Nautical Dictionary “A”


Philippine plant, of plantain genus, from which manilla hemp is made.


Said of a sail when the wind is on the fore side of it.


On the after side of. Further towards the stern.
Abandonment. Surrender of an insured vessel and of all claims to ownership. Made by owners to underwriters when vessel is a constructive total loss and insurance is to be paid.

Abandonment of Voyage. 

Renunciation of, or withdrawal from, an
intended voyage — whether done voluntarily or through force of circumstances.

Abandon Ship. 

Entirely to vacate a ship and to relinquish, or to
repudiate, all duties towards her preservation. Done only when the carrying out of these duties is impossible, or when the destruction of
the ship is imminent.


Position or direction that lies at right angles to ship’s fore and aft line.


‘A wandering from the path’. In astronomy, is the
difference between the true and apparent positions of a heavenly body when caused by Earth’s movement in space: it is too small to affect navigation. In meteorology, is the difference between directions of true and apparent winds that is caused by ship’s movement when inclined to wind direction. In optics, is the deviation of light rays from a true

Able Seaman. 

An experienced seaman competent to perform the usual and customary duties on deck. In sailing ships, had to be able to ‘hand, reef and steer’. In Merchant Navy, has to have served satisfactorily on deck and pass an exam. In Royal Navy, has to have served a specified period at sea and satisfactorily completed certain courses of instruction.

Abnormal Refraction. 

Displacement of visible horizon and observed
objects by an unusual amount. Objects that would, normally, be below horizon may be seen above it. Usual check is by ‘Back Altitude’.


On board. In, into or inside a vessel. Close alongside.



‘Aboard Main Tack’. 

Order to haul main tack down to chess tree.
Given when sailing close-hauled in a square-rigged ship.


French collision. The act of boarding and taking an enemy vessel.


Used, in conjunction with other word or words, with reference to changing from one tack to the other when under sail.

About Ship. 

To put a ship, under sail, on the opposite tack. 2. Order to crew to go to stations for tacking or wearing.


Said of yards when those on one mast are braced in a direction opposite to that of yards on next mast.

‘A’ Bracket. 

Forging that carries after end of propeller shaft in twin-screw vessel. Upper arm is secured to shell plating or to a plate inside vessel, lower arm is secured to keel or to a steel casing on keel.


Said of ships on parallel courses when abeam of each other. Objects inside a ship are abreast when they are in the same transverse line.


Said of a flag, or sail, when it is hoisted or extended.

Absence Without Leave.

Remaining away from ship without permis-
sion, but not showing intention of deserting.


One who fails to return to his ship, or place of duty, but who has not shown any intention to desert.

Absolute Force.

In magnetism, is intensity of Earth’s magnetism, or of a magnet’s force, expressed in dynes.

Absolute Humidity.

Weight of water held in a given volume of
atmospheric air. Usually expressed in grammes per cubic metre.

Absolute Pressure.

Pressure of a fluid measured above a perfect
vaccum. In practical engineering, it is taken as steam pressure plus 15lbs. Absolute pressure of condenser is taken to be — in barometric inches — half height of barometer minus vacuum reading.

Absolute Temperature.

Temperature measured from an Absolute zero
at which there is an entire absence of heat. Zero is equivalent to – 273- 1°C (-459-58°F). Usually measured in Centigrade units.

Absolute Total Loss.

Complete destruction, or removal, of ship or
goods from hands of owners; or such a change in them that they cease to be what they were. Term is used, also, in assessment of loss of ship;
absolute loss including loss of freight that ship was earning.

Absorption Coefficient.

Amount of radiation absorbed by a given surface when expressed as a proportion of the radiation falling on it.

Absorptive Power.

Rate at which radiant energy is absorbed at surface of a body. Varies with temperature and wavelength of the energy.


Stowage of casks, barrels, etc., so that they lie lengthwise athwartships.


That volume of ocean lying below 300 fathoms from surface.




Pertaining to the abyss.


Class of sea creatures that sting if touched. Includes jellyfish and ‘Portuguese man o’ war’.


 Star 9 Eridani. S.H.A. 316°;Dec. S 40°; Mag. 3-1.


A hastening or increase in rate of motion. In astronomy, is an apparent gaining of one heavenly body upon another when due to
superior speed, a difference of direction, or both of these.

Acceleration of Fixed Stars.

Progressive earliness of fixed star transits
as compared with Sun’s transits. Owing to Sun’s eastward movement along Ecliptic, stars transit any meridian nearly four minutes earlier
each day when referred to solar time.

Acceleration of Planetary Motion.

Increase in a planet’s angular velocity when travelling from aphelion to perihelion (in accordance with Kepler’s second law).

Acceleration of Sidereal Time.

Amount of sidereal time gained by a sidereal clock in any given interval of mean solar time.

Acceleration of Wind.

Apparent increase in wind-force when due to
ship approaching direction of wind.

Acceleration Tables.

Give the amount by which any mean time value
of an interval must be increased to give the sidereal time value.


A signing of a document as evidence of having read it, and of readiness to fulfil its requirements. Accident Boat. Boat that is kept turned out and ready for instant manning and lowering in case of emergency.

Accident Report.

Statement rendered to Department of Transport by Master when a British ship has been damaged, or when serious injury or death has been caused on board by any accident.


Spaces in ship set apart for messrooms, sleeping
places, ablutions and recreation. Statutory allowance of floor space varies from 12 square feet and upwards for each person.

Accommodation Ladder.

Sloping series of steps, usually of wood, fitted with handrails and extending from waterline to an entry into ship, to facilitate safe embarkation and disembarkation.

Account Position by.*

‘Estimated Position’.

Account of Wages Book.*

Supplied by Shipping Office to Master when
engaging crew. Accounts of each member of crew were kept in duplicate, one copy being given to man, and the other to Shipping
Office, when paying off.


Old name for an arm of the sea with no port or river.

Accumulated Rate.

The daily rate of a chronometer multiplied by
number of days since lastcomparison.


An electric storage battery.

Accumulator Capacity.

Storage power of anaccumulator; usually
expressed in ampere-hours.

Accustomed Average. 

‘Average accustomed’.


Star a Eridani. R.A. Olh 36m; Dec. S 57°;
Mag. 0-6. S.H.A. 336°. Diameter is four times that of Sun, candlepower is 200 times greater. Distant 66 light years.

 Achromatic Lens.

 Two or more lenses, in combination, that correct thechromatic aberration always present in single lens.



Acidity of Boiler Water. 

Is a result of impurities in it. Usually ascertained by use of litmus paper or methyl orange.


Alternative name for ‘Eagre’.

Acker’s Time Scale. 

First system of time allowances in yacht racing.
Introduced, 1843, by G. Holland Acker. Based on length of course and tonnage.

 Acker’s Yacht Code.

 System of yacht signalling embodied in Acker’s
‘Universal Yacht Signals’.


One who steals from a ship in navigable waters. A fresh water pirate.


Formal admission that something has been
received, or that some specified service has been rendered, or that certain liabilities have been incurred.

Aclinic Line. 

Magnetic equator. Line passing through all positions on Earth at which there is no magnetic dip.


State of an anchor when suspended from cathead by the cathead stopper only. State of a yard when one yard arm is topped by the lift, the other arm being boused down. This is done when using yard as a derrick; also done to prevent yard projecting over the side when
vessel is berthed.


Ornamental finish, resembling an acorn,
at head of an upper wooden mast. Usually indicates Dutch built.


Formal and written discharge from a specified duty, liability or undertaking.


Name sometimes given to star p Scorpii.


Said of a heavenly body that rises at sunset and sets at sunrise.


Bow ornament, usually circular or spiral,
carried by ancient warships.


