Terrestrial Navigation PHASE 1 NAVIGATION

 

Terrestrial Navigation

 Terrestrial

• Compass bearing

A bearing line obtained by the use of an azimuth circle or similar instrument relative to true/gyro/magnetic North.

• Relative bearing line

The relative bearing may be 'Red – To Port' or 'Green - To Starboard'. 

• Transit bearing line

When two objects are in line then the observing vessel will be on the extension of the line joining them. If the objects are charted then the compass transit bearing can be obtained.

• Horizontal sextant angle (HSA)

The sextant is used to obtain the horizontal angular separation of two charted objects and a position circle is obtained. Two HSA’s will give a position.

• Range from vertical sextant angle and raising and dipping of lights.

A range is obtained which, when crossed with a bearing line, gives a position.

You must take the quiz only after you study the eBook contents in this chapter, including watching the videos. The self-assessment quizzes are drawn from the complete chapter. Please take this as often as you wish. Please make sure that you return here after you have finished reviewing this topic.

Ability to Use Appropriate Charts

Use of Appropriate Charts

General information

The mariner should always use the largest scale chart appropriate for his purpose.

In closing the land or dangerous banks, regard must always be had to the scale of the chart used. A small error in laying down a position may mean only a few metres on a large scale chart, whereas on a small scale the same amount of displacement on the paper may mean several cables.

For the same reason bearings to near objects should be used in preference to objects farther off. although the latter may be more prominent. as a small error in bearing or in laying it down on the chart has a greater effect in misplacing the position the longer the line to be drawn.

Scale

The larger the scale of the chart, the greater the detail that can be shown on it.

Each Admiralty chart, or series of charts, is designed for a particular purpose. Large scale charts are intended to be used for entering harbours or anchorages or for passing close to navigational hazards. Medium scale charts are usually published as series of charts intended for navigation along coasts, while small scale charts are intended for offshore navigation and passage planning.

The mariner using the medium scale charts for passage along a coast need not transfer on to a large scale for short distances, except where this depicts more clearly intricate navigational hazards close to his intended route. Although the larger scale chart depicts information in more detail, those on the next smaller scale show adequately all the dangers, traffic separation schemes, aids to navigation, etc, that are necessary for the purpose for which the chart is designed.

The principle followed in planning Admiralty charts of foreign coasts is that they should be on a scale adequate for coastal navigation or to give access to the major trading ports: this principle is generally adopted by other Hydrographic Offices which chart areas outside their own waters.

In some parts of the world, charts on a larger scale than those of the Admiralty series are published by national Hydrographic Offices covering their coasts and ports. The mariner intending to navigate in an area where the largest scale Admiralty chart is not adequate for his particular purpose should take steps to acquire the appropriate foreign charts. 

You must take the quiz only after you study the eBook contents in this chapter, including watching the videos. The self-assessment quizzes are drawn from the complete chapter. Please take this as often as you wish. Please make sure that you return here after you have finished reviewing this topic.

Chart correction

Correction entry at the bottom of a chart must be a continuous record of all corrections made as shown below:

Notice to Mariners – 2010 -371-847 2011-258-341

Therefore before a fresh entry of correction is made, all interim corrections should be made in sequence; use of latest cumulative list NTM can be Made.

• During correction first priority should be given to the charts to be used in the immediate future.
• Then charts in the geographic area and lastly other charts on board
• For the permanent corrections P(NM) the corrections are made directly on the chart by hand at the given the longitude and latitude using a chart correction pen with violet color permanent ink. Red and black colors are not preferred so as to differentiate from printed matter which is black. Use small number (diameter) nib to insert information received through NTM and thicker nib for deletions. 

Second method of making corrections on the chart is through the tracing provided; this is done where several spots have to be marked close to each other. The information to be inserted will be in a box with each exact position marked by a dot with a circle around it, aligning with the latitude and longitude lines or prominent marks, such as buoys, or other marks, such as soundings. Using a hard pencil poke each position on the tracing; the depressed mark on the chart is the desired position of the insertion, to be entered by hand.

