the forecast wind into the plan which will then calculate the probable boat speeds in the various wind strengths and directions telling you when you should tack using the boat s actual performance data sailing polars Good software will allow for the changing tidal flows as well An alternative to manually inserting the various wind conditions is to download a weather file from the Internet Most weather routing software uses the standard GRIB The weather route s tacking points and courses to steer can be calculated Weather routing 2 136 EST a ne a nas BeSRESHhS Wind data can be inserted manually changing at intervals of your choice for the duration of the voyage allowing the most advantageous route to be chosen according to both wind and tide Weather routing 1 Sa See ei ee ee Se Se IT it TEEF Un Fg TE SO bie 20 Lo iio ied papas Pogo Pee ee gy biog pfocteches POF op oa oe G Poo pied gra eA Pawo ad oe pfs ra a Ba HA i 5 eE fitges ee i PYiivwscovsooger ed a hi ALD Aa e EGE e
59. ackets ___ Useless unless worn A charity registered in England Scotland and the Republic of Ireland
60. al depth the sounding at any given time cent Drying heights above chart datum LAT are subtracted from jan the tidal height to find the depth uch on Bt ae Sein apt a Yc pte at any given time by the very Tide levels and height references nature of the beast this depth may actually be above the present water level Overhead power cable Safe vertical clearance Oharted Magenta elevation Fre ly 2 EA Height of tide Observed de The Tidal Curve All major ports known as standard ports or reference ports have tide tables prepared for them by various authorities These are projected for at least 12 months in advance and often considerably longer They are based on historical records which allow real tides to be matched to astronomical data Formulae are then deduced that match the data so that projections may be made for future dates Generally the match is good but differences will always occur Tidal data cannot take account of transient metrological conditions Atmospheric pressure of 10 millibars 0 03 inch of mercury above average 1013 2 millibars 29 92 inches of mercury will force the water level down by 0 1 metre 4 inches and conversely the water level will rise by the same amount if the pressure is 10 millibars below average A strong wind blowing from a constant direction for several days can also raise or lower the water level considerably and it is not unknown for
61. ald l M ME vE W hmin h min T VE is equivalent to spring tides ME is equivalent to neap tides SHOM differences from standard ports Tidal Streams When planning a passage plotting an estimated position or calculating a course to steer CTS we will need to know the direction and speed of any tidal stream This information is provided in tidal atlases which can be bought as a separate publication found in almanacs or on some charts e Each diagram of the atlas shows the average direction and speed over a period of 1 hour e Each diagram is for a specific 1 hour relative to the time of high water at a reference port e The reference port may be for a port some distance from the area covered by the atlas e Do not assume that the reference port is the same port that you will use for your tidal height calculations e The atlas will make it clear which port is to be used 161 A Tidal Atlas Shown here is a tidal atlas for an area to the east of the Isle of Wight The diagrams are labelled from HW 6 hours to HW 6 hours Each diagram is valid from half an hour before the stated time until half an hour after the stated time and is the averages for the whole hour There are two values for the speed the higher being for spring tides and the lower for neap tides It s quite valid for the practical navigator to estimate the values in between Tidal atlas page 2 e Label the HW diagram w
62. alibrating the Log Traditionally the boat would have covered an official measured mile in both directions and the log distance would have been averaged to calibrate the log 58 Boat Speed Chapter 6 Today the GPS speed over ground can be observed and the predicted tidal flow used to calibrate the log Two Ways to Do lt Slack Water e Calculate the time of slack water e Proceed to a buoy or post so that you can check that the tide is slack by observing its wake e Adjust the log speed readout to agree with the GPS SOG Any Other Time e Use the tidal atlas or chartplotter tidal flow facility to find the tidal flow at the current time e Find a buoy or post and motor into tide to ETOT make the boat stationary relative to the post SOG should be zero and the boat speed should indicate the strength of tide which should agree with the prediction e Motor at your normal cruising speed and adjust the log speed to agree with the GPS SOG allowing for tide that is if you are motoring into a tide of 2 knots the boat speed should read 2 knots more than SOG 59 Depth Sounders Chapter 7 i o itt l i 3 r SSS eS SSS _ ee ee ee ee peie re TE O 7 peher 30 3AN 30 Depth Sounders How They Work Depth Units Calibration Depth Alarms False Echoes Fishfinders T he depth of water in which the boat is floating is measured by a depth or echo sounde
63. allow for an error of up to 10 of the distance run when working out our next course Draw a circle of radius 10 of distance run since the last reliable fix centred on the EP Assume that your position isina position within the circle nearest to danger In other Ad da th Drea i i tual position st OL di side the circle at error words navigate the circle rather than the boat which has a radius of 10 of the distance run Ten percent circle of error EP with Multiple Headings You don t need to work out an EP at each change of heading Provided that you note the log distance at each change of heading you can run a series of DR positions and insert the tide or tides at the end when you are ready This will not give you an indication of the ensuing ground track but give a good EP Standard Symbols EP with multiple headings We must use the standard symbols for our chart work so that any other person will understand what we have plotted e The course through the water has one arrow e The course over the ground has two arrows e The tide has three arrows 148 i i l i i il l H il l il i i H Hi z Course to Steer Appendix B irn a R n e Sa R a ARA S E T E gt a S Course to Steer Where Do You Want to Go What Time Interval Do You Choose Draw in the Tide Draw in the Boat Speed Ground Speed Comparison with EP U n
64. ance run and the time of the EP so that anyone looking at the chart will have all the intormation they need at a glance The tidal atlas diagram from 05 30 until 06 30 i ee 2 PEE Wace ITEP OO O ee ai d i m EP at 06 30 Probable ground track If we are interested in where the boat had actually travelled over the ground since the last fix then all we have to do is join the fix position to the EP This is the average track that we have made good though because it has used the average tide for the period it won t represent the true picture exactly 147 Leeway Wind can blow the boat sideways through the water Boats will be affected in different ways according to their shape both above and below the water the direction and strength of the wind the boat s speed and the direction of the wind relative to the boat It s normal to allow for O degrees 5 degrees or 10 degrees according to conditions Leeway can be estimated by measuring the direction of the wake of the boat Keeney with a hand bearing compass and comparing it with the boat s heading The boat will be blown down wind from the boats heading It s a good idea to always sketch a wind arrow on your chart so that you apply leeway in the correct direction T T 7 a i a omai Error in EP Because an EP relies on information that may not be as accurate as we would like it s normal to
65. as it sounds Boal has reached the centreline of the small boal channel and is nhani Tma turning through 018T onto a heading of 334T Tha boat ii now genepe centraine and Following the plan 4 Following the plan 5 119 e Approach the Swashway centreline from a safe distance Here we are approaching on a northerly heading and have about a quarter of a mile to run e Turn onto the inbound heading and settle down on the centreline adjusting the heading as required to allow for wind and tide e Keep monitoring the depth throughout the approach e As you approach the junction of the two legs be ready to initiate a turn onto the heading of the small boat channel e Now keep on the centreline of the small boat channel Parallel Indexing j hiir a The boat is well along the small boat channel on iis controling and heading 24T Following the plan 6 Using one floated VRM EBL and one normal EBL the screen can be set up for the equivalent of the professional set s parallel index e Set up one VRM EBL with the course as the bearing and the required distance off VRM e Float it sideways so that the floated EBL sits on the target echo e Set up the second VRM EBL with the VRM at the required distance off the target echo e Wheel the normal unfloated VRM which remains attached to the boat along the floated EBL e This will allow you to steer the boat along the parallel course compensating
66. ass deviation themselves and some leisure compasses allow some simple form of correction Owners of steel vessels need to take special precautions with their compass installations as the steel hull has a significant magnetic influence DIY Compass Swing It is pretty easy to measure compass error and the process is called swinging the compass Although the process used by the amateur will not be as accurate as when carried out by a professional compass adjuster it will be entirely adequate for quantifying any major compass errors F 0340 BE T 3 e Align the boat on a northerly heading using the steering compass e Using a hand bearing compass in known position of minimum deviation note the heading to the bows of the boat i e Continue the procedure noting xo both the steering compass 330 and hand bearing compass 360 E bearings every 30 degrees TT OE Ma Ton r a e until you reach north Measured deviation Deviation corrected for A error 210 240 Heading degrees magnetic Heading degrees magnetic a A ANTTIA AAH AI EX ni na Bu pI ii id Ni ni ia 3 Magnetic Deviation course west Magnetic Deviation course west Total 040 Average A error 3 Rotate compass 3 degrees eastwards Deviation corrected Measured deviation for A error e Draw a deviation curve Fang bolts and siots owing fed adjustment of A7 error e f the curve s
67. at all vector charts are WGS84 compatible e Electronic chart plotters use vector charts so no correction is required e Personal computers may use either raster or vector charts so the user needs to set or allow for the relevant map datum Chart Errors There s a general feeling that electronic charts because they are of the computer age must be correct This is a dangerous assumption because it is simply not true Before we explore the reasons for these errors just study the three accompanying illustrations All are of the north coast of the island of Ibiza D030 LOE EAF O90 in the Mediterranean All are different versions of modern electronic charting The up to date Navionics chart shows an island at the head of the bay The very old C Map chart shows no island and the latest C Map chart shows the reality Compare all these with the Google Earth photograph So the first rule of using electronic charting is caveat emptor 22 Sourced Google Maps mapping service Our Address on the Earth s Surface Chapter 2 When was the Survey Carried Out UK Hydrographic Office charts always have a source diagram on the chart This shows both how and when the survey was carried out Unfortunately not all charts have a source diagram and no vector charts have seen have them either Raster charts will if the original paper chart has one Vector charts will generally show the date of issu
68. at this to the coast and place the EBL just touching the NW edge of the fort Set up the second EBL VRM to the direction of the Swashway and the distance off from the fort e Float this to a position where the Swashway starts and so that the VRM touches the first EBL e Move the first EBL so that it is superimposed on the second This is the centreline of the Swashway e Reset the second now redundant EBL VRM to the direction of the small boat channel and the distance off the north east shore where you will start to follow it 118 VRM EBL 2 is set to BRG 334 T 0 29 nm It is then floated so that the VRM touches the shoreline Having constructed the plan on the radar all you and is centred on EBL 1 need to do is to follow it This marks the centreline of the small boat channel and The boat is heading 000T and is about 0 25 mile trom the point at which the change of course is made the centre line of the Swashway Radar preparation 3 Following the plan 1 boat is now steered to maintain the centreline Heading is now 049T and the boat is now approaching the of the Swashway the current heading is O40T small boat channel Following the plan 2 Following the plan 3 e Float this EBL VRM so that the VRM just touches the shore and its centre is on the Swashway centreline This probably sounds a bit complicated but follow the procedure through on the radar simulator screen shots and you will see that it isn t half as complicated
69. at you know which way to turn should you wander off the alignment Official transits marked on a chart always have their directions given in degrees True A single position line derived from a linear depth feature A position line derived from being ona transit 68 Finding Position Chapter 8 Single Position Line Derived from Radar Radar can allow us to measure both distance and bearing from a geographical position Bearing is the least accurate and should not be relied on unless you have nothing better Range distance is much more accurate A distance from your boat to a feature as measured by radar will provide a curved position line so you will need a pair of compasses to draw this on your chart Radar range position line Fixing Your Position Using Position Lines Fixing your position using position lines should normally consist of three lines with an angle between each line of 60 degrees for best accuracy though this is often not possible Features chosen should be unambiguous easily identified both on the chart and on the skyline If you are under way measure the bearing that changes most slowly first the one nearest ahead or astern and the bearing that is changing most rapidly the one nearest abeam last The time that you take the last bearing is the time of the fix Your position at the time of the fix is where the position lines intersect The convention is to 69 A th
70. atural transits or Sailing along contours e Course to steer Distance time run e Recognition of buoys lights Pilot pilots helmsman steers Making a Pilotage Plan To make this exercise more realistic we ll make a pilotage plan from Plymouth breakwater to the river Yealm on Ist August 2007 In making the plan you will also be rehearsing how you will conduct the passage e Firstly put the general route onto the chart Choose a scale so that you can get the complete passage on one chart and then measure distances and NOREEN ae PAn TOM E cal bearings list the bearings in degrees magnetic as all my direction instruments at the helm also use degrees magnetic e Now if necessary on a smaller scale chart look at how you can pilot the first leg At Duke Rock east cardinal buoy you can check your depth sounder which should read 6 metres plus the rise of tide The compass can be checked for gross error as you head for Pivmouth breakwater the eastern end of the breakwater as there should be little cross tide here If you have GPS the COG should be monitored at all times to help ensure that you are achieving the desired tracks e Continue on this heading until you reach the East Tinker cardinal buoy Maintain the heading of 185M until you see the Pilotage for first part of passage East Tinker cardinal behind you aligned 98 Pilotage Chapter 10 with the Breakwater fort Now
71. aypoint number two GPS is to be my main means of fixing our position so will be just plotting our GPS position on the chart every hour with the occasional bearing to check the GPS This way should we loose our GPS or it becomes inaccurate we will never be more than an hour away from the last reliable fix and it s from this position that would start my traditional navigation see Appendix A It often makes sense to base the time of the hourly fix on the changeover time of each page of the tidal atlas rather than the top of the hour If were travelling in a fast motor cruiser Tidal atlas Salcombe 05 00 BST Tidal atlas 18 00 BST me DIST CTS Leg ETA WP Position iM time DEST e e e Taa aa aara 7 z 5010 26 N 343 38 W 50 31 70 N 02 09 75 W ER iero E d d 50 37 97 N Of 54 00 W EZ 16 39 SO 40 24 N 0156 02 W Passage plan HW time HW ht Date senescent to tees Se ARG BSR SIE cA tetat PORT iwime HW ht Wht i R E e a Sele a ea Sp Range Tidal atlas times I d be plotting every half hour but see below for the method check the distance run between each fix and compare this with the distance logged and the tidal flow to make sure it makes sense If the logged distance is 6 5 miles and the tide is running at one knot with us would expect the two fixes to be about 7 5 miles apart At displacement boat speeds it pays
72. backwards over amy time span to investigate various tactical options Tidal flow 142 Personal Computers Chapter 14 e Itis used for passage planning when wind against tide is of consideration e It is used for passage and re routing planning where an ebb tide would preclude entry or a flood tide would preclude departure e It is used en route for tactical considerations such as avoiding tide races etc Tidal Heights Tidal height software is available as standalone software or may be integrated with the chart plotting software Standalone Software Completely independent of any chart plotting software tidal height information is available in both numerical and graphical format The number of tidal stations and geographical area covered will depend on the software used Some software will also run on hand held computers PDAs Built In Software Some chartplotting software has built in tidal height data As well as having a list of tidal stations you may also be able to click on tidal station logos which will then display the real time data for that station Other dates and times can also be chosen for planning purposes rs rr ee ee ee eS ee e it aaa Sy a ea eg S8 See a rs g T i HE iy ay if ae ae a e 352 BOAR Tidal height curves are often available within chart plotting software sometimes for many secondary ports as well as standard ports Tidal height curves Conne
73. bulges rotate around the Earth At the Equator the ground speed of the Earth due to its spin is approximately 1000 miles per hour and at 45 degrees North and South this speed is approximately 700 miles per hour At 45 degrees latitude high tide rushes towards us from the east at 700 miles per hour Makes you think doesn t it Clearance under a bridge rotation ot tidal bulge around Rotation of earth the Earth Rotation of the tidal bulge around the earth Te er ce Strength of tidal current Where there is a constriction to the flow of the tidal bulge such as in the English Channel this speed is considerably modified with the bulge taking around 6 hours to travel from Dover to Falmouth a distance of about 250 miles a speed of around 40 miles per hour What Causes the Tidal Currents The prime mover is the difference between the heights of tide at any two places Water wants to flow downhill which is exactly what it does Thus you would expect there to be zero current at high water as the tide changes direction This is called slack water The same applies at low water 50 Chapter 5 However this is not always the case as there may be another current flowing as well which will add to or subtract from the tidal current Consider a river estuary There may be a river current of three knots flowing towards the sea The flood tide may be flowing at two knots upstream so although the tide is rising the curre
74. card pivot Angle of mesia dip Northern Hemisphere compass Equatorial compass Southern Hemisphere compass The Magnetic Compass Chapter 3 Compass Deviation A boat is likely to have a magnetic field of its own due to the magnetic materials such as its engine incorporated into it When the boat remains in a fixed position for some time its own magnetic field becomes aligned with that of the Earth s magnetic field When the boat is moved onto any other heading the magnetic field experienced by the steering compass is a combination of the Earth s and the boat s fields and so the compass does not point directly towards magnetic North This error is called deviation and will vary in value as the boat s heading changes Not only that but also the error will vary as the boat heels although this is difficult to allow for and is normally ignored Compass Correction Compass errors should be measured and corrected With possible errors as large as 30 degrees relying on an uncorrected steering compass can result in dangerous navigational errors Prior to electronic navigation steering compasses were routinely checked and adjusted if necessary These days many boat owners rely on the electronic element of their navigation to take them to their destination and never even consider compass deviation Commercial vessels have their compass corrected by professional compass adjusters Leisure boat owners can check comp