Star a Crucis. S.H.A. 174°; Dec. S 63°; Mag. 1-1.
Actinometer. Instrument for measuring intensity of Sun’s rays, or of actinic rays.


Class of sea creatures that includes jelly
fish, sea anemones and the coral polyps responsible for coral reefs.


Engagement or battle with hostile ships or forces.

Action Stations.

Positions manned by personnel of a warship when battle is imminent.

Active Bond. 

A written undertaking to pay that commences to earn interest directly it is issued.

Act of God. 

Casualty due to extraordinary natural causes and circumstances, to which there was no human contribution and which could not
have been foreseen or averted by the exercise of any amount of reasonable intelligence or endeavour.

Actual Total Loss.

‘Absolute Total Loss’.

Address Commission. 

Commission payable at discharging port.


Star e Canis Major. S.H.A. 256°; Dec. S
29°; Mag. 1 -6.


Applied to changes in temperature, pressure
or volume of a fluid when occurring wthout heat being taken in or given up.

Adiabatic Lapse Rate. 

Falling rate of temperature of atmosphere by
54°F for each 1000 feet of height (0-98°C per 100 metres). Due to atmospheric expansion through reduced pressure.


Former name of a ‘Kew Pattern’ barometer.
Adjustment. Putting into correct relationship, or into proper place.

Adjustment of Average. 

See ‘Average Adjustment’.

Adjustment of Instruments.

Correct setting of those parts that havevariable positions, or that have become displaced.

 Adjustment of Magnetic Compass.

Name loosely given to the compensation made at a magnetic compass.



Adjustments of Sextant. 

Comprise the setting of index and horizon
mirrors so that they are perpendicular to plane of arc, setting the mirrors parallel when the index is at zero, setting line of collimation
parallel to plane of arc.


Naval officer competent to command a fleet of ships. In Elizabethan times denoted ship in which senior officer of a group of ships was borne. In the fishing fleet, may be applied to the senior skipper of a group of drifters working in company.

Admiral of theBlue.*

Originally, admiral commanding rear division
of a fleet. Later, a rear-admiral.

Admiral of the Fleet.

 Highest rank in Royal Navy. Distinguishing flag
is Union Flag at mainmast head.

 Admiral of the Red.* 

Senior admiral, commanding centre division of a
fleet. Later, an admiral.

Admiral of the White.*

 Originally, admiral commanding van division
of a fleet. Later, a vice-admiral.


1.Control of the seas.
2. The Lords Commissioners for
executing the office of Lord High Admiral of Great Britain, etc.
 3. The Board of Admiralty.
4. The buildings in which the offices of the
Board of Admiralty are situated.

Admiralty Charts. 

Charts produced and issued by the Hydrographic
Department of the Admiralty.

Admiralty Coefficients. 

Values used for comparing efficiency of hull
forms. Based on displacement, speed, indicated horse power, and fuel consumption.

Admiralty Court. 

Usual name for the ‘High Court of Admiralty’ in
which shipping cases are investigated and adjudicated upon.

Admiralty Flag. 

The proper flag of the Lord High Admiral of Great Britain, and of the Lords Commissioners for executing that office. Is a red flag with a horizontal yellow anchor.

Admiralty Hitch. 

Name sometimes given to a marline spike hitch.

Admiralty List of Lights, 

Fog Signals and Visual Time Signals. Nine volumes, arranged geographically, giving full particulars of navigational aids mentioned in title. Do not give particulars of buoyage.

 Admiralty List of Radio Signals. 

Volumes published by Hydrographic Department of Admiralty. Give general regulations and
signals for communicating with coast stations and services; give details of Radio Beacons, Time Signals, Ice and Navigational Warnings, etc.

Admiralty Method of Tidal Predictions. 

Method of finding tidal state at a required position by use of data in Admiralty Tide Tables and in conjunction with form NP159,

Admiralty Pattern Anchor. 

Older type of anchor in which shank and arms are fixed and stock is at right angles to arms.

Admiralty Sailing Directions. 

Series of volumes, issed by Hydrographic Department of Admiralty, covering all navigable waters of the world. Give all possible information to the navigator concerning
navigation in the waters they cover. Often called ‘Pilots’.

Admiralty Tide Tables. 

Volumes giving daily predictions of times of
high and low waters at principal ports and positions in the world, together with data and instructions for obtaining times and height of
high and low water at ports for which predictions are not given.

Admiralty Warrant.

Official authority from Admiralty to wear a blue
ensign, a red ensign defaced or a yacht club burgee on a British vessel. Warrants are issued for other purposes.


Unattached to the shore or ground and at the mercy of wind and tide. Colloquially used to mean missing from its place; absent from
place of duty; broken away from fastening.


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 Passage rates in emigrant and passenger ships consider any person of 12 years of age, or over, to be an adult. Two persons less than 12 years of age count as an adult.

Ad Valorem. 

According to value. Used when goods referred to are assessed by their value, and not by weight or quantity.


Distance between position at which a vessel commences to alter course and the position at which she is on her new course. It is measured along a line parallel to original course.

Advance Freight.

Proportion of contracted freight that may be paid on completion of loading, if mutually agreed. As freight is not due until cargo is delivered, this advance is debited with insurance and interest (charges. Advance Note.* Issued, at Master’s option, to a newly-engaged seaman. Authorises payment of a stated sum to the holder of the note after man has sailed in ship. Charged to a man’s account. Rarely exceeds one month’s wages.


In meteorology, denotes the horizontal transfer of heat by air currents.


In insurance, is any undertaking that involves a risk or hazard.


To announce or publish in such a manner
that a matter should come to the notice of those concerned in normal circumstances.


Formal notification of information concerning a transaction.

Advice Boat.* 

Small vessel employed in distributing written or verbal orders and information to vessels of a fleet or squadron.


Single wire, or system of wires, forming a radio antenna (US ‘antenna’).


Meteorite that consists mainly of stone.


Study of the atmosphere, particular] y the upper reaches of it.


Solemn declaration made before a person legally authorised to administer an oath.


 Ratified and confirmed.


 To charter or hire a ship. Affreightment. The
chartering or hiring of a ship. Afloat. Completely waterborne.


Forward of; before.


Towards the stern, near the stern. Sometimes used as denoting officers’ quarters. Applied to wind, means within four points from right aft.


 Further aft; nearer the stern. After date. In a financial document, means ‘after date mentioned in document’.


Sunlight reflected from high clouds inwest after Sun has set.


Originally, the hands who worked the after sails,
and who were frequently berthed aft. Later, become synonymous with officers— for the same reason.

After Leech. 

Lee leech of a square sail when yard is braced round.Sometimes used, incorrectly, for leech of a trysail—to differentiate itfrom the luff (or ‘fore leech’).

After part.

That part of a vessel, or of any space or fitting in a vessel, that is nearer the stern. 2. That part of a watch who work, or would have worked, the after sails.

 After Peak. 

Enclosed space immediately forward of stern frame. Enclosed by a transverse bulkhead and side and bottom plating. Used as a ballast tank or store.

After Sight.

 In a financial document,
means ‘After payer has endorsed
it as an acknowledgement of sighting it’.

After Swim.

after part of hull that is shaped to give a lead in
for water to propeller and rudder, and to give increased area of water
plane with increased draught.


Furthest aft. Nearest the stern.


Against the Sun. Anti-clockwise circular motion.
Left-handed ropes are coiled down in this way.


 One who acts for another. In ship’s business, is one who acts for one or more of the parties interested in the charter. The same agent may
act on behalf of the shipowner and the charterer.

Age of Diurnal Inequality.

 Interval between instant of Moon’s transit
and the occurrence of maximum declinational effect in tide. By harmonic constants:
Age of Diurnal Irtequality = —0-91 (K°-O°).