Using Notices to Mariners and corrections using tracings

The following media explains how to insert a submarine on a nautical chart

                                                                                                                                  ⛶🢅

 ⛶ click on the full screen beside the volume control for a better experience.  

The following media explains how to insert a light sector on a nautical chart

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 ⛶ click on the full screen beside the volume control for a better experience.  

The following media explains how to insert a buoy on a nautical chart

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 ⛶ click on the full screen beside the volume control for a better experience.  

The following media explains the use of tracings

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The following media explains how to apply Notices to Mariners to Nautical Charts 

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 ⛶ click on the full screen beside the volume control for a better experience.  

The following media explains how to apply an NM block on a nautical chart

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 ⛶ click on the full screen beside the volume control for a better experience.  

The navigating officer is expected to maintain a chart correction log/record book and similarly a publication’s correction book.

You must take the quiz only after you study the eBook contents in this chapter, including watching the videos. The self-assessment quizzes are drawn from the complete chapter. Please take this as often as you wish. Please make sure that you return here after you have finished reviewing this topic.

Mercator Sailing

Mercator sailing is the most widely used method by the navigators for following a rhumb line track. It can be used to calculate course and distance between two positions or to calculate arrival position when initial position, course and distance are known.

It is similar to the plane sailing method but without the limitation of 600 Nm which is overcome by using DMP in place of D’Lat. The MP of a latitude is the number of minutes of longitude scale that can fit between the equator and that parallel of latitude on a mercator chart. DMP is the number of minutes of the longitude scale that can fit between two latitudes on a mercator chart. The MP of a particular latitude can be obtained by referring to Norie’s Nautical Tables. DMP between two latitudes is obtained by adding (if different names) or subtracting (if same names) the MP of each latitude.

Formulae used in mercator sailing

Tan Co = D’Long / DMP - (1)

Dist = D’Lat / Cos Co - (2)

The following media explains about mercator sailing

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Procedure of calculation to find course and distance

1. Find D’Lat and D’Long between the initial and final positions.
2. Enter the tables for meridional parts and find MP of both initial and final latitude.
3. Find the DMP by adding or subtracting both the MP.
4. Use the formula Tan Co = D’Long / DMP and obtain the Co.
5. Course obtained is quadrantal; now give name to it according to D’Lat and D’Long. Convert it to three figure notation.
6. Use the formula Dist = D’Lat / Cos Co and obtain distance in Nm.

Example of calculation to find Course and Distance:

Q. Calculate the rhumb line course and distance from position A Lat 04^o 30’S Long 054^o 42’W to position B Lat 11^o 24’N Long 007^o 07’E

Initial pos A Lat 04^o 30’S Long 054^o 42’W

Final pos B Lat 11^o 24’N Long 007^o 07’E

Find D’Lat and D’Long

D’Lat = 15^o 54’N = 954’N

D’Long = 61^o 49’E = 3709’E

Find DMP

MP of Lat A = 268.44

MP of Lat B = 683.94

DMP  = 952.38

Tan Co = D’Long / DMP

Co = N75.6^oE

Co = 075.6^o(T)

Dist = D’Lat / Cos Co

Dist = 3836.1’

Course    = 075.6^o(T)

Distance  = 3836.1 Nm

Procedure of calculation to find arrival position:

1. Convert the course to quadrantal notation. 
2. Use the formula Dist = D’Lat / Cos Co and obtain D’Lat.
3. Apply the D’Lat to initial Lat and obtain final Lat.
4. Enter the tables for meridional parts and find MP of both initial and final Lat.
5. Find the DMP by adding or subtracting both the MP.
6. Use the formula D’Long = DMP x Tan Co and obtain D’Long.
7. Apply the D’Long to initial Long and obtain final Long.

Example of calculation to find Arrival Position:

Q. A vessel departed from position Lat 03^o 22’S Long 176^o 48’W and steamed 1560 Nm on a course of 312^o(T). Calculate the position arrived using mercator sailing.

