Coastal Skipper and Yachtmaster Offshore Part 1

Millennium 2000 Edition

Fully Revised and Updated for International UsersAlso available through http://www.yachtmaster.co.za

COASTAL SKIPPER / YACHTMASTER OFFSHORE

Shorebased Course

PART 1NAVIGATION

USCG CompatibleA Royal Yachting Association Syllabus

and S.A.M.S.A. (D.O.T. SA) and SA Sailing

approved Courseincorporating the syllabus of the

Australian Yachting Federation

By

HENTON JAABACK

Yachtmaster Ocean Services CC

Copyright © YACHTMASTER OCEAN SERVICES CCReg No. CK 90/38623/23

This document contains proprietary information which is protected by copyright.

All rights are reserved. No part of this document may be photocopied,reproduced, or translated without the written permission of

YACHTMASTER OCEAN SERVICES.

Edition Number 1, November 1991. Edition Number 2, December 1991.Edition Number 3, June 1992. Edition Number 4, January 1993.Edition Number 5, September 1993. Edition Number 6, April 1994.Edition Number 7, September 1994. Reprint Number 8, February 1995Reprint Number 9, November 1995. Reprint Number 10, May 1996. Edition Number 11, October 1996. Reprint Number 12, July 1997Reprint Number 13, August 1999. Millennium Edition, April 2000

Written as course study material for classroom or home study courses. By the same author:

The Radiotelephone Operators' Restricted (Marine) Certificate Course.

Competent Crew / Yacht Hand Practical Course.

Yacht Skipper (Local Waters) Practical Course Notes.

Competent Crew and Yacht Skipper, Part 1, (Inland Waters),and Part 2, (Local Waters)

Shorebased Courses.

Yachtmaster Ocean*- The Complete Syllabus Course.

Astro - Nav in Emergencies, For the Non-Navigator. (The GPS back-up.)

All courses conform with the Royal Yachting Association, AustralianYachting Federation, and CruisingAssociation of South Africa syllabuses, and are Department of Transport (Marine) approved.

Written to be the most comprehensive syllabus coverage course notes anywhere, for an instructor toissue to his or her students.

* Acclaimed by a Yachtmaster examiner who assessed the instructional value of the work, as ...'The best I have ever seen'.

A senior corporate executive who attended the course describes the books as...... 'Absolutely excellent' and 'well worth the price'.

Copyright © Yachtmaster Ocean Services CC, 1991, 1992, 1993, 1994, 1995, 1997, 1999,2000.

PO Box 12181, Mill Street, 8010, Cape Town, South Africa.Telephone and Fax: + 27 21 462 34 13, Mobile/cell 082 901 1296

e-Mail: [email protected] http://www.yachtmaster.co.za

Coastal Skipper/Yachtmaster Offshore Shorebased course

Yachtmasters’ courses and books give you all the detail in an easy to follow way.

ii

Coastal Skipper/Yachtmaster Offshore Shorebased Course


iiiTABLE OF CONTENTS

Content PageIntroduction to this Course iv

PART 1 ............................................................................................. 100 - 199

Chapter 1: Introduction to NavigationWhat is ‘Navigation?'; Basic Tools of Navigation ....................................... 101The Earth's ‘Rings'; Latitude ...................................................................... 101Meridians; Position..................................................................................... 102Charts; Mercator Projection, Scale............................................................. 102Distance; Nautical Mile, Cable.................................................................... 104Great Circle; Rhumb Line and Meridional Part........................................... 104Chart Markings.......................................................................................... 105Chart Statement........................................................................................ 106Chart Symbols and Abbreviations............................................................. 107Conversion Scale .................................................................................... 110Compass Rose, Variation......................................................................... 111Course To Steer; Waypoint...................................................................... 112Line of Position; ....................................................................................... 113Deviation; Swinging a Compass............................................................... 114Deviation Cards....................................................................................... 114Speed ..................................................................................................... 116Directions, Chartwork Symbols; Course Steered, Ground Track, Set, Line of Position, Advanced or Transferred Line of Position .................... 117Dead Reckoned (DR) position; Estimated position (EP) ............................ 118 Leeway; A ‘Fix' position; .......................................................................... 120Transits, Clearing Lines; Other tools; Navigation Drawing Instruments ..... 125Stationery: Other Aids.............................................................................. 125Notes....................................................................................................... 125

Chapter 2: Coastal NavigationIntroduction................................................................................................ 127Techniques of Visual Position Fixing.......................................................... 127The Use of Measurements......................................................................... 128Methods of Taking a Fix............................................................................. 130Actions Common to All Methods................................................................. 130One LOP and Depth................................................................................... 130Two LOPs.................................................................................................. 131Two LOPs and Depth................................................................................. 131Three LOPs - The ‘Simple Fix'................................................................... 132The Simple Fix and Depth.......................................................................... 132The ‘Running Fix'....................................................................................... 132Fix by ‘Dipping' or ‘Bobbing' a Light............................................................ 134LOP by Radio............................................................................................. 136Routine for Coastal Navigation................................................................... 137Actions Prior to Departure.......................................................................... 137Actions While Under Way.......................................................................... 138Actions After Tying Up............................................................................... 138



ivStrategy for Course Laying........................................................................ 139The Sextant, the Composition and Use of the Sextant............................... 140Calibration Adjustments............................................................................. 140Setting the Index Mirror, Setting the Horizon Mirror.................................... 142Index Error................................................................................................. 143Collimation Error, Other Errors................................................................... 144Practical Tips............................................................................................. 145Notes ........................................................................................................ 145Appendix A, Example Departure Form, ............................................... 147Appendix B, Form for Departure from Cape Town..................................... 149

Chapter 3: More Coastal NavigationIntroduction, Remaining ‘Fix' Methods, ‘Distance-Off' by Vertical Sextant Angle............... 151Fix by Horizontal Angles........................................................................... 153The ‘Four Point' Fix................................................................................. 154Fix by ‘Doubling the Angle at the Bow'..................................................... 156Position from Line of Soundings............................................................... 156Navigation Publications............................................................................ 157Electronic and Mechanical Aids to Navigation.......................................... 161Appendix A: UK Weather Bulletin and Forecast Recording Forms............ 166Appendix B: Weather Map; Areas around the UK..................................... 167Appendix C: Schedule of South African Radio Transmissions of

Weather Bulletins for Shipping....................... 168Appendix D: Weather Forecast Areas for Shipping, USA, Australia, RSA ..169Appendix E: Example from a Country’s Harbour Regulations

Applicable to Small Craft and to Pleasure Craft.......................... 172Appendix F: Compass Checking by the Sun's Amplitude............................ 173Appendix G: Rhumb Line by Meridional Part ............................................. 176Appendix H: Intercept Course to Steer ...................................................... 180Appendix J: Dipping Distance Table ......................................................... 181Notes........................................................................................................ 182Practice Navigation Questions.................................................................. 183Answers to Practice Navigation Questions............................................... 184

Coastal Skipper/Yachtmaster Offshore Shorebased Course


vGENERAL INTRODUCTION

Arrangement of Parts

Part 1 General Introduction Chapter 1 Introduction to Navigation Chapter 2 Coastal Navigation Chapter 3 More Coastal NavigationPart 2 Chapter 4 Tides Chapter 5 Tidal Streams Chapter 6 Buoyage, Lights and Pilotage Part 3 Chapter 7 Meteorology Chapter 8 Passage Planning Chapter 9 Safety at Sea Part 4 Chapter 10 Rules of the Road Chapter 11 Anchoring, Mooring and Docking Chapter 12 Communications at Sea

Pre-Course Qualifications

There are no, repeat NO pre-course qualifications required for people wishing to do thiscourse. However, students should either have the Skipper (Local Waters) certificateof competence or an equivalent, or be at a standard of knowledge and skill which wouldqualify them for such a certificate if they were to be tested.

Equipment Required(These items are supplied to students attending Henton's course.)

Students of this course will need to have:

1. A parallel rule and/or a plotter (e.g. Portland [Breton] or Hurst), and marinenavigation dividers (ordinary mathematics set dividers will do).

2. Charts. If navigation questions, issued separately, are to be attempted, one of: i. Australian chart Aus 197. ii. British Admiralty training chart 5050. iii. South African Navy training chart 3002. iv. USA chart Miami (e.g. 3699)

3. A sextant if possible (do NOT buy one unless you have decided you really wantone).

4. A copy of the following are desirable (not essential):i. ‘Rules for the Prevention of Collisions at Sea' (latest edition).ii. A book or books containing ‘List of Lights, Fog Signals, and Radio

Services', or an ‘Admiralty List of Lights' volume for your area.iii. ‘Chart Symbols and Abbreviations', British chart/book 5011 or your

national equivalent.



vi

5. For the student's own practice purposes, copies of a Yachting Association's‘Exercise Questions' (oral and written) and ‘Exercise Tables' are highly recommenced.Practice questions and correct answers are also available from us on request.

6. A notebook or pad, pencil (2B), pen, drawing compass (for circles/arcs), ruler, eraserand pencil sharpener.

Examination

The aim of this course is to help candidates prepare themselves for their examingauthority’s examination. Whereas voluntary progress and end-of-course tests areconducted, students eligible for the qualifying examination must make their ownarrangement to be examined by the appropriate examiners. Tests conducted duringthis course are only intended to check that the student’s understanding of the subjectmatter is correct: if not, extra tuition may be supplied. The differing fees for theexamination by the various Associations, for members and non-members, the differentvenues, and the duration of the examination, preclude this examination being part ofthe course. Certificates

Students who attend all lectures and are assessed by the instructor as having reachedan acceptable standard, or students who study by correspondence or via the Internet/e-mail and who pass the progress and end-of-course tests (or on reaching the passstandard even if at a later stage) will receive the ‘Course Completion Certificate' forthe Royal Yachting Association's syllabus course. Students who undergo this courseon their own and will not, unfortunately, be eligible for this certificate.

Coastal Skipper/Yachtmaster Offshore Shorebased Course Page 101

BY HENTON JAABACK INSTRUCTOR EXTRAORDINAIRE AT ‘YACHTMASTERS’

CHAPTER 1

INTRODUCTION TO NAVIGATIONWhat is ‘Navigation?’

‘Navigation’ has been defined as the art of guiding a person, persons or vehicle(s) (motor vehicle, aircraftor ship) across the land, air or sea, SAFELY, from one place to another. The Concise Oxford Dictionary,1999, defines ‘navigation’ as ‘Any of several methods of determining or planning a ship's or aircraft'sposition and course by geometry, astronomy, etc’. The dictionary also defines to ‘navigate’ as ‘to manageor direct the course of a ship or aircraft’.

We are concerned with navigating at sea near land. The presence of the land enables the navigator to usemany different methods of determining a vessel's position, and thereafter, plan the course to steer to getto a place. The navigator has tools to assist in performing this task.

Basic Tools for Navigation The Earth’s ‘Rings’

Our round earth spins on its axis which passes through the poles, and for convenience, we split the upperhalf from the lower half by an imaginary circle around the earth which we call the equator. The top half wecall the northern hemisphere and the pole in that hemisphere we call the North Pole. The bottom half isthe southern hemisphere, and at the bottom we have the South Pole.

Fig. 1.

Latitude Rings

The planes of rings around the earthwhich are parallel to the plane of theequator , fac i l i ta te an angularmeasurement at the earth's centre, of howfar the rings are, north or south, relative tothe equator. We call the angularmeasurement from the equator, thelatitude. Note also that the further theserings are away from the equator, theshorter their circumferences become.

Fig. 2.

Page 102 Coastal Skipper/Yachtmaster Offshore Shorebased Course

BY HENTON JAABACK - YACHTMASTER OCEAN INSTRUCTOR -RYA AND SA SAILING

Meridians

There are also imaginary circles which have their centres at the centre of the earth and whosecircumferences pass through both poles. Therefore, any part of the circumference of any one of these ringsis always in a ‘north - south’ line. If we use one half of one of these rings, from one pole to the other, as anangular reference ‘zero line’, we can measure at a pole or anywhere along the axis, the angle formedbetween that reference line and any other half-ring joining the poles. These half-rings we call meridians,and the reference meridian has been universally accepted as that meridian which passes through a specificspot in Greenwich, England. It is, therefore, called the Prime Meridian or Greenwich Meridian (often justcalled ‘Greenwich’) and all other meridians (one can imagine as many as one likes at differing anglesapart) can be stated to be an angle east or west of the Greenwich Meridian, up to 180º. The angle betweenthe Greenwich Meridian and any other meridian is a measurement of the latter's longitude.

Fig. 3.

Position

The position of a place (or ship) can be expressed as being at the intersection of a ring of latitude and ameridian of longitude. The position is ALWAYS stated ‘Latitude first, Longitude last’. For example,Southampton is approximately ‘50º54' North, 1º24' West’, and Cape Town ‘33º55' South, 18º25' East’. (Often the ‘North’ and ‘South’ are written as ‘N’ and ‘S’, and the ‘East’ and ‘West’ as ‘E’ and ‘W’.) Position can also be expressed as ‘Direction (from a known /marked point on the chart), Place (that point)and Distance (in nautical miles)’, e.g. ‘135ºT, Gibraltar Lighthouse, 15 n.m’. (For ‘T' - see page 111.)

CHARTSThe primary tool for any navigator is a chart. Because the earth is round whereas charts are flat sheets ofpaper representing sections of the round earth's surface, you might expect distortions of the vertical and/orhorizontal axis in the drawn chart to result. To overcome this, there are several techniques in the make-upof a chart, and these result in different styles of charts known as ‘Chart Projections’.

Sailing in polar regions involves the use of ‘Gnomonic Projection' charts and sailing in low and mid-latitude areas (where most of us do all our sailing) requires the use of ‘Mercator Projection’ charts. (By‘Low’ and ‘Mid’ latitude is meant low/small angles at the earth's centre, i.e. for places nearer the equatorthan a pole.) The illustrations in Figure 4 show the idea behind the make-up of these two types of charts.

The Mercator Projection is the projection we will be dealing with, as it will get us from the equator aroundCape Horn to the south or to Norway in the north. Notice how the horizontal ‘Scale‘ taken from the equatorremains constant and how the vertical scale of the mercator projection increases the greater the distancefrom the equator. A small scale mercator projection chart and a large scale chart's vertical scale areillustrated in Figure 5.



GNOMONIC PROJECTION MERCATOR PROJECTION

For Polar Navigation Two dimensional increase in scale with increaseFig. 4. in Latitude.

A chart’s scale may be shown to be, for example, ‘1:100 000' (one in one hundred thousand) meaning oneunit of length on the chart (let's say one centimetre) represents one hundred thousand units (centimetres)of the land. A ‘1:50 000' scale chart is regarded as a very big scale chart as it shows a small area in great(big) detail, but a ‘1: 250 000' is a small scale chart as it shows a large area and can therefore only showsmall detail. REMEMBER: Big scale, big detail (small area); Small scale, small detail (big area). E.g.:

SMALL SCALE LARGE SCALE (60' = 1º) (1º = 60')

Fig. 5.

We measure distances on a Mercator chart using the side vertical scale only - horizontally opposite thearea of interest. This is to ensure we get the right proportion of scale depending on the distance from theequator:

Fig. 6.



Distance is measured in nautical miles (abbreviated M or nm); we NEVER use kilometres. Distancesinvolving a fraction of a mile are shown as a decimal of a mile to the nearest single decimal only, e.g. 6M, 7,3 M, or 6 n.m., 7,3 n.m., not 7,33 M.

A Nautical Mile is the length of an arc of a Great Circle (the e.g. equator) subtended by an angleat the centre of the earth of one minute. It is 1 852 metres long which is over 200 metres longerthan a statute (land) mile.

A Cable is one-tenth of a nautical mile (185,2 metres or +/- 200 yards) e.g. 0,3 n.m. = 3 cables.

A Great Circle is ANY circle around the earth whose centre is also the centre of the earth.

The shortest distance between any two places on earth is a measurement of the shortest arc of a greatcircle passing through both of those places.

Fig. 7.

A great circle course is a straight line on a Gnomonic chart, and unless a vessel is sailing due north orsouth, or along the equator, the angle between the course line and successive meridians will be constantlychanging, albeit slowly.

GNOMONIC CHART MERCATOR CHARTFig. 8.

A great circle course, unless towards the north or south poles, or to the east or west ALONG THEEQUATOR, will not be a straight line as seen on a Mercator Projection chart.

A Rhumb Line course is a straight line course on a Mercator Projection chart and has the advantage thatthe compass heading being steered does not change - the angle the course makes with successivemeridians is constant. For voyages less than +/- 500 miles, it does not involve a significant difference indistance compared with a great circle course, but for longer distance voyages a great circle route isnormally preferred. The rhumb line course is not the shortest course. If one does not have a chart, theRhumb Line course and distance can be calculated using the ‘Meridional Part' method - see AppendixH, or by trigonometry.

Let's get back to charts.



Markings on the Charts' Reverse Side

Charts usually have on their reverse side against and centred along one of the shorter edges, the chart'sname describing the area it depicts, and its chart number, e.g. ‘2127' is the number of the British Admiraltychart for the ‘Atlantic Ocean’ (north and south). There is frequently the crest or logo of the authority printingthe chart, and the following:

‘Folio number. ... '.

If a vessel's navigator wishes to group his or her charts by areas (or whatever other criteria), each batchor folio can have its own number. Within each folio, each chart has its own sequence or page numbercalled:

‘Serial number. ... '.

The serial number (a page number within a folio) enables a chart to be returned to the right place if everit is temporarily removed. Charts are sometimes removed for inclusion in a ‘voyage folio’ and they are thenarranged in the sequence they will be used during the voyage. While in the ‘voyage folio', each chart's pagenumber or sequence in the folio is determined by its:

‘Consecutive number. ... '.

Consecutive numbers are written in pencil because after the voyage the charts will be returned to theirnormal folio. During the voyage, if the master or navigator wishes to remove a chart from the voyage folioto examine its detail, it can be returned to the right place in the sequence due to the presence of thisnumber. Sometimes the consecutive or serial number is omitted. The reverse of the chart referred to aboveappears below:

2127Atlantic Ocean

Folio Serial Consecutive Fig. 9. Markings on the Front of Charts

Charts are framed by a black ruled border. Outside the border, at the top left and bottom right hand corners,is the Chart Number. Outside the bottom edge starting at the left corner is the record of corrections to thechart. Corrections to charts are made as a result of amending instructions being published in ‘Notices toMariners’ - notices are serially numbered from ‘1' upwards from the start of each year, so the chart ismarked with the year and notice number to indicate that the correction has been done to the chart. Forexample, ‘1990 . 14 . 39' would mean that ‘Notices to Mariners’ numbers 14 and 39 of 1990 had correctinginstructions for this chart AND that they have been applied to this chart. The third and last piece ofinformation outside this black margin is the detail of printing showing when it was printed, who printed it,the date of the latest edition, etc.

Fig. 10.

The black framing margin contains the longitude scale and longitude angle (with reference to theGreenwich Meridian to give the actual longitude) along the top and bottom horizontal margins, and the sidevertical scale shows the latitude scale and latitude angle (with reference to the equator to give actuallatitude). Look at your chart. Notice how distance is only measured on the vertical latitude scale - each 1º



= 60' or 60 n.m. and each 1' is 1 n.m., and the length of line for 1' is subdivided into five (or ten) equal partsrepresenting 0,2 n.m. (or 0,1') each. If it is 0,2', we must interpolate for odd numbers of decimals.Remember, we only work to one decimal place of a mile. Compare the actual length of 1' on the vertical,Latitude, scale with the equivalent length on the horizontal scale for Longitude. The further one is awayfrom the equator, the bigger the difference. Check the chart you are using; each may differ according toits scale.