Age of Diurnal Tide. 

Interval between time of Moon’s maximum
declination and time of the following diurnal spring tide.

Age of Moon. 

Interval in days and fractions, since Moon was new. Maximum value of about 29j days.

Age of Parallax Inequality.

Interval between instant when Moon is in
perigee and occurrence of maximum parallactic effect in tide. Usual value is between one and three days after.

Age of Phase Inequality.

‘Age of Tide’. Age of Semidiurnal Tide. Interval between syzygy and occurrence of spring semidiurnal tide.

Age of Tide. 

Interval between syzygy and the occurrence of the spring tide due to it. Value may be from more than 7 days after syzygy to nearly a day before it. Average age of British tide is about { days.

Ageton’s Tables.

 H.O. 211 (USA) give, by inspection, azimuth and
calculated altitude when latitude, hour angle, altitude and declination are known.


Name sometimes given to a ‘double tide’.


 Sand or other material mixed with cement when making concrete. For marine work sand is usual, and may be used in proportion of up to six times the amount of cement.

Aggregate Freight.

Balance of freight due at port of delivery when all additions and deductions, for demurrage, advanced freight, etc., have been taken into account.

Aggregating Clause. 

Clause, in any agreement, that allows several
items to be collected under one heading. One of the ‘Institute’ clauses.

Agonic Line. 

Line on Earth’s surface that passes through all places where there is no magnetic variation of compass.


Short name for ‘Articles of Agreement’ entered into by Master and crew of a vessel.


 State of a vessel when she ceases to be completely waterborne and her weight is taken, partially or completely, by the ground.



Agulhas Current. 

Warm current flowing southward and
westward from Mozambique Channel and Indian Ocean to SE Coast of Africa. Width is up to 50 miles; rate is occasionally nearly 4 knots. A.H.
Initials of ‘Anno Hegirae’ (the year of the Flight of Mahomet). Epoch of Mahommedan Calendar, A.D. 622.


Direction in front of ship. Position in front of ship. ‘Ahoy’. Seaman’s call to attract attention. Said, on good authority, to be a Viking cry.


 Said of a vessel riding out a gale broadside on,
under bare poles and with helm lashed a-lee.


Gaseous mixture that forms the atmosphere. Composed of, by volume, 78% nitrogen, 21% oxygen, and traces of neon, helium, krypton, hydrogen, zenon and ozone. Has low thermal conductivity.

Air Almanac. 

Ephemeris specially compiled for use in air navigation. Arranged in daily pages for ready reference and determination of Greenwich Hour Angles to nearest minute of arc.

Aircraft Carrier.

 Warship specially designed so that aircraft can take off and alight upon her.

Air Density. 

Weight of air of a given pressure and in a given volume at a given temperature. At temperature 273°A, pressure 1000mb, density is 0-001276 grammes per cubic centremetre.

Air Mass. 

Meteorological term for a mass of atmosphere that is bounded by fronts and differs from surrounding atmosphere.

Air Meter. 

Small portable anemometer, on windmill principle, for measuring wind-speed.

Air Pipe. 

Pipe that allows air to escape as a tank is filled. 2. Pipe through which air is pumped to a diver.

Air Pocket. 

Descending current of atmospheric air; such as those that develop on the lee side of steep cliffs.

Air-Speed Indicator. 

Portable instrument, with pitot head, used for
measuring wind velocities between 10 and 70 knots.


Scottish word for a direction by compass.

Air Thermometer. 

Thermometer filled with dry air. Expansion and
contraction of enclosed air, due to heat content, are measured by pressure required to keep the volume at a constant value. Pressure thus
indicates temperature. Range is exceedingly large, readings to -300°F being obtainable.

Airy’s Figure of Earth. 

Dimensions of Earth as computed by Sir
George Airy (1801-1892), Astronomer Royal. Equatorial diameter 20,923,715ft.,polardiameter20,853,810ft.,compression^•5. Used in British Ordnance Survey.

Airy’s Method* 

of Great Circle Sailing. Used for finding position of mid-point in a great circle course between two places when rhumb line is laid off on a Mercator chart. Rhumb line is bisected and a perpendicular to it is extended towards or through Equator. Tables then give latitude in which the great circle course cuts the perpendicular.

Aitken’s Nucleus Counter.

 Instrument for counting number of hygros-
copic particles in a given volume of air, which is cooled adiabatically by expansion. Water droplets, each containing a nucleus, are
deposited; these are counted with aid of a microscope.


Name given to a tidal bore sometimes met with in estuaries. Cognate with ‘Eagre’, ‘Acker’.


Old name for a lighthouse or beacon.
Albacore. Small edible fish of mackerel family. Found near West Indies and in Pacific Ocean.


Light reflecting power ofMoon, planet or satellite. Value is expressed as a fraction that denotes proportion of light that is reflected.
Term may be used in connection with radiations other than light.

Albert Medal. 

Established by Queen Victoria, in 1866, and awarded for saving life at sea. Later, extended to include saving life on land. Ribbon is blue for sea medals, red for land medals.


 Star (3 Cygni. S.H.A. 68°; Dec. N 28°; Mag. 3-2.


 Name of a small star close to Mizar in Ursa Major. Is often called ‘the rider’ (of one of the horses of Charles’ Wain), or ‘the Tester’ (of


Star a Tauri. S.H.A. 304°; Dec. N 24°, Mag.
3-0. Name is Greek for ‘Kingfisher’. At one time was thought to be the central star of the Universe.


Star Tauri. a R.A. 04h 33m; Dec. N 16°;
Mag. 1-1. S.H.A. 292°. Diameter is 60 times that of Sun; distant 57 light years; temperature 3300°A. Is one of the Hyades. Name is Arabic for ‘Eye of
the Bull’.


Star a Cephei. S.H.A. 41°; Dec. N 62°; Mag. 2-6.

Aldis Signal Lamp.

 Electric flashing lamp for signalling. Beam is
focussed on receiver, and cannot easily be seen by anyone on whom it is not trained or directed. Range exceeds 20 miles.


Towards, or on, that side of a ship that is further from the wind.

Aleutian Current. 

Ocean current setting STy through Aleutian Islands until it meets Alaskan Current, some of which it deflects into the North Pacific Drift.

 Aleutian Lows. 

Meteorological depressions that frequently form over the Aleutian Islands.


Flowerless aquatic vegetation usually known as seaweed.


 Name sometimes given to constellation Orion, usually by poets. Means ‘The strong and valiant one’.


Star 7 Leonis. S.H.A. 206°; Dec. N 20°; Mag. 2-3.


Star 7 Pegasi. S.H.A. 357°; Dec. N 15°; Mag. 2-9.


Star 3 Persei and, also 3 Medusae. Is a binary star, one dark and one light, and varies between 3rd and 5th magnitudes in less than 3 days. S.H.A. 314°; Dec. N 41°. Name is Arabic for ‘ghoul’ or’demon’. Was probably looked upon as the winking eye of a monster.


Star 7 Geminorum. S.H.A. 261 °; Dec. N 16°; Mag. 1-9.


Pivoted sight bar that moves over a graduated arc.


Star e Ursae Majoris. S.H.A. 167°; Dec. N 56°; Mag. 1 -7.

Alkaid (Benetnasch). 

Star T| Ursae Majoris. S.H.A. 154°; Dec. N 50°.
Arabic for’The Chief. All Aback. With the wind on fore side of the sails. Used colloquially to mean ‘astounded’ or ‘flabbergasted’.

All Aboard. 

Order to embark.

 All Hands. 

All the crew.

 All in the Wind.

 With all sails shaking through wind being on their luffs. Normally occurs when ship passes through wind from one tack to the other, but can also be caused by bad steering when close hauled.