Initial Pos Lat 03^o 22’S Long 176^o 48’W

Course = 312^o(T)

Distance = 1560 Nm

Convert course to quadrantal notation

Co = 312^o(T) = N48^oW

Use formula D’Lat = Dist x Cos Co and obtain D’Lat.

D’Lat = 1043.8’N = 17^o 23.8’N

Apply the D’Lat to initial Lat and obtain final Lat.

Final Lat = 14^o 01.8’N

Find DMP

MP of Lat A = 200.74

MP of Lat B = 844.67

DMP  = 1045.41

Use the formula D’Long = DMP x Tan Co and obtain D’Long

D’Long = 1161.0’W = 019^o 21.0’W

Apply the D’Long to initial Long and obtain final Long.

Final Long = 163^o 51.0’E

Final position Lat 14^o 01.8’N  Long 163^o 51.0’E

Mercator sailing

There are two types of problems involving Mercator sailing:

1. Given starting position and destination, more than 600 NM apart, to find the course and distance.
2. Given the starting position and the course and distance, to find the position reached.

Example 1

Find the rhumb line course & distance from starting position P 10° 19'N 140° 40'W to arrival position Q 02° 12'S 160° 18'W.

Point P	Lat.	10° 19' N	Long.	140° 40' W	MP	618.2'N
Point Q	Lat.	02° 12' S	Long.	160° 18' W	MP	131.1'S
	D’Lat.	12° 31' S	D’Long.	19° 38' W	DMP	749.3'S
		= 751' S		= 1178' W

Tan Course = D’Long.  DMP = 1178  749.3 ; Course = S  32' W =  32'

Distance = D’Lat.  Cos Co. = 751'  Cos  32' = 1399.0 miles

Example 2

Find position arrived after sailing 301° (T) for 1408 M from starting position P 00° 04'S 178° 20'W.

Course =  = N  W

D’Lat. = Distance  Cos Co. = 1408'  Cos = 725.2' N =  05.2' N

Lat.P =  04.0' S --- MP 004.0' S 

D’Lat.= 05.2' N

Lat. Q =  01.2' N ---MP 721.7' N

                                  DMP 725.7'N

D’Long. = DMP  Tan Co. = 725.7'  Tan  = 1207.8' W =  07.8' W

Long. Q =  20' W +  07.8' W - =  32.2' E

Errors in Position Lines

The cocked hat

When three position lines do not intersect at a single point, the triangle so formed is called a cocked hat because it resembles a three cornered hat worn by some soldiers in Europe in the olden days.  Having obtained a cocked hat, a doubt arises as to the correct position of the ship. Ideally, when observing three objects, the angle of cut between any two lines of position should be 45º but never less than 30º. 

If the cocked hat is small, say less than a mile from each position line, its centre could be taken as the fix without much danger.

In case of a terrestrial fix, using compass bearings, the error could be due to 

1. Wrong identification of shore object or 
2. Error in reading the compass bearing or 
3. Wrong application of compass error or
4. If the ship is on voyage, undue delay between bearings whereby the ship’s position would have changed between bearings. 

There should be no reason to try to sort this out. A quick set of fresh bearings, using a different object/s and ensuring that the compass error is applied correctly would suffice.

In the case of celestial LOPs, it is not practicable to take the sights again! It is a good practice to take four observations but work out the fourth one only in case of a large cocked hat. Then the odd one can be weeded out. Here also, undue interval between the sights would result in a cocked hat as the ship’s position would have changed during the interval, especially on fast ships. In such a case, shifting the LOPs to allow for the run of the ship during the interval may solve the problem.

A cocked hat may be caused by systematic or random errors.

• Systematic Error: The same error in all three lines of position (LOPs). This could be wrong chronometer error, wrong Index Error, etc., affecting all three LOPs equally. 
• Random Error: A mistake in one of the LOPs may be causing the cocked hat.