Fig. 11.

Chart Statement

Inside the framing margin, usually over land areas so that it does not obscure any relevant land, coast orsea area, we find the Chart Statement which comprises most of:

1. The publishing authority's crest. 2. The title of the chart e.g. ‘Approaches to San Diego Harbour'3. The type of ‘projection' used in the make-up of the chart e.g. ‘Mercator Projection'.4. The scale of the chart.

5. The reference or datum from which all heights above sea level are measured, and the units of measurement used e.g. feet, or metres.

6. The reference datum from which all depths are measured, and the units of measurementof depth e.g. feet, fathoms, or metres.

7. ‘Notices’, ‘Warnings’ and/or ‘Cautions’ applicable to navigating in the area depicted by the chart.

Coastal Skipper/Yachtmaster Offshore Shore Based Course Page 107

BY HENTON JAABACK -YACHTMASTER OCEAN INSTRUCTOR- RYA AND SA SAILING

8. A table headed ‘Tidal Levels Referred to Datum of Soundings'. (It may also have a separate table for ‘Tidal Stream' information - see Chapter 5.)

This is the statement from chart Aus 200, Port Jackson (Sydney, Australia):

Fig. 12.

Look at a chart and study the statement - not every chart's statement is the same although they are similar.Look at the statements on your chart(s) and the British Admiralty chart 5050. Some countries abbreviatedidentity appears as a refix to the number, e.g. South Africa uses “SAN 123". The ‘SAN’ in the numberindicates ‘published by the South African Navy’. A chart number with “INT” is an international chart whichalso has two logos; one is the appropriate hydrographic authority’s logo and the other is the InternationalMaritime Organisation’s logo for international approved charts.

Chart Symbols and Abbreviations

Charts representing large areas do not have enough space to fit in all the detail and names, explanations,descriptions, etc. Therefore a universal system of symbols was accepted by the world's maritime nations,and these, together with the abbreviations used on English language charts, enable the charts to remainrelatively uncluttered yet contain a wealth of information. Extracts appear below. There are many more andthe serious yachtsman or woman should initially study the complete list and thereafter have the book orchart (British Admiralty 5011 or your county’s equivalent) available as a reminder when necessary. Readthe fine print for explanations such as ‘fS’ - it means ‘fine sand’ ... the ‘f’ as an adjective is not a capital letterwhereas the ‘S’ as a capital letter is a noun. Knowing this, it is often easier to work out what a ‘forgotten’abbreviation means.

Do not try to learn them all - there are too many, but do remember the symbols for rock awash, rock awashat chart datum, and rock of unknown depth considered dangerous to all vessels.





Fig. 13.



See how they come together on a chart to make ‘the picture’:

Fig. 14.

Conversion Scale

A conversion scale for converting units from one type to another is usually included on large-scale charts.An example, using part of the table from a chart (they are all the same) appears below. Part of a table isvisible on the right in Fig 14 above. This table is ONLY used to convert between feet, fathoms, and metres,and is not related to the scale of the chart.

Fig. 15.



The Compass Rose

A Compass Rose usually appears in either two or three places on a chart. Look at a typical compass rosefrom the south-west of Cape Point, South Africa, on chart SAN 3002 (shown below - ANGLES NOT TOSCALE):

Fig. 16.

Notice that the outer ring showing the 360º graduations of a circle is orientated to point the 360º ( or 000º)mark towards the north pole, or to ‘True North’. It is then called ‘360ºT’. The inner ring also shows 360ºbut it is orientated to point its 360º mark in a different direction. The direction it is pointing is towards themagnetic North Pole or ‘Magnetic North‘ as it appears from the centre of the circles. As the influence ofthe earth's magnetic field varies according to the place on earth, the difference in directions to the true andmagnetic north poles will differ depending on where it is measured.

Variation

The compass roses on a large scale chart are there to inform the navigator of the magnitude of themagnetic effect on the compass, or ‘magnetic variation’, in the vicinity of those compass roses. Thenavigator uses the information from the compass rose nearest to the relevant area. At the centre of thecompass rose is a statement of what the angle difference is, between the directions ‘True North' and‘Magnetic North', as measured at that place. This direction towards the Magnetic North may be east or westof the direction to True North. (In the Atlantic and Indian Oceans it is west; in the Pacific Ocean it is east.)

In Figure 16 it is ‘23º13'W (1989)’. The year is stated because the magnetic field of the earth is notstationary - it is moving, albeit very, very slowly. This results in a calculated forecast of annual rate ofchange to the magnetic variation and this information appears near the centre of the compass rose. InFigure 16 it is shown as ‘nearly stationary’ (i.e. too small to worry about!) but the compass rose in FalseBay, some 30 miles away, shows, on new charts, “(1'W)”, and older charts it is shown as ‘increasing 1'annually’. So in 1992 the variation is: 23º13' W + 3' (3 years since 1989 at 1' per year) 23º16' W



We always do this updating sum to correct to the present year, then, although it seems as if we havewasted our time, we ‘round-off’ to the nearest integer (whole number) of degrees. Thereafter we only usea whole number.

So in False Bay, variation will be 23ºW until the year 2006. In 2007 the sum works out at 23º31' (W), whichis closer to 24ºW when rounded off.

It may seem a pointless exercise, but it must be remembered that not all charts that the navigator useswere published in recent years. An old chart, for a place where the annual rate of change of variation islarge (e.g. Bristol Channel, UK, it changes 7' per year), may result in an updating calculation correcting theprinted variation by several degrees. If this is ignored, it could mean the difference between a safe passageand landing on rocks.

To convert a direction's description from a ‘True’ direction to a ‘Magnetic’ direction, look at Figure 16 or yourown chart. Take a soft lead (2B) pencil and a ruler and rule three or four lines from the centre of the roseso that the lines cross both the rings. Each line ruled represents a direction, and, because variation is‘west’, the number of degrees read from the scale on the outer (True) ring is seen to be smaller than thenumber on the scale on the inner (Magnetic) ring. The actual direction is the same, in line with the pencilline(s) ruled, but the True and Magnetic numbers of degrees differ BY AN AMOUNT OF THE VARIATION(e.g. 23ºW). When variation is west, the magnetic number IS ALWAYS the bigger of the two numbers.When variation is east, the Magnetic number is always smaller (the lesser or least value) than the True.

So when variation is ‘West', the magnetic number is bigger, or ‘Best'. We remember this by saying:

"Error west, compass best"

and when variation is ‘East’, the magnetic number is smaller/lesser/the least value, so we say:

“Error east, compass least”where the ‘variation’ is called ‘error’.

Any calculation converting a ‘True’ direction to a ‘Magnetic’ direction requires the (westerly)variation to be added.

To convert a ‘Magnetic’ direction back to a ‘True’ direction the (westerly) variation must besubtracted.

Getting this wrong has resulted in many a vessel's grounding.

Until one is 100% familiar with this conversion procedure, OR WHEN ONE IS TIRED, write it down whendoing the calculation - and if possible get someone else to check - don`t be proud, it could cost you thevessel and one or more lives. It is surprising how easy it is to make simple arithmetic errors when one istired, or cold, or both! And ...

MOST NAVIGATION ERRORS RESULT FROM FAULTY SIMPLE ARITHMETIC.

Course to Steer and Waypoint

So, if a navigator needs a magnetic course to steer, he or she will begin by placing a parallel rule or plotteron the appropriate chart, and ruling a pencil line (soft lead, do not press hard) from the start point to thedestination. If this would result in the course crossing an area where the vessel should not go (e.g.restricted area or shallows), an intermediate turning point - called a waypoint - is used to ‘go around’ theobstacle. There will be two straight line courses, not one. Or there may be two or more waypoints.

The parallel rule is orientated along the line(s) ruled (one at a time), then ‘walked’ to the compass rose sothat one edge is aligned with the centre of the rose. Rule a pencil line from the centre of the rose in thedirection the course will require the vessel to go, crossing the inner and outer rings of the rose. The outerring gives the True direction and the inner ring the Magnetic direction.

See Fig. 17 on the next page.



Fig. 17.

If the chart is old and the annual change in variation large, the inner ring will be somewhat out oforientation. In addition, on small-scale charts showing a whole ocean, the compass rose does not showan inner ring, but instead shows isogonals, the equivalent of contour lines joining all points of the samevariation, leaving it up to the navigator to interpolate the variation at the place of interest. In these twocases, the navigator must read the ‘True’ degrees, and convert to ‘Magnetic’ by adding the westerlyvariation or subtracting the easterly variation.

If ‘True’ (T) = 330º, and ‘Variation’ (V) = 23º W, ‘Magnetic' (M) = 353º. To avoid confusion as to whichnumbers of degrees are True and which are Magnetic, we write ‘T’ or ‘Mag’ [or just M] after the number.

So we could have written 330º T + 23º W = 353º M. (The ‘M’ here is not to be confused with the ‘M’ which means ‘miles’: since the ‘M’ here follows the degreesymbol, it must refer to ‘Magnetic’.)

If we know the Magnetic direction and need the True direction:

353º M - 23º W = 330º T(Since the True is always smaller than Magnetic when ‘Var = W’.)

Line of Position

While sailing along that course, the navigator may wish to take a magnetic bearing from the vessel to alighthouse using the vessel's Hand-Bearing Compass.

The magnetic reading that is obtained is converted to a True direction by subtracting the westerly (or addingthe easterly) variation. By reversing the process with the ruler, orientating it along the True directioncalculated and compass rose centre-point line, then ‘walking’ it to the lighthouse on the chart so that oneedge of the ruler lies on the middle ‘dot’ of the lighthouse symbol, a pencil line can be ruled from thelighthouse to seaward, representing a line along which the vessel’s position was located at the time thebearing was noted. This line is called a Line of Position, (or L.O.P.).

Fig. 18.

The same reverse procedure can be used if a magnetic course is being steered and it is desired to plot thiscourse on a chart. Since charts are orientated to True North, we need to know the True equivalent of theMagnetic value obtained from the compass.



Deviation

The course steered according to the ship's compass is not always the Magnetic direction. Every vessel hassome amount of ‘magnet-affecting metal’ in its make up, such as the engine, tanks, mechanical andelectronic equipment on board, tools, etc. These metallic objects affect the compass, and they affect thecompass by differing amounts depending on whether the vessel is facing north, south, east or west - or anyother direction. The effect is called deviation. See Figure 19.

Swinging the Compass

To establish what the deviation of a compass is on any particular ship's heading, the first step is to obtainthe services of a qualified ‘compass adjuster‘ who will ‘Swing the Compass‘. This process of swingingthe compass involves sailing the vessel away from the immediate surrounds of other metals into ‘open’water, then slowly turning the vessel through 360º and checking the compass readings against knowncalculated values of what the compass should read. Transits and conspicuous objects on land are usedfor this check. Any difference is the deviation, and the compass adjuster will attempt to adjust thecompass's ‘compensating magnets’ to get the deviation to a minimum on all headings. Once the adjustingprocess has minimised the deviation, any remaining deviation is reported to the vessel's skipper in the formof a Deviation Card. (If there is no qualified adjuster available for the task, DO NOT attempt to adjust thecompass. Determine the deviations as described above, short of doing the adjustment.)

Fig. 19.

The Deviation Card supplied to the skipper must remain on the vessel. It can take the form of a table ofdeviations (corrections), see Fig. 20 below, or a graph. See Figure 21.

TABULAR DEVIATION CARDShip's Name

Name and Type of Compass ...................... (e.g. Plastimo, Steering), Date: ................

Compass Deviation Magnetic Compass Deviation Magnetic

360ºº 1 º W 359º 180º 2º E 182º

022,5º 2 º W 020,5º 202,5º 3 º E 205,5º

045º 3 º W 042º 225º 3 º E 228º

067,5º 3 º W 064,5º 247,5º 2 º E 249,5º

090º 2 º W 088º 270º 2 º E 272º

112,5º 1 º W 111,5º 292,5º 1 º E 293,5º

135º 0º 135º 315º 1 º E 316º

157,5º 1º E 158,5º 337,5º 0º 337,5ºFig. 20.



GRAPHIC DEVIATION CARD

Fig. 21.

Graph deviation presentations are rare these days, most vessels having the tabular layout card. A compassshould be readjusted (re-swung) every three years, or additionally whenever major ‘metallic’ changes tothe vessel are made.

When taking deviation into account, if deviation is ‘West’ on a particular ship's heading, we apply thewesterly deviation to the equation just as we did the westerly variation, since it has the effect of pushingthe compass needle further west than variation does on its own.

First we change the True direction to a Magnetic direction by adding the westerly variation or subtractingeasterly variation. Then we change the Magnetic direction to a ‘compass direction’ by adding westerly, orsubtracting easterly, deviation. Remember:

‘Error west, compass best (bigger); error east compass least’.(If both are west, compass is ‘bigger’ than Magnetic which is bigger than True.)

If a vessel is sailing south, 180º T (True) where magnetic variation is 23º W (West), the magnetic coursewill be:

T + V (Var W) = M 180ºT + (v is west) 23º W = 203ºM

and the compass course, using the Deviation Card at Figure 21, will be:

M - D (Dev is E) = C 203ºM - (D is east) 3º E = 200ºC

We can put it all in one line: T V M D C 180ºT + 23ºW = 203ºM , - 3ºE = 200ºC



Notice how each number of degrees has a letter behind it so that there can be no confusion as to whateach is. This is most important when any one number is written on its own. For example, to write in the logbook that the ship's course was ‘275º’ is ambiguous - is it 275º True, Magnetic, or Compass? A bearingto a lighthouse stated as ‘145º’ could be True or Magnetic. A letter behind the number removes allconfusion.

If we know the compass course being steered by the helmsman, we can find the True equivalent in orderto plot it on a chart by working the arithmetic backwards (and reversing the plus and minus signs).

T V M D C

becomes

C D M V T and

C D M V T 200ºC + 3ºE = 203ºM , - 23ºW = 180ºT

It is often necessary to interpolate when using the Deviation Card - we use the nearest Magnetic headingshown on the card to that being steered or to be steered, to read off the deviation. It may also be necessaryto interpolate the number of degrees of deviation in the rare case of a difference of 2º or more betweensuccessive deviations shown.

Deviation and the Deviation Card apply to the ship's steering compass. The compass is mounted in a fixedposition relative to the ship's ‘interfering' metals’ and the Deviation Card's values remain valid for anyheading of the ship. The hand-bearing compass, however, is seldom used in or from the same place everytime it is brought on deck, and therefore a Deviation Card would be necessary for each position or placeit is used. This is not practical, so we use no deviation at all with this compass. To minimise the disturbinginfluences of other metals on the vessel, we use this compass as high as we can and as far as we can getit from the ship's compass and other metals. The minimum distance it should be from the steering compassis approximately two metres. When moving away from the ship's steering compass, do not move close toother interference sources e.g. the metal in items included in the life-raft and strong magnets inloudspeakers of music hi-fi's mounted just under the deck. To check a compass' deviation at sunrise andsunset using the sun's amplitude, see Appendix H, page 173.

Speed

Everyone knows that motor cars travel at speeds described as ‘miles per hour’ or ‘kilometres per hour’. Inmarine terminology we use the term ‘Knots‘. A knot is the unit of speed of a vessel at sea, and is onenautical mile per hour. To say ‘knots per hour' is wrong because it translates to ‘nautical miles per hour "perhour"'! Since the nautical mile is longer than the statute (land) mile, knots do not apply on land.

As ‘speed’ (knots) is determined by distance (miles) per time (hour), if we know any two of these valueswe can calculate the third. Remember the triangle: Speed = Distance , and Time S = D T Time = Distance , and T = D Speed S

Distance = Speed X Time. D = T x S

So, if a vessel has to cover a distance of 30 n.m. and it sails at 6 knots, it will take 5 hours to do the trip.Also, if a vessel covers a distance of 15 n.m. in 2 hours, its speed is 7,5 knots. Similarly, a vessel travellingat 5 knots for 4 hours will cover a distance of 20 n.m.



Directions

Directions (courses, set, bearings, etc.) of less than 100º must have a zero first so that there are alwaysthree digits, and if the direction is less than 010º it must have two zeros first for the same reason. Onlyangles such as variation and deviation may have less than three digits. So we could have 300º, 030º or003º, all being directions. Directions should also always be qualified as T, M, or C.

Chartwork Symbols

One navigator may hand over the navigating duties to another, or the work of the navigator may bechecked by the skipper or master of the vessel, or the navigation work may be the subject of a study lateron. All these situations require that what has been done by one person, is easily understood by others. Forthis reason standard chartwork symbols are used. Marking a chart with courses lines, chartwork symbols,etc. is called ‘Plotting’. Let's look at the symbols for chartwork.

Course Steered Fig. 22.

This is represented by a line on the chart showing the direction the vessel is pointed (its heading) as itproceeds on its way. The single arrowhead is near the centre of the line. The course, although ruled in thedirection of its True number of degrees, may have the number of degrees as True, Magnetic or Compass,T, M or C, stated/written along the line.

Ground Track (or Course Made Good - CMG, or Course over the ground COG)

Fig. 23.

Although a vessel may be pointed/headed in a direction while sailing, wind from a side may cause thevessel to ‘slip sideways’ away from the wind. This sideways slip off the course steered is called leeway.In addition, a current or tidal stream may be flowing at an angle to the course steered, also pushing thevessel, or drifting it sideways off the course steered. The resulting route taken by the vessel above/overthe ground (the sea bed below) is called the ground track - sometimes also called the Course Made Good,abbreviated to ‘CMG’, or Course Over the Ground,’COG’. Notice the CMG has two arrowheads near thecentre of the line. The direction, T,M,or C, may also be written next to this line, as explained above.

Set

Fig. 24.

The direction of the current or tidal stream, called the ‘Set‘ of the current or tidal stream, has threearrowheads near the centre of the line. The direction of the set is always ONLY expressed in relation toTrue headings. The direction, True, may also be written next to the set line on the chart.

Line of Position (LOP)Fig. 25.

Here the single line from the lighthouse in the earlier explanation of an LOP (page 112), has one arrowheadat its seaward end. The direction, as True or Magnetic, SHOULD be written along this line or near itsseaward end as well as the Time it applied and the ship's Log reading (distance travelled counter) at thattime.

Advanced or Transferred LOPFig. 26.

Where it is required to plot a line parallel to a LOP, the parallel line is called an ‘Advanced’ or ‘Transferred’LOP - it has no separate abbreviation. It is denoted by the two arrowheads at the end of the line, optionallyat both ends.



Position (of a Vessel)1. DEAD RECKONED POSITION or ‘DR’

Fig. 27.

A short line crossing the course line at right angles, or a vertically orientated cross, indicates a ‘DR’ or Dead(from ‘Deduced’) Reckoned position. It is obtained from taking into account only the factors direction, time,and speed (time and speed give distance). It ignores factors of current/tidal stream set, and leeway. TheLog, Time and Date (the date if at sea for more than the one day) MUST be written next to the DR mark,and the letters ‘DR’ may be written next to the symbol.

2. ESTIMATED POSITION or EP’

Fig. 28.