75. ch also makes the grid useful for plotting GPS positions on passage e Make a table of running tidal offsets for each hour e Mark the offsets on the grid Tidal offsets e Joint the offsets with a continuous line e This line is the planned ground track e When you steer the single CTS you should follow this planned ground track Any error is the error compared with the planned ground track not compared with the direct track e If you are monitoring GPS cross track error the error should mirror the running tidal offsets not remain at zero Planned ground track using single CTS 168 Credits Devout not have been possible to illustrate this book in the way that had envisaged without the charts and simulations made possible by the cooperation of C Map Euronay Lightmaster Software and Standard Horizon Charts Have Been Drawn Using Software Supplied by C Map with the kind cooperation of Mr Paul Sumpner MD of C Map UK Euronav seaPro with the kind cooperation of Dr Brian Morris MD Radar Simulations Lightmaster Software with the kind cooperation of Mr Martin Quaintance FRIN Chartplotter Simulations C Map with the kind cooperation of Mr Paul Sumpner MD of C Map UK Standard Horizon with the kind cooperation of Yeasu UK Space Pictures Some of the diagrams use images of the earth courtesy of NASA and this imagery may be viewed online at Visible Earth http visibleearth nasa go
76. cting to the Boat s Systems The Industry standard communication language is NMEA 0183 with NMEA 2000 becoming common Different manufacturers use their own languages as well but any communication with a PC will be in one of the NMEA standards 143 Instrument Wiring Where a number of different instrument systems are mixed it wen is notoriously difficult to get them to interface satisfactorily Using a multiplexer to combine the instrument Multiplexer outputs into one combined NMEA antiin meni data stream should solve any Route transfer problems Wired Connection Added complexity requires a multiplexer to ensure only one talker per channel The boat s NMEA output is in the form of an RS232 connection which connects directly to the PCs serial port Most modern PCs have no serial port connection so you will need a serial USB adaptor some of which seem unreliable One proven to work with your software may be a better though more expensive option A particular snag with using a serial USB interface with Windows 2000 Windows XP and Windows cl Vista is that your computer is likely to think that the NMEA data are mouse inputs so you will lose control of your cursor and be unable to use your computer You can modify your registry Microsoft Knowledge Base Article Q131976 http support microsoft com default aspx scid kb LN Q131976 but the safest way is to ensure that you connect your computer to t
77. cult Having pulled a boat off a mud bank when the skipper had tried to pass a channel buoy on the wrong side he continued down river still ee chanel te Starboard Lae 1 G General direction of buoyage Aground the wrong side of the marker North Cardinal trying to pass the buoys on the incorrect side He Ke the NORTH of obviously found it difficult to comprehend the reversal of i dii i the colours i International Buoyage All Areas West Cardinal Fastcaxins The rest of the international system of buoyage is the the WEST of he EAST same in all areas Cardinal Buoyage System ee This consists of four different buoys that may be placed safe water to to the North East South or West of a danger They Pehi have differing top marks colours and light sequences Cardinal buoyage system IALA A amp B 91 Both prints UP if et Contuqus quick flashes Points EGS shaped made to a compass Safe Water Mark Indicates safe water and often used at the start of a channel as an aiming point if bt Three quick flashes Both points DOWN if iit Sie quick flashes plus one long fash if it Aine quick flashes jewel Isolated Danger The BLACK areas are where the points ae pointing to Mark Timing of sequence Flashes may be quick or very quick OS 60 or 90 flashes per second White light Timing may be 5 10 or 15 seconds Placed on or very close
78. de 3 hours before high water 2 6 metres e From this point draw a horizontal line until it reaches the line joining today s HW and LW heights e From this point draw a vertical line to the height of tide scales at the top or bottom of the chart 157 e This is the height of tide at the required time i li E e The process can be reversed to find the time that the g HRH Z tide will be at a particular height useful for crossing 5 aya wt shallow water a hes i A RE y 7 _ jos Another Way of Looking at the Process ae a a a a Oe mee e It s not always obvious why the height of tide part of the a a Oo calculation works as it does Tt E e f we turn the tidal curve on its side the method becomes L a el much more obvious Emws 1 e The chart datum is coloured red on the bottom of the ers al chart EITT EERS e The height of today s HW is on the left and the height of i al ul in ORE LW is on the right ELITI Erre e The line joining the two heights represents how the height K EN E Ge Ge E S aa of tide varies from HW to LW ET i ae e Where the time line hits the tidal height line we can Or look at it this way read off the height of tide Secondary Ports Data are published for secondary ports to HU TESS LN LSI allow calculation of times and heights of HW and LW There are complicated ways for obtaining differences at times other than those shown in the differences tables H
79. e able to operate with any system How Your GPS Receiver Tells You Which Satellites lt Can See On startup a GPS receiver starts looking for satellites and will display a page showing you its sky view all around the horizon The outer ring is the horizon the inner ring is at an elevation of 45 degrees and the centre represents the position in the sky vertically overhead the zenith The predicted positions of satellites are shown as empty circles which become coloured when a satisfactory satellite signal is received The serial number of the satellite is shown in the circle Alongside the diagrams are vertical bars representing the signal strength in fact the signal to noise ratio or quality of the signal and again each bar is numbered In this way you can see the number of satellites and the quality of the signals being received in order to form an idea of how good a fix you are likely to get There s often a number giving an indication of the fix accuracy more of which later Almost overhaad Near horizon bo North west GPS satellite positions The Global Positioning System Chapter 1 How GPS Works Semi random code of transmitter and receiver signals From Timing satellite In order to find its position on the Earth s surface a GPS receiver needs to find its distances from at least four satellites Theoretically it needs only three but delay the clock on the receiver is not accurate enough
80. e broad picture an overview then you need to consider the plan in detail Overview Look at the entire passage on a small scale chart preferably a chart that covers the complete route and consider the following e Are there any tidal constraints at departure destination or port of refuge e Best route to make best use of tidal streams and available navigation aids e Large scale charts for passage and possible alternative ports e Shipping lanes and traffic separation schemes e Sunrise and sunset times light identification times e Charted depths which might give a progress check Overview e Draft outline plan note distance and likely passage time Tidal Gates Tides and Tidal Streams Neda fuourable June 20 23 00 wittl July It 06 00 e Note the times and heights of HW and Alderney Race favourable July Lit 11 00 17 00 LW at departure and destination Guenaey Jiwe Lt 12 00 17 00 e Time of HW and range at reference point for tidal atlas and tidal diamonds Marina open HW 3 hours 18 00 23 59 e Identify limiting depths and fast streams causing tidal gates correcting plan as necessary Tidal gates 78 Passage Planning Chapter 9 Navigation Aids e Visibility of lights Coverage of local radio stations for forecasts Area of coastguard coverage VHF channels Racons buoy with a radar beacon ati t Metts Novis D Albay sae Aliaaey tasn te Gureaty Tital Daitance Ya
81. e bulkhead check the installation instructions Autopilot Compass Swing The fluxgate compass is swung in a special calibration procedure detailed in the operating manual for the autopilot Although not a perfect procedure it is likely to result in the removal of most of any deviation but should be followed by a normal compass swing for the autopilot display and a deviation curve or table provided Combined deviation card 33 E E iil gi ma a d a a a a a a a a E a a a ee o a a M L irar ma Constructing a Route Chapter 4 Constructin a Route Using Second Hand Waypoints Loading the Route into the GPS Constructing a Route on an Electronic Chartplotter or PC T days we probably think of a route defined by a series of waypoints places to which we wish to go in the process of getting from one place to another The term waypoint is relatively modern stemming from the need to find the latitude and longitude of a point so that we could then enter it into a navigation receiver s processor via a keyboard When navigation was less sophisticated we would put some lines on the chart and plot our position to endeavour to keep as close to track as possible There was no need to extract and write down any latitude and longitude at all unless we were using a sextant 35 These days we should be able to enter into the navigator the coordinates latitude and longitude of a
82. e circle 10 metres contour 3 9 metres sounding 0 0 metre sounding that is chart datum Rock of unknown depth consider dangerous to surface navigation Rock awash at chart datum Area which covers and uncovers Drying height of 0 2 metres Rocks which cover and uncover Rock which does not cover height 1 3 metres Wreck of unknown depth dangerous to surface navigation Foul ground if you drop your anchor here it may become fouled Recommended anchorage Anchoring prohibited A lit navigation aid is shown with a magenta flash Navigation marks Some chart symbols SCA KV THmMoIooS The major hydrographic organisations publish books containing all the symbols that they use and many of the charts produced for leisure boaters have lists of chart symbols printed on their reverse Most almanacs also contain a list of commonly used symbols Some heights and depths are shown inside brackets such as 1 7 This means that it can t be put on the chart in exactly the correct place as it would obscure the detail they put it as close as possible and enclose it in brackets Some symbols are much bigger than their physical counterparts they are out of scale The geographical location of the symbol a buoy say is shown by a small circle at the base of the symbol Lit navigation aids are shown with a magenta flash Safe clearance under a power Symbols Depicting Dangers to Navigation transmission cable where pub
83. e dangerous because of the small size of are in fact the running the screen This danger can be avoided by constructing _ totals not the distance a of each leg as one should the route on paper charts first and then transferring it to expect th be displayed on the chartplotter or by meticulously zooming in and out the route review page and panning backwards and forwards on the plotter or PC screen as you construct the route Reviewing the route 38 Chapter 5 aT Ehi SE pp es et pp pg nah ee ee ee renin Cs cei 30 ow ou 2 amp in a Z 7 iil i i i 1 i i i i H i 1 i i i i I Tidal Heights Tidal Flow Finding the Value of the Tidal Flow Tidal Heights The Earth and its oceans are subject to the tidal pull of the Sun Moon and planets As far as navigators are concerned it is the combined effect on the level of the surface of the seas that is of interest and this is primarily affected by the relative positions of the Sun and the Moon whose gravity causes a bulge of water in the direction of the gravitational pull The bulge is stationary but the rotation of the Earth on its axis makes it appear that the bulge rotates around the Earth once every 24 hours At this point most of the books suddenly draw in a second tidal bulge opposite the first to give us our two tides a day without any explanation A simple way to view this is that the Earth gets pu
84. e ee Sa Fav ak IME EXERCISE a ee iy a a Jisa hybaj Aeh 5 i j nt nal 4 et A rel searro eo With a long cross tide passage the cross track displacement of the ground track will be significant Chartplatting software that displays the ground track is at a distinct advantage over those that don t Display of ground track The more comprehensive software is then able to calculate the time en route according to the time and date of departure allowing for the tidal flow The course to steer and the elapsed time on each leg are also calculated Even better some software allows the track over the ground to be displayed This is invaluable especially where the course is predominantly across the tidal flow as the cross track displacement may be considerable and could run the boat into danger Sailing Yacht Route Planning A sailing boat s speed depends on the wind strength and direction You can assume a single average speed and calculate the route using this If the wind is from ahead then you ll have to tack down this route and the plan will be very inaccurate 135 Sailing Polars Sailing polars are the performance data for various sail plans in different wind strengths at different angle to the wind Initially they are the designer s predictions but these are then modified in the light of sea trials The polar shown in the diagram is a default polar diagram from Euronav s se
85. e entered the route correctly is to check the route once it has been entered and this is where the tracks and distances table comes in Once the route is loaded go to the GPS display that shows the distances and tracks between each waypoint Some early GPS sets didn t allow this and were potentially dangerous Check that the distances and tracks tally with your paper plan You may see a constant error in the tracks This will probably be because you have measured true directions on the chart but have told the GPS to display bearings in magnetic or vice versa Any discrepancy must be investigated and usually it s because a latitude or longitude has been miss keyed or misread from the chart This procedure is mandatory if you wish to avoid potential disaster but see the next paragraph r i The courses shown Problems with Some GPS Receivers ae ea When you try and review the route on some GPS leg to leg bearings receivers you may find what appears to be a serious discrepancy in the leg distances This is because the distances shown on these sets are not the leg distance but the running totals This is unhelpful to the conscientious navigator who is now required to carry out additional arithmetic to ensure that the route has been correctly entered GPS 2 Constructing a Route on an Electronic Chartplotter or PC This is much simpler than the previous example but These distances shown potentially mor
86. e of the paper chart on which it was based but this chart may well use cartography several hundred years old Some charts are still based on Captain Cook s surveys and some Pacific Islands are reported to be up to 8 miles out of place Note how this area around the Channel Islands in the English Channel was surveyed mostly in the nineteenth century Surveying is very expensive and will not be carried out just to satisfy the leisure market Where commercial needs dictate up to date surveys will be carried out but this may be only in the channels and approaches used by commercial shipping leaving the shallower areas unsurveyed by modern means In the United States of America 40 of the shoreline has not been mapped since 1960 Around half of the soundings were carried out by lead line survey prior to 1940 US Federal Advisory Committee Report 2007 which stated depending on the boater s location can render these charts slightly to grossly inaccurate Any electronic chart of the US will be based on these charts UK Hydrographic Office source diagram Who Drew the Chart You cannot assume that the chart s publisher carried out the original cartography The source diagram above shows that although it s from a British Admiralty chart some of the cartography is French One can probably make an assumption that not all cartography will be as good as that of the major seafaring nations Who Copied the Chart Vecto
87. e origin of the term neap being unclear but probably originating from the old English nepflod used to describe the lowest high waters Small tidal bulge Neap tides occur at times of Half Moon Tidal Range Whether a tide is neap or spring or an intermediate is determined not by the height of high water but by the difference between the height of high water and the next or preceding low water This is called the tidal range Spring tides have a large range and neap tides a small one The mean sea level remains roughly constant At springs the high water is very high and the low water very low while at neaps the high water is much lower and the low water much higher With the introduction of international The various standards for electronic charting there is a spring titles trend for all hydrographic authorities to adopt throughgut year the same terminology for tide levels Although there are many different tidal height definitions in the United States of America such as MLW mean low water MLLW mean lower low Mean high and low water levels Variation from spring tide to neap tide Al water MHW mean high water and MHHW mean higher high water which are still used on paper charts the following are understood and becoming more common MHWS mean high water springs MHWN mean high water neaps MLWS mean low water springs MLWN mean low water neaps Approximately
88. e so that silly errors can be avoided The reference port is always stated on the tidal atlas You could and mostly would be approaching a destination whose standard port for tidal height calculations is different from the reference port used to obtain the tidal flow This is normal but sometimes confusion arises as to which information should be in use The rule is simple use the reference port shown on the tidal atlas for the tidal flow and the standard or secondary port shown on the tide tables for the height of tide Tidal Flows on Chartplotters The electronic charts supplied with modern chartplotters usually have a database that allows the tidal flow to be shown in real time on the plotter s screen The arrows often have different colours to represent different soeed bands Some allow the tidal flow at different times and the flow at a specific point to be displayed Tidal Flows on PC Charting Software Tidal flow arrows can be shown on many brands of chart plotting software Often by placing the curser at a particular point the actual value can be shown for that point New time Actual value of tidal flow at the curser i Using the keys to increment or decrement n en time in one hour steps the change in flow Tidal flow arrows on C Map max can be investigated A specific time can also _ Change keys electronic chartplotter be set Investigating the flow C map max 55 Toolbar allows time to be changed so that tida
89. e two of We can see the entrance to Portsmouth Harbour The route we wish to follow into Porismouth Harbour so we just peintandgo If we look at the chart using the Swashway and the small boat channel that we can see that we sland a very good chance of runs just outside and to the south west of the deep running aground using this tactic water channel shown here in red 114 z po a p esp racenystensqusneeyernrayeTerperensprenmqrverayersextrearye7 Deepest Teepen paranee erara prener a aTa E f a The distances we need to set up the VAMs and the tracks we need to set up the EBLs on the radar display Closing shore now on a heading of 015 T radar range set at 3 miles Well established in Swashway at a distance off of about 0 63 nautical miles on a healing of 045 T one VAM wheeel over the shoreline the other clear Radar range still set at 1 5 nautical miles i Initial approach VRM EBL1 set to 049 4 T 0 604nM VRM EBL2 set to 325 7T 0 705nM Boat s heading 355 T to close shore to maintain a distance off of 0 6 to 0 71 nautical mile The radar is sat to display north up and the range is set at 3 miles and for clarity the range rings have been switched off Initial pilotage approach _ im HOG MODE MARPA Almost at the correct distance off on a heading of 035 T Radar range set at 1 5 nautical miles 0 60 4008 HDG MODE ARX 5 SCREEN