Working out the fourth sight may give a good fix pointing out the ‘rogue’ LOP resulting from a random error in its working!

Resolution of Cocked Hat obtained due to fixed error in three terrestrial bearings

Data given --- Three bearings of three objects, having unknown fixed error, which do not meet at a point, and hence form a cocked hat.

• Calculate difference between first and second bearings, and between second and third bearings.
• Consider the two differences to be two horizontal sextant angles.
• Construct two position circles as explained in Sub-Sub-Topic: How to determine ship's position by Horizontal Sextant Angles.
• Intersection of the two circles is the correct position.

Notices to Mariners

The navigating officer is responsible for keeping all charts and publications on the bridge corrected and updated using the latest Notice to Mariners (NTM) received. The Admiralty Notice to Mariners is published every week and carries week numbers serially.

Contents of ADMIRALTY NOTICES TO MARINERS

Section I - Publications List

At the beginning of the Publications List is an index of ADMIRALTY Charts affected by the Publications List. Thereafter there are a number of standard lists which contain details and announcements concerning charts and publications relevant for the particular Weekly Notice. Full details of how to use the various lists contained in Section I are available in NP294. Special Announcements and Errata are occasionally included at the end of this Section.

Section IA - Temporary and Preliminary (T&P) Notices

A list of T&P Notices in force (along with a list of those cancelled during the previous month), is included in the Weekly NM each month (see below).

Section IB - Current Nautical Publications

Information about Publications including the current edition numbers is included in the Weekly NM at the end of March, June, September and December.

Section II - Updates to Standard Nautical Charts

The notices in Section II give instructions for the updating of standard nautical charts and selected thematic charts in the ADMIRALTY series. Geographical positions refer to the horizontal datum of the current edition of each affected chart which is stated in the notice alongside the appropriate chart number. Positions are normally given in degrees, minutes and decimals of a minute, but may occasionally quote seconds for convenience when plotting from the graduation of some older-style charts. Where Leisure Products are referred to different horizontal datums from the standard nautical charts for that geographical area, positions in the notices cannot be plotted directly on these products. Bearings are true reckoned clockwise from 000° to 359°; those relating to lights are from seaward. Symbols referred to are those shown in NP5011. Depths and heights are given in metres or fathoms and/or feet as appropriate for the chart being updated (abbreviated where necessary to m, fm and ft respectively). Blocks and notes accompanying notices in Section H are placed towards the end of the section.

T&P Notices. These are indicated by (1) or (P) after the notice number and are placed at the end of Section H. They are printed on one side of the paper in order that they may be cut up and filed. To assist in filing, the year is indicated after the notice number and an in-force list is published monthly. Information from these notices is not included on charts before issue; charts should be updated in pencil on receipt. Associated diagrams are reproduced with Blocks at the end of Section H. Original Information. A star (*) adjacent to the number of a notice indicates that the notice is based on original information.

Section III - Navigational Warnings

NAVAREA I Navigational Warnings in force at the specified time quoted in the header are reprinted in Section 1H. It is recommended that this reprint should be kept in a file or book, followed by subsequent weekly reprints. Only the most convenient ADMIRALTY Chart is quoted. The full text of all Warnings in force is included in Weeks 1, 13, 26 and 39 each year.

Section IV - Sailing Directions

Updates to all Sailing Directions are given in Section IV. Those in force at the end of the year are reprinted in the Annual Summary of ADMIRALTY Notices to Mariners Part 2 (NP247(2)). A list of updates in force is published in Section IV of the Weekly Edition quarterly. Updates may be cut out and pasted/changed directly into the book or alternatively it is recommended that updates are kept in a file with the latest list of updates in force on top. The list should then be consulted when using the parent book to see if any changes, affecting the area under consideration, are in force. It is not recommended that changes be stuck in the parent book.