An estimated position takes the DR factors, direction and distance, into account AND the influences ofcurrent/tidal stream ‘set’ AND/OR leeway. The position is indicated by being enclosed in a triangle, and theLog, Time and Date (date if at sea for more than the one day) MUST be written next to the triangle.

An estimated position due to set only, is obtained by first ‘plotting’ (ruling in its correct place) the courseline - let's say a course of 080ºT. Mark the start point. Let's call it A:

Fig. 29.

a. If we wish to ‘steer-off’ to counteract the effects of the set, we must take action from the start (place, A,and beginning time) of our voyage/leg so that we end up at the right place, we plot (rule) a line in the set'sdirection and make a mark along this line at the place where a drifting object would get to after one hour -call it B. (This drift distance in 1 hour is the ‘rate’ [speed] of the current or tidal stream.) Remember:

Fig. 30.

‘SET’ is the direction of surface water flow due to current or tidal stream.‘DRIFT’ is the distance a free floating object will move in a period of time due to the tidal stream orcurrent. ‘RATE’ is the speed in knots of surface water flow due to the current or tidal stream.

Assume a set of 225ºT (here we do not have to write ‘T' as it is current or tidal stream being referred to -they are always only ‘True’) at a rate of 2 knots. From B, plot a line using the same units of length used forthe current drift in 1 hour, to be the length/distance the boat will travel over the water in the same periodof time i.e. 1 hour - if its speed is 6 knots then this line must be six units of length long where it meets thecourse to be travelled line (080ºT) - at C .


Fig. 31.

The direction of line BC is the course to steer to overcome the set, AB, and the boat will then move alongthe line AC - which is the Ground Track, Course Made Good (CMG), or Course Over the Ground (COG).Since the time frame is one hour and the boat moves from A to C in that hour, a measure of the length ofline AC will be the speed of the vessel over the ground - Speed over the Ground (SOG) or Speed MadeGood (SMG).

After the 1 hour the boat will be at C - C is the ‘EP’ and we mark it by drawing a triangle around the spot,and we write the Date, Time and Log.The point C is where the boat will be after 1 hour. It is the EP at that time.

b. If no allowance for set was made at the beginning of the trip, the vessel would end up at a differentplace. To see where a vessel being steered on a course will end up if no allowance is made for the set, weapply the set line at any point near the end of the course steered line (let's call it X). From that point the setis plotted to scale. Assume a course steered of 080ºT and the same current or tidal stream as above, i.e.225º (T) at 2 knots. Call the end of the set line Y:

Fig. 32.

Measure back from X along the course steered line, six units of length (the boat’s speed) and make a mark- call it Z.

Fig. 33.

ZY is the Course over the Ground (COG), Ground Track or Course Made Good (CMG), and its length willreveal speed. (The time frame being used is 1 hour.)

Fig. 34. If Z was the actual start point, then after 1 hour the EP would be at Y.

Fig. 35.

If the actual start point was somewhere else other than Z, plot a line parallel to ZY starting from the actual



start point (e.g. at A, a harbour exit). This line will be the Ground Track, COG, or CMG, and since we knowthe new speed (line ZY ‘per hour’), we can ascertain an EP at any time after starting. The EP after 1 hour30 minutes is:

Fig. 36.

Leeway

There is one other aspect to EP's and that is ‘Leeway’. Remember that an EP is a position obtained fromincluding the factors ‘current/tidal stream AND/ OR leeway’.

Assume the course is approximately towards the east and the wind is northerly (blowing FROM the north).While sailing along we look in the water behind the yacht to see the wake - its trail left in the water. If thewake is not fairly consistently in line with the ‘fore and aft’ line of the yacht, allowing for the slight swing ofthe yacht about the course steered due to swell/waves, then there is either leeway present, or thehelmsman needs to improve! If there is leeway, use the hand-bearing compass and take bearings on thefore and aft line and the direction of the wake. The difference in these bearings is the leeway angle. Toovercome the leeway, adjust the course steered by the angle measured TOWARDS THE WIND. This willmean turning towards the north by an amount equal to the Leeway angle. By turning slightly towards northwhile sailing east, the course steered direction as seen on a compass rose, will be changing anticlockwise -it will get smaller by the leeway angle:

Plotted or calculated course to steer ‘minus’ leeway when wind from the port side.

If the wind had been from the south, it would be plus the leeway - we would be turning clockwise towardsthe wind.

If there is current or tidal stream present, and we experience leeway, we first would plot the course to steerdue to the current/tidal stream, then start sailing, then check for leeway, and if it is present we then adjusttowards the wind by the leeway angle. We can not know in advance what the leeway will be, if any - so theleeway part of the exercise is always last.

IF leeway is ever plotted on a chart, it is likely to be for or in an examination ONLY - it is not otherwiseplotted. Here is how to show it if plotted; course ‘East’, wind from the north. (A-making allowance for it, B-ignoring it):

Fig. 37.

Back to Chartwork Symbols.3. A ‘FIX' POSITION

Fig. 38.

Coastal Skipper/Yachtmaster Offshore Shore Based Course Page 121The position of a vessel established as a result of taking measurements from fixed objects on land (or theseabed, or even celestial bodies - the sun, stars, moon and planets), is termed a ‘Fix’ or a ‘Fixed Position’.The symbol is a circle around the position, and again it must have the Time, Log reading and Date (ifapplicable) written next to it. There are several methods of taking a ‘fix’, and these will be dealt with in thenext chapter.

Transits

A transit is an imaginary line between two fixed objects on land and extending seaward. A vessel can sailalong that line by keeping the two objects in line - ‘in transit’. The symbols used, if a transit is to be plottedon a chart, are a circle around the object furthest from the water and a circle with a line through it, in linewith the two objects, around the nearer object:

Fig. 39.

Clearing Lines/Bearings

A clearing line/bearing is a magnetic bearing, for use with the hand-bearing compass, from the vessel toan object on land; it is safe for the vessel to be on one side of that line but unsafe on the other. While onthe safe side of a clearing line, a bearing to the object may be larger or smaller (depending which is thesafe side) than the clearing line direction, BUT NOT BOTH. There can be two clearing lines forming a ‘V’with the object at the junction of the two sides of the ‘V’, or the two bearing lines could be taken fromseparate objects. Either way, two clearing lines can form the sides of a `safe corridor'. It will be safe if thebearing to the object is either ‘Not More’ than (‘NM’) and/or ‘Not Less’ than (‘NL’) pre-calculated values.

Foul

NL 282º M

NM 320º M

Fig. 40.

OTHER TOOLS

Navigation Drawing Instruments

1. Drawing Compass. A mathematics set drawing compass for arcs of circles and circles. Its use will bedescribed in the next chapter.

2. Navigator's Dividers. The ‘one-handed’ operation type with the bulge near the pivot point is best,leaving the navigator's other hand free to hold the chart and other items on the moving chart table still. Thelonger the arms, the better.

Fig. 41.



3. Plotters - only one is necessary. The Portland (Breton) Plotter is recommended:

a. The Parallel Rule. (Graded 6 on a scale of 10 - ‘3/10'.)

Fig. 42.

b. The Douglas Protractor. (Graded 3/10)

Fig. 43.



c. The Rolling Rule. (Graded 1/10! Difficult to use on a moving vessel, but preferred by some people.)

Fig. 44.

d. The Hurst Plotter, showing a True bearing of 288º and Magnetic bearing 296º. (Graded 8/10)

Fig. 45.

e. The Portland (Breton) Plotter. (Graded 9/10)

Fig. 46.



f. Navigation Triangles. (Graded 4/10)

Fig. 47.

4. Station Pointer.

Fig. 48.



Stationery

The Navigator will also need:

a. A note pad or jotter for rough work.

b. A pencil with a soft lead (e.g. 2B). If the pencil is not of the ‘clutch pencil’ type, a good sharpenerwill be necessary to keep it sharp. Do not press hard on the chart so that all markings can beerased without trace indentations in the paper. Rule short lines, only as long as necessary.

c. A soft rubber eraser.

Other Aids

Also necessary for the navigator to complete the navigation task are:

i. A sextant.

ii. Tide Tables.

iii. A means of telling the time.

iv. A hand held/hand-bearing compass.

v. Binoculars.

vi. The vessel's log for distance and speed measurements.

vii. A log book being either the vessel's log book, or a separate navigator's log book in which all themajor navigation activities, etc., are recorded. See Part 3, Chapter 8, page .

NOTES



NOTES


BY HENTON JAABACK - AT YACHTMASTERS’ - FOR ADVANCED INSTRUCTION

CHAPTER 2

COASTAL NAVIGATION

Introduction

The ways of determining a vessel's position at sea have been described as being either a DR, an EP, ora ‘fix’. Of the three, the DR is the least accurate as it makes no allowance for a vessel being pushed off itscourse by the current or tidal stream, or by leeway due to the wind. The EP does take these factors intoaccount and is, therefore, more accurate than the DR.

However, the EP is not as accurate as we would like it to be. For example, current or tidal streaminformation supplied on the chart or in Tidal Stream Atlases is obtained from studies of the current or tidalstream over a long period of time. These studies resulted in ‘averaged’ readings. Therefore at a stage ofa year or tide cycle, the readings are not necessarily the same as at the same cycle stage earlier or later.Averages imply some faster and some slower rates. Therefore, the values we use are not necessarilyaccurate at the time we use them. A recent storm can also change the rate of a current or tidal stream.

A vessel's log showing speed and distance is not always 100% accurate - the further the vessel goes, thegreater the error becomes. The ability of some helmsmen or -women to steer a vessel accurately alonga specified course is questionable - and then there are the problems of a compass whose deviation haschanged since the deviation card was issued, or the navigator who may have been a little inaccurate incalculating the course intended. We need to be more positive, regularly confirming our position by sightingson land objects. Fixes are positions resulting from (some) measurements taken at the time of the fix.

Techniques of Visual Position Fixing

If one travels a particular route frequently, and knows the area well, whether walking, driving or sailing fromone place to another, one does so without conscious thought as to where one is at any moment, when toturn or how much to turn. One's eyes are seeing and the subconscious brain is assimilating and giving thecorrect controlling instructions. If, suddenly, the eyes could not see, one would stop immediately and theconscious brain would get involved - ‘Where am I?’ Progress thereafter would be a problem.

The ability to see, and the knowledge of where one is at sea, are most important to the skipper andnavigator. What one sees while navigating at sea, allows one to make instant decisions as to the courseto be steered. Some visual aids to navigation are natural and some man-made; some are very good,accurate and reliable, while others can be misleading, lack consistency, and be dangerous to safenavigation. Passing close by a marker buoy is a quick, positive way of knowing the vessel's position (unlessthe buoy has been moved or has broken loose from its securing chain!). Two buoys, especially at low tideand more so if it is a normally shallow area, may appear to be suitable to use as a ‘transit’, but counter-currents could deceive.

Eddy currents causing buoysto drift in opposite directions.

A - The direction of theexpected transit.B - The direction of theobserved transit.

Fig. 49.

So buoys should be treatedwith suspicion. Large old buildings and trees which have been in place for centuries, are unfortunatelyseldom shown any respect by the modern day developer who can demolish them in minutes - thenavigators' landmark of today is gone tomorrow. Similarly towers, the ‘permanent caravan camp’, mastsand flag poles - in fact anything man has put there, despite being conspicuous and a good, convenientlandmark, can be moved - or removed. A flagstaff or ‘conspicuous building’ shown on a chart is far less


HENTON JAABACK, MASTER OF YACHTS TO 200 TONS (U.K./RYA; DECK OFFICER, S.A.)

likely to disappear suddenly, but then one must consider ‘Will it be visible from my position?’ The flagstaffwill not be seen from three miles away, or at the angle where it is obstructed by an adjacent building, ora headland.

On a chart, one hill may appear prominent and show a Trig Beacon at the top - but from the sea, it is notnecessarily obvious which the right hill is.

Fig. 50.

High features may be conspicuous on the chart, but a vessel's position close inshore may shield them fromview.

Fig. 51.

The rule, therefore, is to select objects (from which to take bearings, use as pre-calculated transits andclearing lines) which are unlikely to be moved by man or nature, and which will be conspicuous from wherethe vessel is expected to be. A bend in a cliff may seem a good point for a bearing as seen on a chart, butfrom seaward it may be totally different:

Fig. 52.

The Use of Measurements

The further we go using EPs, the less accurately the vessel's position is known. We can rectify this by‘taking a fix’ - determining the vessel's position by taking measurements, using basic navigation tools, toor of fixed objects on land that can be seen AND POSITIVELY IDENTIFIED, and the sea bed. (In ‘astro’or ‘celestial navigation’, measurements are taken from the sun, moon, stars and planets - see ourYachtmaster Ocean - A Complete Syllabus Course).

There are several ways or methods of taking a fix, some more accurate than others and some easy andquick to do, others needing a bit more effort and time. What is important though, is that THE SKIPPER



AND NAVIGATOR MUST KNOW THE VESSEL'S POSITION AT ALL TIMES - on the sea and on thechart. If ever there is doubt, and the vessel may be near an obstacle, `STOP' - do not proceed. Ifnecessary, turn about and go back. The recent maiden voyage of a cruising yacht from Cape Town to theport of Natal, Brazil, ended in its being wrecked on a reef because this rule was ignored. BE SURE THECOURSE AHEAD HAS ADEQUATE DEPTH, INCLUDING SAFETY CLEARANCE before continuing. Ifentering an unfamiliar harbour or marina for the first time, do so only in the hours of daylight, and exercise‘Pilotage’ - see Part 2, Chapter 6.

Make sure the hand-bearing compass is reading accurately - to test it, try doing a ‘Swinging the Compass’exercise and making a deviation card for it - you may just get a shock. Take bearings from the nearestpossible objects because, the further away the compass is from an object, the bigger the inaccuracy of thereading obtained, as the compass is not a precise measuring tool. Movement on a swaying deck alsomakes accuracy hard to achieve - if necessary, read the upper and lower values of the direction as thecompass disc or ‘card’ swings from side to side, then ’average’.

Fig. 53.

Where two bearings are taken to get an intersection, try to select land objects which will result in theintersecting bearings being at or near a right angle - the area of possible error is smaller.

Fig. 54.

Where three bearings are taken, the angles formed between them should, as near as possible, result inan equilateral triangle.

Fig. 55.



METHODS OF TAKING A FIX

Actions Common to All Methods. USE THE LARGEST SCALE CHART AVAILABLE. When takingreadings for a fix, ALWAYS make a note of the time, the log (distance) reading, and, if within range, thedepth from the depth sounder. Course and speed noted will assist in DR or EP navigation subsequent tothe ‘fix’. When using depth, the reading obtained, after correction for depth of transducer, must be reducedby an amount which is the height of tide at that time - obtained from the Tide Tables (see Chapter 4). Theremainder is the depth using the same reference level as the chart's ‘Datum’. WARNING: The object(s) on land used to take bearings MUST be POSITIVELY identified, both bysight AND on the chart. Do not assume, hope or accept an object to be what you want it to be - BE SURE.

1. One L.O.P. and Depth. Take a bearing with the hand-held compass on the nearest prominent featureon land. As it is a magnetic value, use the inner ‘magnetic’ ring in the compass rose, or change it to a ‘True’value so that it can be plotted on the chart. (Remember charts are printed with their ‘north' orientated to‘True North' so all the lines drawn by a navigator on a chart MUST be ‘True' - even if labelled with theequivalent magnetic value of degrees.)

From the object as seen on the chart, rule a pencil line to seaward passed where you imagine the vesselto be. As this line represents an LOP, use the correct chartwork symbol and draw an arrowhead at theseaward end of the LOP. Note the time, log and depth (corrected for transducer depth) at the time of takingthe bearing. The height of tide is subtracted from the depth sounding and the remaining figure comparedwith depth contours and depth ‘numbers' as shown on the chart. By interpolation if necessary, PROVIDINGthe sea bed slope or shape is not a straight line at a shallow angle (where a small depth error could meana large error in position of the vessel), we can ascertain where along the LOP the correct depth applies -the Fix Position. Draw the chartwork symbol of a circle around the point, and write next to it the date,time and log (reading).

Assume a bearing taken with the hand-held compass on Eddystone Lighthouse (chart 5050 - or see theillustration below)) was seen to be 060º M when the depth sounder read 55 metres. If the (magnetic)variation is 8º West, the True bearing would be 052ºT. This can be ruled on the chart as an LOP GOINGIN THE DIRECTION 052º T FROM THE VESSEL TO THE LIGHTHOUSE - do not make the commonmistake of regarding it as 052º T from the lighthouse to the vessel.

Fig. 56.

Subtract the height of tide (let's say 4 metres) from thesounding and you are left with 51 metres - look at the chart andby interpolation assess where the 51 metre depth is on theLOP, it may be on a depth contour making it easy. Make a dot,circle it, and write the date, time and log applicable.

Fig. 57.



2. Two L.O.P.’s. The magnetic bearings for two LOPs taken in quick succession such that they cross atas near 90º as possible, will ‘fix' the vessel's position at the intersection point with the least possible error.The magnetic bearings are converted to True bearings and the two resulting LOPs are plotted on the chart.The fix symbol, a circle, is drawn around the intersection point and the Date (if at sea for more than oneday), Time and Log are written next to the symbol. If, while sailing out of San Diego (chart 2885),bearings recorded were ‘Chimney at Coronado Yacht Club’, 018ºT and the light at the southern point ofPoint Loma, 281ºT, the plotted fix would be as shown below:

Fig. 58.

NB: When taking two (or more) bearings with the hand-held compass, bearings to objects abeam shouldbe taken first as they will be changing more rapidly than bearings to objects near the fore and aft line ofthe vessel which change slowly. Also choose closer objects rather than objects further away.

3. Two L.O.P.’s and Depth. The two LOP fix is plotted as explained in method 2 above. Remember thatcommon to all fixes, the navigator may note, among other details, the depth at the time of taking the twobearings for a two LOP fix. He or she is able to adjust the depth sounding by subtracting the height of tideat that time to get the depth as shown on the chart. This third factor, depth, as determined by the soundingand corrected for the state of the tide, is now compared with the depth as seen on the chart at the LOPsintersection point - whether it is obvious, being on a depth contour, or by interpolation/ assessment.

If the corrected sounding and chart indication of depth at the intersection point are the same or nearly so,the fix is good. The corrected depth may be ‘out' by a small percentage of the chart depth (or one or twometres or just a few feet if the vessel is in shallow waters) - this is because the depth sounders are never100% accurate, and the ‘transducer' (see Chapter 3) which is mounted below the vessel's water line is notgiving a sounding from the water surface as expected (unless adjusted for this).

If the corrected sounding (depth) and the depth as indicated on the chart at the LOPs intersection pointdiffer by more than a small percentage, one two metres or about five feet, when in shallow waters,SOMETHING IS WRONG. If and whenever there is doubt about any one factor of a fix not matching thepattern of the other factors, DO NOT IGNORE IT. Check and re-check until the mistake is identified andcorrected.

Let's assume that when the two bearings as plotted in Fig. 58 above were taken, the depth was also readfrom the depth sounder. Lets say that after correction for the depth of the transducer below the water line(which is added) and the height of tide (which is subtracted), the depth was seen to be 50 feet. The depth



as seen on the chart at the fix is a little over 48 feet. The difference between the chart depth and the depthfrom a sounding was less than 2 feet - quite acceptable, so the fix from the intersection of the two LOPscan be accepted as good. 4. Three L.O.P.’s - The ‘Simple Fix’. Probably the most common and popular fix method - someauthorities say that the previous methods mentioned are not really recognised ‘fix’ methods whereas thesimple fix is - it allows the navigator to get an idea of how accurate he or she is being.