90. electronic charts on your chartplotter are accurate Read on e If you want to know the depth of water over the rocks Read on e If you think pressing GO TO will take you safely to your destination Read on xi Foreword Foreword The methods of navigation used by the modern boat owner have changed quite rapidly from the traditional methods still currently taught This doesn t make the old methods wrong it just means that the emphasis has changed With GPS used in many cars the level of computer skills of the general public being high and the so called paperless office the modern boat owner desires a different approach to navigation Practical Navigation for the Modern Boat Owner will lead you through all aspects of navigation of your boat in a logical order The pencil and paper chart part of the subject is not introduced until it s demonstrated that some knowledge of traditional navigation is necessary This practical approach to the subject will ensure that although the modern electronic methods of navigation remain at the forefront the reader will never be lacking in sufficient knowledge to navigate his her boat safely in any circumstance Proper passage planning is not only desirable but it is also a legal requirement This topic is thoroughly covered in an entirely practical manner The boat owner cannot rely entirely on electronic navigation for pilotage Pilotage will introduce the well established and pract
91. epart Yarmouth at HW Dower 2 hours Tide at 2 hours from Yarmouth Tide at 3 hours from Yarmouth Tide at 6 hours from Yarmouth e make a table of the actual tides experienced for each hour along the route as shown include more detail than absolutely necessary at this stage but it saves work further along the process Knowing the total distance to be covered is 90 miles looking at the distance run column can see that the ETA at Guernsey will be a little after 16 00 say 16 10 The method of working out course to steer is shown in Appendix B and Appendix D e can now refine my original plan with more accurate timings Ideal departure time 2 Estimated arrival time 3 Pilotage for departure port destination and possible ports of refuge 4 Open sea passages Tracks distances and methods of navigation 5 Dangers Distance off to pass clearing lines 6 Shipping lanes Cross at right angles 7 Ports of refuge Good shelter Tidal or other restrictions 8 Fuel Gals hour passage time reserve 20 9 Watch system 10 Food Just Prior to Departure Check the weather Don t keep the plan a secret discuss it fully with your crew so that they understand your intentions and have confidence in their skipper 80 Passage Planning Chapter 9 Passage Planning Procedure If you work your way through the following procedure you ll have a plan Preplan How far to go How fast will you t
92. ers The Publisher is not associated with any product or vendor mentioned in this book This publication is designed to provide accurate and authoritative information in regard to the subject matter covered It is sold on the understanding that the Publisher is not engaged in rendering professional services If professional advice or other expert assistance is required the services of a competent professional should be sought Other Wiley Editorial Offices John Wiley amp Sons Inc 111 River Street Hoboken NJ 07030 USA Jossey Bass 989 Market Street San Francisco CA 94103 1741 USA Wiley VCH Verlag GmbH Boschstr 12 D 69469 Weinheim Germany John Wiley amp Sons Australia Ltd 42 McDougall Street Milton Queensland 4064 Australia John Wiley amp Sons Asia Pte Ltd 2 Clementi Loop 02 01 Jin Xing Distripark Singapore 129809 John Wily amp Sons Canada Ltd 6045 Freemont Blvd Mississauga Ontario L5R 4J3 Canada Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books Library of Congress Cataloging in Publication Data Manley Pat Practical navigation for the modern boat owner Pat Manley p cm Includes index ISBN 978 0 470 51613 3 cloth alk paper 1 Navigation Handbooks manuals etc 2 Global Positioning System Handbooks manuals etc I Title VK555 M267 2008 623 89 dce22 2008003730 British Library Catalogu
93. est about 100 to 125 metres in length Thus at the lower ranges two buoys 30 metres apart will show as two echoes on the screen while at the longest range the targets would need to be 100 metres apart before they showed as two echoes Horizontal Beam Width To distinguish between two targets close together the beam should be as narrow as possible Beam width is controlled by the width of the scanner a smaller scanner having a larger 112 Entrance to Portsmouth Harbour is invisible at this range Horizontal beam width of 8 degrees Chapter 12 beam width Typically a 12 inch Entrance to Portsmouth harbour is visible scanner will have a beam 8 degrees clad wide while a 24 inch scanner beam is about 3 degrees wide The average 18 inch scanner has a horizontal beam width of 5 degrees Any two targets falling within the width of the beam will show up as only one echo When navigating this may mean that a harbour or river entrance may not be visible on the radar screen until you are close enough to allow the beam to pass through the entrance Radar horizontal beam width 2 5 degrees Vertical Beam Width A typical vertical beam width is between 25 and 30 degrees wide This allows the boat to roll from side to side without lifting the radar beam off the surface of the water A boat has only to roll 12 to 15 degrees before Boat is upright in the water the beam is lifted off the surface so a sailing boat goin
94. field and gives magnetic direction e The vertical component of the field forces the needle to tilt in a downward direction towards the nearest pole This is the detrimental part of the field which makes the magnetic compass unusable as it nears the magnetic poles The angle of the field downwards is known as dip Steering Compasses A steering compass is designed to be fixed in position on the boat and is used by the helmsman to steer the boat on a compass course It is mounted in a gimbal so that the compass stays level regardless of the heeling or pitching motion of the boat To best cope with the problems caused by the dip of the Earth s magnetic field the magnet is suspended under the compass card according to the hemisphere in which it is designed to be used In fact there are three types of compass Northern Hemisphere Equatorial and Southern Hemisphere In reality have a number of friends who have completed full circumnavigations on their yachts using a northern hemisphere compass and they reported experiencing no problems as a result 30 Compass magnet Horizontal plain of the compass North magnetic pole Earth s magnetic field Compass needle aligns itself with Earth s magnetic field horizontally North magnetic pole Earth s magnetic South magnetic field pole Compass needle aligns itself with magnetic field vertically Compass Compass vertical
95. g to windward may have to de power to reduce the angle of heel to make the radar useable Navigation Using Radar Wh more than 12 5 degrees of heel the fadar beam is lifted off surface of sea The radar horizon is slightly farther away than the visual horizon because the beam curves slightly around the Earth s Fffect of heel on the radar beam surface Atmospheric conditions can alter the curvature so that in high pressure conditions radar can see farther and in low pressure situations less far Radar power output determines the maximum range so that distant high points can be seen farther away with a more powerful radar However the most important advantage of high power is that the radar can see smaller targets more easily Target projects upwards into radar beam beyond horizon Visual Radar Distance A 3 8 nautical miles z Distance B 1 8 nautical miles horizon horizon Distance C 3 6 nautical miles Distance D 3 25 nautical miles The radar horizon Navigation by radar ranges 113 When taking a three position line fix one normally tends to think of using bearings When using radar bearings are not the tool of choice Firstly radar bearings are not very accurate for various reasons they need to be corrected for deviation and variation and you need to allow for the horizontal width of the radar beam Radar ranges are more accurate need no correction and are easy to plot so think range f
96. harts may not look exactly like their paper counterparts Vector charts bring huge flexibility to the system Electronic Charts for PC Based Chartplotters In the past each software provider has produced their own electronic charts but this is getting prohibitively expensive There is now a tendency to use third party electronic charting especially as there is now an international standard for electronic cartography Professional Cartography Most new commercial vessels use electronic chart displays on the bridge and where legislation controls the type of equipment used all electronic charts will be according to the S57 vector International Standard Leisure Cartography ee ee Detail appropriate to the view chart scale 1 15000 oy H MlM ihe detail is increased appropriately chart scale 1 3500 and even mare detail is shown chart scale sill 1 3500 i ee l l Ml l Zooming in on a vector chart LE mail Eune 8 a S 57 chart Electronic charts used in the leisure sector are much more variable and will depend on the software provider some using only one sort of chart and others able to use several including S57 Probably the ideal is the ability to use multiple types of charts including those used by dedicated chartplotters such as C Map and Navionics The user then gets 132 Personal Computers Chapter 14 This Navionics vector chart used on many chartpl
97. has been moved since it was last switched off it will take longer time than a hot start but much less than a cold start Measurement of Speed There is nothing inherent in the GPS signals that measure speed However the receiver does have a lot of built in information that it can use to present useful information Once the GPS receiver has worked out its position it can use its Fix at 0903 knowledge of the shape and size of the Earth to determine the distance between any two points so that once it is in motion it can work out the distance between two fixes and taking the time taken to travel this distance it can deduce its speed This speed is the speed over the ground SOG not to be confused with the speed through the water Fix at 0904 Distance travelled in 1 minute 0 2 nautical miles Speed over ground SOG 12 knots Boat speed SOG Is Not Boat Speed sip groune Boat speed is the speed of the boat through the water and is displayed on the water speed display Wind waves and tide will cause the speed over the ground to differ from the water speed s Speed over ground GPS Measurement of Course n The GPS signal contains no information on the direction in which the boat is moving Because the GPS receiver knows the shape of the Earth it can determine the direction that it has travelled from one fix to another This course over the ground COG is exactly what it says and may not be the same as t
98. he course steered by the boat Effect of tide on speed o2 degrees Fix at 0904 Fix at 0903 Because the GPS receiver knows the shape of the Earth it can calculate the bearing of the second fix from the first It is thus capable of calculating the course over the ground COG The Global Positioning System Chapter 1 COG Is Not Heading The heading is the direction that the boat is pointing and is displayed on the compass The wind waves and tide can push the boat sideways over the ground and it s this movement over the ground that is displayed as COG Only in calm conditions with no tide running will the heading and COG be the same Measurement of Heading GPS can t measure the boat s heading and can measure only the COG Once the GPS receiver is moving because it can determine COG it knows the direction of true north We will find later in this book that some instruments such as radar and chartplotters can make use of heading information to allow the display to be aligned with north to give a north up display Although GPS can provide this information there are two disadvantages The information is available only once the boat is in motion and the alignment is based on COG rather than which way the boat is pointing Errors in COG and SOG Any random errors in the fixes used to calculate COG and SOG will produce errors in speed and course displayed on the GPS The rate at which the GPS po
99. he hull and sends the information to the speed instrument Modern speed transducers consist of a paddlewheel protruding slightly below the Fixed part of hull into the water Any flow of water past mandaa the paddlewheel causes it to rotate and the below hull electronics counts the number of revolutions in a given time This allows the electronics to calculate boat speed and distance travelled The log as the transducer is known often incorporates a water temperature transducer as well Some earlier logs had a little propeller Mesei i shaped transducer mounted behind a small fin The traditional trailing log used a propeller on Panne wines iog a long length of line let out behind the boat and a mechanical counter that displayed distance travelled The navigator had to calculate his own speed Logs with no moving parts using the Doppler shift in frequency to measure boat speed have been tried but did not find favour Log Errors The log will read the correct speed and distance only if the speed of the water flowing past the hull is the same as the boat s speed through the water Seems pretty obvious but because of friction the layer of water close to the hull gets slowed down In reality of course it s the boat that s moving through the stationary water but the effect is the same The boat drags some of the water close to the hull along with it To allow for the friction effect the log must be calibrated C
100. he live NMEA output before you switch your computer on Senay USh adap Lantos computer Wireless Connection A convenient way to supply your PC with NMEA data is via a Wi Fi connection The NMEA data is fed to a Wi Fi transmitter which then transmits all the NMEA data to a Wi Fi enabled PC The PC can now AE ges es tA ou be used anywhere on the boat including the cockpit and there are no problems with losing control of the mouse cursor Multiplexer Wi Fi link between NMEA and computer 144 30 3 Deduced Reckoning and Estimated Position W aids to navigation are in short supply due to equipment failure or lack of any aids the navigator must resort to traditional methods of navigation 145 S DR Navigation DR navigation is the method of deducing your position using only heading steered and distance run This is deduced navigation and is often known erroneously in my opinion as dead reckoning rather than ded reckoning but anyway it s commonly called DR If you know where you started from the direction in which the boat has been travelling and the distance travelled it s very easy to plot where you are on a chart This makes no allowance for tide or wind so is only of use in relatively calm conditions where there is little or no tide DR distance ru
101. i Functional Satellite Augmentation System MSAS provide the same service in areas covered by these A WAAS compatible receiver will operate with EGNOS and MSAS Range rings at 25 metres spacing WAAS GPS errors The Modern GPS Receiver Modern GPS receivers normally have 12 or more channels which can receive data from 12 different satellites simultaneously Satellites are moving fairly rapidly along their paths and the ability of the receiver to lock onto a large number of satellites means that they are always using the best data available It also means that their startup times are very quick The oldest receivers have very few channels so they have to divide their time between using data from only one or a few satellites and searching for new ones They are inherently slow GPS 57 A modern GPS receiver Switch On Delays Cold Start When a new GPS receiver is first switched on it has no idea of the time date where it is or where the satellites are As the information about the whereabouts of the satellites is transmitted only every 12 5 minutes it will be some time before the GPS can compute its first fix This is known as a cold start Hot Start When the GPS is switched in the same geographical position as when it was switched off it knows where to expect the satellites to be the date and the time so modern 12 channel receivers can compute their first fix very quickly Warm Start If the GPS receiver
102. ical aspects of entering and leaving a harbour or anchorage Radar is another area where legally the boat owner is required to know how to use this valuable tool Again this topic is approached using a practical and easily understood approach xiii Introduction Introduction When I gained my Flight Navigator s License in 1973 other than when I was actually on the ground never knew where was only where had been By the time you had worked out and plotted a fix you were at least 60 miles further on Even when flew Boeing 747s without a Flight Navigator the inertial navigation system which used three onboard gyroscopic platforms to measure acceleration in all three planes to determine where you were could be 10 miles in error by the time you had flown 12 hours Incidentally the Apollo spacecraft to the moon used only one of these inertial systems for navigation Modern airliners use a combination of inertial navigation systems continually updated by automatically tuning into ground based aids to remove any inherent errors This has the huge benefit of using at least three different types of data on three completely separate systems to continuously monitor each other for errors which if found are reported to the pilots The first time that ever knew where was all the time was when started using GPS on board my own yacht assuming of course that what it was telling me was correct Fortunately for me had around 10 m
103. icult to achieve an accuracy of better than 5 degrees due to the motion of the boat A legs apart stance to brace your body is advised Single Position Line Using a Hand Bearing Compass In this case a bearing from a boat to a lighthouse is measured as 277 degrees magnetic using a hand bearing compass The magnetic variation Is 8 degrees East so the true bearing is 285 degrees Using the plotter as described in Chapter 2 it Single position line using a hand bearing compass 67 is aligned with the base of the lighthouse symbol The boat must lie somewhere on the position line drawn along the plotter s edge shown in red Single Position Line on a Depth Feature Here we are crossing the English Channel If we suddenly find that our depth corrected for height of tide is between 1 6 and 2 7 metres we must be somewhere along this very narrow depth feature so we have an excellent single position line Single Position Line from a Transit A transit is the visual alignment of two geographical features If these features are aligned you must be exactly on a position line joining them It is the most accurate form of position line available A transit may be the alignment of two natural features or the alignment of two deliberately placed navigation marks provided for safe navigation through a hazard strewn area In the latter case the most seaward of the two marks is lower than the most landward one to ensure th
104. illion miles of real navigation behind me and knew when could trust my GPS and when to treat it with a certain amount of suspicion My aim in this book is to show you how to use all the navigation tools at your disposal to the best advantage and to be able to weigh up which ones to place more reliance on according to the circumstances To me navigation has always been more than a means to an end and hope you will get as much enjoyment out of it as do XV ES i ee ee eee 3 Positioning System The Global i T he original global positioning system GPS consists of 24 satellites orbiting the Earth at a distance of around 11000 miles Each orbits once every 12 hours in six orbital plains so there will be between five and eight satellites in view at any time from any point on the Earth s surface The drawing here shows only three orbital plains for clarity There are a number of spare satellites in orbit on _ Artwork courtesy of US Dept of Defense in case of failure and each satellite has a life ohne eens expectancy of about 7 years New satellites are launched by the US military as required Fears about the American monopoly of accurate position fixing amongst non USA countries have lead to the establishment of GLONASS a Russian system and the pending establishment of GALLILEO a European system They work in a similar manner and new versions of GPS receiver may b