Sheets attached to a Bill of Exchange for further endorsements when there is no more room on the Bill itself.

All other Perils.

Phrase used in marine insurance policy to mean ‘perils similar to those specifically mentioned,.

Allotment Note. 

Authority given by a seaman for the shipowner to pay part of the seamen’s earnings to a near relative, or to a savings bank, nominated by the seaman. The amount to be paid and the intervals
between payments are, within limits, at the discretion of the seaman.


Short name for’Fresh water allowance’. 2. Name often given to gratuity given to cargo trimmers and others by shipmaster.

All Standing.

 Applied to a sudden stopping of a ship when brought about without engines being eased or sail reduced. 2. To turn in all standing is to lie down fully dressed.

All Told.

 All being counted.


 Star 7 Andromedae. S.H.A. 330°; Dec. N 42°; Mag. 2-2.


Presentation of certain information day by day for a year.


Circles parallel to horizon and passing through each degree of the vertical circles.

 Almucantar’s Staff.* 

Olden instrument, made of pear wood or
boxwood with a 15° arc. Was used for measuring amplitude.

 Al Na’ir.

 Star a Gruis. S.H.A. 29°; Dec. S 47°; Mag. 2-2.


Star e Orionis. S.H.A. 276°; Dec. S 01°; Mag. 1-8.


 Has a variety of meanings. In the 18th century often meant above the mess deck. More usually means above the highest part of the upper
deck; above the sheerpole; above the lower tops.


Close beside a ship, wharf or jetty. In charter parties, means that ship is so close to wharf or lighter that cargo can be transferred from one to the other by tackles.


 To windward.


Below; low down; not aloft.

Alow and Aloft. 

When applied to sails, means below and above the lower yards.


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a First letter of Greek alphabet. Commonly used as a symbol to denote a known quantity. Prefixed to name of a constellation it denotes principal star in that constellation.


Star a Hydrae. S.H.A. 219°; Dec. S 08°, Mag. 2-2. Also called ‘Cor Hydrae’.


 Star a Coronae Borealis. S.H.A. 127°; Dec. N 27°; Mag. 2-3.


Star a Andromedae. S.H.A. 358°; Dec. N 29°; Mag. 2-1. Alt. Abbreviation for’altitude’.


Star a Aquila;. S.H.A. 63°; Dec. N 9°; Mag. 0-9. Diameter is about that of Sun; candlepower is nine times greater; temperature is 8600°A; distance is 16 light years.


Step in a dry dock, on which lower ends of shores rest.


Contraction of ‘Altitude-azimuth’, the two horizon coordinates for fixing position of a heavenly body.


Instrument. One that measures altitude and azimuth simultaneously—such as a theodolite.

Alternating Current.

Electric current with rapidly alternating positive
and negative polarities. Alternating Light. Navigational beacon light that changes colour in
each period of its visibility.


Aneroid barometer graduated to show height instead of pressure.


Angular distance of a heavenly body above
the horizon. Linear distance above sea level or other datum.

 Altitude a Double.*

 Obsolete term for a pair of altitudes taken to
determine latitude.

Altitude Azimuth. 

Usually shortened to ‘Alt-azimuth’. Applied to
problems, methods, tables and instruments in which these two coordinates are inter-dependent.

Altitude Circle. 

Great circle of celestial sphere that passes through zenith and so cuts horizon at right angles. Also called ‘Vertical Circle’ or ‘Circle of Altitude’.

Altitude of Heavenly Body. 

Intercepted arc of a vertical circle between
horizon and the body. The altitude may be the ‘observed’, ‘apparent’ or ‘true’ according to the horizon from which it is measured, and the point
at which the angle is situated.


 Prefixed to name of cloud form, denotes that it is at middle level.


Cloud form consisting of flattened globular, small clouds in regular layers.

Altocumulus Castellatus. 

Altocumulus cloud form with top edge shaped somewhat like battlements.


Gauzelike cloud form, at middle altitude, resembling mist or fog. Density varies, sometimes stars can be seen through it, at other
times it may hide Moon or even Sun.


 Star 3 Draconis.

Always Afloat. 

Charter party stipulation that a ship shall not be
required to load, discharge or wait turn at a berth where she would take the ground at some state of the tide.


Quickly and suddenly.

Amalfian Code. 

‘Amalphitan Code’.


Compound of mercury with another metal.

Amalgamated Trough.

Metal trough into which mercury i s put to form
an artificial horizon. Inside of trough is amalgamated to prevent metallic action by the mercury.

 Amalphitan Code.

 Collection of navigation laws codified at Amalfi in 1 lth century. Was generally accepted as authoritative for many years.

Amazon Current. 

Outflow of river Amazon, which is manifest for a
very considerable distance north and east of river mouth.


 Valuable and sweet-smelling substance ejected by the cachalot whale. May be found floating on sea in tropical latitudes.


 Schooner yacht that won ‘America’s Cup’, 22nd August, 1851, in race round Isle of Wight. Length 94 ft., tonnage 171. Built by G. & J. R. Speers, New York. American Carriage of Goods by Sea Act, 1936. Legislation that affects all contracts of carriage by sea to or from ports in USA.

American Grommet. 

Brass eyelet that is clinched into a sail, awning or
other canvas article.

American Practical Navigator. 

Book on navigational methods, together with appropriate tables. Written by Nathaniel Bowditch, LL.D., in 1802. Has been revised and brought up to date frequently.

American Whipping. 

Similar to a common whipping except that the
two ends of twine are brought out in middle of whipping and are finished off with a reef knot.

 America’s Cup.

 Internationa] yacht racing trophy. Given by Royal Yacht Squadron and won by yacht ‘America’ in 1851. Held by USA until 1983. When ‘Liberty’ was beaten by ‘Australia IF. In 1987 the
United States regained the cup when ‘Stars and Stripes’ beat the Australian yacht ‘Kookaburra IF at Perth.


Middle part of a ship, or a middle line in her—either fore and aft or athwartships. ‘Amidships’. Order to helmsman to move wheel or tiller so that rudder is in ship’s fore and aft line, and has no turning effect.


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Unit of electrical current. Amount passed by one volt through a resistance of one ohm. When passed through standard solution of silver nitrate deposits 0.001118 grame of silver per second.

Ampere’s Rule. 

Expresses deflection of a magnetic needle when in field of an electrical current. Current flowing south to north above a magnetic needle will deflect red end westward, and eastward if
flowing below needle.


Animals capable of living both under water and on land.

Amphidromic Point. 

Point at which cotidal lines meet, and at which
there is no range of tide.

Amphidromic Region. 

Area around an amphidromic point, and in
which there is no range of tide.

Amphidromic System. 

One in which cotidal lines meet at a point.
Amphitrite. In Greek mythology, was wife of Poseidon (Neptune).


The extent of any oscillation, swing or excursion.

Amplitude of Heavenly Body.

 Value of intercepted arc of horizon between the prime vertical and the vertical circle passing through the body when rising or setting. Measured, in degrees, from east or west
point of horizon, and towards the nearer pole.

Amplitude of Tide.

 Distance between mean tide level and high or low water level of a tide or constituent tide.

Anabatic Winds. 

Those winds that have an upward trend, such as
daytime winds that pass upward from valleys.


Separation into component elements, or into predetermined groups or categories.