Three objects, positively identified on land and on the chart, are selected so that the resulting LOPs willcross to form a triangle which is close to an equilateral triangle. If the navigator is very accurate, and thehand-held compass is good, or it has been a ‘fluke’, the three LOPs will cross at the same point. The ‘fix’will be at that point.

Fig. 59.

If the three LOPs do not all cross at the same spot, they form the three sides of a triangle. This triangle iscalled the ‘Triangle of uncertainty’, or as it is better known, a ‘Cocked Hat’. The centre of the triangle is the logical place to select for the fix. A navigator can assess his or her accuracyby the size of the triangle - THE SMALLER THE TRIANGLE, THE MORE ACCURATE THEMEASUREMENTS HAVE BEEN. (Use the largest scale chart possible.)

In coastal navigation, because we are always near land, we are always near danger. To increase our safetymargin we do not use the centre of the triangle as the ‘fix’ - we take the corner of the triangle closest to landor to danger as the ‘fix’ position. We circle and label it with the ‘Date, Time and Log’.

5. The Simple Fix and Depth. The same ‘simple fix’ procedure as above can go one better - at the timeof taking the bearings for the LOPs, the reading of the depth sounder (as well as Log and Time) isautomatically noted. As with the ‘Two LOPs and Depth’, the depth comparison is done with the fix obtainedfrom the three LOPs ‘simple fix’. So long as the depth indication is approximately the same on the chartas the depth sounder, the ‘fix’ is good. If not, even with a small triangle formed by the three LOPs, check!And re-check. Only when all measurements agree is it safe to accept the resulting ‘fix’.

6. The ‘Running Fix’. A great deal of coastal sailing is on courses approximately parallel to the generalcoastline. Often only one object on land can be seen and positively identified (and too often, none - whenDRs or EPs are used in lieu of ‘fixes’). A ‘One LOP and Depth’ fix can be done, but if the sea bed is flat andhorizontal for miles around, or if the sea bed is too deep for the depth sounder to register a depth, thenanother method is called for. One such option is the ‘Running Fix’. ...

Plot the course being steered anywhere near where it is guessed to be. As the vessel comes in sight of



the identifiable object on land, take a bearing on it using the hand-held compass and plot the resultingLOP so that it crosses the plotted course line. Note the Time and Log (and depth if a further check, later,is required). Let's say the course is 340ºC (using the deviation card, Fig. 20, on page 114, deviation is nearenough nil, so it = 340ºM, and lets assume variation is 10ºW; -10ºW variation becomes 330ºT), and thefirst LOP bearing (#1) on an island lighthouse is 055ºM (= 045ºT). Let the time be 10h00, and the Log be3456,7 M. The course direction is ruled in anywhere at random.

Fig. 61.

When the vessel has moved a distance such that a new LOP from the object and the original LOP will forma reasonable angle (say from about 30º or more - up to about 150º), take the bearing for, and plot asecond LOP. Note the Time and Log (and if you wish to do the extra check, the depth).

What is the difference between the two log readings? The difference is the distance the vessel has movedalong its course direction in the time between the two LOPs being recorded. Remember that the coursedirection line is only an arbitrary line at this stage.

In our example, the difference in log readings is 4,5 M.

If we therefore measure, from the intersection of the (arbitary) course line plotted and the plot of the firstLOP, in the direction the vessel moved, the distance it travelled (4,5') between the taking of the two LOPs,we can mark on the course line where we think the vessel may be. Let's say the second LOP was 105ºM(= 095ºT) and Log 3461,2 M at 10h45 when the corrected depth was recorded as 40 m.

Fig. 62.

Since, at the time of the first LOP, the vessel's position was somewhere along that line, and at the time ofthe second LOP the position is somewhere along this second LOP line, if we move the first LOP thedistance the vessel moved, the actual position must be where the moved LOP intersects the second LOP.The moving of an LOP in this way is called ‘Advancing’ or ‘Transferring’ a LOP.



Fig. 63.

This intersection is the ‘fix’. We label the ‘fix’ with the Date, Time and Log. (The ‘Time’ being that of thesecond LOP).

We can also if we wish, check the depth at the ‘fix’ to see that it conforms with that expected from the depthreading taken at the time of the second LOP. If it does not, check the depth as at the first LOP. The vessel'sposition having been fixed, the course line can now be ruled in the correct place from the ‘fix’. Extend thenewly ruled course line backwards to intersect with the first LOP and check the depth as at that time - dothe chart-indicated and the recorded depths agree?

If one of the depths recorded does not agree with the chart depths at the respective places they wererecorded, it is possible that there is an isolated hole or tall reef/rock which is not shown on the chart whichis responsible for the confusing depths. If both depths checked do not match the chart depths, be very waryof accepting the ‘fix’ - rather take another fix, even if it just confirms the first as correct.

In our example, the recorded depths, adjusted for height of tide and depth of transducer, match the chartdepths at those places. We can relax in the knowledge that our fix is good!

NB: The depth check aspect described above is NOT part of the standard Running Fix - it is included hereas an extra check you can do if you wish. The same depth check MAY also be carried out when doing ANY‘fix’.

7. Fix by ‘Dipping’ or ‘Bobbing’ a Light. We all know the earth is round and that, therefore, if we travelon the sea in a straight line towards an object which is initially beyond the horizon, a stage will be reachedwhen we can first see the top of that object. If the top of that object is the light of a lighthouse, as it firstcomes into view, we say we are ‘dipping’ or ‘bobbing’ the light.

Fig. 64.

If the height of an object (a lighthouse light or the observer's eye) is known, the distance from that objectto its natural horizon can be calculated. Since the curvature of the earth is near enough constant and itsdiameter and circumference are known, the following formula gives the distance between the object andits horizon.

Distance (n.m.) = 2,04 X Height (m)where the 2,04 is a constant.



So if the light of a lighthouse is 9 metres above sea level, its horizon is:

Distance (n.m.) = 2,04 X 9 (m) = 2,04 X 3 = 6,1 n.m. (to the nearest single decimal)

A navigator on the average size sea-going yacht will see the lighthouse when his or her eyes are about 3metres above the water line. The navigator's horizon is therefore:

Distance (n.m.) = 2,04 X 3 (m) = 2,04 X 1,73 = 3,5 n.m. (to the nearest single decimal)

The vessel is 9,6 M (6,1 M + 3,5 M) from the lighthouse when the light is ‘Dipped’ (or ‘Bobbed’), asillustrated in Fig. 64.

What effect does the Height datum have? In the UK this datum is MHWS, but in South Africa it is MSL.These terms and abbreviations are explained in Chapter 4, Tides.

If it had been high tide at that time, and ‘Springs’ as well, then at low tide the light could be 14 m above sealevel (assuming a difference of 5 m between high and low tides). The horizon distance would then be:

Distance (n.m.) = 2,04 X 14 (m) = 2,04 X 3,74 = 7,6 n.m.

The state of the (low) tide has made a difference of 1,5 n.m. - a 25% increase on the high tide’s 6,1 n.m.!

So, where the tide is significant, and especially where the object on land is not high up, remember to allowfor the state of the tide.

In parts of England, especially near Bristol, the tidal range can be more than 10 metres. If a light is ‘10 m’as shown on the chart measured from the high water mark or Mean High Water Springs mark - see thechart statement of the chart in use - its height above the sea level at the low tide stage could be over 20m. The ‘horizon’ distance will be:

At Low Water: Distance (n.m.) = 2,04 X 20 (m) = 2,04 X 4,47 = 9,1 n.m. (to the nearest single decimal)At high tide it could be: Distance (n.m.) = 2,04 X 10 (m) = 2,04 X 3,16 = 6,5 n.m. (to the nearest single decimal)

A difference, due to the tide, of 2,6 n.m.! Clearly the tide is relevant. EXAMINATION CANDIDATESREMEMBER - many aspiring Yachtmasters fail the test the first time due to this type of mistake. In South African waters the tidal range is small (just over 2 metres at the worst) and most lighthouses arehigh, so the tide variations are negligible, especially when their square roots are used e.g. a lighthouseshown as ‘47 m’ means it is 47 metres high measured from mean sea level (on South African charts). So:At high tide: 46 m = 6,8 (to the nearest single decimal)At half tide: 47 m = 6,9 (to the nearest single decimal)At low tide: 48 m = 6,9 (to the nearest single decimal)

A difference of less than 1,5% - it can be ignored.

The distance from the vessel to the light at the time the light is ‘Dipped’ (or ‘Bobbed’) is determined. If at



the time a bearing was taken on the lighthouse and the resulting LOP plotted, we can measure along theLOP from the lighthouse the distance calculated by the ‘Dipping’ formula and a make a mark on the LOPat that point. The point marked is where the vessel was when the light was ‘Dipped’ - it is the ‘fix’. The ‘fix’symbol is drawn around the point and the Date, Time and Log reading written near the symbol.

There is a Dipping Distance Table alternative method to the calculation. See Appendix J.

Now, if we had also checked the depth at the time of ‘Dipping’ the light, we would have a cross check toconfirm the ‘fix' is good.

There are other methods of determining the ‘fix’ position of a vessel at sea, and these will be explained inChapter 3.

L.O.P. by Radio

When a vessel starts to close with the coast which is still not visible, or when fog, poor visibility or lack ofdetail due to distance prevents a navigator from seeing enough to identify an object on land from which abearing for a LOP can be taken, a RADIO DIRECTION FINDER (RDF) can be used to get a LOP.

A place where a radio beacon is located along a coast is marked on a chart by a purple or magentacoloured circle which has the letters RC next to it. The detail applicable to that radio beacon is to be foundin the ‘Admiralty List of Radio Signals’ (‘ALRS’) Volume 2 for beacons world wide, and for the SouthAfrican coast only, in the South African ‘List of Lights, Fog Signals and Radio Services’, SAN HO-1.

The detail for a beacon is shown like this:

‘1830 Danger Point LtHo (D6320) 34º37,45'S 19º18,05'E Frequency 308,5 A2A Range 100 miles

Characteristic: Period 30 seconds ZDP * 6 seconds * Silent 2 seconds Long dash 20 seconds Silent 2 seconds Period 30 seconds

Beacon Service: Continuous.’

The 1830 is the beacon number and D6320 the number of the lighthouse at which it is located, thelighthouse being at Danger Point. The latitude and longitude enable one to find it easily on a chart. The‘A2A’ refers to the type of radio signal and the range is ‘for the average receiver’. Many of the cheaperyacht-type Radio Direction Finders (RDFs) will only receive the beacon's signal a lot closer to thetransmitter, typically 75% of the range stated.

The 30-second cycle breakdown needs no further explanation, and the transmitted signal cycle is normallyrepeated 24 hours a day. Some beacons are part of a chain of beacons; these latter beacons transmit onthe same frequency but each has an alloted number of minutes of each hour to transmit.

The frequency units are ‘kilohertz’. The vessel's RDF is turned on and tuned to the frequency and the callsign, in the above example ‘ZDP’, is listened for. When a morse code signal is heard, from the morse codefor ZDP shown in the beacons' detail book, try and identify the code. It is not difficult because the code istransmitted very slowly.

If the code is not ZDP, adjust the frequency tuner on the radio slightly up and then down from where youhad set it initially until you hear ZDP. Adjust the volume and frequency to get the best signal, even if thismeans the radio, held so that it is vertical and therefore the antenna inside is horizontal, has to be turnedin the horizontal plane. When the signal is strong or as good as you can get it, wait for the start of the 20seconds ‘long dash’, then slowly turn the RDF (or its antenna if separate) in the horizontal plane until theweakest signal is heard. It may be necessary to turn down the volume control to hear a decrease in signalstrength, or a weak beacon signal may result in an arc of no signal.

The direction to the weakest signal or to the average of the bearings on each side of the ‘no signal’ arc, is



the direction from which the RDF receives the long dash tone - if the radio wave has not been bent on itsway to the vessel, it is also the direction from the vessel to the beacon. It could alternatively be 180º in theopposite direction as the RDF only reacts when its antenna is in line with the transmitter, off either end.

While sailing along a coast line, it is easy to tell which of the two possible directions is the correct one.However, an attol mid ocean or a low island's beacon to one side of a course can be located by plottingtwo LOPs a few hours apart and plotting them across the course line - the correct side is the convergingLOP’s side.

RDF receivers have a means of giving direction information to the user - either by a built-in compass or ascale to give an angle relative to the vessel's heading. This is then compared with the vessel's steeringcompass to get the direction to the beacon.

The direction bearing obtained is converted to a True bearing and it is plotted on the chart. It is an LOP andit was obtained by radio - the RDF.

At sunset and at dawn, and to a certain extent during the night, the path of the radio waves is often bentso that when it arrives at the receiver, it is not coming in the direction of the beacon. The amount and timesof the bending varies from day to day and there is no way to know ‘when’ or ‘how much’. The navigatormust therefore be wary of results obtained from a RDF at these times.

Routine for Coastal Navigation

Actions Prior To Departure

The first steps in making a coastal voyage should be an examination of the questions:

a. ‘What?’ What vessel is to be used and is it and all its equipment ready for and up to making thevoyage? What needs to be done to get it ready, what has to be inspected, checked, bought, fitted , fixed,amended, loaded, serviced or replaced to make the vessel seaworthy?

b. ‘When?’ How much time is available for the planning and preparation? The date of sailing may well be,and often is, dictated more by time required to get ready and weather than any other factor. The numberof ‘things to do’ may take too long for one person, so...

c. ‘Who?’ Decide on what is to be done and who is to do it. The crew for the voyage must be chosen,informed/invited, and if agreeable to the venture, should where possible become involved at an early stage.They may need advance notice so that leave can be arranged in time.

d. ‘Why?’ The boat must be seaworthy, correctly prepared, loaded and crewed before departure. All safetyequipment must be checked and all publications to hand and studied. Charts must be checked for the latestupdating ‘Notices to Mariners’ corrections, and the state of the tide checked, if relevant, so that departurecan be arranged to be at high tide. The state of tide at a nearby destination after a short voyage may berelevant, e.g. Saldanha Bay to Port Owen, or Chichester Harbour to Buckler's Hard - arrival should be athigh tide and this may affect departure time.

e. ‘Where?’ Where is the start point and where is the voyage to? Therefore what route is to be used, whereare the obstacles and dangerous areas to be avoided, as well as the good natural and man-madenavigation aids to be used on the voyage? What waypoints are to be used and where are they to be? Onarrival at the destination, where can the vessel be moored or berthed? Is any advance booking required?

f. ‘How?’ How is all the preparation work to be done? Some may be delegated to crew members, somethe skipper must do and some he can do, and other tasks may have to be done by contractors as itinvolves specialists' attention. A control is probably best facilitated by making a list of everything to be doneand how it is to be done, right down to Customs and Immigration clearance and the departure formsubmission.

LISTS of things to be done on a boat, NEVER have an end. As one task is completed and struck from thelist, so two new items are added. Do not be surprised - it will happen to you! See Chapter 8, ‘PassagePlanning’, for an ‘in depth’ look at this subject.



Actions While Under Way

g. Log Book Entries. From the moment of departure, the vessel's Log Book must be entered at regularintervals, hourly for coastal sailing, every three to four hours for trans ocean sailing, and whenever thereis a course change, duty watch change, or anything significant happens on the voyage.

h. A ‘Duties List’ should be prepared so off-duty crew know when they can go and rest - and when tocome on watch. As meal times near, unless someone has been nominated or has volunteered for the galleywork, spare crew disappear in case the task of getting the meal is given to them. Meals then becomeirregular, and often consist of packets of biscuits or similar. Cleaning duties should also be specified.

i. Cleaning. A vessel at sea gets dirty quickly and needs to be cleaned - AND TIDIED. ‘An untidy shipbecomes a dangerous ship’. Put away personal kit when it is not in use, and put all vessel's kit andequipment back in its respective stowage places so it can be easily found later if needed in ahurry/emergency.

j. Plotting. The course, allowing for tides, obstacles and waypoints, and current or tidal stream influencesas well as leeway, and frequent DRs, EPs or ‘fixes’ should be plotted unless the skipper (and navigator)are very familiar with the route. Even then, progress along the route should be plotted - REMEMBER: theskipper and navigator should know where the vessel is, both on the sea and the chart position, at all times.Use the ‘Publications’ - they are there to help e.g. Sailing Directions.

k. Routine maintenance checks while under way are recommended. Check the engine oil and coolantlevels, that all engine parts are tight, there are no fuel, oil or air/exhaust gases leaks, the electric wiring andequipment is secure, and that wires and pipes are not being subjected to chafe or excessive heat. The bilgeshould be checked periodically for water level and for smells of gas if gas is leaking. Standing rigging canbe checked for turnbuckles/bottlescrews that may be coming loose and for signs of stay or shroud wires'strands starting to part. Split pins are not always opened correctly and can drop out leaving clevis pins freeto work loose and then a stay or shroud's support is lost. Checks and continual maintenance are well worththe trouble, and they amount to good seamanship.

l. Weather watch. Monitor the weather pattern, forecasts, reports and bulletins as well as the vessel's ownbarometer and the wind and cloud activity so that the crew and vessel are ready in advance for any roughconditions.

m. Stock Control. Keep a check on the rate of consumption of drinking water and victuals so that they lastthe duration of the voyage, even if delayed en route.

n. Crew. As a skipper, keep a watch on the health and morale of the crew - they are your most importantresource.

o. Duty Crew. Make sure the helmsperson is familiar with the ‘Rules of the Road’, especially the need tokeep an ALL ROUND LOOK-OUT at all times, and that all crew know that they are to call you wheneverthe vessel approaches within a specified distance of any other vessel or an obstacle. They must feel freeto call you at any time if they are in doubt about any aspect of the navigation or safety of the vessel.

p. Lights at Night. From sunset to sunrise, remember to display the appropriate lights for other vesselsto see.

Actions After Tying Up

One of the actions after a voyage, while events are still fresh in one's mind, is to think back about thenavigating process and see if we could have done better. Were any mistakes made or any ‘close shaves’experienced during the trip? If so what lessons can be learnt from them? Was there any danger at anystage and if so, why? Was there too much reliance on any one navigation aid when others could andpossibly should also have been used? Was any confusion experienced regarding the navigation at anystage? If so, why? What could have been done to avoid the confusion? Were log book entries and theplotting satisfactory?

Finally, all charts used must have any pencil markings erased so they can be put away clean for the nexttime they are needed. The log book entries are closed off and the skipper should then check and sign atthe bottom of the entries to signify ‘journey complete’. It also shows that he or she is familiar with all the



entries, especially any involving the crew's comments or aspects about the vessel which may needattention.

Strategy for Course Laying

It is considered important to emphasise that a skipper is responsible for the safety of the vessel and all thepeople on board. For any voyage it is his or her decisions only that count. These decisions result from theconsideration of various factors, including inter alia:

1. The probable duration of the voyage. Short journeys of less than 24 hours require far less planning andpreparation than longer trips. Longer trips need more charts, therefore more chart checking for the latestcorrections from ‘Notices to Mariners’, more reading up in advance and more chart checking for obstaclesalong the intended route; weather forecasting en route becomes involved, night sailing becomes necessary,and more victualling is involved. Reserves of water and victuals (25% minimum) must be included andpossibly also reserves of fuel.