105. im that he needs to aim off to port and keep the buoy on the starboard bow If there s an object on the horizon above the buoy that tree again tell him to keep the tree and the buoy in transit and explain what you mean if necessary If the buoy moves to port you must steer to port to bring them back into line and vice versa If there s nothing to use as a transit ahead or astern give him a course to steer allowing for the tide or use the GPS COG as an aid e At night if you re on a transit help the helmsman as he will be steering a course 10 If you re on a back transit that is the transit is behind you remember that the course corrections are the same if the nearer object moves to port then you steer to port Don t use the terms left and right as these are reversed when you look behind you If you are keeping on a bearing to an object or a clearing bearing the helmsman should be given a course to steer You should monitor the bearing as often as necessary and give the helmsman course corrections come 5 degrees port onto 045 Once you know that the helmsman is established on the current leg of the passage monitor him loosely but start looking for the next object If you re looking for an object a tower say then identity it in good time using your hand bearing compass and binoculars if necessary If you can t find the next object check your time and distance run s
106. imt Dat 20imi Porn POTTERYRPER Cwe Passage Planning Chapter 9 Moon we 22 21 Mont 05 26 hll noou Sune 05 05 Cuat 21 07 Skipper on wateh O1 30 04 30 07 30 09 00 12 00 14 00 15 00 18 00 Crew on witek 04 30 07 30 09 00 12 00 14 00 18 00 If itong wind against tide in Alderney race 3 0 kuott Roul via weit of Aldermey or change destination to Alderney on Cherbourg Final plan doing this manually is given Appendix B can now draw the tracks on my navigation chart and check the distances and bearings If were entering this data manually into a GPS receiver it s essential that thoroughly check all the bearings and distances rubbish in equals rubbish out My system allows me to send the route directly from my laptop to my GPS but still need to check that it has been sent to the correct place On the Way don t mark the pages of my tidal atlases with the high water times have a card on which can enter the times and heights based on HW time plus and minus half an hour rather than HW time itself This means that can instantly see what page should be looking at just by reference to the clock and the card 83 Tidal atlas Salcombe 04 00 BST Tidal atlas Salcombe 03 00 BST We leave Salcombe using pilotage rather than navigation see Chapter 10 so apart from entering our departure in the log don t start my chart work until we reach w
107. ince the last Don t run blindly on into dangerous waters in the hope of seeing it Either the tide is a lot different to what you assumed or you have made an error in measuring the distance or bearing On many occasions when teaching pilotage the lost towards the buoy and noW aground E Just keep heading towards the buoy buoy is just off to one side but the student navigator has been concentrating on just looking ahead If the helmsman or other crew members are all in the picture they are likely to have spotted it 102 SE i p o R J oa os H SRN HOM j Automatic Identification System 103 What is Automatic Identification System Automatic identification system AIS allows a transmitter on a ship to broadcast information about the course speed and position etc dynamic data navigation information and also destination type MMSI and name etc static information of the vessel Receivers on other ships and shore stations can display this information as an aid to collision avoidance traffic control or national security The system is compulsory for vessels of 300 tonnes or more and the experience gained over the last couple of years has been very positive although there are problems that are discussed below How Does AIS Work Each minute of time is divided into 2250 discrete time stamped slots in each of two VHF line of sight channels
108. ing in Publication Data A catalogue record for this book is available from the British Library ISBN 13 978 0 470 51613 3 HB Typeset in 10 12 Futura by Thomson Digital Noida India Printed and bound in Italy by Printer Trento Trento Contents Contents Cover Points xi Foreword xiii Introduction xv 1 The Global Positioning System How Your GPS Receiver Tells You Which Satellites It Can See How GPS Works Accuracy of the Fix GPS Blackout Deliberate Interference GPS Is Line of Sight Selective Availability Differential GPS Wide Area Augmentation Service Switch On Delays Measurement of Speed Measurement of Course Measurement of Heading Errors in COG and SOG O O WON DOA AAA KR O N 2 Our Address on the Earth s Surface The Equator Latitude N N Greenwich Meridian Longitude Our Address International Date Line Measurement of Latitude and Longitude Distance and Direction Direction The Flat Earth The Spherical Earth and Map Data Chart Errors Chart Scale Measuring Latitude and Longitude Chart Symbols 3 The Magnetic Compass The Earth s Magnetic Field Steering Compasses Compass Deviation Compass Correction DIY Compass Swing Fluxgate Compasses 4 Constructing a Route Using Second Hand Waypoints Loading the Route into the GPS Constructing a Route on an Electronic Chartplotter or PC 5 Tides Tidal Heights Tidal Flow Finding the Value of the Tidal Flow 6 Boat Speed vi
109. ion from a known point before you use them Passage Grid The passage from Salcombe to Poole outlined above could have been made using a passage grid The GPS set will give the distance to the next waypoint and the cross track error provided that the route is active Using the grid you can plot your fix by eye using the cross track error and distance to go This method is very quick and as accurate as you require Passage grid Approach Spider s Web If you are approaching your destination you can use an approach spider s web The closer you get to your destination the more accurate it is which is just what you need This method uses the bearing and distance to your waypoint just ensure that the GPS bearing and the grid use the same units either magnetic or true Spider s web grid 86 Passage Planning Chapter 9 Tacking towards a waypoint The spider s web is also very good if you are tacking towards your destination giving shorter tacks as you get nearer Compass Rose as a Waypoint You can avoid a lot of chart preparation by inserting a compass rose as one of your waypoints You don t actually intend going to it so you mustn t attempt to navigate towards it The GPS gives bearing and distance to an active waypoint so all you need to do is place a position line through the centre of the waypoint in this case the compass rose aligning it with the far side as it s a direction toward
110. irable to have a list of directions and distances between each buoy 92 Pilotage Chapter 10 the channel curves steer the boat round a curve as well especially on the inside of a bend If you go in staight lines between the marks Narrow channel IALA B with depths in feet and you may run aground NOAA chart symbols Deatreutecrner Just follow the buoys In a curved channel the channel will curve between individual buoys or beacons so if you follow a straight line between buoys you may run into shallows which curve between them You need to allow for this curvature In a very narrow channel the buoys or especially any beacons may be in water too shallow for your boat at low water so don t get too close to them You have to balance this with the requirement to keep as far to the starboard of the channel as safely possible Colregs Rule 9a Channel Marked by Buoys or Beacons Some Distance Apart In this type of channel you definitely need to have a list of directions and distances between buoys At night or in poor visibility you may depart one buoy and may not see the next for some time You can easily lose your sense of direction especially if there s a crosstide so use the hand bearing compass when looking for the next buoy The reason for the marker is obvious The channel markers are there Channels Marked by Transits for a purpose As outlined in Chapter 8 transits are the most accu
111. irst and use bearings only if you have nothing else You need to be able to recognise suitable points both on the chart and on the radar screen Don t be tempted into using the wrong bay Measure the width of the bay on the screen using the range rings and your fingers and compare this with the width of the bay on the chart using the chart scale I ve seen students identifying a 4 mile wide bay on the radar as a l mile wide bay on the chart Whereas range from a point is marked on the chart as a curved position line using a pair of compasses a distance off a beach say is marked by a line parallel to the beach A radar fix obtained this way will give you a position relative to the real land not in terms of latitude and longitude as when using GPS which may be in error Note B is parallel to the shore not a radius Navigation fix by radar ranges Pilotage Using Radar If you see your destination on radar don t just point and go Underwater obstructions and shallows can t be seen by radar and doing so a recipe for disaster Do use north up display for pilotage It gets very messy and complicated if you don t as you will have to keep resetting the electronic bearing lines EBLs every time you change heading Radar pilotage needs planning as before but you have an additional tool which is distance from an object Use is made of the radar s EBL and variable range marker VRM Most sets hav
112. is or the charted visibility which ever is beast 7 are too small to be recognised from even this short distance An object beyond your horizon can still be seen if its highest part is high enough to project above the horizon The things that determine how far away any object will be visible are e The meteorological visibility Is it foggy e How big it is Is it actually large enough to be discerned by your eye e Your eye height If you are standing on top of a hill you can see further e How high the object is Is it high enough to project above your horizon e At night how bright the object s light is Nautical almanac s provide tables of distance to the horizon for different eye heights and different object heights Charts detail the heights of terrain vertical structures such as chimneys and the heights of lights They also show the visibility of lights in standard atmospheric conditions Experience tells you how far away you can discern a buoy typically no more than a couple of miles at most When All Else Fails wg a oe If you know where you started from i en 7 the course you have been steering the Ne compass hess 2 distance you have travelled you can ie Kee deduce where you are This is called DR deduced reckoning or DR often called ded reckoning or more frequently dead reckoning Take your pick If you re in tidal waters then by applying how far the tide
113. ish All magnetic eel compasses show direction in degrees magnetic with an error due to deviation Read off direction on compass rose if this is applicable in this case 069 degrees true or 074 degrees magnetic When steering the boat using a Measuring direction with a parallel rule magnetic compass to determine the direction we need to know the course to steer in degrees magnetic It is therefore traditional to convert all directions to magnetic Global positioning system GPS and electronic chartplotters have the Earth s variation chart built in so that if they know where they are they will know the local variation Therefore if you wish you can tell the GPS or chartplotter to show all directions as degrees magnetic prefer to do this as can compare all direction information directly with my magnetic compass without having to tax my poor old brain If you have an electronic compass and use your magnetic compass only as a back up you can use true direction if you prefer If you do so ensure that all the electronics use 18 Our Address on the Earth s Surface Chapter 2 true direction and that your crew understands what you are doing At the present time this is a non standard procedure but in the future this may become the norm The Flat Earth Have you ever tried peeling an orange and laying the peel out on a flat surface Difficult isn t it As soon as you try and make a chart paper or electr
114. it International Date Line Address is 22 degrees North 66 degrees West ur address on the Earth s surfare With the Earth spinning around its axis once per day the date clicks up a day at a time at midnight If you were to travel around the world faster than the Earth s rotation you would have time travel so a mechanism needs to be found to stop that happening and the answer is the International Date Line When you cross the 180 degree meridian the date changes either jumping forward a day if you re travelling west or dropping back a day if you re travelling east For much of its length the 180 degree meridian is the International Date Line as well However in order that the jump doesn t occur over land the date line has some wiggles both east and west so that the whole of any country or Rie arp territory is on the same date moman cata liia Measurement of Latitude and Longitude One degree is divided into 60 minutes Normally 1 minute is divided into 60 seconds however this is rather cumbersome when measuring on a chart so for navigation purposes minute is divided using the decimal notation so we write down and say degrees minutes and tenths or hundredths or thousandths of a minute So for instance 35 degrees 43 minutes and 456 thousandths of a minute is written as 35 43 456 Thus we write a position as Latitude 35 degrees 43 456 minutes North Longitude 026 degrees 12 765 minutes
115. ith the time of HW e Label the left hand bottom corner with half an hour before HW and the right hand bottom corner with half an hour after HW e This gives the times between which this diagram can be used e All the other diagrams need to be labelled only with their start and finish times e The diagram for HW 3 is shown 162 hour before until half an hour after the central time of that particular tidal time This shows the tine that each diagram applies to This makes life much easier when you use the tidal atlas Tidal atlas page 1 The tidal atlas diagram from 05 30 until 06 30 Tidal Heights and Tidal Streams Appendix C Tidal Diamonds Many charts have tidal diamonds marked on them and a table showing the value of the direction and speeds of the tides at these discrete points They are fine for estimating the tide at a particular point for such operations as diving and fishing but are cumbersome to use for planning and plotting purposes Just as when using a tidal atlas each tabulated value for a diamond is the average for hoe eee oF if T the 1 hour period However there s insufficient MiEdg room on the tables to label the values with a Sa Ta time I ve found that many people make mistakes si i E when working out which hour to use so you may find it helpful to use a pro forma to do n Tep SHEET Gath OF BG ROU this You can print off a proforma from Wi
116. l flow can be investigated deen OES jia Ht 7 Gee FT bigi LOUT EA a A TE a me eaan re et e E i ne as Tidal flow arrows on Seapro PC plotting eapro tidal flow software TOTOE arsta Tidal flow at a specific point and time Seapro It is of help when planning a trip to scroll the displayed chart backwards and forwards in time to see how the tidal flow changes during the day for any date This is much the same as looking at the various plates on a tidal atlas but with the computer doing all the high water time calculations for you 56 Boat Speed Chapter 6 Qo ee ce ee ca ee ee Ce Se as a a l F 1 ste kd de ai n aia tat nat nn ji ji i ee ee ee Boat t Speed Speed over the Ground Speed Through the Water Measuring Speed Through the Water Log Errors T are two sorts of boat speed speed through the water and speed over the ground Speed over the Ground Speed over the ground SOG is measured by GPS and is the total sum of boat speed tidal effect and wind effect It is covered in Chapter 1 O7 Speed Through the Water This is the resulting speed through the water due to the power of the engine or sails overcoming the drag of the boat in the water and in the air It is a measure of the boat s performance and is used for traditional chart work and navigation Measuring Speed Through the Water A transducer measures the flow of water past t
117. l the data for each target can be viewed or E E alternatively if a target is clicked then its data can be A tf displayed Individual targets can be chcket to display al its data Al display 3 138 Personal Computers Chapter 14 Radar on a PC Several versions of the PC chart plotting software are able to act as a radar display These require a special radar scanner rather than taking signals from the usual scanner provided with a conventional system The scanner output is sent directly to the PC and all control of the radar is carried out from the PC software The radar display can be whole screen radar only split screen alongside the chartplotter display or superimposed on the chart Stand Alone Radar The radar display fills the PC monitor screen and all the radar controls are operated using the computer mouse Because all the controls are visible and not immersed in various menu levels operating the radar is very straightforward much easier than a modern leisure radar The radar may be operated in north up or head up modes at a click of the mouse button i js et aif OU fy a lat TATLO ICENA TUR Range 2 miles head up display heading 228 Split Screen Radar When the PC chart plotting software is in use the radar may be displayed in its own window on the PC screen alongside the chart plotting software Alternatively it may be displayed in its own window on the t
118. l three sides representing the same period of time Since we are going to start off with a guessed time it makes sense 150 Course to Steer Appendix B to use an easily handled time interval which will normally be 1 hour However sometimes we can use half an hour or even one and a half hours depending on whether the triangle will fit the paper chart or not Draw in the Tide e Transfer the tidal direction from the tidal atlas to the chart with the tidal flow three arrows pointing away from your starting point A e Estimate the tidal speed with reference to neaps or springs e Mark the tidal vector with how far the tide will take the boat in the time interval of the triangle C That is for a 1 hour triangle use hour of tide for a half an hour triangle use half an hour of tide Draw direction of tidal stream Draw in the Boat Speed e Open up your dividers or compasses to the distance that the boat will travel through the water in the time of the triangle That is 1 hour of boat speed for a 1 hour triangle or half an hour of boat speed for a half an hour triangle e Mark this distance from the end of the tidal vector C to a position where it cuts the line joining A to B and beyond D Give it one arrow ni maye nry T q Loder in the ees e Se rem For rsg Eh bakine to th a Ae s F a th D at The tidal atlas diagram from 05 30 until 06 30 Estimate the tidal stream
119. l view of his surroundings that is able to look outside ee aie i ms ee Superimposed radar and split screen radar being used for pilotage This utilises two completely different tools with different sources of data one of which is the land itself giving much greater confidence Split screen pilotage GPS emor of about 30 metres the lower of the twa traces 1 would hawe made pilotage in fog dangerous wAhout radar With the radar to 0 25 mile range very accurate which would hawe shown up the error If you look carefully set g z ry i af the previous diagram this difference between the GPS pilotage is possible position and the superimposed radar position can be seen Accurate pilotage GPS enor Used at a suitable chart scale on the plotter and a very low range on the radar then any discrepancy between GPS cartography and radar can be seen Provided the radar is set up properly its view of the world is correct We can see in the accompanying diagrams that the ideal is to have a superimposed chart radar in one half of the screen and the stand alone radar in the other Obviously the bigger the screen the better This technique can also be used with a radar superimposed chartplotter but often the screen is too small for accurate use 141 PC Radar for Collision Avoidance Personally do not like superimposed radar for collision avoidance as find it too confusing would use split sc
120. lective availability be degraded It s possible that the signal may be received as it bounces off another surface so it will take longer time to arrive and will give an inaccurate range Again this can degrade the fix accuracy The signal can penetrate some solid surfaces such as glass GRP and canvas and it is sometimes possible for a receiver antenna mounted inside the boat to work satisfactorily Selective Availability Originally civilian users had their signals deliberately degraded by the US military inducing a randomly varying error known as selective availability ensuring that accuracy was no better than 100 metres for 95 of the time This selective availability has been switched off but the US military may reintroduce it without warning at any time This must always be considered a possibility On the accompanying chart the error that disappears northward off the chart was over 800 metres Errors that occur from a corrupt satellite signal will be incorporated into the fix by a GPS receiver and can lead to very large errors measured in miles and will continue until the satellite is switched off by the monitoring team which could take up to one and a half hours Differential GPS A GPS receiver fixed in one place will know exactly where it is Any position derived from the received M K satelites GPS signals can be compared with its known position w and any error deduced If this error was transmitted to e V Pi the