Implement by which a ship becomes attached to the ground at sea bed, and so rendered stationary. Parts are: shank, arms, flukes, bill
(or pea), stock, ring. They fall into three main groups: Admiralty Pattern, Close Stowing, Stockless. The Admiralty Pattern has a stock
at right-angles to the arms which causes the anchor to lie so that one of the flukes will bite into the ground. The Close-stowing anchor has a
stock in line with the arms, in the Danforth anchor the stock is attached at the same end of the stock as the arms. The Close-stowing and
Stockless anchors have tripping palms which cause the flukes to bite into the ground. The Plough, or C.Q.R. anchor, has flukes shaped like a
plough-share. Ship’s equipment of anchors is laid down by law and is based, primarily, upon her length. The ‘Anchors and Chain Cables
Rules 1970′ demands that exhaustive tests be made on ships’ anchors. The ‘Merchant Shipping Acts’ require that every anchor shall be marked, in two places, with name or initials of maker, and shall carry a serial or progressive number.


An area in which the holding ground is good, and suitable for ships to anchor. 2. A position in which ships are anchored. 3. The hold of an anchor in the ground. 4. Dues paid, in a port, for
use of an anchorage ground.

 Anchor Bed. 

Strongly-built fitting, on either side of forecastle in ships having stocked anchors, on which an anchor is stowed and secured.

Anchor Bell. 

Bell, in fore part of ship, rung during fog in accordance with Rule of ‘Regulations for Preventing Collision at Sea’. Sometimes used for indicating to bridge the number of shackles of cable that are out.

 Anchor Buoy. 

Small buoy, or block of wood, with its mooring rope made fast to crown of anchor. Used for indicating position of anchor when on the bottom.

Anchor Clinch. 

Alternative name for ‘Inside Clinch’. Was often used when bending hemp cable to ring of anchor.

Anchor Flags. 

Small red, green and numeral flags used in Royal Navy when anchoring or weighing. Red or green flag used on bridge to indicate which anchor is to be let go; numeral flag used forward to indicate to bridge the number of shackles out.

Anchor Ice.

 Ice, of any form, that is aground in the sea. Anchor Lights. All round lights shown by vessel at anchor, in accordance with Rule of Collision Regulations.

Anchors and Chain Cables Rules 1970. 

Statutory regulations concerning making, testing, marking and certifying of anchors, cable and connecting shackles used by seagoing vessels.

Anchor’s Aweigh.

(Away.) Report that anchor has been hove out of
ground and is clear of it.

 Anchor Shackle.

 Used in joining end of cable to anchor ring. Differs from joining shackle in being fitted with forelock for securing a protruding pin. Now obsolescent.

 Anchor Stock.* 

Method of wooden shipbuilding in which butts of timbers were placed at middle of timbers above and below.


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Anchor Watch.

 Officer and a few men of duty watch who remain on deck when ship is at anchor in an open roadstead.


Old name for ‘Ensign’.


Naval seaman’s nickname for Royal
Navy. See ‘Andrew Miller’.

Andrew Miller. 

Naval nickname for the Royal Navy. Said
to be name of a zealous press gang officer.


Constellation situated between R.A. OOh and 02h; Dec. 28° to 42° N. Contains three bright stars, Alpheratz, Mirach, Almak.


Record made by a recording anemometer.


 Instrument tor recording wind torce and, sometimes, direction.


 Instrument for measuring wind velocity or pressure.


 Science dealing with measurement of wind pressures.


Instrument for detecting wind and indicating its direction.


Aneroid barometer fitted with clockwork and a
paper carrying a pen to give a continuous record of barometric pressures. Seamen usually call it a ‘barograph’, but this term included mercurial
recording barometers.

Angle Bar. 

Rolled steel section of L shape.

 Angle Iron. 

Iron or steel stiffener inserted in an angle.

 Angle of Cut. 

The smaller angle at which a pair of position lines intersect on a chart.

Angle of Incidence. 

Angle, at a point in a surface, between a
perpendicular and a light ray coming to that point.

Angle of Position.

In great circle sailing, is angle that great circle track makes with meridian at any given point. In celestial triangle, is angle at the heavenly body which is subtended by the colatitude.

Angle of Reflection. 

Angle, at reflecting surface, between a light ray
and its reflected ray; its value is twice the angle of incidence.

 Angle of Refraction.

 Angle that a refracted ray makes with the line of
its original path.

Angle of the Vertical. 

Difference between the perpendicular at a place
and the extended radius of Earth passing through the place. Arises through Earth being an oblate spheroid. It is, therefore the difference
between True and Reduced latitudes of the place. Value is maximum in Lat. 45° (about) and is minimum at Poles.

Angular Diameter.

Diameter of an observed object when expressed as the angle it subtends at eye of an observer.

Angular Distance.

Distance between two observed points when
expressed as angle it subtends at eye of observer.

Angular Momentum.

 Product of mass, distances from centre and
angular velocities of all particles in a rotating body. Also defined as moment of inertia multiplied by angular velocity. Often called
‘Moment of moments’.

Angular Velocity.

 Rate of revolution whenexpressed as angle passed through in unit time.

Angulated Sails. 

Triangular sails in which upper cloths are parallel to leech, and lower cloths are parallel to foot. Cloths meet at a girth band that is perpendicular to luff.


Star a Phoenicis. S.H.A. 354°; Dec. S 43°; Mag. 2-4.


Process by which metals, and other substances, are heated to an appropriate temperature and then allowed to cool very slowly; so that internal stresses are removed and resiliency and elasticity are restored or induced.

Annual Constituent (of tide).

 That part of a tidal undulation that varies with Earth’s distance from Sun.


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 Annual Inequality.

Variation in a tidal undulation that is more or less seasonal and periodic.

Annual Parallax. 

Apparent displacement of a heavenly body from its true position when caused by Earth’s elliptical movement around Sun. Is negligible in stars.

Annular Eclipse. 

Moon’s occultation of Sun when outside edge of
Sun’s disc is unocculted although centres of both bodies are in line. Due to Moon’s diameter being less than diameter of Sun, through Moon being in or near apogee.


 Irregular: uneven. Applied to motions, intervals and values that are basically uniform but are made irregular through the action of one or more disturbing factors.

Anomalistic Month.

Time taken by Moon to go from perigee to
perigee. Interval is about 27-55455 days.

Anomalistic Period of Planet. 

Time taken by a planet to go from perihelion to perihelion. Interval is irregular through movement of perihelion point.

Anschutz Gyro Compass.

 German type in which three gyros revolve
in air. Sensitive element floats in a mercury bath. Damping is effected by oil.

Answer the Helm.

 A ship is said to do this when she alters her
direction in response to movements of tiller and rudder.


 Region of Earth’s surface south of latitude 66° 33′ S. Pertaining to this region.

Antarctic Circle. 

Region enclosed byparallel 66° 33′ S. Name is often given to the parallel itself.


 Star a Scorpio. S.H.A. 113°; Dec. S 26°; Mag. 1 -2. Diameter is 430 times that of Sun, temperature 3100°A. Name means ‘rivalling Mars’—in the redness of its colour.


People living in same latitude and longitude, but on opposite sides of Equator. They have same length of days, but at opposite times of the year.


To date a document so that its effect counts as from a date previous to the date of signing.

Ante Meridiem.

 Between midnight and noon. Before midday (Latin).


Arrangement of wires for sending or receiving radio waves.

Antenna Resistance. 

Sum of all leaks, resistances and abatements, in
antenna, that reduce maximum current.


Faintly luminous disc seen in sky opposite Sun. Is due to reflection of Sun by ice particles in atmosphere.


Inimical to corrosion. Applied to paints, processes and preparations that are intended to prevent corrosion.


Area of relatively high barometric pressure, around which wind circulation is clockwise in northern hemisphere, and anticlockwise in southern hemisphere. Generally associated with fine and settled weather. (Also called a High).

Anticyclonic Regions.

Areas in about 30° N and 30° S latitudes; in
which anticyclones are fairly prevalent and persistent.


Paints and preparations that attack and kill marine life that tries to attach itself to ship’s underwater skin.


Waterproof leggings.


 Natural number that is represented by a logarithm.