2. The date of departure. Adequate time must be allowed for thorough preparation - nothing should beoverlooked because of a rush to get going.

3. The best time for departure or arrival. A day start gives all on board several hours of daylight to settlein and get the routine started. Night departures do not, however, present any special problems, but nightarrivals can be dangerous unless the skipper is already familiar with the destination. Some harbours' lightsdo not work and no effort is made to get them working - and the unsuspecting skipper is none the wiser!The same also applies to radio beacons. It is a fundamental rule of Pilotage (see Chapter 6) to wait out atsea rather than to enter a strange harbour at night.

4. The height of tide wherever shallows may be experienced. Allow for a generous safety clearance if theshallow area can not be circumvented. 5. Currents and tidal streams can be used to advantage. If possible, choose the time so that the tidalstream will be flowing in favour of the vessel's course, not against it. Currents far off shore are often in theopposite direction to inshore ‘eddies’ - use the flow going your way!

6. Weather forecast. A study of the weather pattern before departure must be kept up to date by constantlymonitoring forecasts and doing one's own forecasting, especially by observing the vessel's barometer.

7. Traffic to be encountered and traffic lanes. If separation schemes are to be joined or crossed, rememberthat a sailing craft has no rights in such areas - try and cross in daylight when visibility for all vessels is best.Avoid areas where large fishing fleets set their nets - rope from a net or a net in the rudder or around thepropeller is a problem!

8. Obstacle areas are to be avoided. Foul ground, shallow reefs, pipelines near the surface and anythingin the water that can interfere with the boat's progress are to be avoided.

A study of the charts' detail in advance, as well as ‘Sailing Directions’ and books such as the relevantvolume of the Ocean Pilot will show most of the obstacles. Beware; obstacles like shark nets off beacheshave caught more than sharks! Select a safe course away and around obstacle areas.

9. Navigational aids to be used. Choose navigation marks that will be easy to use and which permit the useof the easy position-fixing methods. Lighthouses' ‘Dipping’ distances can be scribed in as arcs using adrawing set compass. Areas where there are few if any navigation marks can be identified so that thenavigator will know in advance to be ready to use other methods of navigation.

10. Limitations imposed by Customs and Immigration clearances. Some countries' Customs andImmigration authorities do not work at week-ends, nor from late afternoon to mid morning. Clearances inthese cases must be done at the right moment. Once cleared make sure actual departure occurs withinthe time allowed or the clearing procedure may have to start all over again.

11. The submission of a Voyage Plan or Departure Form (‘Flight Plan') to the local Club, Marina, or PortAuthority. Nearly all ports from which one will depart, have a form of some type that has to be completedbefore a vessel may depart. It has space for the adequate identification of the vessel, details of the route



to be sailed, and details of the skipper's identity and all persons on board and their next-of-kin detail.

(Local rules vary slightly from place to place. For example, in South Africa, only in the case of Cape Townand the immediate surrounds - a 100 mile radius around Cape Town - may a yacht leave one port to goto another nearby port WITHOUT first submitting a Departure Form. A booking out, and in, book is kept inthe club in lieu - see Fig 65 below. In all other South African harbours, a form similar to that shown atAppendix A must be used. Leaving from Cape Town for a destination more than 100 miles distant requiresthe use of the form shown at Appendix B. Check with the authorities nearest you for the type and useagecircumstances for using the equivalent form.)

Booking In/Out RegisterDate Vessel m Skipper Sail # Route ETR Phone

#Returned

Fig. 65.

The Sextant

So far we have examined, inter alia, the significance of charts, compasses and navigating by DRs, EPs andsome of the methods of obtaining a ‘fix’ position. There are more ways to determine a vessel's positionaccurately, and we will soon examine the remaining methods - when we are done, you will know everypossible method, whether navigating on a yacht or an ocean liner. Two of the coastal ‘fix’ methods involvethe use of the sextant*, so we need to find out what it is and how to use it. We will also examine a few otherrelated aspects. *It may be that the need for and knowledge of the use of a sextant is no longer requiredby the testing authority in your area. I recommend that you DO NOT buy one unless you have to or youintend deep sea sailing away from the coast. In the latter case, it is still optional according to manyauthorities.

The Composition and Uses of the Sextant

Let's deal with the use of a sextant first. A sextant measures angles. Accurately. To one decimal placeof a minute of arc (1/10th of 1/60th of a degree, or 1/10th of a minute). It does nothing else, unless youthrow it at someone!. Next, its composition. Look at the illustration on page 141. Read the labels naming the parts and identifythe equivalent parts on your sextant.

The FRAME holds the HORIZON MIRROR, the EYE PIECE, the INDEX SCALE and HANDLE, whileproviding a pivot for the INDEX ARM to be able to move through the arc of the scale. The HORIZONMIRROR has two adjusting screws behind it. The adjustable EYE-PIECE allows the user to focus on distantobjects. The INDEX ARM has a graduation mark next to the INDEX SCALE to enable the user to read offwhole numbers of degrees, and a rotatable DRUM to show the fractions of a degree as ‘minutes’ anddecimals of a minute.

Near the drum is a QUICK RELEASE mechanism to enable coarse adjustments of the INDEX ARM setting.The INDEX MIRROR is mounted on the INDEX ARM at the pivot end and therefore moves with the INDEXARM when it is moved. This mirror has only one adjusting screw behind it.

Check the mirrors' alignments and therefore INDEX ERROR before using it to measure any angle(s).

Calibration Adjustments

Begin by setting the INDEX ARM to zero degrees, zero minutes. Hold the sextant in your right hand andhold it up to the eye so that the frame is vertical and the eyepiece enables you to see a distant object ...



Fig. 67.

... which has a distinct horizontal line. The horizon is best - it is far away. If the object chosen is not faraway, you may get a false reading. You will see one of these three images:

A B C Fig. 68. A IMAGES IN LINE - MIRRORS PROBABLY SET CORRECTLY B and C IMAGES NOT IN LINE - MIRRORS NEED ADJUSTING

The reason we see these images is because the left half of what we look at is viewed directly from theeyepiece but the right half involves the visible picture reaching the eye after reflecting off the mirrors:

Fig. 69.



If the two halves, the left and the right, of the distant horizontal line are in line, incline the sextant 45º to oneside and then to the other - the images must remain in line. If they do, the mirrors are correctly set. If at anyof the three positions the images are not in line the mirrors' settings need checking - one or both will needadjusting. Setting the INDEX MIRRORSet the index arm at about 50º. Now hold the sextant (see Figure 70) so that the frame is in anapproximately horizontal plane with the index mirror between your eye and the index scale. You need tobe able to see over the pivot point, past the index mirror's right edge (as seen when the sextant ishorizontal - the same edge which would be its bottom side if the sextant were held in the vertical plane),to the index scale near the zero degrees part of the scale. At the same time look into the right (normallybottom) part of the mirror to see the reflection of the index scale near its maximum reading. The far edgesof the index scale arc should be in line.

If they are not, turn the adjusting screw (there is only one) behind the index mirror. The two images of thefar edges of the index scale will either get closer or further apart as you turn the screw. Turn the screw inthe direction that brings them together. When they are in line, the index mirror will be vertical orPERPENDICULAR to the plane of the frame of the sextant - the index mirror will be correctly aligned. If theyare not in line you will experience the ERROR OF PERPENDICULARITY - a tendency to see doubleimages, one higher than the other.

A B C

Fig. 70. ALIGNMENT OF THE INDEX MIRROR A. IMAGE TOO HIGH B. IMAGE TOO LOW C. IMAGE AND INDEX SCALE IN LINE

Setting the HORIZON MIRROR

(The index mirror must be correctly adjusted before starting these adjustments.)Set the index arm to 0º and the drum to 0'. Hold the sextant in the right hand, bring it to the eye so that itis in the vertical plane, and look at a far distant object or horizontal line selected earlier (preferably thehorizon). Are there two images of the object or line, or is there only one image or line? You will see one ofthe three images shown in Figure 68. When using the horizon or a distant line, if the two images are in line,tilt the sextant to one side, 45º off the vertical. Are they still in line? Now tilt the sextant 45º to the oppositeside of the vertical. Are they in line? If at any of the three positions the images were not in line, the horizonmirror will need adjustment. It will need to be set exactly parallel to the plane of the index mirror which wasset PERPENDICULAR to the frame of the sextant. ‘Double’ images, side by side, must be removed. Thesedouble images are called SIDE ERROR.

Checking that the drum is still on 0.0', hold the sextant so that you can see the distant object or horizontalline through the eyepiece. If viewing a distant object (e.g. a cliff, the moon, a street lamp), keep the sextantvertical as you adjust the two screws behind the horizon mirror to get the two images to become one i.e.they overlap exactly. If viewing the horizon, with the sextant tilted 45º to the right, note the difference inlevels between the left and right halves of the distant horizontal line. Now by turning the higher of the twoadjusting screws behind the horizon mirror, reduce the difference in the two levels BY HALF. If you turn thetop adjusting screw the wrong way, the difference in levels will increase - turn the adjusting screw in theopposite direction.



A B C Fig. 71. THE RIGHT TILT ADJUSTMENT

A. THE TOP ADJUSTING SCREWB. THE DIFFERENCE BEFORE ADJUSTINGC. THE DIFFERENCE AFTER ADJUSTING (DIFFERENCE REDUCED BY HALF)

Now tilt the sextant 45 degrees to the left of vertical and do the same again, this time using the bottom ofthe two adjusting screws behind the horizon mirror.

A B C Fig. 72. THE LEFT TILT ADJUSTMENT A. THE BOTTOM ADJUSTMENT SCREW B. THE DIFFERENCE BEFORE ADJUSTMENT C. THE DIFFERENCE AFTER ADJUSTMENT REMEMBER ONLY TO REDUCE THE DIFFERENCE IN LEVELS BY HALF AT EACH TILT ANGLE. Nowrepeat the process with the sextant inclined 45º to the right. ONLY REDUCE THE DIFFERENCE INLEVELS BY HALF AT EACH ANGLE OF TILT. Now repeat again, with the sextant tilted to the left.Continue the left and right tilting adjustments until the difference in levels is eliminated.

With the sextant held in the vertical plane, check the left and right halves of the distant horizontal line. Theyshould be in line. They should be in line whether the sextant is vertical, or tilted 45º to either side. If theyare not, re-check the index mirror as it is possible you turned its adjusting screw by mistake while adjustingthe horizon mirror. If this is the case, start again. If the index mirror is still correctly aligned, re-check thehorizon mirror and re-adjust.

INDEX ERROR

It is possible that you do not have time to complete the mirror adjustments, or while you are still gettingused to the procedure, you get close to ‘in line’ but not exactly ‘in line’. There will be a small amount of errorremaining at the time you wish to use the sextant to measure an angle (take a sight?). You therefore needto know what this error is. It is called the ‘Index Error’ (IE).

Hold the sextant to the eye so that it is vertical and you can see the distant horizontal line. While KEEPINGTHE SEXTANT VERTICAL, adjust the drum until the left and right images of the distant horizontal linecome in line while KEEPING THE SEXTANT VERTICAL. Note the reading on the drum. It will either bea few minutes (and/or decimals?) of an angle greater than zero (zero degrees, zero minutes) i.e. a positiveangle (‘ON’ the scale), or less than zero, i.e. a negative angle (‘OFF’ the scale). Note that the ‘scale’ werefer to is, on the drum, from zero minutes, towards 55' (off the scale) or towards 5' (on the scale).



A B C

Fig.73. INDEX ERROR: A, NO INDEX ERROR B, ‘OFF’ THE SCALE. C, ‘ON’ THE SCALE

The index error found must now be added or subtracted to any angle measured with the sextant. If the errorwas 3.5' ‘ON’ the scale, this would represent the zero position of the sextant at the time. The sextant overreads by 3,5'. So any angle measured will include this error. The true angle required must therefore havethis error subtracted; we say ‘Index Error "on" the scale, subtract’.

Fig. 74. INDEX ERROR ‘ON’ THE SCALE, SUBTRACT If the index error was 3.5' ‘OFF' the scale, we must add it to any angle measured. We say ‘Index Error"off" the scale, add’.

Fig. 75. INDEX ERROR ‘OFF’ THE SCALE, ADD

Index error should be checked just before a sextant is used - it can be dangerous to assume that it will bethe same as the last time the sextant was used. Anything can happen to alter it and plastic sextants willhave index errors which change with temperature changes - plastic sextants' errors should be checkedbefore and after use and the average taken as the index error for the angle measured.

COLLIMATION ERROR

Collimation error is the error which results when the axis of the telescope or eyepiece not being correctlyaligned with the plane of the sextant. A good sextant will not have any collimation error, and the averagesextant used in the present day does not have any means of adjusting for it.

OTHER ERRORS

There can be other errors caused by the pivot point on the index arm not being correctly aligned with theindex scale, incorrect graduation of the index scale, or imperfect lenses used in the telescope eyepiece.They cannot be adjusted and the manufacturer normally supplies a table of values to be used tocompensate for these errors. The values one would see in a good sextant's table would be very small andfor the yachtsman or yachtswoman who is not needing the accuracy used by oil rigs (!), they can beignored.



Practical Tips

Before we end the subject of the sextant we need to cover tips for its practical use and care at sea. So:

1. A sextant is an expensive, delicate and accurate measuring instrument - treat it with care andrespect, keeping it in its box when it is not needed. Store the box in as dry a place as possible andwhere it cannot get knocked about, or have heavy things dropped or placed on top of it.

2. Keep the sextant in the box until you are in the cockpit. You do not want to stumble or fall with it inyour hands while on your way out of the saloon.

3. As soon as you remove it from the box, place the lanyard around your neck (if your sextant does nothave a lanyard, fit one immediately - a strong, thin, nylon cord, one metre in length tied as a looparound the handle such that the loop length is just less than half a metre). If you then stumble andhave to grab on to the yacht as it lurches, the sextant will not fall and it is very unlikely that it will getdamaged.

4. When handling the sextant, do not apply any pressure or force(s) to any part of it. To reduce the riskof applying unintentional force, keep it held in the right hand, using the handle at all times exceptwhen necessary to hold it otherwise, for example, when calibrating/adjusting for index error, etc.

5. When using a plastic sextant, take your left hand off the drum after rotating it for fine adjustment, so

that no twisting force is applied to the frame giving incorrect readings.

6. Check index error often but only adjust to reduce this error when it is greater than 4.0'.

7. In rough weather or with a big swell running, try to take sights from the top of swells as a moreaccurate view of the horizon is possible - sometimes it cannot be seen at all!

8. As soon as you have finished using the sextant, clean it and put it back in its box and the box backin its proper stowage place. To clean a sextant, wipe it over with a soft dry or just off-dry cloth. If thecloth is damp, it should be because of fresh water, not sea water. Remove any sea spray that mayhave splashed on to the sextant. A wipe with a light oil on a cloth will help to keep it in good condition.Do not do this for plastic sextants.

9. Periodically check that no screws, bolts or nuts are coming loose. If any are, tighten them so that theyare just tight - be careful not to over-tighten them.

10. Keep the sextant box clean and dry!

SUPERVISE CHILDREN/NOVICES WHO ARE LEARNING TO USE A SEXTANT.

NOTES





APPENDIX AEXAMPLE OF A VOYAGE PLAN/DEPARTURE FORM - RECORD OF SAILING





APPENDIX BVOYAGE PLAN

ROYAL CAPE YACHT CLUB



NOTES (Continued)


BY HENTON JAABACK - KNOWLEDGE IS USELESS WITHOUT PRACTICAL SKILLS

CHAPTER 3

MORE COASTAL NAVIGATION

Introduction

Knowing what a chart is and how to use it to advantage, and knowing the elements of determining avessel's position at sea by DR, EP, some of the fix methods and how to use a sextant is all very well - butcan this knowledge be used in practical navigating situations? The closest we can come to finding out isto set a series of ‘Test Yourself’ questions and supply the answers for you to check yourself. In workingthrough these practice exercises and seeing the correct answers, a valuable learning experience isachieved. But first let's look at the remaining ‘fix’ methods and other outstanding aspects. Remaining ‘Fix’ Methods

1. Distance-Off by Vertical Sextant Angle. If three of the six dimensions applicable to a triangle areknown, the remaining dimensions can be calculated, so that the lengths of all three sides and themagnitude of the three angles are obtained.

If a chart shows that a lighthouse is a number of metres above the height datum, it is a verticalmeasurement from the datum level to the top of the lighthouse. By adjusting for the height of the tide at thetime, the height of the lighthouse at that time is obtained. This vertical dimension makes a right angle (90º)with the sea level, on which a vessel is located (or near enough anyway so as to make no difference). Thevertical height measured at 90º to sea level, and the plane of the sea level can be sides; an angle and twosides respectively of a triangle - the third side being a line from the navigator on the vessel some distanceaway, to the top of the lighthouse:

Fig. 76.

Knowing there are:1. a right angle,2. the height of the lighthouse (adjusted for the state of the tide) (BC), and3. if measured accurately, the angle at the navigator, A (âº), between the bottom side of the triangle(AC) (the distance from the lighthouse to the vessel) and the side from the navigator to the top of thelighthouse (AB), three of the triangle's dimensions are known. The remaining sides and angles can becalculated.

The answer to only one of the dimensions - the length of the bottom side - is needed. In trigonometry it isobtained using the formula:

Tan (of the sextant angle) = Opposite (height in metres) Adjacent (distance in metres)Therefore: Adjacent (distance in metres) = Opposite (height in metres) Tan (of the sextant angle)

The answer in metres is divided by 1 852 (there are 1 852 metres in a nautical mile) to get the distance innautical miles from the navigator to the base of the vertical height of the lighthouse, which is the chartdistance ‘lighthouse to vessel/navigator’. In addition to the trigonometric method, there is an easier way of simply looking up the answer in a set oftables designed for the purpose:(This is a copy of a part of one page of the Tables from Reed's Nautical Almanac - get the book; lots of itscontents never get old.)

Page 152 Coastal Skipper/Yachtmaster Offshore shore based course


REED’S NAUTICAL ALMANAC

TABLE FOR FINDING DISTANCE OFF WITH SEXTANT UP TO 7 NAUTICAL MILESDistancein miles& cables

HEIGHT OF OBJECT, TOP LINE METRES-LOWER LINE FEET Distancein miles& cables

85280

88290

91300

94310

97320

101330

104340

107350

110360

113370

116380

119390

m c º ‘ º ‘ º ‘ º ‘ º ‘ º ‘ º ‘ º ‘ º ‘ º ‘ º ‘ º ‘ m c

00000

00001

11111

11112

22222

22223

12345

67890

12345

67890

12345

67890

24 4412 58 8 44 6 34 5 16 4 23 3 46 3 18 2 56 2 38

2 24 2 12 2 02 1 53 1 46 1 39 1 33 1 28 1 23 1 19

1 15 1 12 1 09 1 06 1 03 1 01 0 59 0 57 0 55 0 53

25 3013 25 9 02 6 48 5 27 4 33 3 54 3 25 3 02 2 44

2 29 2 17 2 06 1 57 1 49 1 42 1 36 1 31 1 26 1 22

1 18 1 15 1 11 1 08 1 06 1 03 1 01 0 59 0 57 0 55

26 1613 52 9 20 7 02 5 38 4 42 4 02 3 32 3 08 2 49

2 34 2 21 2 10 2 01 1 53 1 46 1 40 1 34 1 29 1 25

1 21 1 17 1 14 1 11 1 08 1 05 1 03 1 01 0 58 0 57

27 0114 08 9 39 7 16 5 49 4 51 5 10 3 39 3 15 2 55

2 39 2 26 2 15 2 05 1 57 1 50 1 43 1 37 1 32 1 28

1 23 1 20 1 16 1 13 1 10 1 07 1 05 1 03 1 00 0 58

27 4614 459 577 306 01 5 014 183 463 213 01

2 442 312 192 092 01 1 531 461 401 351 30

1 261 221 191 151 12 1 101 071 051 021 00

28 2915111015744612 510426353327306

249235223213204 157150144138133

129125121118115 112109107104102

29 13 29 56 30 38

etc.