Section V – Lights

Updates to all the List of Lights are given in Section V and may be published in an earlier edition than the chart-updating notice. The entire entry for each light updated will be printed (including minor changes) and an asterisk (*) will denote which column contains a change. In the case of a new light, or where a new sequence is added below the main light, an asterisk (*) will appear under all columns. All Section V entries are intended to be cut out and pasted into the appropriate volume. It is emphasised that the List of Lights is the primary source of information on lights and that many alterations, especially those of a temporary but operational nature, are promulgated only as updates to the List of Lights. Light positions should be regarded as approximate and are intended to indicate the relative positions of lights only. Charts should be consulted for a more authoritative position. When a light is affected by a separate chart-updating notice, its Light List number is always included in the relevant text contained in Section H. The range of a light is normally the nominal range, except when the responsible authority quotes luminous or geographical range - see special remarks for ranges used by each country. 

Section VI - Radio Signals

Updates to all the Radio Signals are given in Section VI. When a chart-updating notice is issued for information that is also included within the Radio Signals, the appropriate volume reference number is quoted, followed in parentheses by the number of the Weekly Edition containing (in Section VI) the corresponding update to the service details. The updates in Section VI should be cut out and pasted into the appropriate volumes.

Section VII - Miscellaneous Publications

Updates to the following selected miscellaneous Nautical Publications are contained in Section VII

NP100 The Mariner's Handbook

NP133A Paper Chart Maintenance Record

NP133C ENC Maintenance Record

NP231 ADMIRALTY Guide to the Practical Use of ENCs

NP232 ADMIRALTY Guide to Implementation, Policy and Procedures

NP294 How to Keep your ADMIRALTY Products Up-to-date

NP136 Ocean Passages for the World

NP350(1) ADMIRALTY Distance Tables — Atlantic Ocean

NP350(3) ADMIRALTY Distance Tables — Pacific Ocean

NP350(2) ADMIRALTY Distance Tables — Indian Ocean

NP735 IALA Maritime Buoyage System

NP5011 Symbols and Abbreviations used on ADMIRALTY Paper Charts

NP5012 ADMIRALTY Guide to ENC Symbols used in ECDIS

All Tides Publications

Nautical Almanac Publications, including Sight Reduction Tables.

Section VIII — ADMIRALTY Digital Services

Information relevant to ADMIRALTY Digital Services.

A notice from NTM and the information contained are to be marked permanently on the chart.

A preliminary notice abbreviated as (P)NM is issued when some changes are expected to become permanent later. For example: Harbor development etc.

A temporary notice (T)NM is issued when the information is valid for a limited period.

Correction entry at the bottom of a chart must be a continuous record of all corrections made as shown below:

Notice to Mariners – 2015 -371-847 2016-258-341

Therefore before a fresh entry of correction is made, all interim corrections should be made in sequence; use of latest cumulative list NTM can be made.

• During correction first priority should be given to the charts to be used in the immediate future.

• Then charts in the geographic area and lastly other charts on board

• For the permanent corrections P(NM) the corrections are made directly on the chart by hand at the given the longitude and latitude using a chart correction pen with violet color permanent ink. Red and black colors are not preferred so as to differentiate from printed matter which is black. Use small number (diameter) nib to insert information received through NTM and thicker nib for deletions. 

Second method of making corrections on the chart is through the tracing provided; this is done where several spots have to be marked close to each other. The information to be inserted will be in a box with each exact position marked by a dot with a circle around it, aligning with the latitude and longitude lines or prominent marks, such as buoys, or other marks, such as soundings. Using a hard pencil poke each position on the tracing; the depressed mark on the chart is the desired position of the insertion, to be entered by hand.

Other Publications

Important nautical publications

In addition to the Chart Catalogue, Navigational Charts, Nautical Almanac and Nautical Tables, the important nautical publications on a ship’s bridge are

1. Admiralty List Lights and Fog Signals
2. Admiralty List of Radio Signals
3. Admiralty Tide Tables 
4. Mariner’s Handbook
5. Distance Tables
6. Tidal Stream Atlas

The chart catalogue, explained in the earlier lesson, gives details of each of the above publications.