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Antilunar Tide. 

Tidal undulation generated on side of Earth opposite to that on which tractive force of Moon is exerted.


Meteorological term for an area in which meteorological factors and conditions are below normal.


That area of Earth diametrically opposite to a given place; thus having the same latitude and longitude as the place, but of opposite names. Sometimes applied to New Zealand and, less
correctly to Australia, as approximately fulfilling these conditions in regard to Great Britain.


Medicinal substances that prevent or allay scurvy Statutory antiscorbutics are lime, lemon and orange juices.

Anti-Solar Tide. 

Tidal undulation generated on side of Earth opposite to that on which tractive force of Sun is exerted.


High level winds that flow above and opposite to the trade winds. They are not surface winds, and so do not affect seamen directly: they do concern meteorologists.

Anvil Cloud.

Cumulonimbus cloud with wedge-shaped projection of its upper edge. Fairly common in thunderstorms.


 Said of anchor when cable is taut and vertical. Said of yards when they are cockbilled in contrary directions.




That point, in orbit of planet or comet, that is farthest from Sun.


Undecked Grecian ship of classic times.


In optics, means ‘without aberration’. Used when spherical and chromatic aberrations have been eliminated.

Aplanatic Refraction.

 Refraction that has been corrected for spherical

Apogean Range. 

Mean minimum range of an apogean tide; usually > about 0-8 of mean tide.

Apogean Tide.

 Tidal undulation occurring about time of Moon being 1 in apogee. Increase in Moon’s distance from Earth reduces her gravitational and tractive efforts. 1


 Point in Moon’s orbit that is farthest from Earth.


To port; towards to the port side.


Removable fittings of a ship—such as sails, tackling, awnings, etc.—as distinguished from her permanent fittings.


When applied to phenomena means ‘as it appears to the human eye’; so disregarding aberration, speed of light, and other factors.

 Apparent Altitude. 

Altitude of centre of a heavenly body when measured from sensible horizon.

Apparent Area. 

Term used in connection with Sun and Moon, whose areas appear to increase or decrease with variations in Earth’s distance from them.

 Apparent Declination. 

Declination of a heavenly body, as it
appears to an observer, when displaced by the aberration of light.

Apparent Light.*

 Navigational aid that appears to emit a light when it reflects or refracts a light more or less remote. Erected in a position where a light would be difficult to maintain.

Apparent Midnight.

Instant when true Sun transits the inferior
meridian of a place.


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 Apparent Motion. 

Movement of a heavenly body as seen from Earth. Due to Earth’s diurnal rotation, annual revolution, periodic nutation and precession, apparent motions bear little resemblance to the true movements. 2. The movement on a relative radar display of the echo of another ship. It is her motion relative to own ship. (‘Relative Movement,’ ‘Relative Course and Speed’).

Apparent Noon. 

Instant when true Sun is on the meridian at a place.

Apparent Right Ascension. 

Right ascension of a heavenly body as it appears to an observer when displaced by the aberration of light.

Apparent Solar Day.

 Interval between successive transits of true Sun
across any given meridian.

Apparent Solar Time. 

Time based on hour angle of true Sun. Differs from Mean Solar Time by the ‘Equation of Time’. Rarely used in civil time reckoning, but frequently used in navigation.

 Apparent Sun.

 The visible Sun, as distinguished from the fictitious
‘mean’ and ‘dynamical’ suns.

Apparent Time. 

Apparent solar time.

Apparent Time of Change Tide. 

Apparent time of high water at a place at full or new Moon. The Establishment of the Port*.

 Apparent Wind.

 Movement of air past an observer when arising from a true wind and motion of observer. May differ from true wind in direction, force, or both of these, according to observer’s motion relative to wind direction.

Appleton Layer.

 Ionised layer of atmosphere about 150 miles above surface of Earth. Reflects short wave radio.


 A minor who was bound by indentures to serve a shipowner for a specified period—usually three or four years—in return for instruction in the duties of a deck officer, together with food, accommodation, and such money payments as may have been agreed.Terms of apprenticeship were governed by Merchant Shipping Acts.


 Getting nearer. As far as the ‘Collision Regulations’ are concerned, a vessel under way but stopped, or hove to, or in irons, is considered to be approaching a vessel that is getting nearer.


Arrival of a heavenly body at a given meridian, or at conjunction with Sun or Moon. Apron. Canvas protection in leadsman’s chains. 2. Piece of timber, immediately abaft stem of a boat, that takes hooded ends of planks. 3. Curved piece of wood erected on fore end of keel of a wooden ship. 4. Projecting ledge of timber along bottom of entrance to a dock, against which the dock gates are closed.


Point, in orbit of a satellite body, at which the body is nearest to or farthest from the body around which it travels. It is perihelion or aphelion in case of a planet, perigee or apogee in case of Moon.


 Apparatus consisting of bottles of compressed air. reducing valve, and face-mask which enables a swimmer to breathe under water.


Constellation lying, approximately, between R.A.s 21 h and 23h. Has many discernible stars, but all are small: a Aquarii is Mag. 3-2. 2. Eleventh sign of Zodiac, extending from 300° to 330° celestial longitude. Sun is in this sign from January 20 to February 20. Name is Latin for ‘Water Bearer’.


 Constellation lying between R.A.s 19h-20h. Dec. 0°-10° N. Contains important star Altair, a Aquilae.


 Olden instrument for measuring star altitudes. Also called ‘Jacob’s Staff or ‘Cross Staff (q.v.).


 Judging of a matter under dispute by a person, or persons, mutually agreed upon by contending parties, and whose decision the contending parties agree to accept. Rules concerning arbitration are laid down in Arbitration Act, 1889 and 1934.


Part of circumference of a circle. Of sextant, is that part on which the graduations are carried.


Method of ship construction introduced by Isherwood. Sharp bilge of box form was done away with and replaced by an arc form from keel to deck line. To regain displacement lost through removing angle at bilge, beam in region of water line was increased. This results in a definite reduction of immersed midship girth and, due to easy sweep of bilge, improved water flow to propeller. Sea kindliness and economical consumption follow.



Archimedean Screw. 

Name given to screw propeller when first


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Archimedes’ Theorem. 

A body partially or wholly immersed in a fluid
suffers an apparent loss of weight equal to weight of fluid displaced.

Arch Type.

 System of cargo ship construction developed by North-East coast shipbuilders. Outboard sides of holds were curved inward and upward towards hatchways, so that trimming of bulk cargoes was

Arc of Excess.

 That small portion of graduated arc of a sextant in which graduations from zero read in a direction opposite to that of the main graduations; thus allowing small angles below the horizontal to be measured.

Arc Proper. 

Arc of sextant graduated from 0° to 120° (about), and excluding the arc of excess.


Pertaining to area of Earth’s surface enclosed by parallel of latitude 66° 33′ N.

Arctic Air. 

Atmospheric air that has come directly from north polar regions and arrives, eventually, as maritime polar air.

Arctic Circle. 

Parallel of 66° 33′ N. Marks limit of Sun’s visibility when in maximum southerly declination.

Arctic Current. 

Ocean current flowing from Davis Strait, along coasts of Labrador and Newfoundland, meeting Gulf Stream in latitude 41° to 42° N. It then turns eastward. From March onwards it brings down icebergs. Also known as ‘Labrador Current’, ‘Davis Current’.

Arctic Sea Smoke. 

Fog on surface of sea when caused by cold air
moving over warm water.

Arctic Zone. 

Area north of Arctic Circle.


Old name for constellation Bootes. Name is sometimes given to star Arcturus. Is Greek for ‘Bear Watcher’.