3119 32 00 32 41 00000

00001

11111

11112

22222

22223

12345

67890

12345

67890

12345

67890

Fig. 77.

As an example, let's assume a ‘Trig’ beacon on a hill is seen on the chart to be 85 m high (above heightdatum being mean sea level) when it is low tide and the tidal range is 2 m. It is therefore 86 m high at thetime of the sighting. The sextant angle measured at the vessel, between the water line below the hill andthe hill top, is seen to be 1º 16'. Using the Table in Figure 77, 86 m is between the two vertical columns of85 m and 88 m, and looking down these two columns we see 1º 16' is between 1º 15' and 1º 18' - so byinterpolation we can deduce that 86 m and 1º 16' results in a distance of 2 miles and 1 cable (2,1 n.m.).At the time of the measurement the vessel was a horizontal distance of 2,1 n.m. from the top of the hill. AnLOP plotted from the hill as at that moment allows us to measure 2,1 n.m. from the hill to the ‘fix’ position.We circle the ‘fix', and label it with the Date, Time, and Log. Using trigonometry, the distance off would be calculated as: Tan 1º 16' = 86 m Distance

So: Distance = 86 m Tan 1º 16'

= 86 m Tan 1,2666 º

= 86 m 0,022111

= 3 889,467 m

= 2,1 n.m. (after dividing by 1 852 m)



A navigator may need to be able to know accurately that the vessel does not get closer (to danger) thana specified distance to an object whose height at a stage of the tide is known. He or she can look up theangle applicable to that height and distance, then monitor the angle as seen through the sextant - the anglemust not become greater than the angle found from consulting the tables; the vertical Danger Angle.

If the requirement was to ensure that the distance of the vessel does not get greater than a specifiedamount from the object whose height at a time is known, the navigator can find the applicable sextant anglein the tables, then monitor the actual angle to ensure that it remains more than the angle from the tables.

2. Fix by ‘Horizontal Angles’ Method. This method can involve the use of the hand-bearing compassor the sextant - far greater accuracy will be achieved if the sextant is used.

While at sea when the coast is visible, three objects on land, and which are also clearly marked on thechart, must be positively identified. The magnetic bearing to each must be noted, or the angles betweenthe left and centre objects and the centre and right hand objects must be measured using the sextant ina horizontal plane.

The result is two angles having one common side - the line from the navigator to the centre object, and acommon intersection point (where the navigator/vessel was located). These angles can be reproduced ontracing or thin paper, or they can be set up in a Station Pointer which is intended for this purpose.

Fig. 78.

The tracing paper or Station Pointer (do not let the ‘arms’ slip/angles change) is then placed over the chartand the three sides of the two angles manoeuvred so that the line of each passes through the centre ofeach respective object, as shown on the chart. The three ‘arms’ will all ‘fit’ with the paper or Station Pointer in one position only. When in this position, thecommon intersection point is the chart position from where the measurements were made - it is the ‘fix’position (by the ‘Horizontal Angles’ method).

If, at the time, the navigator did not have thin or tracing paper, nor a Station Pointer, a mathematics setdrawing compass can be used to help find the ‘fix’.

To understand the method, a little revision of geometry is called for.

A straight line joining any two points on the circumference of a circle is the base of an isosceles triangle



whose two equal length sides meet at the centre of the circle. The sides are therefore radii. Using the samebase line, an isosceles triangle whose equal-length sides meet at the centre of the circle, has an angle atthe centre of the circle twice that of the third angle of a triangle whose sides meet at the far circumference:

ABC = CAB Angle D, Xº, is the same wherever D is on the circumference of the circle ACB = 2 x ADB (providing D is on the same side of AB as C).

AND D is half the angle at C.

Fig. 79.

Angle ADB is half the angle ACB. If we can measure the angle at D with a sextant (or by other means), wecan find, by doubling that angle, the angle at the centre of the circle, namely ACB.

Since the three angles of a triangle add up to 180º, if we subtract the doubled angle D (=C) from 180º, weget the balance which will be shared equally (ABC is an isosceles triangle) by angles ABC and BAC. Sowe can calculate angles ABC and BAC.

On the chart we rule a line joining A and B.Using a protractor, we measure off the angleat A and at B and rule the lines whichbecome the radii intersecting at the centre ofthe circle. Now we use our drawing compassand scribe the circle. Our position, D, Issomewhere on this circumference.

Fig. 80.

Now we repeat the process using place A or B as one of the places on the circumference of a new circle,and a third place, E; lets say B and E. We now go through the same procedure for the two places B andE. We will get another circle whosecircumference contains B, E, and thenavigator’s position, D. The two circles’circumferences intersect at two places.These two places will be at B and at D. Sincethe navigator (and therefore the vessel) canonly be at one place on both circumferencesat one moment, he (and the vessel) have tobe at D. The vessel’s fix position is D; wecircle the point (it is a fix) and label it withthe Date, Time, and Log reading whichwere recorded when the angles weremeasured.

Fig. 81.

3. The ‘Four Point’ Fix. The old method of describing a direction using the ship's compass was to usevarious combinations, shown on the compass face, of the names of the cardinal points, North, South, Eastand West. Young sailors had to learn to ‘box the compass’ - to describe these directions, from north,clockwise, all the way round, in jumps of one ‘point’ (11º15') at a time:



360 º 00' = North 011 º 15' = North by East 022 º 30' = North, North East 033 º45' = North East by North 045 º 00' = North East 056 º 15' = North East by East etc. (See Figure 82.)

So ‘four points’ is a way of saying 45 º, e.g. ‘Alter course "four points" to starboard’:

Fig. 82.

A navigator on a vessel, seeing an object on land which is also marked on the chart, can monitor thebearing to it and note the log reading when the angle between the vessel's course line and bearing to theobject is 45 º (or ‘four points’).

Fig. 83.

The angle between the course line and the bearing to the object will be seen to increase as the vesselcontinues along its course. When this angle becomes eight points, or 90º, the log is again noted and thedistance travelled from the first to the second bearing is obtained. The angle between the course line andbearing to the object has changed by 45º (‘four points’).

Fig. 84.

A triangle's three angles total 180 º. If one angle is 45º while another is 90 º, the third angle must be 45º.If two of the angles of a triangle are the same (e.g. 45º), it must be an isosceles triangle, and the length ofthe two sides not common to both angles must be the same length - if we know the length of one side fromthe comparison of the log readings, we know the length of the other. The second bearing from the courseline to the object is that side of the triangle - the distance of the vessel from the object is therefore nowknown, and the bearing is plotted on the chart. The distance measured along that line from the object gives



the ‘fix’ position of the vessel, by the ‘four point fix’ method. We draw a circle around the spot to show it isa ‘fix’, and we label it with the Date, Time and Log.

In practice, the navigator, having established the first bearing (and log reading at that time) to the objectwhen it is 45º off the bow, plots this ‘LOP’ across the assumed course line. The second bearing directionis then calculated when it will form an angle at the bow of 90º. Knowing what the second bearing must befor the angle to double, the navigator watches the land object via the hand-bearing compass until thesecond bearing applies, then a note is made of the log and time. The rest is as above.

4. Fix by Doubling The Angle at the Bow. This method is exactly the same as the ‘four point fix’,except that the first angle (at the bow) between the course line and the bearing to the object on land canbe ANY angle - not just 45º. At the time of the second bearing, the angle between the course line and a lineto the object on land must be double the first angle (at the bow) with the first bearing. Therefore there isstill an isosceles triangle so the logic of the ‘four point fix’ applies equally with doubling the angle at thebow.

Fig. 85.

5. Position from a Line of Soundings. If a navigator has a fair idea of where a vessel is, and as itscourse is known, a record of the depth soundings at regular intervals can help establish the vessel'sprogress along the course line.

This is only possible where the sea bed shape is distinctive, having easily recorded changes to depth,preferably in an irregular pattern. It is not possible if the sea bed is flat and smooth and has little, if any,change in charted depth. Soundings (and the time and log reading for each) are recorded at regularintervals, say every 0,1 n.m. as per the log or, if one is able to measure equal, shorter distances, moreregularly. The depths as per the depth sounder are then adjusted by subtracting the height of tide in orderto ascertain the charted depth at each sounding. Using a plain piece of paper having a straight edge, thedistances between soundings are marked off to scale on the paper's edge and the chart depth at eachplace is written next to its applicable mark.

The piece of paper's straight, marked edge is then placed over the chart and manoeuvred around in thegeneral area the vessel is thought to be, keeping the straight edge of the paper in line with the course beingsailed as per the chart. The markings showing the depths as recorded are compared with the depths anddepth contour lines on the chart, until a ‘match’ is obtained. A position can then be taken from the mostrecent sounding (when time as well as log were noted) as marked on the chart from the paper's straightedge. See page 157.

Finally, Practice, Practice, Practice

We still need to learn one or two navigation techniques. However, all possible methods of coastalnavigation have now been explained. To master the art of navigation completely, practice with navigationquestions is essential. Questions for practice purposes, and their worked solutions, can be found inelsewhere on this CD and in Navigation Exercises books, obtainable from all nautical book retailers. The Associations' (RYA, ASA, AYF, and other national sailing associations) books of practice questionsare recommended - try all the questions, including those which involve the use of the Exercise Tables - theyhelp in getting used to extracting relevant information as will be the case in actual navigating, e.g. the useof the Tide Tables and Sailing Directions. However be warned - the South African Sailing book, after yearsof their attempts to get it right, still (January 2000) contains many errors, especially in the solutionssupplied.



Fig. 86.

Navigation Publications

a. Admiralty list of Radio Signals - 1993 (ALRS). A set of six volumes, some of which consist of twoparts (books) each. They contain, inter alia, world-wide details of:

i. Volume 1. Coast Radio Stations; Medical Advice by Radio; INMARSAT Maritime Satellite Service;Regulations for the use of Radio in Territorial Waters; Distress, Search and RescueProcedure; and a brief extract of the International Radio Regulations.

(This volume is in two parts - for two halves of the world.)

ii. Volume 2. Radio Beacons; Radio Direction Finding (RDF) Stations; and Radar Beacons (Raconsand Ramarks). Radio Time Signals, and Electronic Position Fixing Systems includingsatellite systems.

iii. Volume 3. Radio Weather Services and Navigational Warnings, in two parts. (The weather forecast

and weather bulletin recording forms, and the weather areas map used for waters aroundthe United Kingdom, are shown in Appendix A and B; Appendix C shows the schedulefor radio weather broadcasts around South Africa and Appendix D shows the forecast areas around South Africa.

iv. Volume 4. Meteorological Observation Stations.

v. Volume 5. Global Maritime Distress and Safety System (GMDSS).

vi. Volume 6. Matters related to port Traffic Management; Pilot services; Port Operations and Information. (Volume 6 is in two parts, one for each half of the world.)

Handy for the long distance yacht skipper are Volumes 1, 2, 3, and 5. However, they are big, heavy, andexpensive, and only a few pages from each apply to a voyage. Most cruising yachts manage without thesebooks - maybe you can borrow them before a voyage and extract only the detail you will need.

b. Almanac. i. Nautical Almanac. A nautical almanac is used only when you are involved with celestial

navigation.(See our Yachtmaster Ocean - A Complete Syllabus RYA and SA Sailing Course.)

ii. Yachtsmens' Almanacs. ‘Reed's’ and ‘MacMillans’ Silk Cut' are two of the best known yachtsmens' almanacs in the UK. Many other countries have their own equivalents. They contain a wealth of

information of direct use to the skipper and to the navigator. Included are extracts from Tide Tablesand abbreviated celestial tables applicable to the year's edition.



c. Charts and Chart Catalogues. Charts are produced by many countries having a coastline, for their owncoast areas. The British Admiralty and the United States of America Hydrographic Offices produce almostidentical styled charts covering the whole world. The Australian, South African and other authoritiesproduce similar charts for their coast lines. Charts numbered “INT .. (number) ...” are International MaritimeOrganisation approved charts - their logo appears next to the standard logo. Charts are available in avariety of scales, and adjacent charts overlap. When choosing charts for a voyage, consult a ChartCatalogue (see example below) and allow for the journey having to ‘over- or under- shoot'. Get the largestscales possible (Large scale, large detail, small area), eg: Large Scale 1:10 000, Small Scale 1:250 000.

Fig. 87.SAN chart numbers are an indicator of scale - two digits is a small number/is a small scale/large area ofcoastline. Three digits is ‘intermediate’, and four digits is a big number, big - large - scale, small area ofcoastline. Private commercial chart producers, such as Imray, also produce a catalogue:

Fig. 88.

d. Chart Symbols and Abbreviations. British Admiralty publication number 5011 explains all the symbolsand abbreviations used on Admiralty charts. They save an incredible amount of chart space and thereforeenable more information to be shown on charts at the right place than would otherwise be possible. See



the extract in Chapter 1, pages 108 to 110. The symbols and abbreviations used on South African chartsare available in chart or book form, both having the South African Navy publication number SAN-HO 3001.

e. “Admiralty List of Radio Services” (ALRS) and “List of Lights, Volume ...” (UK, for world widecoverage), and the “List of Lights, Fog Signals and Radio Services - 1999", the South African Navypublication equivalent of some of the volumes of the Admiralty's ‘ALRS’. Navigation lights' and lighthouses'locations and characteristics around the South African coast are listed from the north west border aroundthe Cape to the Mozambique border. Examples of the contents are as follows: i. Using Admiralty List of Lights, Volume J (Caribbean) the light at Bermuda, St Davids:

N/W4472 St Davids. Mount Hill 32 21,8 Fl(2)W 20s 65 15 White 8 - sided tower, red 2 fl of 0,4s. RC 031E 380 m from (BE) 64 37,6 band light. Partially obscured over land

.. F RG 63 20 Same structure R 135E-221E(86E), G221E-276E(55E).R276E-044E(128E), R044E-135E(91E)unintens and partially obscuredoverland.

Fig. 89.

ii. The detail for a fog signal is normally included with the detail for the navigation light at which it is located- if it is located separately from any light, it will be listed in the lights section, as if it were a light, in the

sequence anticlockwise around the country:

Fog Signal at a Navigation Light: Fog Signal Located Independently:

Fig. 90. Fig. 91.

The books (UK) or sections (SA) on Radio Services lists the names of the transmitting stations, their callsigns and frequencies, the type of modulation used (how the radio wave signal is constituted), and thetimes for each transmission type. The times stated are Greenwich Mean Time (GMT or UTC - UniversalTime Co-ordinated), so allowance must be made for the navigator’s time zone adjustment (e.g. add 2 hoursin South Africa). The full schedule for South Africa is reproduced at Appendix C and a diagram showingthe demarcated weather forecast areas referred to in UK forecasts is shown at Appendix B; American(USA), Australian, Mediterannian, New Zealand, and South African forecast areas are shown at AppendixD. Also in other countries equivalent books are details of ‘Racons' (radar beacons and how they work),definitions on ranges of lights (Luminous, Nominal, Visual and Geographical), Notes on Fog Signals, aGeographical Range Table (horizon distance depending on observer's height), a schedule of Time, Stationand Frequency for regular ‘Navwarnings’, a ‘Table of Broadcasts of Immediate Navigational Warnings’, adiagrammatic schedule of the coastal stations transmissions of weather forecasts and bulletins on FM, theinternational distress signals, distress radio signal transmitting procedure, Air Search and Rescue, and, inthe South African book, a diagrammatic chart catalogue of Namibian and South African charts. f. Nautical Tables. See ‘a. Almanac’, above. The Nautical Almanac is an essential reference for astro- orcelestial navigation. The identical British and American versions have, since 1989, contained their own‘Concise Sight Reduction Tables’ which are intended for use when more elaborate tables are not available.They are, in fact, excellent in their own right, making reference to the Air or Marine Sight Reduction Tablesunnecessary. For the celestial navigator used to other methods, there are Norries' Tables, Inman's Tables,and Burton's Tables. Norries Tables also contain tables which are very useful in coastal navigation e.g.‘Distance-Off from Vertical Sextant Angle’, etc.

g. Pilots and Sailing Directions. The British Admiralty and the American Hydrographic Authority have bothproduced their own set of books called ‘Ocean Pilots’ - or just called ‘the Pilot’ - one book for each oceanor part of an ocean. Some countries like South Africa have produced their own set of books, but not for the



ocean; for the coastal areas around the country's coastline and these books are called ‘Sailing Directions’.‘Pilots’ and ‘Sailing Directions’ both describe the applicable area of coastline in detail, with photographsof what the mariner will see, sometimes from several directions and ranges. They contain advice regardingroutes, seasonal variations, currents, obstacles, good and poor anchorage areas, harbours, and they makea point of explaining the detail of what on a chart would be briefly listed under the headings ‘Warnings’,‘Cautions’, or ‘Notes’. In addition, Pilots describe conditions at sea in the applicable ocean or part of theocean covered by the volume. An example from the ‘Africa Pilot, Volume 3' (Mombasa) is shown on thenext page. On page 160 is an example from South African Sailing Directions, Volume 2, for Saldanha Bay.

h. South African Harbour Regulations. Specific to South African harbours only, but very similar to mostcountries ports, they contain regulations which, in the main, apply to larger vessels. The book also containsan appendix which is a reproduction of the ‘Collision Rules’ (ColRegs). Most of the rules and regulationsapplicable world wide to small craft and to pleasure craft are repeated at Appendix E.

i. Tide Tables and a Tidal Stream Atlas. The importance and application of Tide Tables and a TidalStreams Atlas are explained in Chapters 4 and 5.

j. Other Books.

i. Any book containing the ‘Rules for the Prevention of Collisions at Sea’ (ColRegs or Rules of theRoad) - this subject, the rules, are reproduced in many books, including Harbour Regulations. SeePart 4, Chapter 10.

ii. The International Code of Signals. This is a listing, in groups by subject matter, of two or more letters,with or without a number following, each having a specific meaning, e.g. RY together, even as a flagdisplay of R over Y, means ‘Do not make a wake, pass slowly at a safe distance’.

iii. First Aid for Yachtsmen, or similar. Also the Ship Captains’ Medical Guide.

iv. Engine Repair manual.

v. The Yachtsman's Cook-Book.

vi. A ‘Ship's Log Book’.

vii. Ocean Passages of the World.

viii. The complete set of Henton Jaaback's notes from "Yachtmaster Ocean Services CC".

ix. World Cruising Routes and other Jimmy Cornell books.

x. Ropes, Knots and Splices.

xi. Sail Repairs for the Yachtsman.

xii. Equipment owners' Handbooks. (e.g. GPS, autopilot, plotter, Radar, the wind instruments and log,the gas cooker, bilge pumps, toilet servicing, fridge/deep freeze operation, etc.).

xiii. An atlas, and an atlas of the oceans.

ivx. A multi-language words and phrases dictionary.

vx. A file containing all yours, and the vessel's important papers.

vix. A library of general reading books - fiction or whatever your fancy. Allow for all the crews' tastes.