121. less you are operating in tideless and windless waters you will need to calculate a course to steer to get from A to B If you just steer the direct track between the two points the wind and tide will take you in a different direction 149 At the first sight it may seem a little complicated but A C practice a few times and it should become second nature One essential reminder is that unlike estimated positions EPs the tide comes first not last In order to strive for clarity the first diagram shows the completed vector triangle while the subsequent diagrams show the step by step method Where Do You Want to Go D e Draw a line from your starting point A to and beyond your destination B This is so that if the trip takes more than the nominal time you have guessed the line will be B long enough Because this is the ground track it must The vector triangle have two arrows Distance from 05 30 fix to destination is 8 3 miles At 6 knots it will take about 1 hour 24 minutes The required ground track e Measure the distance from A to B e Using the probable speed through the water calculate the estimated time taken to cover the distance A B Distance divided by speed gives time in hours Multiply by 60 to get the time in minutes e This time is used to form the basis of the calculation of tidal effect What Time Interval Do You Choose The velocity triangle you are going to construct must have al
122. ley efore and after the time of high water i Nautical s website www wileynautical co uk tre pouon for cach nto bo You don t need to fill in all the blanks just those Siren dala that you need as shown As before the actual speeds if not neaps or springs can be estimated E Fomor lt B gt Teron lt gt Teor PENON e E m KIRIA 13 07 am OL 11085 zolo 18 09 og loeelas tus L9 toe Tidal diamond pro forma Tidal diamond calculations 163 3 i 5 rire i iw 3 z Tidal Planning and Plotting Appendix D Tar Tidal Planning and Plotting A Long Passage Using a Single CTS Where will the Tide Take You A open water passage will require the use of a number of tidal diagrams You could of course calculate a new course to steer every hour but if the passage is to be across tide this is a very inefficient way to work You will always be pointing into tide and a 12 hour passage could easily take an hour or more to complete using this strategy Passage chart A Long Passage Using a Single CTS On a long passage leg a single course to steer can be calculated using many tidal vectors all in one operation and this is much more efficient 165 e Draw ground track to destination e Measure ground distance e Estimate passage time e Label tidal stream atlas with times from the tide table e Draw ground track on tidal atlas diagram e Mark a strip of
123. lished otherwise the actual Certain symbols should be committed to memory as you clearance is shown in black may not have time to look them up before you encounter an Vertical clearances 27 unmarked obstruction e Shallow water e Rocks e Wrecks Overhead cables e Bridges with low clearance l Rock which does not cover If you are approaching a charted symbol you height above chart datum don t recognise check what it means before you get too close e E 1a pv wor Rock which covers and uncovers height above chart datum where known Rock awash at the level of chart datum Underwater rock over which the depth is unknown but which is considered dangerous to surface navigation 28 i i I I i i w i i I I i li i SS O O eee acme aes oo E S i 4 bi IL HH Piu ee ee ee ee es ee ee ee ee ee ee es ee ee ee ee ee ee ee ee es ee Ziz T O ee re re age The Magnetic Compass T he magnetic compass has a magnetised pointer that aligns itself with the Earth s magnetic field It therefore points towards the Earth s north magnetic pole and so allows the user to know where North is 29 The Earth s Magnetic Field There are two aspects of the field which directly concern the compass needle e The horizontal component of the field determines the direction the needle points towards the poles This is the useful part of the
124. lled by the gravitational effect as well but being solid it gets pulled as one lump whereas the oceans being fluid are distorted Thus the Earth is moved within the distorted oceans to give two tides a day The bulge closest to the Sun is of a slightly different shape to that on the opposite side of the Earth so that successive tidal curves are slightly different in shape and height 39 The gravitational pull on the fluid oceans a bump is pulled towards the gravitational source The gravitational pull on the solid earth the whole earth is pulled towards the gravitational source within the oceanic bump How gravity causes two tides a day In the open ocean the tidal effect is very small with a daily rise and fall of sea level due to gravity of approximately only 0 3 metre or 1 foot However where the proximity of land channels the tidal bulge the rise and fall is increased and values of up to 15 metres nearly 50 feet are seen in some parts of the world The Mediterranean and other inland seas and Great Lakes are considered to be tide tree although there is a small tidal effect Trieste in the Mediterranean for instance has a spring tidal range of just over a metre whereas other parts of the Med have ranges of only 0 3 metre 1 foot Spring Tides When the Earth Sun and Moon are on the same axis the Large tidal bulge gravitational effects are at maximum and the tidal bulge
125. m illogical to use anything other than GPS as a means of finding ones position Indeed one can argue that to proceed to sea without GPS could be construed as negligent However in Chapter 1 GPS and Chapter 2 Charts we have seen that errors are possible On top of this the failure of a single GPS receiver or its power supply can deprive us of this vital piece of equipment GPS fix brg dist and XTE 66 Finding Position Chapter 8 The most obvious alternative to GPS is visual navigation or pilotage If you are passing a named buoy or obvious landmark you know where you are There are other well tried methods as well Position Lines A position line is a line on the chart or earth s surface on which you must lie There are a number of means of obtaining position lines and different means may be mixed to fix your position Hand Bearing Compass A small hand held compass can be aligned with a geographical feature and the magnetic bearing from the boat to the feature measured In order to plot this bearing on a paper chart it must be converted to a bearing of the boat from the feature by adding or subtracting 180 degrees This is known as the reciprocal bearing The magnetic bearing must also be converted to a true bearing by adding the variation if East or subtracting if West Using a Portland type plotter all the conversion can be achieved on the plotter rather than in the head or on paper It is very diff
126. me of arrival ETA Distance divided by speed gives the elapsed time in hours Multiply by Measure ground speed 6 7 knots Distance to destination 8 3 miles Time to destination 1 hour 14 minutes ETA destination 06 44 Calculate ETA 60 to get the time in minutes Add this to the time you started to get your ETA 152 Course to Steer Appendix B Comparison with EP e Have a look at the accompanying diagram DR and CTS and you will see that the two triangles will bring you to the same point on the chart for the same time interval A reassurance that the initial guessing was just a tool to get the correct answer Our EP after 1 hour will be the same position as that found when calculating course to Steer for 1 hour This is logical as ail the data are the same DR and CTS 153 age a aa no SE ES SS eee a HW i353 UT He 4 Sw LW 0656 UT HEO BANGE 3 4m ua A t T L Lz i eal a amp a obs horey cesz ess MGs e pepe 96s pres Jasaliesg ees 053 HEIGHT OF TIDE 2 HOURS BEFORE HIGH WATER Om Tidal Heights and Tidal Streams I is possible to obtain heights of tide for any day using online sources However the navigator is often forced into a position where there s a need to calculate the height of tide at a particular time manually There are a number of different methods of doing this some more accurate than others 153 Where the tidal curve
127. n 6 miles _ DR position Positions labled The course steered must be converted from a Compass course to a True course by applying deviation and variation The distance run is taken from the speed log which should have been calibrated If it under reads you would have travelled further than you thought and may be standing into danger Estimated Position The estimated position EP is determined by applying any tidal and wind effects to the DR position We ll look first at applying only tide We will need to establish in what direction and at what speed the tide has been pushing the boat for the time since we last knew our position This is obtained from the tidal atlas If for instance the last fix was 1 hour ago we will need to examine the tidal 146 Deduced Reckoning and Estimated Position Appendix A atlas page for that particular hour As we will be transferring the direction using our plotter we need only line it up without actually reading the direction We will however need to determine its speed by noting if the day s tidal range is neaps springs or in between Now we will mark the direction of the tidal flow on the chart using the plotter Then we can mark the distance the tide will have carried us since the last fix The symbol for an EP is a triangle to distinguish it from a fix The resulting position is our estimated mean tidal stream direction position We must mark on the chart the total dist
128. nce of E ON another vessel shall determine if a close quarters situation is developing and or risk of collision exists If so she shall O wa take avoiding action in ample time provided that when Lifeboats such action consists of an alteration of course so far as possible the following shall be avoided e an alteration of course to port for a vessel forward of the beam other than for a vessel being overtaken e an alteration of course towards a vessel abeam or abaft the beam Rule 19 e or which cannot avoid a close quarters situation with another vessel forward of her beam shall reduce her speed to the minimum at which she can be kept on her course She shall if necessary take all her way off 123 Rule 19 Rule 19 of the Colregs can be summarised in the following diagram there is no stand on vessel and all vessels are give way vessels and if you are going to use your radar in restricted visibility you must be aware of it Remember that you can slow down or stop as well as turn Astem I you need to make a tum to avoid a close situation this diagram tells you which way to tum Take extra care in thes ambiguous zone the area between Yorward of abeam and abee The essence of rule 19 124 Autopilots Chapter 13 z am T g mz a ee ee ee Sosa oe ot ee a pea E sy iR i oe da Aa n A a A SS SF SSS SS ES SS SSS SS
129. ncy as it heats up so it should be adjusted again after about 10 minutes The magnetron also changes temperature as the range is changed and needs to be checked again If you find that automatic tuning gives a good display you may as well use automatic although again you may loose a little performance Radar Used for Collision Avoidance This is a book all about practical navigation You ll find other books telling how to use radar for collision avoidance Wiley Nautical s Radar Companion is one 122 Chapter 12 However think it appropriate to remind readers that special rules come into force when vessels are not in sight of one another and conflicting traffic can be seen only on ra d ar fom hurt at Pat Manley Colregs The normal rules of the road governing stand on and RADAR give way vessels apply only to vessels in sight of one another rule 11 Conduct of Vessels in Restricted Visibility Rule 7 b Proper use shall be made of radar equipment if fitted and operational including long range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects 4 THE BEAM E THE SCREEN Rule ve 9 STABILISATION Assumptions shall not be made on the basis of scanty 10 MAIN CONTROLS information especially scanty radar information 13 NAVIGATION Rule 19 d 15 PILOTAGE A vessel which detects by radar alone the prese
130. nd COG Start turning the boat preferably into tide Distance V kow arrow pointi t NOB to make the yellow arrow point to the top to MOB of the screen 50 09 951N 001 02 143H Continue the turn The MOB is 0 356 miles distant and you will arive in 3 minutes The MOB is now dead ahead alliqned with the red line 150 metres 170 yards over a 1 minute period Look at the chart page to find the direction of drift Other Functions There are many other functions available so do read the user s manual for full details 76 Passage Planning Chapter 9 e oo a 2 ee ee 2 ee es ee a es ee 2 2 ee ee ee ee ee ee ee ee 2 ee H mie Fs ss in E zZ i E 30 FW 30 2 Passage Planning Overview Detailed Plan Just Prior to Departure Passage Planning Procedure Preplan For the Planned Day of Departure Passage Making Passage Grid Approach Spider s Web Compass Rose as a Waypoint Unmarked Danger as a Waypoint Clearing Bearing 77 Y should have a plan for any passage you intend to make This plan can range from a quick look at the weather and tides for a short passage you ve made many times before to a detailed written plan for a longer open water one The basic plan can be made well in advance with only a check of the weather being required just before you start the passage The planning process has two stages Firstly you need to consider th
131. nearby GPS receivers they could take account of ar i this error in deducing their own position to give a much more accurate result with a 95 probability error of 3 metres This is known as differential GPS DGPS To take advantage of this the GPS receiver needs both a separate DGPS receiver and to be within range of a DGPS station usually about 200 miles This is commonly used for survey GPS and was beginning to be common for leisure users until selective availability was switched off when its need for normal leisure use disappeared because of the inherent 15 metre accuracy Wide Area Augmentation Service Wide Area Augmentation Service WAAS uses a network of ground stations to monitor the GPS position accuracy The error corrections are sent to two master stations which in turn send error correction information to the constellation of satellites The continuously varying error correction information is broadcast by the satellites and is then available to all WAAS compatible GPS receivers The 95 error is then reduced to 7 5 metres Manufacturers usually optimistically claim a 3 metre accuracy Integrity che monitoring is part of this system so anomalous WAAS 6 The Global Positioning System Chapter 1 signals from under performing satellites are automatically discarded WAAS is available only in the United States of America but European Geostationary Navigation Overlay Service EGNOS and the Japanese Mult
132. ner Solid surface perpendicular to radar beam lt e lt lt pawl Ee Solid surface at small angle to radar beam Tan a on gt q m pe as Reasonable echo 5 towards boat Solid surface at 45 degrees to radar beam All target reflections vertical No echo toward boat he Solid rough surface at 45 degrees to radar beam A Small echo towards boat wee Radar target visibility The Size of the Pulse A long pulse contains more energy than a short one and so can travel farther to a target and return to the scanner before the pulse is too small to be detected by the radar set _ Two targets close enough together so that they are A aa bulbs aith illuminated by the pulse at the same time will show Raytheon SL 70 radar 111 up on the radar screen as only one target Ideally then the pulse should be as short as possible exactly the opposite to the requirement for the pulse to travel as far as possible Professional sets allow the operator to select the pulse length manually but on a leisure set the pulse length is controlled by the range selected Generally there Spacing shorter than pulse length one echo Spacing greater than pulse length two echoes are about three different pulse lengths associated P with different Pulse length Horizontal beam width range scales The shortest is about 25 metres in length and the long
133. ngs occurs at approximately 12 midnight and 12 noon High water neaps occur at approximately 6 a m and 6 p m If you look in your diary to check the phase of the Moon you can get a reasonable idea of the time of high water which can be useful if you don t have your tide tables to hand 42 Chapter 5 Chart Datum Nothing To Do with Map Datum the Reference for Latitude and Longitude For navigation purposes any water depth has to be referenced to a common datum for it to have any meaning Most authorities use a datum called chart datum CD which to all intents and purposes is the lowest astronomical tide LAT for that length of coastline or that particular port In the United States of America this is LLW lowest low water However MLLW may be used as the tidal datum for tidal curves in the United States of America and is not as low as lowest astronomical tide In the United Kingdom it is called CD or LAT and in France it is Niveau zero the lowest equinoctial tide The reason for using LAT is that there will always be at least the depth shown by the soundings even at low water Any higher datum will inevitably mean that sometimes there will be less water than the charted depth There is a common misunderstanding that chart datum is constant for the whole of a chart but this is not so Coastal effects could cause the lowest astronomical tide to be significantly different at two places close together on the same char
134. nnot revert to DR navigation if needed e Steering a compass linked course allows any compass errors to become obvious Coupling up to the route or waypoint means that a constant compass course is not being steered and any compass error is difficult to assess e A short lived GPS error can cause the boat to suddenly veer off course have witnessed such incidents STANDBY HSH e The helmsman navigator loses positional awareness of the operation of the boat e Steering a compass linked course allows the navigator to assess the effect of leeway and the accuracy of the tidal current predictions essential if he needs to revert to DR navigation Morth 13 2 Using the Autopilot Heading 050 e The autopilot when not being used will be in the standby mode e When set to auto mode the heading can be adjusted to that required by the navigator pilot e By monitoring the bearing and distance to waypoint and the cross track error the heading can be adjusted to either regain track or go directly to the waypoint if that is a safe course of action Manually steering 050 126 Autopilots Chapter 13 COG A45 BRG A55 LAs oR EF a 6 E Heading set on autopilot controller Active Bearing to waypoint waypoint _ iiie ay Active track Course over ground Autopilot in heading mode Cross track error to an active waypoint e If you wa
135. now in the river but your plan doesn t end until you are where you intend to moor I ve had many students who having entered the harbour have no idea which way to go or even what they are looking for e Some harbours though not the Yealm have a Port Signal Station that shows e a series of traffic lights controlling The river Yealm your progress Ensure you know what these lights mean The Paper Plan to Use in the Cockpit There are a number of methods of writing your notes What is essential is that pilotage is done from the cockpit This is not the time when you want to be at the chart table Your notes need to be simple concise and clear e If you are good at sketching draw a sketch map with all the details on it e The other method is a strip plan Pilotage Plan HW Kala OSOS the LW Virdee 1420 0 Fa E G ten inal 12 46 16 00 hey Jit 2007 Sketch pilot plan Strip pilotage plan 100 Pilotage Chapter 10 e The problem with using a proper chart is that there s just too much detail although you can put one inside a transparent chart folder and use a wax pencil to draw on the plastic This also keeps the chart dry and prevents it blowing overboard Working as a Team The pilot needs to ensure that the helmsman understands what is intended so brief him properly If you are both pilot and helmsman use the autopilot if you have one When in pilotage waters in a sailing boat