Star a Bootes. S.H.A. 147°; Dec. N 19°, Mag. 0-2. Diameter is 30 times that of Sun, candlepower is 100 times greater. Distant 41 light years; temperature 4100°A. Name is Greek for ‘Bear Warden’.


Said of a vessel under sail when she tends to run up quickly into the wind, and requires an unusual amount of weather helm.


Skin layer of fishes. It makes them iridescent by reflecting light.


 Southern constellation in about R.A. 6h to 11 h; Dec. 37°-70° S. Named after mythological ship of Jason. Divided, by Herschel, into various parts: keel (carina), mast (malus), poop (puppis), sails (vela); stars being named by astronomers—but not seaman—after their part of ship. Canopus is principal star. 7 Argus (Carinae) is a variable star, going from Mag. 1 to 1 in 70 years.


Gas forming nearly 1 per cent of atmosphere.


Legendary companions of Jason, in ship ‘Argo’, when he sailed to regain the Golden Fleece. 2. Sea creature, with tentacles and a shell, often seen floating on surface of sea.


Large Adriatic merchant ship of middle ages. Word is used, poetically, for freight-carrying ships in general. Is a corrupt form of Ragusa, the principal port from which the argosy sailed.


When using navigational, or other tables, is the known value, or values, with which the tables are entered.

Aries (The Ram). 

Constellation situated between R.A.s Olh 45m and 03h and Dec. 15° to 25° N. Has navigational stars a (Hamel)


First sign of Zodiac, extending from 0° to 30° celestial longitude. Sun is in this sign from March 21 to April 20 (about). Name is often used as a short form of ‘First Point of Aries’.


 Old or damaged material that remains when repairs or refitting have been carried out.


Any enclosed vessel that will float. 2. Vessel, about the size of a medium liner, built by Noah. 3. Large boat formerly used on rivers of USA for transporting provisions.


A fleet of warships.

Armed Mast. 

A built mast. Armed Merchant Cruiser. Ocean liner taken over by Admiralty, in time of war, armed with guns and other weapons, manned by naval officers and ratings and employed on active service.


 Former astronomical and navigational instrument consisting of rings that represented great circles of the celestial sphere. When aligned and suspended from a point that represented the zenith it indicated position of Ecliptic or Equinoctial. Equinoctial armilla was used to determine arrival of Equinox; solstitial armilla measured Sun’s altitude.

Armillary Sphere. 

Armilla having nine skeleton circles. Used for
astronomical purposes from 3rd century B.C. until 18th century A.D.


 Tallow or soap put in cavity at heel of a sounding lead or sinker to obtain a specimen of sea bed.

Arm of Anchor. 

That part of an anchor which extends from crown to fluke.

 Armstrong’s Patent.

 Humorous nickname for manually-worked


 Temporary detention and restraint of action
when imposed by lawful authority.


Choke end of a common wood block.


Small Foresail of ancient Mediterranean vessels.


Short name for ‘Regulations for Preventing Collisions at Sea’,*—or for the ‘Articles of Agreement’ between master and crew.

Articles of Agreement. 

Legal and binding agreement, entered into by
master of ship and crew, concerning duties, conditions of service and remuneration. Terminates on fulfilment of embodied conditions or on a specified date. May terminate before time intended by mutual consent of master and seaman; by physical inability of seaman to continue service; by wreck or loss of ship.

Articles of War.

 Royal Navy code of discipline. Defines duties and embodies maximum punishments for stated offences.

 Artificial Eye.

Made in end of a rope by unlaying one strand, turning over the part from which strand has been taken, so that an eye is formed, and relaying single strand in opposite direction. Finished off by tucking ends.

Artificial Horizon. 

Perfectly horizontal reflecting surface used when obtaining altitudes where no horizon is available. Mercury is usual, but highly-polished surfaces, correctly levelled, may be used. Can be employed only when ashore. Bubble sextants are the usual alternatives for marine work.

Artificial Projection.

 Projection, of surface or sphere to a plane, in which fixed laws are evident but which entails distortion and alteration of perspective shape of area projected.

Ascending Node. 

Node inwhich Moon or planet passes to northward ofEcliptic.


Formerly: was arc of Equinoctial intercepted
between east point of horizon and First Point of Aries when a heavenly body was rising. Was qualified as ‘right ascension’ when referred to an observer at Equator, ‘oblique ascension’ when referred to an observer away from Equator. The latter term has lapsed.

Ascensional Difference.

Difference between the right ascension and
oblique ascension of a heavenly body. Ascension Verse. French equivalent for the British ‘Sidereal Hour Angle’.


As used in ‘Collision Regulations’, has been ruled as meaning ‘determined distinctly and unequivocally’.


People living in regions where, at some time, they have no shadow: thus living between tropics of Cancer and Capricorn.


Device for detecting submerged submarines, and ascertaining their distance and direction, by making a sound signal in water and timing interval until return of echo. Name is taken from initials of ‘Allied Submarine Devices Investigation Committee’ of 1914-18 war. Now called Sonar.

Ash Breeze.

 No wind at all.

Ash Cat. 

Name given to steam ships, by sailing ship men, in early days of steam.


On shore, on the land. Ship is ashore when aground on or near the shore.

‘As long as the Maintop Bowline’.

 Said of a long-winded statement or yarn; this bowline being the longest in a ship.


Old astronomical term for a planet’s position relative to another planet. Five aspects were Conjunction, Sextile (60° different), Quartile (90° different), Trine (120° different), and Opposition. The first and last aspects still remain. 2. The nearer angle between another vessel’s head and the line of sight. It is expressed in degrees (0° to180°) and qualified red or green according to whether the port or starboard side of the other vessel is visible, e.g. Green 20.


 Those to whom certain rights, or property, have been allotted or transferred by signed document.

Assmann Psychrometer. 

Hygrometer with a clockwork fan that drives
air at a constant rate past wet bulb. This causes exaggerated depression of wet bulb, so giving more precise values of humidity when referred
to appropriate tables.


Those who have insured, or have been insured, against loss.

‘A’ Stars. 

Spectrum classification of stars in which hydrogen lines are very evident. Their light is white, and temperature is 10,000°A. Sirius
and Vega are in this class.


 Arrangement of two or more magnetic needles on a single suspension so that there is no torque when in a magnetic field.


Said of anchor cable when its line of lead approximates a continuation of line of fore stay. Also called ‘short stay’.


Outside a ship and directly behind her. On extended centre line over the stern.


Large number of very small planetary bodies, the mean point of whose orbits lies between Mars and Jupiter at approximate distance (2 8 astronomical units) required by Bode’s Law. Orbits of about 1200 have been observed; between 200 and 300 have been named; many have been observed for short periods only. Vesta is the only one discernible by the naked eye. The largest, Ceres, has a diameter of 480 miles; the majority are very much smaller.


 Lens and mechanism, in a rangefinder, that causes a point of light to appear as a line of light, which can then be used to determine distance off.

Astres Fictifs. 

Name given to hypothetical bodies assumed to be responsible for component tides in harmonic analysis. More usually termed ‘satellites’ or ‘constituents’. Fr. = ‘False stars’.


 Probably oldest of navigational instruments. In its more advanced form consisted of a disc of metal, or wood, graduated in degrees and suspended from a ring representing the zenith. A movable bar, or alidade, pivoted at centre of dial, carried sight vanes that were aligned on observed body. Bar then indicated altitude. In all cases, vertical and horizontal planes were established by plumb line. 2. Optical instrument formerly used in surveying. Now super-seded by theodolite.


Investigations into effects of Sun and Moon on


Conducting of a ship by observations of heavenly
bodies, as distinguished from observations of terrestrial objects.

Astronomical Bearing. 

True bearing of a terrestrial object when
derived from angle between a vertical circle passing through the object and another vertical circle passing through a heavenly body whose azimuth has been computed.