1. Admiralty List of Lights and Fog Signals

ALLFS is the expansion of Admiralty List of Lights and Fog Signals. ALLFS contains 12 volumes which cover all navigable areas in the world. Various geographic areas are covered by each volume.. A unique name and alphabet A to M (excluding I) is given for each volume of the book.  For example the alphabet letter F denotes Bay of Bengal.

USE OF ALLFS

• Each volumes of the book gives vast information on the following:

                 1. Lighthouses

                 2. Lightships

                 3. Light floating marks

                 4. Fog signals and

                 5. Other lights of navigational significance.

• Characteristics of lights and fog signals and foreign language descriptions of lights are also provided by these publications. 
• We can evaluate the geographical and luminous range of light by using tables.
• Information about all lights are listed as follows:

                 1. International number

                 2. Location

                 3. Name

                 4. Nautical miles

                 5. Geographical coordinates

                 6. Intensity

                 7. Elevation (in meters)

                 8. Range (in nautical miles)

                 9. Description of structure

How ALLFS are kept up to date

All the corrections are updated in Section no: V of the AWNM/NTM. The procedure to keep the corrections record is the same as that for pilot books. Many changes may be made in the contents; new editions need to be published after 12 months (1 year). For every month one volume should be re-edited and the information regarding this is given in section 1 of AWNM/NTM. 

2. Admiralty List of Radio Signals

Information on all characteristics of Maritime Radio Communications is given by the ALRS. In particular the data of ALRS is divided into six volumes, but some of the data are divided into several parts. These six volumes are presented in an easy format with colorful pictures and diagrams. 

The following table represents the six volumes of ALRS.

Volume Number	parts	Topic
Volume 1	1 and 2	Maritime Radio Stations
Volume 2		Radio Aids to Navigation Systems of Satellite Navigation Legal Time Radio Time Signals Electronic Position Fixing Systems
Volume 3	1 and 2	Maritime Safety Information Services
Volume 4		Meteorological Observation Stations
Volume 5		Global Maritime Distress and Safety System (GMDSS)
Volume 6	1 to 7	Pilot Services Vessel Traffic Services Port Operations

The use of ALRS 

ALRS contents ranges from an entire listing of radio stations handling Maritime Public Correspondence to all range of products and services. These products and services are essential for the Global Maritime Distress and Safety System. These volumes also provide information about the radio stations broadcasting weather services and forecasts. The volumes of ALRS also provide the explanation of Global Satellite Position Fixing Systems. GMDSS consists of four areas such as A1, A2, A3 and A4.

All the volumes of ALRS are updated in Section: VI of the AWNM. The procedure to keep the corrections record is same as that for pilot books. Many changes may occur in the contents; new editions need to be published at intervals of 1 year.

3. Admiralty Tide Tables

ATT is the expansion of Admiralty Tide Tables. ATT consist of all tidal information for all ports in the world. Admiralty Tide Tables contains four volumes. Each volume is divided into three parts.

The following table represents the four volumes of ATT

Volume 1	United Kingdom and Ireland (including European Channel Ports)
Volume 2	North Atlantic Ocean and Arctic Regions
Volume 3	Indian Ocean (including Tidal Stream Tables)
Volume 4	South Pacific Ocean (including Tidal Stream Tables)
Volume 5	South China Sea and Indonesia (including Tidal Stream Tables)
Volume 6	North Pacific Ocean (including Tidal Stream Tables)
Volume 7	South West Atlantic Ocean and South America
Volume 8	South East Atlantic Ocean, West Africa and Mediterranean (including Tidal Stream Tables)

Each volume ATT contains three parts as follows:

Part I: This covers all the important ports (standard ports) in a particular area. This will also provide the following information:

• Daily times
• Heights of high water
• Heights of low water

It also provides the information for evaluating the intermediate times or heights.

Part II: This covers more number of less important ports (secondary ports) in a particular area. All the secondary ports are based on the standard ports. Therefore, by applying a time and height difference to high water and low water at the standard port, we can obtain the time and heights of HW and LW at the standard port. 