136. nt is still flowing out to sea at one knot opposite to that which you might expect The speed of the tidal current will be strongest at spring tides and weakest at neaps because the slope of the water is steeper at springs as the high water is higher and the low water lower Currents due to Eddies Less intuitive is somewhere such as the Channel Islands situated in the English Channel Because the Channel Islands are situated in a large bight and the English Channel becomes very much narrower at this point a large rotating tidal eddy is set up which at times runs counter to the current set up directly by the tidal bulge In parts of this area slack water occurs at half tide up and half tide down a 1 hour before Aha tide falling hour after alf tide falling a Slack water at St Peterport Guernsey Rotary tidal flow occurs at half tide up and half tide down Eddies in a channel close to the shore can cause the tidal current to reverse some time ahead of slack water Knowledge of these is very useful if you are trying to cheat the tide Currents Caused by Wind Tidal currents can be modified by wind A strong wind blowing for some time sets up a general movement of the surface water due to friction This wind driven surface current 51 can counter or add to the tidal current and needs to be considered when considering the tidal set and drift the tidal effect on the boat when
137. nt to couple up to an active waypoint then Track or Nav is selected If you are already on the correct track to the waypoint the autopilot will steer such headings as will Active waypoint maintain the cross track error at zero e If you are not on the correct track when you select Track or Nav the autopilot will immediately turn the boat to regain the correct track You need to be aware which way the boat will turn and by how many degrees in case there s another boat or obstruction in the way When the cross track error has been reduced to zero the boat will again be turned so keep monitoring what is happening and then steered to maintain zero cross track error Active track Boat on track with no cross track error ATE e If you have coupled up to a route you need to be aware of what will happen when you get to the next waypoint The majority of autopilots will give an audio warning that the waypoint has been reached and if no action is taken will revert to heading mode and continue on the last heading They will not make an unsupervised turn to the next waypoint as this could cause a collision with any nearby boats Autopilot coupled to an active waypoint If you do decide to use navigation mode you must continue to navigate the boat mentally and not be distracted 127 a eo _ G pe eee J a e e ee eee lorera ara es I I i I I R
138. nutes to Poole entrance Salcombe has a shallow sandbar in the entrance with a least depth of 1 1 metres so it s worth checking what depth will be available at 03 00 Salcombe s tidal curve shows that the tide will be rising and there will be about 3 7 metres over the bar at 03 00 i Show as UTC UTE Depth is Chaatsrcn en i DOSAD 020205 7m 17m Poole Harbour entrance is narrow and the a tide runs very strongly so need to ensure that we get there on the flood We ll be getting there a little before high water so that s ok If we re a bit late there s a high water stand and l Il have a good couple of hour s leeway If lm very late I ll have to anchor outside which with a forecast wind from the north is fine Checking the tidal atlas see that the tide outside Salcombe starts to run to the east just after we leave It starts to run against us halfway across Lyme Bay where the tides are weak turning favourable again around Portland Bill giving us a fair tide all the way to Poole This confirms that Seapro has come up with a good answer Seapro also has given me the course to steer for each leg their distances and bearings and the times The method of 20m 82 tidal Lurwe 1 ee nn inn he en Oe rrr Ome Deh 1 1 m Dit 20m Pon SALCOMBE Ces E Show UTC UTE Heihi jm Depihjim Olearsnce fm Za ooer fies asm asm tm seaPro 00m ml ___Depthoo
139. ny position that is on our way These are the waypoints The process will differ according to the type of navigator we are using GPS receiver or GPS chartplotter Using Second Hand Waypoints You can buy books of waypoints Also pilot books almanacs and boating magazines list waypoints never use waypoints that have not plotted myself and never join waypoints from a list to form a route unless have inspected the area on a recognised chart paper or electronic What is the point of using waypoints the author of which states that you use them at your own peril and that they should not be used for navigation A Route for Use with a GPS Receiver Here our starting point is a paper chart on which we can draw a complete route It may not have sufficient detail in areas where we are close to danger but we can see the whole route on one sheet Choose your route so that it is as short as possible but avoids passing too close to any possible hazard It s possible that you may have to adjust the route when you look at smaller scale charts where the route needs to be inspected more closely Do not use the actual position of navigational marks as waypoints GPS can be so accurate that you might collide with the buoy and if other navigators also use the same mark you may collide with their boat Aim 100 metres or so off Let us construct a route from Annapolis to St Michaels in the Chesapeake We ll need a chart with a
140. o follow highway display highway or compass Allow You to Estimate the Height of Tide Many chartplotters allow the tidal curve for a specitied point to be displayed There will be a number of tidal stations within the database signified by a special logo on the chart If the cursor is hovered over the logo the curve can be displayed Allow You to View the Tidal Flow Many chartplotters are able to display the tidal flow in real time Both the size and colour of the arrows vary according to the strength of the current Tidal curve for a designated point Man Overboard Most chartplotters have a man overboard key This operates much like the GO TO function except that when a you press the MOB key the geographical point at that Tidal flow arrows red strong instant is the point to which you wish to go It is very worth while you experimenting with this function It won t send any alarms to anybody Remember The position shown for the casualty does not take into account any tidal drift You will have to look down tide for the casualty A 1 knot tide will cause a drift of Distance and bearing to MOB rme aii Press Man Overboard MOB button This tells you that MOB has been activated Z3 Track of boat MOB position TOOM IN Boal position i Press any key along bottom 2 Press key under NAV Position of MOB Red line is your COG course over grou
141. onic you run up against the problem of transforming a spherical surface into a flat sheet It s fine if the area covered is no bigger than a football ground but if you want a sizeable portion of land or sea you just can t do it easily Strictly speaking mariners and aviators use charts while maps are used on land though for serious navigation on land such as in the desert and then we are back to charts again Chart Projections Ever since man realised that the Earth wasn t flat many different ways of depicting the Earth s surface have been tried All have disadvantages From looking at some maps many people think that Greenland is a massive island bigger than South America Australia or the United States of America In reality Greenland is smaller than Algeria and less than a quarter the size of the United States of l America and one third the size of Australia So why The shae s right the size is wrong is this contusion There is no projection that shows both correct size and correct shape of the continents If we have the correct shape we have the wrong size and vice versa So it depends what use is to be made of the chart or map which of the many projections is chosen It doesn t matter if we are considering a paper chart or an electronic one they all suffer from the same problems There are many projections that are used by cartographers but as this is a practical book we ll just look at a couple of basic principles
142. op of the chart plotting software r m m t m YOO Oa OO Se 2 ae n See o gt Geetha a Radar and chart plotting software side by side Superimposed Radar The radar display may be superimposed onto the chart display This has two major advantages e Certainty of identifying large cartographic or GPS errors You need to know where you are relative to the land and its dangers Only the radar will tell you this The accompanying diagram shows a deliberately induced GPS error which would have been invisible had we not used superimposed radar Another interesting error which showed up when preparing this section of the book was an apparent angular error in the superimposed image This was probably due to some form of compass or radar alignment error A deliberate GPS emor of 1000 metres North and 1000 metres West has been introduced On the chart plotter alone this would not have been seen With the radar overlaid on the chart the error is immediately obvious the radar must be correct and the GPS or cartography must be wrong GPS cartographac error e Ease of identifying topographical features on the radar Because the radar can t see around corners it s often difficult to match the radar image to the chart Superimposed radar overcomes this difficulty especially if there are extensive mud flats which show up SSS n aee reppe m e a r me m o mee o oe o o e e cee F
143. or curves close to being in the shape of a sine wave Also offered is a mathematical solution able to account for any skew in the sine wave Duration of tede La fo HW or Duration of tide HW to LW Tidal range Den 7ean Dien Jien d D je ie Js ja Ses Ges Fics Bes Dies Wes Dee Eee pepo nafohnen at A fogera ad EE S S S E O A dd E a a a e joge ot ir ua ro oo coe ess en A Rn LAR PG See e a P E E a A E ee ey Se ee eee shows Thou Than Tir O Imee lme Ime dma Smee Greiner Time of inberest before or after LW Height abowe Li Ti ia a after hv Height below HW SHOM graphical method of calculating table of coefficients height of tide The easiest method for boat owners is their graphical solution 199 Tidal Height Coefficients SHOM provides an annual table of tidal coefficients to distinguish how high and how low are the heights of tide relative to mean sea level niveau moyen which has a coefficient of O zero Spring tides have a coefficient of approximately 1 0 whilst neap tides have a coefficient of approximately 0 5 HAT and LAT are equivalent to 1 2 and zero respectively The diagram shows the SHOM definitions and their approximate UKHO equivalents SHOM Graphical Method The graphical method can be found in votre livre de board published annually by Bloc Marine www blocmarine com The graph used for the solution is shown here and here s how to use it to calculate the height of tide
144. otters can also be used with seaPro s PC based chart plotting software It has many enhancements for the leisure boater including photographs of marinas etc Full seaPro passage planning can be made using the Navionics charts Navionics charts on a PC the value added facilities including photographs and marina information valuable to some boat owners Selecting the Software A visit to the chart plotting software vendor s web site should show you what facilities are available There are often several versions to choose from extra facilities costing more money Upgrades from one version to another are usually possible You need to ask yourself will the computer be e The only chartplotter on the boat e Used only for constructing a route e Used for planning a route including tidal planning with best time of departure and track made good over the ground e Used to construct plan a route and send the route to a GPS or a chartplotter e Used to combine with wind forecasts over the period of the route to plan the best route to take account of the varying wind direction and strength e Used to display lay lines tacking angles sailing polars etc to optimise best navigate the route of a sailing yacht e Is it compatible with the chart type of my choice raster or vector e Can it be used with my chartplotter s memory card 133 134 Constructing a Route Constructing a route on a PC based chartplo
145. oundings What you need to know is how much the tide will fall from now until the time of low water Add to this the draft of your boat and the safety allowance you would like under your keel what the French call the navigator s foot pied de pilote and that s it That s the minimum depth in which to anchor If you are staying over more than one tide remember to check the lowest low water over the period that you expect to anchor If it s getting more springy your under keel clearance will get less each tide 47 Fall from now until low water Fall from now 42 until low water Depth to anchor Calculating the Depth of Water For this you will need to consider the chart datum and the charted depth or drying height Add the charted depth to the height of tide or subtract the drying height from the height of tide to find the depth of water A8 Chapter 5 Chart datum LAT Calculating the depth of water Calculating the depth of water with a sounding with a drying height Is There Enough Depth of Water to Allow My Passage Here we use the depth calculated as above and compare it with the draft of the boat plus the safety allowance If the depth is greater we re fine if it s less we can t proceed Often we need to find the earliest and latest times we can pass over a sandbar into or out of a harbour For this we need to know between what times the depth of water will be at leas
146. oute data to be uploaded to a global positioning Some systems allow the software to control the boat s autopilot Some systems allow the use of chartplotter memory cards which can be used in the PC Of considerable importance is what type of electronic charts can be used Raster Charts e Raster charts are electronic clones of a paper chart e They look just like its equivalent paper chart e They should be viewed at a specific scale UKHO raster chart scanned from the UKHO paper chart Maptech raster chart scanned from the UKHO paper chart SeaPro livechart vector chart redrawn using data from UKHO paper chart Raster and vector charts Viewed at the correct zoom for the scale of the chart 1 3 500 obtained by using the 1 1 control icon the detail on a chart of a given scale is always the same because there is onhy one layer Over 7oomed no extra detail but the chart becomes pixelated Over zoomed even more giving even greater pixelation Raster zooming 131 Vector Charts Vector charts are redrawn completely by the electronic chart cartographers There are many layers each with different types of data and these layers may be switched on or off either by the user or automatically as you zoom in or out Photographs pilots information etc can all be embedded Errors may be introduced in the cartography during the copying process Vector c
147. owever believe that for most purposes the information may be obtained by inspection e Draw an arrow between the HW times shown at approximately the correct proportion of the distance between them for instance if the time of HW at the standard port were 0400 the arrow would be two thirds the distance between Tidal differences at Bembridge 0000 and 0600 that is closer to 0600 than OOOO At this stage we must work in the same time zone as the tide table In this case we have not yet added the one hour for BST 158 Tidal Heights and Tidal Streams Appendix C e Note a time difference of 0020 means 00 hours and 20 minutes a time difference of 0115 means 01 hours and 15 minutes There s no full stop or colon between them 0115 does not mean 115 minutes e Use the same procedure for the time of LW e Similarly draw arrows for the heights of HW and LW according to their closeness to springs or neaps e This allows us to read off the values of the differences directly from the table e Apply these differences to the times and heights of HW and LW for the standard port to get the data for our secondary port e We can now adjust for local time that is add 1 hour for BST in this case SHOM Tidal Predictions The equivalent to the UKHO in France is SHOM SHOM offers several methods of calculating the height of tide at any particular time The simplest is the rule of twelfths which is often sufficient f
148. pass rarely points at the magnetic pole this error being called deviation Deviation is specific to your boat changes according to the heading and heel of your boat and must be reassessed annually as it will change with time and any additional equipment fitted Compass correction is dealt with in a later chapter Measuring Direction on the Chart There are a number of different instruments for measuring direction and users have their favourites Probably the two easiest to use on a small chart table are the Portland type course plotter and the parallel rule Course Plotter This plotter needs nothing except a meridian to line up on although in practice parallels of longitude may be used as well on the type of chart normally used e Place the edge of the plotter on the line joining two places with the main arrow pointing in the direction of travel e Rotate the centre knob to align the grid on the central wheel with the latitude longitude graticule e Read off the direction against the O on the centreline of the plotter e Variation can be applied as you work using the east or west error offset This allows the direction to be read directly from the plotter 2 j te F Ei a y Ee at this point read off magnetic direction A against 6 degrees East lt error in this case fs me E 044 magnetic Read direction Wi wae against 0 Poco in this case a
149. ppropriate to the scale of the chart To obtain the latitude and longitude of any point we need to compare the position of this point with the grid Several different tools may be used to do this and navigators have their own preference Using dividers is the only correct method where the meridians are not parallel such as on a conical projection However on such charts the errors using a parallel rule or course plotter will be very small unless the chart s scale is small If the meridians look parallel then the error will be too small to be significant for normal navigation We ll look at how we would measure the latitude and longitude of a special mark buoy near Sydney Australia whose position is 34 06 548 S 151 24 962 E Using a Parallel Rule Measuring Latitude The parallel rule is placed on the nearest part of the longitude grid and opened out to touch the point of interest The position of the rule is adjusted so that one edge cuts a latitude graticule and the latitude read off Measuring latitude with a parallel rule Measuring longitude with a parallel rule Measuring Longitude The parallel rule is placed on the nearest part of the latitude grid and opened out to touch the point of interest The position of the rule is adjusted so that one edge cuts a longitude graticule and the longitude read off Zo Using a Course Plotter Measuring Latitude The edge of the course plotter is placed on the point of intere
150. r 6 How They Work A transponder sends a pulse of energy aoe downwards from the bottom of the boat i L This pulse is reflected by the seabed and returned to the transponder which is now listening for the return The time taken for Depth transducer I ji the pulse to travel from the boat to the ie seabed and return can be translated by the i depth sounder s electronics into the depth T of water below the transponder This depth tt is displayed on the screen of the depth Tansmited g instrument y Seabed Depth sounder operation Depth Units Depth sounders can be set to fathoms one fathom equals 6 feet feet or metres Ideally the units displayed should be the same as those of the navigation chart you re using Calibration By default the depth displayed will be the depth below the transducer which is of no use to anyone Normally you ll be able to adjust the display to show the depth below the keel or the depth below the waterline This is known as an offset Many users set the depth to depth below the keel However if you wish to use the depth sounder as a navigation tool it s much better to set the offset so that depth below the waterline is displayed This is the actual depth of water If you want to know the depth below the keel all you need to do is to subtract the draft of the boat and this becomes an automatic action How to Calibrate Your Depth Sounder if an ad