BY HENTON JAABACK [email protected] FOR ANY HELP YOU NEED

Electronic and Mechanical Aids to Navigation

1. The Log. This is one of the most important of all pieces of equipment on board to help a navigator.There are essentially three types in common use:

a. The Trailing Log.

Fig. 92.

A torpedo-shaped weight, fitted with offset fins so that it will spin in the water when towed, is pulledbehind a moving vessel. The tow line is forced to rotate, and it is connected to a revolution counter whosedial does not show revolutions but is calibrated to show miles and cables moved. The ‘Walker Log’, (thelatest models also have the ability to indicate speed) is regarded by many as the most reliable and accurateof logs available - BUT, the ‘spinner’ is occasionally removed by over-optimistic sharks or fish, it can getfouled by debris (e.g. submerged floating dead trees), and, if not recovered on deck before the vessel stopsand starts manoeuvring, the tow line will lose an argument with the propeller! Spare tow line and spinnersshould be carried.

b. The Paddle Wheel Log.

Fig. 93.The paddle wheel is mounted as low as possible below the water line and approximately 25% of the

vessel's water line length from the bow. The bottom half of the wheel protrudes outside the hull's surface,and is, therefore, turned by the flow of water as the vessel moves. The paddle wheel has a magnetmounted in the wheel, passing the centre axis at right angles so that one end or magnetic pole is at thewheel's circumference and the other is 180º away at the other side of the wheel's circumference. As thewheel turns, the magnetic poles are alternating, passing a point above and inside the hull. At that point iseither a transistor three-wire sensor which is made to ‘open - close - open - close’ a DC circuit, or theturning magnet causes inductive reactance changes (an increase - decrease - increase - decrease) in thestrength of a low-voltage circuit. Either way, pulses are conveyed via the wires to the log counter, and asit is electric (battery-powered) it usually has an in-built clock. The time and number of revolutions arecomputed as ‘distance travelled’ and ‘Speed’ which are displayed at the instrument's dials. For racing (orgeneral cruising use if required) there is also a dial which shows whether the vessel is accelerating,remaining at the same speed, or slowing - adjustments made to sail trim can then be measured as to theircorrectness.

c. The Mini Skeg-Mounted Propeller.

Fig. 94.

Page 162 Coastal Skipper/Yachtmaster Offshore Shorebased course

HENTON JAABACK - GET ON A BOAT AND DO IT; PRACTICE, PRACTICE, PRACTICE.

This propeller is forced to rotate by the passing of the water as the vessel moves. A cable inner, like thecable of a bicycle's brake, is connected to the propeller directly or via a right angle gear system. This innercable is connected at its other end to a counter which shows speed and distance travelled.

d. The Electronic Doppler Log.

Fig. 95.

The two transducers, A and B, are always in opposite conditions, one transmitting while the other isreceiving. They are both rapidly alternating in unison between transmit and receive respectively, to receiveand transmit, and back again. At any one stage, the time taken for a transmitted pulse's wave to get fromthe one transducer to the other (say, from the front to the back), is compared with the following time of thesignal in the opposite direction (from the back to the front). Any difference in the times measured is dueto the vessel's movement. A continuous input of time differences can be displayed electronically as‘Speed’, and with a built in clock, ‘Distance Travelled’ can also be computed and displayed. It has theadvantage that there are no moving parts, and therefore there is less likelihood of anything going wrong.They are expensive units and are best suited to vessels longer than the average yacht.

e. The ‘Old-fashioned’ Method. Before the luxury of the types of logs described above, ‘speed’ wasmeasured by allowing a plank of wood, the ‘Log’, when thrown overboard and attached to a line, to pull theline out behind the ship. The time was measured against the flow of sand from full to empty in an-hourglass. The length of line pulled overboard by the log in the fixed time, was a measure of speed. The linehad knots tied in it at specific intervals, and the number of knots pulled overboard was the vessel's speedin ‘Knots’.

A similar method can be used by the crew or navigator on a vessel whose normal log is not serviceable.Knowing the length of the vessel, a buoyant object can be thrown into the water from the bows and the timetaken for it to pass the stern measured by stop-watch. Knowing the length and time, speed is easilycalculated:

Speed = Distance Time

2. Depth Sounders. An electronic depth sounder emits a low-frequency wave pulse from a ‘transducer’fitted low down in the hull of a vessel. The same transducer receives the echo back from the sea bed andthe instrument can measure the time ‘out and back’. Since the speed of such a wave through water isknown, a measure of the time is computed into distance, half the ‘there and back’ time being the time takento get to the sea bed, and half the total distance being the distance from transducer to sea bed i.e. depthwill be that distance plus the depth of the transducer from the water line.



Fig. 96. If the power of the transmitted wave is too strong, the returning echo will rebound off the hull and returnto the sea bed, only to be reflected back up to the vessel for a second time. This will result in the depthsounder indicating a ‘second trace’ echo - two depths will be indicated simultaneously. In shallow watersand with a strong transmitted wave, third and fourth trace echoes are possible. Therefore, in shallowwaters, the power of the transmitter is decreased. Conversely in deep waters, the power is increased toensure the wave gets to the sea bed and back to the hull.

The wave spreads out from a transducer at an angle of approximately 30º; 15º either side of the vertical.It should therefore be mounted sufficiently to one side of the centre line so as not to let the wave strike thekeel. If a yacht heels more than 15º, one can expect the depth indication to be lost. Most yacht-type depthsounders will indicate depths up to 75 to 100 metres, and the very good quality, more expensive types willindicate up to approximately 150 metres.

3. The ‘Wind Instruments’. Part of the ‘kit’ for electronic logs purchased nowadays is a masthead unitwhich also measures the apparent wind speed and apparent wind direction. (With the boat’s speed, truewind speed and true wind direction can be computed.) It is an unfortunate side-effect of having this typeof instrumentation, that many yachtsmen and women today are unable to sail properly without theseinstruments - they have either lost or never had the ability to tell by feel where the wind is coming from! Thedirection steered when on the wind (beating/close hauled/on a close reach) is taken from theseinstruments, as is the wind strength for reefing purposes. If your ability to read the wind in the sail is lacking,fit ‘tell-tails’ and get used to sailing by watching the sails. Reefing decisions should be made on the amountof heel of the vessel, not from the wind speed indicated on an electronic instrument which does not knowhow much wind a specific yacht can take before reefing is necessary, and which is unlikely to be accuratelycalibrated anyway.

4. Radar. Without a modern day Log, a yachtsman or woman can get by - navigating even by DR is stillpossible. In restricted visibility such as thick fog, one is blind. Totally blind. Blind to any danger that mayarise. Arriving at or proceeding among atolls and small islands at night where no navigation lights or anylights exist to aid the mariner, one is again blind. Proceeding in or crossing shipping lanes at night or in fog,blind, is potentially as dangerous, if not more so, than experiencing a hurricane at sea. Most experiencedyachtsmen and women agree - a radar is one of the most desirable navigation aids to have on board - ahigher priority than GPS, Decca, or any other navigation system. A radar if used and interpreted correctly,is the eyes of the navigator. The proper use of a radar is explained in ‘A Guide To The Planning AndConduct Of Sea Passages’, British Department of Trade, and is available from Her Majesty's StationeryOffice, London, or on order through any reputable book store. The operation of any particular type of radaris described in the owner's manual for that set.

5. Global Positioning System (GPS). The Global Positioning System effectively commenced service forthe US Department of Defence from the start of the 1990's, and it became fully operational in 1993. Its mainfeatures are the very high degree of accuracy of the position fixes, and the high speed of updating fixes.

The system has been arranged so that at any one moment at least eight out of the 24 (plus 4 spares



already in orbit) satellites are in a suitable and accurately known position for their signals to be receivedat one place on the earth’s surface. There is, therefore, no delay in receiving updating information due tosatellite availability. The time interval of a GPS receiver’s updating information as seen by the user ismeasured in seconds - or fractions of a second, depending on the brand and model.

The key to this accuracy is in the ability of the satellites to transmit, at extremely high precision, signalswhich can be timed by the receiver to determine the time taken from the satellite to the GPS receiver. Sincethe speed of a radio wave through space is known, the distance travelled in the time measured can becalculated by the receiver’s computer. This distance, accurately calculated, is the radius of a circle aroundthe satellite. The GPS receiver is somewhere on the circumference of that circle. If the receiver is receivingseveral satellites’ signals simultaneously, and if the exact position of each satellite at the time is known,the resulting circumferences of circles around each satellite all intersect at one place - the location of theGPS receiver. This position is calculated by the receiver and shown as a Latitude and Longitude. Updatedpositions are very quickly displayed, and changes in position are calculated to give course and speed over the ground.

Fig. 97.

Accuracy, in addition to the speed of update, are the two main features which delight the users. Theaccuracy from tests taken in the UK (see Practical Boat Owner magazine, No 297 of September 1991 and316 of April 1993) was such that comparisons of position fixes from various makes of GPS differed by onlya few metres. However, the US have now cancelled the “Selective Availability” (a facility to downgrade theaccuracy for non US military users to a nominal 100 metres) and much greater accuracy is now normal.

Manufacturers were able to overcome this accuracy downgrading by getting the receiver to hold in memorythe last 50 position coordinates and to average them, showing only the average. As number 51 positionis received by the GPS, number one drops out, so there are always the latest 50 fixes used to get the latestaverage. Equipment made this way still averages so the resultant position is very accurate.

Differential GPS uses two GPS linked by radio and computer; one is at an exact known position on land(e.g. on a trig beacon) and the other could be on a vessel at sea. When a fix is received giving an error ofa distance and direction from known position, this error is communicated to the other GPS (on a vessel atsea?) and the latter’s fix is then corrected for the known error. Since the two are in the same general areathey will be using the same satellites and therefore they are receiving the same data and getting the samefix error.

7. Other Systems. In the northern hemisphere, and in some parts of the southern hemisphere, some ofthe other systems such as Omega, Consol, Loran (LOng RAnge Navigation), and Loran-C exist. They aremainly for use in and near European coastal waters and northern oceans, and are not for global use.

They mainly rely on the timing of synchronized timed transmissions from a Master and then slavetransmitters, in sequence. The time the signal takes to arrive at the receiver is used in a calculation tocompute distance away from the transmitters. These distances are all radius’ of circles around thetransmitter sites, each of which has its location accurately recorded by the receiver. Where thecircumferences of the circles all intersect is the position of the receiver.

Their accuracy and area covered do not compare with the GPS, and as with Decca, they are inferiorsystems. Some have already been declared obsolete in many countries.



NOTES



APPENDIX AWEATHER BULLETIN (TOP) AND FORECAST RECORDING FORMS (UK)





APPENDIX CSCHEDULE OF SOUTH AFRICAN RADIO TRANSMISSIONS OF WEATHER

BULLETINS FOR SHIPPING (As amended 12/99)



APPENDIX DWEATHER FORECAST AREAS FOR SHIPPING

a. Americas USA, East Coast:



b. Australia



d. South Africa

Page 172 Coastal Skipper/Yachtmaster Offshore - Shore based course


APPENDIX E

TYPICAL HARBOUR REGULATIONS APPLICABLE IN MANY COUNTRIES TO SMALL CRAFT AND TO PLEASURE CRAFT

1. Vessels must be registered with the local authority for the current year.

2. Vessels must be seaworthy.

3. The skipper must hold the applicable qualification for the size and type of vessel and for the voyage.

4. The skipper must be sober at all times while underway.

5. There must be adequate competent crew on board to manage the vessel under the control of theskipper.

6. On duty crew must be sober.

7. The total number of people on board must not exceed the design limit for the vessel nor the scale ofsafety equipment.

8. Vessels under way within port limits must monitor the port authority’s radio channel at all times, andthey are to get radio authority to leave moorings and depart to sea, or to enter the port on their wayback to their moorings. In fog, a vessel MUST report by radio, its position, course and speed.

9. The vessel’s speed is limited to 8 knots in the harbour, and 3 knots in the small craft areas with theproviso that it must not make a wake.

10. No anchoring is permitted within a harbour unless:a. There is a designated anchoring area within the harbour, orb. It is essential by virtue of an accident or emergency situation.

In the latter case, the port authorities must be informed by radio as soon as possible to inform themof the situation.

11. No vessel may tie up to a buoy unless in an emergency, in which case the port authority is to beinformed of the situation as soon as possible.

12. There is to be no fishing where such action may in any way impede the passage of other vessels.

13. The International Rules for the Prevention of Collisions at Sea (IRPCS) must be adhered to exceptwhere there are local rules in force; in the latter case local rules, where they may conflict with theIRPCS, take precedence.

14. No small craft or pleasure craft may cross the bow shadow of a ship under way: small craft andpleasure craft are to keep out of the way of all other vessels under way.

15. No waste matter nor pollutants are to be discharged into, nor be allowed to enter the water of the port.This includes the discharge of black water/toilet outlets which must be contained in holding tanks forremoval by the applicable agencies using containers designed for the purpose, or which may bepumped overboard when more than 3 nautical miles offshore.

16. There is to be no diving in any waters of the port unless written permission is obtained in advance fromthe Port Captain’s staff.

17. There is to be no swimming in any part of a port unless a designated swimming area is establishedby the port authorities.



APPENDIX FCOMPASS CHECKING BY THE SUN'S RISING OR SETTING AMPLITUDE:

HENTON'S AMPLITUDE TABLES

Some reference books have what are called Amplitude Tables. These tables tell one, depending on one'slatitude and the date, how many degrees north or south of east the sun will appear at sunrise, or how manydegrees off west it will be at sunset. If, at a place on a date the amplitude was seen to be 6º North atsunrise, it means it will be 6º north of east which will be 084ºTrue. By adding 'west' variation we get whatthe compass bearing to the sun will be if there is no deviation. Any difference noted when taking thebearing to the rising sun will be the deviation (on that heading). We can do a similar check with the settingsun.

To be strictly correct, the bearing by compass from/to the sun at sunrise or sunset should be when thebottom arc of the sun's circumference is one radius (half the sun's diameter) above the horizon.

The date enables us to find the declination on that day, to the nearest degree - see the graph below. OurLatitude can be rounded off to the nearest whole number of degrees. With these two numbers, we can lookup the tables, (see page 117), to find an angle which is called the Amplitude of the Celestial Body (i.e. thesun in our case).

The 'Rising Amplitude' refers to the angle, as seen by the observer (you/the navigator) between true eastand the direction of the sun, north or south of true east (the sun rises in the east). If we know this angle,we can determine the true direction of the sun in terms of the 360 º notation. For example, if our DR is 28 º 15' N, 57 º 50' W on 18 June at sunrise, we can look up the Declination of the sun in the Almanac andsee that it is, to the nearest degree, N 23 º. Our latitude to the nearest degree is 28 º N. When we look upthe Amplitude Tables, we see (next page) the angle is 26 º (when Dec is 23 º and Lat is 28 º).

(Note that whether Dec and/or Lat are North or South is of no relevance in the make up of the tables.) This means the direction (True) to the sun from that latitude, is 26 º north (because Declination is North)of east, i.e. 26 º north of 090 º = 064 º. If the Declination had been South, this angle, and therefore thedirection to the sun, would be south of east, i.e. 116 º True (090 º + 26 º).

Knowing the true direction and the magnetic variation from the chart for the area, we can compare themagnetic direction with the observed compass direction to the sun at that time - if the compass andmagnetic directions are the same, there is no deviation. If they are not the same, there is Deviation; theDeviation is the difference between the two values. If the compass value is the larger, the Deviation is'West'. If the magnetic number is the larger, the Deviation is 'East'.

The Amplitude Angle of the setting sun can be as useful a check of your compass deviation. From thesame DR and date above, i.e. when the Amplitude Angle is 26º, the true direction to the sun will be 244ºif Declination is South (270 º - 26 º), or 296 º if Declination is North (270 º + 26 º).

Fig. 102. TRUE DIRECTION OF THE SETTING SUN.

See page 175 for a graph to determine Declination on a date.


HENTON JAABACK - RECOMMENDS COMPASS DEVIATIONS BE CHECKED OFTEN

AMPLITUDE OF THE RISING AND SETTING SUN: LATITUDES UP TO 57º N/S

Lat Declinationº (nearest degree) North or South

º 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

0- 56789

10

0 1 20 1 20 1 20 1 20 1 20 1 2

3 4 53 4 53 4 53 4 53 4 53 4 5

6 7 86 7 86 7 86 7 86 7 86 7 8

9 10 119 10 119 10 119 10 119 10 119 10 11

12 13 14 1512 13 14 1512 13 14 1512 13 14 1512 13 14 1512 13 14 15

16 17 18 1916 17 18 1916 17 18 1916 17 18 1916 17 18 1916 17 18 19

20 21 22 2320 21 22 2320 21 22 2320 21 22 2320 21 22 2320 21 22 23

1112131415

0 1 20 1 20 1 20 1 20 1 2

3 4 53 4 53 4 53 4 53 4 5

6 7 86 7 86 7 86 7 86 7 8

9 10 119 10 119 10 119 10 119 10 11

12 13 14 1512 13 14 1512 13 14 1512 14 14 1612 14 15 16

16 17 18 1916 17 18 1916 18 19 2017 18 19 2017 18 19 20

20 21 22 2421 22 23 2421 22 23 2421 22 23 2421 22 23 24

1617181920

0 1 20 1 20 1 20 1 20 1 2

3 4 53 4 53 4 53 4 53 4 5

6 7 86 7 86 7 86 7 96 7 9

9 10 119 11 1210 11 1210 11 1210 11 12

13 14 15 1613 14 15 1613 14 15 1613 14 15 1613 14 15 16

17 18 19 2017 18 19 2017 18 19 2017 18 19 2017 18 19 20

21 22 23 2421 22 23 2421 22 23 2421 22 23 2421 22 24 25

2122232425

0 1 20 1 20 1 20 1 20 1 2

3 4 53 4 53 4 53 4 63 4 6

6 8 97 8 97 8 97 8 97 8 9

10 11 1210 11 1210 11 1210 11 1210 11 12

13 14 15 1613 14 15 1613 14 15 1613 14 15 1713 14 16 17

17 18 19 2017 18 20 2117 19 20 2118 19 20 2118 19 20 21

22 23 24 2522 23 24 2522 23 24 2522 23 24 2522 23 24 26

2627282930

0 1 20 1 20 1 20 1 20 1 2

3 4 63 5 63 5 63 5 64 5 6

7 8 97 8 97 8 97 8 97 8 9

10 11 1210 11 1210 11 1310 11 1310 12 13

14 15 16 1714 15 16 1714 15 16 1714 15 16 1714 15 16 17

18 19 20 2118 19 20 2118 19 21 2218 20 21 2218 20 21 22

22 24 25 2623 24 25 2623 24 25 2623 24 25 2723 25 26 27

3132333435

0 1 20 1 20 1 20 1 20 1 3

4 5 64 5 64 5 64 5 64 5 6

7 8 97 8 97 8 107 9 107 9 10

11 12 1311 12 1311 12 1311 12 1311 12 14

14 15 16 1814 15 17 1814 16 17 1815 16 17 1815 16 17 18

19 20 21 2219 20 21 2319 20 22 2319 21 22 2320 21 22 23

24 25 26 2724 25 26 2724 25 27 2824 26 27 2825 26 27 29

3637383940

0 1 30 1 30 1 30 1 30 1 3

4 5 64 5 64 5 64 5 64 5 7

7 9 108 9 108 9 108 9 108 9 11

11 12 1411 13 1412 13 1412 13 1412 13 14

16 16 17 1916 16 18 1916 17 18 1916 17 18 2016 17 18 20

20 21 23 2420 22 23 2421 22 23 2421 22 23 2521 22 24 25

25 26 28 2925 27 28 2926 27 28 3026 28 29 3027 28 29 31

4142434445

0 1 30 1 30 1 30 1 30 1 3

4 5 74 5 74 6 74 6 74 6 7

8 9 118 9 118 10 118 10 119 10 11

12 13 1512 14 1512 14 1513 14 1513 14 16

16 17 19 2016 18 19 2017 18 19 2117 18 20 2117 19 20 22

21 23 24 2622 23 25 2622 24 25 2623 24 25 2723 24 26 27

27 28 30 3127 29 30 3228 29 31 3228 30 31 3329 31 32 34

4647484950

0 1 30 2 30 2 30 2 30 2 3

4 6 74 6 75 6 85 6 85 6 8

9 10 129 10 129 11 129 11 129 11 13

13 15 1613 15 1614 15 1714 15 1714 16 17

17 19 20 2218 19 21 2218 20 21 2319 20 22 2319 21 22 24

23 25 26 2824 25 27 2924 26 28 2925 27 28 3025 27 29 30

30 31 33 3430 32 33 3531 32 34 3631 33 35 3732 34 36 37

51525354555657

0 2 30 2 30 2 30 2 30 2 40 2 40 2 4

5 6 85 7 85 7 85 7 95 7 95 7 95 7 9

10 11 1310 11 1310 12 1310 12 1411 12 1411 12 1411 12 14

14 16 1815 16 1815 17 1915 17 1916 18 1916 18 2016 19 20

19 20 23 2420 20 23 2520 22 24 2621 23 25 2621 24 25 2722 24 25 2722 25 26 28

26 28 29 3127 28 30 3227 29 31 3328 30 32 3429 30 33 3529 30 33 3630 31 34 37

33 35 37 3834 36 38 3935 37 39 4136 38 40 4237 39 41 4338 40 42 4439 41 43 45

In practice we all know that a yacht 'zig zags' at sea - it is impossible to keep her on a perfectly straightcourse, and the bigger the swell or rougher the sea, the worse it is. So this exercise could only be done inrelatively calm conditions. A well adjusted compass will have no or small amounts of deviation which forpractical purposes can be ignored - we cannot steer to an accuracy of a degree or two anyway. DO NOTleave on a voyage when the vessel's compass deviation involves large numbers. Something is wrong. Getit professionally checked.