Part III: For the purpose of tidal prediction, this part consists of harmonic constants. These harmonic constants are simplified by harmonic method. 

Use

If there is a need to evaluate the water availability at a place (find the depth of water), tide tables can be used. The actual depth of water is calculated to ensure safe passage for our ship over that area. 

Updating

Every year the tide tables are published a few months before 1st January. The corrections in the volumes are recorded and given in AWNM no: 1 of that year. 

The ships need not take all the volumes of the book. A ship should take only the volume which covers the expected area of the ship to trade so that spending too much money can be avoided. Efforts in correction of volumes can be saved, because these volumes are unnecessary and are not at all going to be used by the ship. 

4. Mariner’s Handbook (MHB)

The expansion of MHB is Mariner’s Handbook. MHB contains the following information:

• Collection of some important maritime details on charts
• Characteristics of tides, currents and sea
• Basic meteorology
• Navigation in ice
• Navigational hazards and restrictions and
• IALA buoyage system.

Use of MHB

Mariner’s handbook is used as a reference book. This gives more details about different matters regarding navigations. 

Updating

This book is updated in section: IV of the AWNM. The procedure to keep the corrections record is same as that of pilot books. Supplements are provided if necessary and important. Previous supplements will be superceded by each supplement. For every five years new editions need to be published. 

5. Admiralty Distance Tables

These tables, sub-divided by regions, give the shortest distances in nautical miles between positions and chief ports in the world. These distances may differ from those used in Ocean Passages for the World, which, though longer, take advantage of favourable climatic conditions and currents.

There are supporting diagrams and text as well as link tables for places not in the same or adjacent table.

Volume number	Locations
Volume 1	Atlantic Ocean NW Europe Mediterranean Sea Caribbean Sea Gulf of Mexico
Volume 2	Indian Ocean Southern Ocean (South Africa to New Zealand) Red sea Persian Gulf Eastern Archipelago
Volume 3	Pacific Ocean Bordering Seas of Pacific Ocean

In the left margin side of the page the main ports are listed in alphabetical order (along Y-axis). The important ports are also listed on the top of the page (along x – axis). The intersecting cell of the departure port and arrival port exhibits the distance between those ports. This distance is denoted in nautical miles. If there are two reasonable alternate routes, both can be mentioned clearly. 

Use

Admiralty Distance Tables gives reference for evaluating route time, need of fuel oil and so on. The passage plan should be made.

Example: Assume that a ship approaches Indonesia on the east coast to load a full cargo of coal. After loading the coal the navigator wants to know the journey time and need of fuel oil for the ship to take the cargo to Sri Lanka. Distance is the most common factor for these two calculations. This distance can be easily obtained from the Admiralty Distance Tables.

All important ports are listed in alphabetical order in the Y-axis in the left margin and also on the top of the page along the X-axis.  The cell of intersection of the departure port and the arrival port contains the distance in nautical miles (see diagram 4), where there are two plausible alternate routes exist, each is mentioned clearly.

Example:  The distance from New York in the USA to Lisbon (Lisboa) in Portugal is, from diagram 4, 2934 nautical miles.

Updating

The uploaded details in Distance Tables are unchangeable in nature. Although, corrections in Admiralty Distance Tables are uploaded in Section I of the AWNM. If there is any change in the contents, new editions need to be published.

 

6. Tidal Stream Atlas

Admiralty Tidal Stream Atlases include detailed tidal stream direction and strength information for key locations, enabling accurate calculation of tidal stream rates for a particular port when planning a voyage.

 

Each volume of tidal stream atlas includes:

• Pictorial representation of tidal stream direction for each hour before and after the reference port
• Information on the direction and rate of tidal stream
• Mean neap and spring tidal rates in tenths of a knot

A video on finding data of a tidal stream using a tidal atlas,  can be seen on YouTube at

Tidal Stream – using Tidal Atlas