151. r charts rely on people to not to make errors when compiling the chart but naturally errors will occur Chart Corrections Chart corrections are published regularly to correct known errors and to introduce new data The user is responsible for either buying updated charts or incorporating the updates when published 23 Common Sense This all sounds very alarmist but common sense and the use of as many navigation tools as possible must be used at all times It s an old axiom that groundings occur not because the navigator is uncertain of his position but because he is sure that he knows where he is but is wrong Navigators uncertain of their position navigate very cautiously The accompanying illustration from the chartplotter of a cautious navigator an ex airline pilot shows the planned inbound route to Figeuvira da Foz in Spain The red Xs are his planned waypoints The red track line shows where the chartplotter thought they were but of course our cautions navigator followed the buoys leading lines and the lie of the land to complete a successful arrival But if it were night or foggy another gung ho navigator would have ended on the rocks The longitude was correct but the latitude had an error of about 0 15 minute about 300 metres 900 feet Was this a datum error a cartographic error a vectorisation error or a GPS error Who knows but it could have ended up as a shipwreck whatever the cause
152. rate form of position line Harbour authorities often install transits lit or unlit to mark the centreline of their channels If you 93 m a _Transits apen a Transits closing Multiple lit transits in the shallow Chesapeake bay allow accurate alignment in the channels without Transits in line recourse to too many buoys u Transits lit by high intensity Using a transit directional lights haven t used a particular transit before check the bearing to make sure it s the correct one and remember that the charted bearing is in degrees true Transits designed specifically for ships with high bridges may give false information to leisure craft At Hamble BP Oil terminal there are transits to guide the tankers onto the berth Although the back transit is higher than the front as it should be from the cockpit of a small boat the front appears higher so you could easily turn in the wrong direction to keep the lights in line Aseries of seven tightly sectored red green and white lights guide the pilot into Devonport Harbour reducing the number of channel markers required in the deep water channel Very tall transit towers give impression that the front light is higher than the back light from the cockpit of a small boat Tall transit towers Sectored lights 94 Pilotage Chapter 10 In place of transits some channels are marked by sectored lights some to avoid dangers outside the channel and some so
153. ravel How long will it take Look at tidal streams When should you start finish to make best use of the tides Look at tidal heights Are there any tidal height stream restrictions at departure alternates or destination Do these modify start time If these times are incompatible where can you wait Read all pilotage notes almanac pilot book Prepare pilotage plans Prepare route plan plot on chart s check all tracks and distances Load route into GPS plotter check all tracks and distances High Wailer Down 00 20 BST Plan catering Ti Tidal Tidal Ground Running ETA Plan watch roster loss speed distance Yo el 22 2 L5 i Z5 18 owo For the Planned Day o llie los Jes 75 ose of Departure eS rac 3 1 17 0 4 _ g 20 4 osod T and heights of bell high low a fos les 268 cecal dtd oe a Ps epe os Pelee fon e ae 0 8 5 102 5 8 239A osod Times of sunrise sunset gt osl ssd To steer a constant heading forthe e T 125 Tio eoor whole cross channed leg the most re tor far Lis 147 suo effiecient way the course to steer is 10 7122 15145 60 4 200 obtained from considering all the tides gt osjo 16064900 see Appendix D The course to steer and SERRE the planned ground track is shown here 113 22 22 32 80 6 eoo ee a 7 a7 _ 77 leede _ 15 20 20 80 96 4700 Passage Making Tial Dettanee Voom
154. re known as tidal diamonds A table is included with specific values of tidal set spring and neap values and direction for each hour before and after high water at the stated reference port at the position of each diamond The lettered diamonds indicate the position for each set of tidal stream data Geographical ves 50 13 00N LAK 49 38 00N 49 10 00N Position 2 55 00W 3 22 00W 4 37 00W P w S 3 E E xX io oO 2g m E g E g a S S 3 o ari amp Before high water After high water Directions of streams degrees Tidal stream data for each hour before and after the time of high water 5d We can see that there is only one reference port for any tidal flow table The time of high water is not for the position of the diamond or even for the nearest port The reference port may not even be on that chart It is chosen by the hydrographer to give the most helpful and representative reference time of high water for the area under consideration Tidal Atlases Many charts pilot books and almanacs contain tidal atlases showing the tidal currents A small chart has tidal flow arrows marked on it together with the speed of the current There is 1 chart for every hour so there will be 12 charts enabling the user to estimate the tide at any time in the tidal cycle The actual values used in tidal atlases are obtained using the tidal diamond data High water Dover 0540 after HW
155. ree position line fix draw a circle around this position enter the time of the fix and the distance log reading at that time Using the standard convention anyone looking at your chart will have all the data needed without having to look at your written logbook Errors in Position Lines A big advantage of visual and radar position lines is that you are not relying on the accuracy of the cartography to avoid hitting the land The land is where you or your radar sees it not where the GPS or the mapmaker tells you where they think it is The position given by your position lines is correct in relation to the land though it may not tally with the latitudes and longitudes shown on your chart This is important if your charts have large errors as some do If your chartplotter shows that your boat is travelling merrily over the land but your eyes show you to be safely floating on the water which are you going to believe Just have a look at the trace from this chartplotter It is very difficult to achieve an accuracy of better than plus or minus two and a half degrees when using a hand bearing compass on a boat at sea This will lead to errors of 70 Finding Position Chapter 8 Error in fix al due to apptying A 4degrees vanaton Error due to incorrect variation Possible error in fix 800 metres at 10 miles range from the feature 400 metres at 5 miles and 250 metres at 3 miles respectively In
156. reen radar or standalone radar for this purpose Navtex on a PC Sas A AADA Dedicated Navtex receivers are left in S standby mode for the whole time so that they will receive all the messages which are Eien displayed on demand by the user The PC can be linked to a Navtex receiver but for the i best use the PC will need to be left running all 5 the time which is probably not the way you Bal oe H bUane it fd iT inf ali rit flee TELIAS l eee ee A if wi ft will use an onboard PC M Bo Ori Fa EA T LECELEEREE a i 5 ke _ a Navtex window in view you can scroll through the messages Navtex Tides on a PC a Various forms of tidal software are available for use on a PC some of them stand alone and some integrated with the chart plotting software Tidal Flow Tidal flow data may be integrated with the chart plotting software and allows both strategic and tactical planning if the software supports planning e It is used in the initial route planning to obtain the time of departure that gives the fastest passage i et ER a or e a m 15 5 aE oS a mn Been ee ee Oe ee a ie ee Se B B rE WORE oe nar in ini i fi je pee iE Ht Wi i Tidal flow can be displayed on some chart plotting software The flow is given in real time and as the passage progresses the tide vectors change accordingly The time can be scrolled forward or
157. rmonitt te Guowniey Routing east of Alderney Phased erasing speed Eitivectted rt en toul Neila G d ol Hiina Ralie tae Eastbound shipping lane Aedh fe iht o Eaj fale Lao Anale deilast Cherbourg avnilable at all dates of thle and in all weather Alidorney Ol brit nett not be swept panied by tile Urediannble ive diog ME wiad Outline plan Key to overview chart Detailed Plan At this stage you can investigate the plan in more detail and if there are strong tidal streams and tidal gates you will need to keep refining the plan as you home in on the best departure time what s known as an iterative process I ll Outline My Way of Doing This e Using the initial approximate time the trip will take juggle any tidal gates to come up with a departure time This may entail compromise e Knowing the departure time need to see what the actual tides are on the way to get much more accurate route timings use the tidal atlas for the trip having checked the time of high water used by the atlas for the departure date and a strip of paper on which can mark the length of the route to the same scale as the tidal atlas mark along this route hourly marks for my estimated boat speed This allows me to move from page to page of the atlas to estimate the tide at the point expect to be at that time Sounds complicated It isn t as a look at the diagrams will reveal 79 bial arrow fo hour required D
158. rt Datum where known 172 Tidal Planning and Plotting Appendix D Rock which does not cover height above chart datum 173 Safe clearance under a power transmission cable where published otherwise the actual clearance is shown in black Vertical clearances 174 Tidal Planning and Plotting Appendix D Duration of tide LW to HW or Duration of tide HW to LW Tidal range Bhous hous Ghows Shows 4hours Des Bese Jere Sree Sete Dars Peon Boe Jare Bides iuas Live RR EE o oe o appre Foen ee cae SAHE Eee i COL Jetski EE E HERA Sa Fip EHARA a 8 ee i Seem AY a t e l e erra oe ees WN A AMAR TR TT TT SSR HA aac Moe BREE EEE EEE Seeaceetiiiy A AN inina BRR RR A a ee NY SCO SN T T T EA NNN Soana ANEN EE E HHH HHHH H ELEELERLEEELEEEED Time of interest before or after LW Height above LW or or Time of interest before or after HW Height below HW MSL 3 81 meters July 14th HW 1146 UT 1 6 05 meters Spring range 5 3meters LW 1823 UT 1 1 45meters Neap range 2 5 millimeters We want the height of tide at 1506 UT 2 Duration of tide HW to LW 6 hours 43 minutes Time after HW 1246 1506 2 hours 20 minutes Range for day 6 05 1 45 4 6 metres Height below HW 1 15 metres Therefore Height of tide is HW 6 05 1 15 4 9metres at 1506 French Summer Time SHOM graphical sulution 175 Duration of tide LW to HW OR Duration of tide HW to LW Tidal Range 7m Bm 9m
159. s Types of Autopilot Using the Autopilot 14 Personal Computers viii What Type of PC What Make of Chart Plotting Software What Type of Electronic Charts Electronic Charts for PC Based Chartplotters Selecting the Software Constructing a Route Sailing Yacht Route Planning 72 Z 97 98 101 103 104 104 104 104 105 106 107 109 110 113 114 121 121 122 125 125 126 129 130 130 131 132 133 134 1353 Contents Sending the Route to the GPS 137 AIS on a PC 138 Radar on a PC 139 Navtex on a PC 142 Tides on a PC 142 Connecting to the Boat s Systems 143 Appendix A Deduced Reckoning and Estimated Position 145 DR Navigation 146 Estimated Position 146 Leeway 148 Error in EP 148 EP with Multiple Headings 148 Appendix B Course to Steer 149 Where Do You Want to Go 150 What Time Interval Do You Choose 150 Draw in the Tide 151 Draw in the Boat Speed 15 Ground Speed 152 Comparison with EP 153 Appendix C Tidal heights and Tidal streams 155 Atmospheric Pressure Corrections 156 Tide Tables 156 UKHO Tidal Predictions 156 SHOM Tidal Predictions 159 Tidal Streams 16 Appendix D Tidal Planning and Plotting 165 A Long Passage Using a Single CTS 165 Where will the Tide Take You 167 Credits 169 Cover points e If you wonder why your in car navigator shows that you are in a field Read on e If you wonder why your in car navigator takes you on farm tracks Read on e If you think that the
160. s and then mark off the distance along the position line from the centre of the compass rose You now have your fix again pretty quick and accurate as long as you use the correct direction either true or magnetic for both the GPS and the compass rose Direction towards waypoint is on far side of compass rose Waypoint at centre of compass rose Waypoint at centre of Compass Rose 87 Unmarked Danger as a Waypoint If you are worried about going too close to an unmarked danger such as a dangerous rock you can put a waypoint at the danger itself Your GPS will then give you the distance and bearing to the danger so that it can be safely avoided GPS gives distance and bearing 1 36 miles 320 degrees to unmarked dangerous rock Pierre au Vraic allowing it to be safely avoided Waypoint at unmarked danger Clearing Bearing Another way of avoiding an unmarked danger is to use a clearing bearing In this case have drawn a line from the next waypoint which is now active towards the danger but giving a safe distance off This is known as a clearing bearing and in this instance is 030 degrees Provided that we don t allow the boat to stray too far to the west so that the bearing to the waypoint doesn t exceed 030 degrees we will be safe Again make sure that both the bearing and the GPS are given in either magnetic or true Clearing bearing 88 io n E LIL iF VS SS OSS
161. s M and not less than 013 degrees M you will have a safe passage provided you don t go north of the inbound transit into the River Yealm Clearing bearings 96 Heading 222M 3 miles Z 30 prinutes Pi Zig zag about 180M 0 7 miles B 47 6 To find the entrance to Helford river from Falmouth in misty conditions you could make a course to the north of the entrance turning South when you get to the 5 metres contour as indicated by your calibrated depth sounder Zig zag along the contour until you get to deep channel and then turn onto the inbound heading Using a depth contour Pilotage Chapter 10 Planning Pilotage requires planning If you ve been there before the plan may be in your head but it has been planned Your old plan will need to be updated for the weather and tide on the day Just like passage planning of which this becomes part start off with an overview and assemble the tools you will need such as large and small scale charts almanac and pilotage notes The Basics of Preparing a Pilot Plan e Pilotage is visual navigation e Pilotage needs to be planned e Use large scale charts e Check dangers e Check special rules e Check VHF channels Aids to Pilotage e Pilot book e Tidal atlas e A pilotage plan e Hand bearing compass e Binoculars e Log distance e Depth e GPS course over ground e Stop watch e Radar Methods e Clearing bearings e Charted transits e N
162. s at any one time showing the distance bearing and name of the vessels although many do have the ability to show more or have a simple PPI Often because of the limitations of older bridge design the AIS data is not within easy view of the Officer of the Watch All new builds from July 2008 will have to have an integrated AIS display but this will not be retrospective 105 The AIS Display on a Chartplotter When the chartplotter is supplied with data from an AIS receiver all AIS equipped ships within range will be displayed on the chartplotter screen These ships will be shown as a triangle with a line projected in front of it representing the ship s COG If you hover the screen s cursor over the triangle more information will be displayed consisting of at least e the name of the ship e the ship s MMSI e the ship s international call sign e the ship s COG e the ship s SOG e the CPA closest point of approach e the TCPA time to CPA The distance and bearing of the cursor from your boat will be given on the screen so if the cursor is on the target ship you will have its range and bearing What the Display Tells You Looking at the basic chartplotter display it s difficult to know if any target will pass ahead collide or pass astern of you You could resolve the situation graphically but the AIS computer will do the sums for you If the transmission from the target contains errors then a false
163. scale of around 1 1 25000 for the overview and charts of a scale of around 1 2 500 for each end where we need more detail Starting at Annapolis we can put the first three waypoints on the large scale chart before moving to the small scale ana chart to add the next seven waypoints The Annapolis end of the route 36 Constructing a Route Chapter 4 Now we ll need to use the large scale chart for St Michaels to put the rest of the waypoints in place Route from Annapolis to St Michaels An overview Route plan Annapolis St Michaels Once you have a safe route mark the waypoints and determine their coordinates There s no standard symbol for a waypoint as there are other navigation details such as position Many navigators however use a square with a cross in the middle Measure the distance and direction of each leg and note these down on a plan It s a good idea to use a printed pro forma for this or on the route planning page of your navigation logbook You will end up with something like this 37 Note that put the waypoints on every second line so that the distance and tracks are on the intermediate lines separating each waypoint This makes it easier to read than some other systems Loading the Route into the GPS The first thing to remember is that rubbish in rubbish out We all know how easy it is to miss key numbers using a keyboard The only way of checking you hav
164. signal on 10 randomly selected slots over a 10 second period If no slot is available it cannot transmit and must wait a further 30 seconds and try again A class B set may thus not be able to transmit regularly even when there are many empty slots as the randomly selected slots may be full AIS Displays On the leisure market there are two a Distance and bearing of the types of display available Ideally the AIS receiver is connected to a chartplotter or pc plotter and the target information is displayed in the form of a ship icon together with its ANE 3 course and speed and whether it is a N Tete ESS danger You can see all the other data Soe foe if required All targets in range will be displayed on the screen in a dynamic way The other alternative is to have a dedicated display such as that from NASA where up to 30 targets are cursor from your boat shown on a circular plan position Your boat AIS targets indicator PPI although no indication of your own course is shown on the AIS display on chartplotter north up display Most merchant ships have a far less sophisticated navigation display than many leisure craft Only the very newly built ships have large colour radar screens electronic chart displays and few have the AIS information co located on the radar or chartplotter Most show their AIS data on a very simplified display This is required to display the data of only three vessel
165. sition is updated is very rapid but to minimise the effect of random errors COG and SOG are averaged over about 5 seconds by default although the user may alter this time The longer the time interval the steadier the reading but the slower the response to a real alteration of heading or speed If the error between two fixes were 15 metres one to port and the next to starboard the error in COG over a 5 second period at 6 knots speed could be greater than 45 degrees Similarly with similar errors but in the direction of movement the SOG displayed could be in error by 6 knots With selective availability switched off the normal g Heading being steered 100 Course over ground 113 The effect of tide on heading Fix at 0904 Fix at 0903 Once the GPS receiver is moving it can determine the direction of North Error in COG Second fix Error in SOG Errors in 506G and COG situation random errors are likely to be very small and COG and SOG are generally stable and accurate With the default setting for the averaging time watch the COG and SOG at a constant speed and heading to get an idea of how they respond in normal conditions If selective availability is switched on by the US military the accuracy of COG and SOG will deteriorate significantly Our Address on the Earth s Surface eee 2 30 Tt aor eT bes aa To 8 i il a at in S jit _ I I Ji
166. st and aligned so that the opposite edge or the plotter s grid is parallel with the longitude grid The latitude is measured where the plotter s first edge cuts the latitude graticule Measuring Longitude The edge of the course plotter is placed on the point of interest and aligned so that the opposite edge or the plotter s grid is parallel with the latitude grid The longitude is measured where the plotter s first edge cuts the longitude graticule Using Dividers Measuring Latitude Place one point of the dividers on the point of interest and open them out so that the other point touches the latitude grid at its closest point Move the dividers so that one point touches the same latitude grid where it has a graticule and read of the point s latitude Measuring Longitude Place one point of the dividers on the point of interest and open them out so that the other point touches the longitude grid at its closest point Move the dividers so that one point Measuring longitude with dividers 26 Chart Symbols Each charting organisation has its own standard chart symbols They are all pretty similar and there s a new international standard set of symbols for electronic charting Measuring latitude with dividers touches the same longitude grid where it has a graticule and read of the point s longitude Our Address on the Earth s Surface Chapter 2 The geographical position is shown by th