HENTON JAABACK - ALWAYS AVAILABLE TO HELP: [email protected]

GRAPH FOR FINDING SUN’S DECLINATION ON A DAY

24 º 20 º 15 º

NORTH

10 º

5 º 0 º

5 º 10 º

SOUTH

15 º

20 º 24 º

22 23 22 23 22

31 31 28 31 30 31 30 31 31 30 31 30D J F M A M J J A S O N D

E A E A P A U U U E C O EC N B R R Y N L G P T V CE U R C I E Y U T O E EM A U H L S E B M MB R A T M E B BE Y R B R E ER Y E R

R

Fig. 103. DECLINATION OF THE SUN - GRAPH FOR ANGLE ON A KNOWN DATE



APPENDIX GFINDING A RHUMB LINE COURSE BY MERIDIONAL PARTS

When sailing distances of up to only a few hundred miles, the effect of the curvature of the earth is smalland a chart of the area can be assumed to cover a section of the globe which is flat. If the absence of asuitable scale chart, latitude and longitude scales can be regarded as equal and the use of planetrigonometry can be employed to resolve a Rhumb Line course and distance. Hence the term ‘planesailing’.

If, however, the distance to be sailed is more than a few hundred miles (say over 300~500 n.m.), then thecurvature of the earth cannot be ignored. A Rhumb Line course must take into account the changingvertical scale of a Mercator Projection Chart, and a suitable chart may not be available. If this is the case,we can use trigonometry after applying the ‘meridional part’ conversion to the vertical scale - the differencein the latitudes between the point of departure and the destination, is measured in units of ‘minutes oflongitude’ or ‘Meridional Parts’.

By definition, 1 Meridional Part = 1' of Longitude (A fixed length regardless of latitude, when using Mercatorcharts).

If we are going from a place on the equator to a place whose latitude is 15 º 00', the number of minutes oflatitude difference between the two places will be: 15 º x 60' = 900'

But if we are to measure the same latitude difference using Meridional Parts (minutes of longitude) as thescale, we will get: 15 º = 904,41 (Meridional Parts - see page 173) As we will not be venturing far from the equator, the difference between minutes of latitude (900) andMeridional Parts (904,41) is small.

But, as we get further from the equator, the difference gets larger due to the expanding or stretching lengthof a minute of latitude on the vertical scale. If the two places (A and B) are at 15 º and 60 º latitude respectively, the difference in latitude minutes willbe: (60 º - 15 º) x 60 = 2 700'

From Nautical Tables containing Tables of Meridional Parts (extracts are shown on the next two pages),we see that, whereas 0 º to 15 º of latitude equals 904,41 Meridional Parts, 0 º to 60 º of latitude contains4507,08 Meridional Parts. So the difference in the two latitudes' in Meridional Parts will be: 4507,08 - 904,41 = 3 602,67

As you can see, there is a big difference between the latitude minutes difference of 2 700 and 3 602,67Meridional Parts (or minutes of longitude).

So what? What is the relevance of this difference?

Knowing the longitudes of the two places, A (say 5 º 30,0'W) and B (say 36 º 45,0'W), and therefore thedifference in the two longitudes (36 º 45,0' - 5 º 30,0') expressed as minutes of longitude (2 205 - 330 = 1875,0'), and the difference in their latitudes' Meridional Parts (units of ‘minutes of longitude’ - 3 602,67),gives us the two sides of a triangle as measured in the same units; the angle at their intersection (C) is 90º:



Knowing three of the six values of a triangle, we can calculate the others by trigonometry. We want to knowthe distance from A to B and the Rhumb Line Course to steer.

We calculate the angle BAC - which can easily be converted to a True direction for AB (relative to TrueNorth) by subtracting it from 360 º: Tan BAC = BC = 1 875,00 = 0,520 AC 3 602,67

BAC = 27,474 º

= 27 º 28,4'

Rhumb Line Course to steer = 360 º - 27 º 28,4' = 332 º 31,6' True To the nearest degree = 333 º T

Since distances are in nautical miles, the difference in latitudes (AC) in minutes/nautical miles was 2 700'(n.m.). And in the triangle ABC: secant BAC = AB (secant = cos x 1 ) AC X Therefore AB = secant BAC x AC = secant 27,474 º x 2 700 n.m. = 3 043,2 n.m.

Tables containing ‘Meridional Parts' are too space consuming to include here, and are not included in mostof the books of tables found in the average yacht's library. However, they can be seen in older tables suchas Nories' Tables.

There is no logical reason why a Yachtmaster should know this procedure nor have the tables, but thequestion ‘Define a Meridional Part’ has been asked of some examination candidates: Deck Officers are,however, expected to know this procedure.







APPENDIX H

INTERCEPT COURSE

When necessary to determine a course to steer to intercept another vessel which is itself moving, e.g. avessel in distress which is able to move slowly towards the coast or a harbour, we go through the followingsteps:

1. Plot your vessel’s latest position, or position at the time the other vessel’s position was stated.

2. Plot the other vessel’s position as at the same time of the plot of your vessel’s position.

3. Rule a line joining these positions.

4. Rule in the course (True) of the other vessel.

5. Measure along the other vessel’s course line its DR after one hour.

6. From the DR just plotted, insert a line whose length is, to scale, equal to the speed your vessel willbe moving at, so that it just reaches the line ruled between the two vessels’ original positions.

7. This new line’s direction is the course you need to steer; rule a line parallel to it from your vessel’sposition as marked on the chart, so that it crosses the other vessel’s course line.

8. Where this intersection is, is where intercept will take place.

9. Measure the length of the line your vessel is to sail along, and divide it by your speed: the answeris the amount of time it will take from the time of the initial position plot until intercept occurs.

Disregard current or tidal stream as it will affect both vessel’s in the same way and have the effect of beingin slack water. Tidal stream sets and rates would only have to be taken into account if, by virtue of theirdifferent locations to begin with, the tidal stream in one vessel’s area was different to that of the othervessel. One would then have to resolve each to their equivalent Ground Track/Course over the Ground/Course made Good.



APPENDIX J

DIPPING DISTANCE/GEOGRAPHIC RANGE TABLE

Distance in nautical miles of light/lighthouse when first dipped/seen:

Distance (n.m.) = D + d D = 2.04 x Height of Lighthouse (m), and d = 2,04 x Height of observer’s eye (m)

Heightof light

m/ft:

Height of observer’s eye m/ft; (Observer’s horizon distance):

2/7(d = 2,9)

3/10(d = 3,5)

4/13(d = 4,1)

5/16(d = 4,6)

6/20(d = 5,0)

7/23(d = 5,4)

8/26(d = 5,8)

10/33(d = 6,5)

10/33 9,4 10,0 10,6 11,1 11,5 11,9 12,3 13,0

15/49 10,8 11,4 12,0 12,5 12,9 13,3 13,7 14,4

20/65 12,0 12,6 13,2 13,7 14,1 14,5 14,9 15,6

25/81 13,1 13,7 14,3 14,8 15,2 15,6 16,0 16,7

30/97 14,1 14,7 15,3 15,8 16,2 16,6 17,0 17,7

35/114 15,0 15,6 16,2 16,7 17,1 17,5 17,9 18,6

40/130 15,8 16,4 17,0 17,5 17,9 18,3 18,7 19,4

45/146 16,6 17,2 17,8 18,3 18,7 19,1 19,5 20,2

50/162 17,3 17,9 18,5 19,0 19,4 19,8 20,2 20,9

55/179 18,0 18,6 19,2 19,7 20,1 20,5 20,9 21,6

60/195 18,7 19,3 19,9 20,4 20,8 21,2 21,6 22,3

65/211 19,3 19,9 20,5 21,0 21,4 21,8 22,2 22,9

70/227 20,0 20,6 21,2 21,7 22,1 22,5 22,9 23,6

75/244 20,6 21,2 21,8 22,3 22,7 23,2 23,6 24,3

80/260 21,1 21,7 22,3 22,8 23,2 23,6 24,0 24,7

85/276 21,7 22,3 22,9 23,4 23,8 24,2 24,6 25,3

90/292 22,3 22,9 23,5 24,0 24,4 24,8 25,2 25,9

95/309 22,8 23,4 24,0 24,5 24,9 25,3 25,7 26,4

100/325 23,3 23,9 24,5 25,0 25,4 25,8 26,2 26,9

105/341 23,8 24,4 25,0 25,5 25,9 26,3 26,7 27,4

110/357 24,3 24,9 25,5 26,0 26,4 26,8 27,2 27,9

115/374 24,8 25,4 26,0 26,5 26,9 27,3 27,7 28,4

120/390 25,2 25,8 26,4 26,9 27,3 27,7 28,1 28,8

Page 182 Coastal Skipper and Yachtmaster Offshore shore based course


PRACTICE NAVIGATION QUESTIONS

(Questions involving tidal streams appear after Chapter 5. See also EXERCISE QUESTIONS andANSWERS TO EXERCISE QUESTIONS for USA, UK, Australia and South Africa elsewhere in this CD.)

Use the Deviation Card in Chapter 1, page 114, Figure 20.

1. British Admiralty Chart 5050

It is ‘Springs’ and the High Water, Plymouth, is at 14H40. A vessel leaves Mevagissey at 08H00 GMT whenthe log was reading 1 234,5 M, bound for Plymouth, heading 096º C. Her speed over the water is 5 knots.

a. Assuming no tidal stream or leeway, what is her position at 09H30?

b. What would her position have been at low tide when she ‘Dipped’ Eddystone Lighthouse, thenbearing 115 º M?

c. What time would the lighthouse have been ‘dipped’?

d. At 09H30 a bearing to the light at Downend Point was 048 º M when the log was 1 242,0 M. At10H30 the bearing to the same Point was 349 º when the log was 1 247,0 M. Establish the vessel'sposition at 10H30, assuming no change to her heading, and no tidal stream.

e. From the position as at 10H30 in d. above, assume the same speed and heading were maintained.If, at 11H30, a ‘Simple Fix' was obtained from the bearings below, what would the set and rate ofthe tidal stream have been during that hour? (Assume no leeway.)i. The tower at Portwrinkle 025 º M,

ii. South point of Rame Head 080 º M, iii. Eddystone Lighthouse 162 º M.

f. At 12H00 the south end of the headland of Rame Head bore 063 º M when the depth sounderindicated a depth of 52 metres. From the Tide Tables it was established that the height of the tidewas 4 metres. Comment on the accuracy of the fix obtained.

g. From the fix at 11H30 (in f. above), the same heading was maintained and when the log was1255,0 M, a line from the vessel to Rame Head formed an angle of 30 º to the port of the vessel'sheading. When the angle off the port bow doubled to 60 º, the log reading was 1256,5 M. (Assumea ‘slack’ tidal stream.) Plot the vessel's fix. What time would this fix have taken place?

h. You are sailing north west of Eddystone Light and wish to ensure you do not come within 4,5 mof the lighthouse so that you avoid the overfall (any disturbed surface water) over the shallows of‘Hand Deeps’. You decide to use your sextant to determine the ‘distance off’. Assuming a heightof tide of 2 metres, what maximum sextant angle will you accept in order not to get closer than the4,5 M ? (Use the formula on pages 149/150.)

2. Chart SAN 3002

a. You are the navigator on a yacht sailing in Table Bay. You are on deck practising with the sextantwhen fog starts to appear. Knowing the ‘drill’, you decide to take a quick fix, but the hand bearingcompass has somehow got a large air bubble in it and it is as good as useless! You thereforedecide to get a fix using the sextant and the ‘horizontal angles’ method. You determine that theangle between Robben Island Lighthouse and the building at Bloubergstrand is 113º, and theangle between that building and the Port Office in the harbour is 136º. Plot the fix.

b. From the fix in a. above, you decide to sail slowly (at 3 knots) towards shallow waters to your east.If it is in the period ‘2 hours before HW Cape Town’, and it is half way between springs and neaps,what course will you steer (compass) to achieve a ground track of 090 º T ? What will be the SMG?

c. While steering a course of 245 º C from Table Bay in a current of 1,5 knots setting 350 º, you aremaking a speed over the water of 5 knots. SE winds result in a leeway of 5 º:


GET MORE EXERCISE QUESTIONS, AND PRACTICE, PRACTICE, PRACTICE

i. what will your COG/CMG be ?

ii. what will the SOG/SMG be ?

iii. what course should one steer, allowing for this current and leeway, to make good a course225 º T?

d. Your vessel's position is "260 º T, Robben Island Lighthouse, 4,7 M". i. what is your course to steer to get to the harbour entrance ?

ii. how far is the entrance from your position ?

iii. at 4,5 knots, how long will it take to get to the entrance ?

iv. what speed must the vessel do in order for it to take one and a half hours ?

e. You require a COG/CMG of 060 º T from the South Cardinal marker buoy when a tidal stream sets330 º at 2,5 knots. Your boat speed is 6 knots. The wind is strong from the south east giving youa leeway of 7 º.

i. what compass course do you steer ?

ii. if you ignored the tidal stream and the leeway, what would be your COG/CMG ?

f. If, when close hauled on either tack, you experience 5 º of leeway, and the compass indicates yourtack angle to be 95 º, what is the change in your COG/CMG when you tack ?

See also the EXERCISE QUESTIONS and ANSWERS TO EXERCISE QUESTIONS for USA, UK,Australia and South Africa elsewhere in this CD.

Get books on practice navigation exercises for more questions - get as much practice as you can. The RYAnavigation exercise books are recommended.

ANSWERS TO PRACTICE NAVIGATION QUESTIONS

Page 184 Coastal Skipper and Yachtmaster Offshore shore based course


1. a. 096ºC = 094ºM, (Dev = 2ºW). Var (1992 - 2000) = 7ºW. Course steered 087º, at 5 knots, after1,5 hours (08H00 to 09H30), distance travelled = 7,5 M. Position 50º 16,5' N, 4º 35,1' W.

b. Height = 41 m (above MHWS). It is now Low Water, and ‘Tidal Level referred to Datum ofSoundings’ shows that at low tide (springs or neaps), Plymouth (nearest mentioned place in thistable to Eddystone Lighthouse) is ‘nil’, but 5,5 m at high tide -the level heights are measured from.So at the time of the dipping/bobbing exercise, the lighthouse is

41 m + 5,5 m = 46,5 m high.

Its horizon distance is therefore 13,9 M, and observer's horizon distance is 3,5 M i.e. the positionis 17,4 M from the lighthouse in the direction 115ºM - 7ºW Var = 108ºT (i.e. from the lighthouseto the position it is 180º opposite, namely 288ºT). Position is 50º 16,3' N, 4º 41,7' W.

c. The position is 3,3 M from the start. At 5 knots it will take 2/3 hour which is 40 minutes. time 08H40.

d. This is a running fix. Position 50º 15,7' N, 4º 28,7' W.

e. The fix is the northern corner of the ‘cocked hat’ (nearest land/danger). The set is the direction fromthe 11H30 DR to the fix, which is 023º (set direction is always stated as ‘true’). The distance theset has affected the vessel's position is 0,8 M in the time span 10H30 to 11H30 i.e. 1 hour. Therate is therefore 0,8 knots.

f. Depth soundings (52 m) = Chart Datum + Height of Tide (4 m). Therefore Chart Datum is 48 m.Along the LOP 056ºT (063ºM - 7ºW Var) the sea bed is 48 m for a long way - the one LOP/depthmethod of getting a fix cannot be used - the position obtained would be too vague.

g. The fix is 1,5 M (1256,5 M - 1255,0 M) on a bearing of 027ºT to Rame Head. (Course is 087ºT,30º off the port bow is 057ºT and 60º off the port bow is 027ºT.)

h. Height of tide is 2 m, i.e. 3,5 m below the 5,5 m MHWS level from which heights are measured.So at the time the lighthouse height is 41 m + 3,5 m = 44,5 m. From the tables similar to thoseshown on page 150 (available in Yachtsmen's almanacs and Norries Tables, etc.), or from the ‘Tan’formula, the sextant angle must not get bigger than 0º 18,3'.

2. a. The position is 33º 49,8' S, 18º 25,8' E.

b. The set is 167º and the rate is midway between 1,0 and 0,5 knots. With boat speed 3 knots,course to steer is 075ºT (098ºM). Speed made good is 3,1 knots.

c. i. 245ºT.

ii. 4,2 knots.

iii. 215ºT.

d. i. 119ºT (+ 23ºW = 142ºM, Dev = nil, steer 142ºC).

ii. 8,7 M.

iii. 1 hour 56 minutes.

iv. 5,8 knots.

e. i. 111ºC + 7º Leeway = 118ºC.

ii. 030ºT.

f. 105º (5º + 95º + 5º).

Documents

Coastal Skipper and Yachtmaster Offshore Part 1