167. stead of the position lines intersecting at a point you ll get a cocked hat The size of the cocked hat will give an idea of the accuracy of the fix The green polygon shown on the accuracy diagram is the area in which you might lie with a plus or minus two and a half degree error in all three bearings In particular avoid the application of variation in the wrong direction otherwise large errors can occur Transits There should be zero error when the position line is based on a transit and hence a pertect fix results from the intersection of two transits Radar The error of a position line based on a radar range should be no more than 1 of the range though identifying the exact position of the geographical feature may not be so easy Radar bearings are prone to error due to the alignment of the antenna the width of the radar beam the difficulty of identifying the feature and the application of deviation and variation so should be used with caution How Far Can You See Because of the curvature of the earth s surface the distance to the horizon which is determined by your eye level is possibly not as far as you might think From an eye Jib aia ale sk ya Nata SS lc P 7 ihe charted height of the object to obtain the distance ft should be visible height of 2 metres it s only a little over 3 miles Therefore a buoy beyond 3 miles won t be seen though in fact most buoys Visible distance For a light use th
168. t The table shown indicates the chart datum associated with different places along part of the UK s Kent coast They are all referred to the UK Ordnance Survey datum situated at Newlyn Cornwall in the United Kingdom this point being the UK s reference for sea level for all UK maps The table indicates that there is a 2 34 metres difference in LAT along this stretch of coast Tidal levels referred to datum of soundings Longiude Heights in metres above datum Datum and remarks N E MHWS MHWN MLWN MLWS Chart datum information as found on UKHO charts It s also worth noting the significant difference in spring and neap tides from place to place along this 35 miles coastline Using Chart Datum Now we have a load of definitions to think about what use are they We need to be very careful when checking depths heights and clearances under obstructions as not all hydrographic authorities use the same standards Because commercial shipping is changing over to the use of electronic charts the International Maritime Organisation introduced a new standard in 2006 2007 Beware then not only the make of chart 43 but also when it was issued You must check the notes on IE Do goes ee any chart or the current list of ici rene symbols and abbreviations to see what standard applies to the charts you are using Charted depths below chart datum LAT are added to the tidal height to find the actu
169. t our draft plus allowance Can We Get Under the Bridge In this calculation we use a different datum If we used LAT there would always be less clearance than that shown on the chart except at lowest astronomical tide LAT or its equivalent This would be potentially dangerous Until 2006 different authorities used some form of higher high water MHWS in the United Kingdom or MHW in the United States America In France they used mean sea level Now all new charts should use highest astronomical tide HAT Check what standard your chart is using if you don t have much clearance The charted clearance under a cable takes into account the electrically safe clearance that is there s an allowance for how far the spark can jump A high voltage cable will have a bigger allowance than if it were low voltage When can we enter or leave 49 This calculation is a little more complicated because the clearance is above HAT but the water level is above LAT All we have to do is add the difference between HAT and LAT to the charted clearance subtract the height of tide and we have the clearance above the water level Ok so a picture is worth a thousand words well here s the picture And yes it s safe to go under We can if we need to find the times between which we can pass safely under the obstruction Tidal Flow The Speed of the Bulge The Earth spins within the tidal bulges giving the appearance that the
170. tance repeating this every time halve the distance As you can see on this passage altered heading only when we started to make leeway as the wind headed us Although we got 3 miles north of the direct track we stayed pretty well on our planned ground track If you are in a sailing boat tacking against the wind tack so that you stay either side of the planned ground track On an open water passage such as this it saves navigation effort if you tack on each hourly fix until you get closer to your destination provided that it s safe to do so and the wind doesn t change direction unfavourably See Appendix A for the procedure Alternative to Plotting Latitude and Longitude Passage plot Plotting latitude and longitude on a small boat at sea is not everyone s cup of tea There are alternative methods that require more chart work before you start but simplify the navigator s work on passage These 85 alternative methods are the only way that you can do any form of chart work on a fast moving boat because of its motion On a fast motorboat or any boat in rough seas thorough planning for all eventualities is a must as you may not be able to do the paper work on the way Note Some of these methods involve entering coordinates into your GPS which don t form part of a route so you have no method of cross checking their accuracy Do double check their coordinates and try to check their bearing and direct
171. ter 24 hour GRIB 4 hour GRIB papi Iji 1 pl aay i mema PEAT H kann maeman ppan i aema F tt im TFR EE FD ek ba Fi E g Weather files orib files can be doan kaded from the internet and the software then aligas the winds from these files to be The wind pattem 72 hours after the initial forecast time ised to calculate the best route to be calculated 72 hour GRIB The fastest route If your software supports weather routing the vendor s web site will have links to various sources of GRIB files Sending the Route to the GPS Although the PC will almost certainly have the boat s position input from a GPS set which allows the navigation to be carried out using the PC it s a very good idea to transmit the route data from the PC to the GPS In this case should the PC fail the route will still be available in the GPS to allow continued electronic navigation If you are using a dedicated electronic chartplotter then the route once constructed on the PC can be transferred to the chartplotter 137 Compatibility of Route Transfer Unfortunately some GPS and chartplotter manufacturers use their own protocol rather than the industry standard NMEA The PC chart plotting software uses NMEA sentences to receive GPS and other data and also uses NMEA to transmit information back to the GPS chartplotter At the time of
172. the distance between each 10 degrees of latitude gets progressively greater Where a chart covers a large portion of the Earth s surface this is especially critical when measuring distance So when measuring distance we should use the region of the latitude graticule at almost the same latitude as the distance to be measured If the distance between two points is longer than the open distance of the dividers measure a convenient length on the latitude graticule and then walk the dividers along the line counting each step Measure the remaining small distance and add this to the number of steps and you have the total distance Under no circumstances should you use the longitude graticule to measure distance Only at the Equator it does give approximately the distance and as you move further away the error increases At 30 degrees North 1 minute of longitude equals 0 866 nautical mile and at 60 degrees North or South it s only half a mile At the poles it is of course O nautical mile When you change chart scales check the latitude graticule carefully to ensure that you know what each coloured part a0 La Latitude graticule markings represents 1 mile 5 miles 10 miles etc It is really easy to make a mistake especially when one chart is lying on top of another and you can see both latitude graticules Direction All meridians pass through the North Pole and so all meridians define the direc
173. the meridians are straight but converge towards the closest pole Within a reasonable distance of the tangential parallel scale is much more consistent Look at how Greenland and Algeria are much closer to their proper areas The direction of north or south is not constant but towards some invisible vanishing point Again we cannot represent the polar regions Polar Projections The only way to show the polar regions on a navigation chart is by having a flat sheet of paper sitting directly on the pole All parallels of latitude are concentric circles about the pole and meridians are straight lines radiating from the pole Scale is correct only at the pole When situated at the pole all directions are south from the North Pole or north from the South Pole The Spherical Earth and Map Data In fact the Earth isn t a sphere it s an oblate spheroid flattened at the poles and with bumps on it These bumps are not the mountains and oceans but irregularities which depart from the regular shape of the Earth They occur over areas large enough for the mapmakers to take them into account when producing maps of their country Because the bumps effecting each country is slightly different each national map making organisation has used complicated formulae which best represent their part of the world so that other 20 Our Address on the Earth s Surface Chapter 2 map makers know what is going on each formula is
174. the purposes Radar echo of shoreline registers with charted shoreline Fam of navigation and pilotage the overlaid radar has considerable merit For the overlay the radar echoes are often coloured magenta which is mostly not present on the cartography so the radar echoes stand out well The radar echoes should correspond with the cartography and this makes identifying the shoreline and navigation marks much easier Any radar echo that doesn t register with a charted feature is likely to O buoy ona a cpp 8d feature be a ship Do the radar echoes correspond with the chart Very large chart error With radar overlay the chart error is very obvious Any error in the cartography or GPS will become apparent because the radar will not agree with the chart The radar is correct Setting up Your Radar Setting up your radar properly is very important Most sets have some form of automatic adjustment of some important functions they re getting better but you can always do better yourself if you know what to do 12 A good illustration of this occurred when was on a long passage in flat calm seas and with little else to do was playing with the radar Having adjusted everything very carefully noticed some fast moving echoes ahead but saw nothing on the water looked up a little and there were some seabirds Gannets flying round ahead and it was their echoes that could see then set all the controls to automatic
175. ticks out more on one side of zero deviation than the other the compass can be rotated in its mount to make the average deviation as close to zero as possible This error is known as A error Deviation of the Hand Bearing Compass Compass deviation occurs due to the boat s magnetic effect where the compass is positioned not due to any aioe enie ter at eit inherent compass problem When using the hand bearing compass you should find a position in the boat where the boat s deviation is zero or a minimum This is likely to be as far away from any magnetic material as possible This could be in the bows or the stern depending on the position of the engine To check the deviation in any position sight the hand bearing compass on a distant but prominent landmark Let the boat carry out a full 360 degree circle If there is no deviation the hand bearing compass will maintain a constant bearing all the way around the turn If the bearing changes the maximum deviation is half the total change of bearing though you won t know the actual deviation on any particular heading Correction for other errors by an amateur on a leisure boat compass is either not possible or not desirable Knowing and allowing for any error is sufficient 32 The Magnetic Compass Chapter 3 Very Large Errors Need to be Investigated One motor cruiser was checking had compass errors exceeding 30 degrees entirely unacceptable Someone had fitted a loudspeaker
176. tion of true north It is true because it refers to the geographical pole For this reason we measure direction relative to a meridian On a Mercator chart the meridians are parallel to each other so direction can be measured relative to any meridian on the chart A conical projection implies that none of the meridians are parallel and so direction must be measured relative to the meridian nearest to where you wish to measure the direction Never measure direction relative to the Line crosses each meridian at a different angle chart s border because this may not be aligned with true north Measuring direction with a course plotter Meridians not aligned with chart border Magnetic North Pole The true North Pole is on the Earth s spin axis However this is not where a magnetic compass points The compass needle is attracted towards the magnetic North Pole which at the present time is situated in the north of Canada about 800 miles south of the true North Pole It moves slowly but noticeably and the annual value must be used for navigation 16 Our Address on the Earth s Surface Chapter 2 Variation The angular difference between the direction of true north and magnetic north is called variation and its value is indicated on a chart together with its annual change Variation may be east or west of true north and is annotated accordingly Deviation Because of the influence of the boat and its equipment the com
177. tter is usually simplicity itself The cursor is placed over the position that you wish to have a waypoint you click the mouse move onto the next position and click again continuing to the end of the route The only problem is that the screen size will limit the amount of detail that you can see though this is much better than the average dedicated chartplotter For safety you ll need to zoom in and out and pan along the route to examine it along its length to ensure that it runs into no dangers Click the mouse where you wish to insert waypoints fo make up a route PC route 7 PC route 3 a_i Py L EECCEFEEEFI 7 a ae cre Until you reach the end of the route PE mule 5 Er o ee g Se Se o m te ee ee E Sake in oe B nga Zoom in and check each portion of the route for safety PC route 2 3 eee ii 1 PE rawie 4 Some chart potting soltware such as seaPro allows various departure times io be investigated to give the shortest tima on route using the Planning departure time Personal Computers Chapter 14 Once the route has been calculated the track Tihe piin vivia aeri coutee ko eer for end elapsed over the gound is displayed as a dashed ling time for sach leg and ETA destination tor the selected and the leg details may also be displayed on dapariure bma the chart if desired Route plan Route plan details PEELED EIR FRANC a a ae j i x ee
178. turn onto 160 magnetic and adjust heading to keep the East Tinker in transit with the Breakwater fort back bearing of 340M until you reach the 20 metre depth contour Continue for 0 15 mile 1 5 minutes at 6 knots and then turn onto O95M e Continue eastwards to make good a ground track of 095M allowing for any tide Your GPS set to display COG will help to ensure you keep on track Ensure that the depth remains at 20 metres or more so that you keep well clear of the drying rock to the south of the Great Mew Stone As you clear the Great Mew Stone start looking for the church tower Looking on about O55M with your hand held compass will help you find it You can start your approach to the Yealm once the bearing of the church tower is O39M or less Ensure that the bearing does not reduce below 019M in order to avoid all obstacles Now start looking eastwards watching for Misery Point to become visible beyond Mouthstone Point You should soon see the transit beacons well up the wooded slope above Cellar Bay Once these are in transit turn onto 093M and keep them lined up As you approach the two red buoys April October you will have to jiggle south and leave them to port Start looking for a red and white marker post high on the north bank If you steer to keep that on a bearing of O50M you ll keep in the deepest water while crossing the inner bar Entering the Yealm avoiding the bar 9 e You are
179. use of small inaccuracies in the receiver s clock there will be an error in its position The position lines will not intersect at the same point and will form what is known as a cocked hat Pseudo Range A clever trick within the receiver converts the ranges into pseudo ranges which allows them to be shuffled around within certain limits The range from a fourth or even more satellites is calculated and added to the fix The extra position line s allows the timing error to be determined and this results in a good fix where all the position lines intersect at only one point Fourth satellite Accuracy of the Fix With range being calculated using the time taken for the signal to travel between the satellite and the receiver any SaaS variation in the speed of the signal and the actual path followed will lead to errors Errors due to these effects will normally amount to no more than 15 metres for 95 of the time being made up from the following e ionospheric effects 10 metres e ephemeris errors 2 5 metres Normal GPS errors e satellite clock errors 2 metres e multipath distortion 1 metre e tropospheric effects 0 5 metre e numerical errors 1 metre or less The Global Positioning System Chapter 1 With my boat moored in the marina normal GPS errors were plotted as shown over an 8 hour period Although most were contained within the 25 metre diameter circle one was almost 100 metres in error
180. v World Currents Chart US Naval Laboratory Ocean currents This image is a copy of ecean_currents_1943 jpg a map from the map collection of the Perry Castafieda Library PCL of the University of Texas at Austin According to the FAQs it is in the public domain 169 Tidal Height and Tidal Currents Diagrams and data for UK UKHO and Nautical Data Ltd Diagrams and data for France SHOM and Bloc Marine Diagrams and data for USA NOAA 170 Standard Port PORTSMOUTH Times Height metres High Water Low Water MHWS MHWN MLWN MLWS 0000 0600 0500 1100 47 3 8 1 9 1200 1800 1700 2300 Differences BEMBRIDGE HARBOUR 0020 0000 0100 0020 FORELAND LB Slip 0005 0000 0005 0010 VENTNOR 0025 0030 0025 0030 SANDOWN 0000 0005 0010 0025 Tidal differences at Bembridge Overhead power cable Charted vertical clearance black Charted vertical clearance Safe vertical clearance Charted Magenta elevation CPEE TETE ET ETET Tr r Ere E E ac Height of tide Observed f Drying height sounding le Pe ge ee ne BE rae at 2 OAS oo EES LI C LI Tide levels and height references Tidal Planning and Plotting Appendix D Tides are UT 1 French standard time For French Summer Time add 1 hour Extract from Cherbourg tide tables 171 Rock awash at the level of Chart Datum Rock which covers and uncovers height above Cha
181. will have carried you while you ve been travelling you can estimate where you now are Unsurprisingly this is known as estimated position or EP This method has been used since navigators started roaming the seas and is surprisingly accurate Using this method it s unlikely that you ll become terribly lost provided that your compass and log have been properly calibrated You ll almost certainly be no more than 10 of your logged distance run from your actual position The chances are that you ll be much closer so don t deride this method EP and DR are covered fully in Appendix A Estimated position 72 Finding Position Chapter 8 Chartplotters An electronic chartplotter is a navigation instrument that displays the position of the boat superimposed on an electronic chart You will find an electronic chartplotter simulator on the Wiley Nautical website at www wileynautical com The boat s position is determined by a GPS receiver The GPS receiver may be part of the chartplotter with either an internal or external GPS antenna Alternatively the chartplotter may be supplied from a separate GPS receiver An electronic chartplotter 50 03 1N 001 02 143H 16 SEP 2002 ao The yellow arrow shows the direction to follow The waypoint is 0 356 miles distant and you will arive in 3 minutes 7 The waypoint is now dead ahead Turn boat to follow highway alligned with the red line
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