Astronomical Clock. 

Timepiece regulated to measure sidereal time.

Astronomical Cross Bearings.

 Crossed position lines obtained from
observations of celestial bodies.

Astronomical Day.

 Interval between successive transits of mean Sun across a given meridian. Since 1924 it has coincided with the civil day: before then it commenced with Sun’s superior transit and was, therefore, 12 hours slow on civil time.

Astronomical Position Line. 

Line of position obtained by observation
of a heavenly body.

Astronomical Refraction. 

Difference between original direction of a
ray of light, from a heavenly body, and its final direction when it reaches observer. Due to refractive effect of atmosphere.

Astronomical Tide.

 Alternative name for ‘Equilibrium Tide’.

Astronomical Time. 

Time measured directly by hour angle of mean
Sun: noon was thus 00 hours. Previous to January, 1925, this time was basic in navigation.

Astronomical Twilight. 

Interval between Sun’s centre being 12°below horizon and 18° below it. Horizon is not distinct but vestiges of sunlight are refracted or reflected above it.

Astronomical Unit of Distance. 

Earth’s mean distance from Sun (93,005,000 miles). Used for expressing planetary and interplanetary distances.


 The principles of nautical astronomy.


Combination of sciences dealing with nature, movements and appearances of heavenly bodies. Divided into various groups, each giving a prefix to the word; e.g. nautical, physical, descriptive, etc.


Branch of astronomy that considers the physical and chemical properties of heavenly bodies, as distinct from the apparent motions, magnitudes and distribution.


 Instrument for teaching and learning relative positions of heavenly bodies. Star globe is an example.


Line towards which a curve approaches but will never touch. Sometimes defined as a tangent to a curve with point of tangency at infinite distance.


Across ,Transversely.

Athwart Hawse. 

Position of one ship when she is ahead of, and at right angles to, the fore and aft line of a nearby ship.


 Transversely across a ship. From one side to the other.

Atlantic Ocean.

 Expanse of sea between American continent and
coasts of Europe and Africa. Bounded on north by lines made by parallel of latitude from Cape Farewell to Labrador, and by lines from Cape Nansen to Straumness (Iceland), from Gerspin to Fugloe and thence to Stadt. Bounded on south by line one mile south of Cape Horn to 40° S and 20° E. Divided into North and South Atlantic by parallel 4° 25′ N joining Cape Palmas, Liberia, and Cape Orange, Brazil.


Gaseous envelope surrounding Earth. Consists of two layers, the lower, or troposphere, and the upper, or stratosphere. Weight of atmosphere on each square inch of Earth’s surface is approx. 14jlb. at sea level.

Atmospheric Electricity. 

Positive potential in atmosphere that gives rise to electrical phenomena when coupled with negative potential on surface of Earth.

 Atmospheric Pressure. 

Set up by weight of overlying air. At Earth’s surface it is equivalent to about 14j lb. per sq. in. In meteorology, usually expressed in millibars.


Crackling noises that interfere with radio reception.

Atmospheric Sounder.

 Instrument by which sea depth is measured by
increased water pressure compressing air in a small bore tube that is carried down by lead or sinker.

 Atmospheric Tides. 

Caused by attraction of atmosphere by Sun and
Moon. Moon’s atmospheric tide affects barometric pressure less than 0-1 mb. Sun’s tide is swamped by changes due to its heating effect.


Oval, or horseshoe shaped, coral reef bordering a lagoon.


Star a Triang. Australis. S.H.A. 109°; Dec. S 69°; Mag. 1-9.


Said of anchor immediately it is broken out of the ground. Topsails are a-trip when they are hoisted close up, or when just started from the cap preparatory to trimming.

At sight. 

Business term put in a financial document when payment is to be made on presentation to stated person or persons.


Service rendered by being at a certain place at a certain time, even though further service was not required.


Formal declaration that the statements in a document are affirmed by the persons or person signing it.

 At the Dip. 

Position of a flag, pendant or hoist when it is not hauled close up but is a fathom or so short of being so. Answering pendant ‘at the dip’ means that signal is seen but not understood.

Atwood’s Formula. 

For finding righting lever of ship-shaped bodies
when heeled. Vol. of wedge displacement x h,h2
GZ = BG sin 0/ Vol. of displacement

Augmentation of Moon’s Horizontal Semidiameter. 

Increase of Moon’s semi-diameter as she rises above horizon, this increase being up to 18″ of arc greater in zenith than in horizon. Semi-diameter tabulated in Nautical Almanac is based on observer being at centre of Earth and, therefore, at centre of all rational horizons.

Augment of Resistance. 

Increase of resistance that accompanies
increase of ship’s speed. Due to increase in size of bow wave and decrease of pressure on stern through partial cavitation caused by propeller action and increased speed.


Circle of light sometimes surrounding Sun or Moon, andbounded by rings of one or more colours.


Name given to areas of faint luminosity in the night sky, more particularly to those in direction of north or south poles of Earth. Latin for ‘Dawn’.

Aurora Australis. 

Southern ‘Aurora Polaris’.

Aurora Borealis. 

Northern ‘Aurora Polaris’.

Aurora Polaris. 

Tremulant light seen in night towards direction of north or south poles of Earth. Is electrical in origin and may take many forms—arcs, bands, coronae etc. Most frequently seen in latitudes 55°-75° N and 60°-90° S.


A hot south wind. Now only used poetically, but Sirocco was so called at one time.



Australian Current.

 Branch of Equatorial Current, setting southwards along E coast of Australia as far as Sydney.

Australian Sea Carriage of Goods Act, 1924. 

Governing shipment of goods from Australia, whether coastwise or abroad.

Autogenous Welding. 

Joining two pieces of metal by heating each of
them and then welding them together without use of any other metal.

Autographic Instrument. 

Any instrument that makes a graphic record

of its registrations. Barograph is an example.

Automatic Helmsman. 

Machine that is controlled by compass and
controls steering engine. Automatically keeps ship’s head on a pre-selected course.

Automatic Tide Gauge. 

Erection near shore of a tidal river, to indicate
height of tide by a system of floats with a connected pointer that moves over a graduated board. By including a constant in the graduation the height of tide at a distant port can be indicated. 2. Tide gauge fitted with a timekeeping unit and a recording apparatus. Used for recording tidal effects over a fairly long period.

Autopilot/Automatic Pilot. 

Automatic Helmsman.

Autumnal Equinoctial Point. 

That point of intersection of Ecliptic and
Equinoctial at which Sun passes from north to south declination.

Autumnal Equinox. 

That time when Sun passes from north to south
declination (about Sept. 23) and length of day and night are equal in all latitudes.

Auxiliary Angle’A’. 

Quantity necessary when ‘clearing a Lunar’. Was
usually obtained by inspection, but such tables are now unnecessary,and are not given. Value of angle was between 60° and 61 °.

Auxiliary Boiler.

 Boiler in which steam is raised for working auxiliary machinery.

Auxiliary Machinery.

All machinery, in a vessel, other than the main
engines and their attachments.


 Order to stop, or desist from, an action.


Contribution to make good a maritime loss.

Average Accustomed.

 Usual small charges—dock dues, pilotage, etc.,
that normally fall on cargo. Formerly called ‘Petty Average’.

Average Act. 

A general average act.


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Average Adjuster.

 Skilled and competent person who computes the
contributions due from various interests when making good a General Average loss.

Average Adjustment. 

Equitable sharing of the liability to make good a General Average loss. Based on the pecuniary value of the property each party had at stake.

Average Bond. 

Secured undertaking to satisfy a demand for a General Average contribution that is to be assessed. Given to ship by a consignee of cargo, or part cargo, when a General Average claim is pending.

Average Deposit. 

Money payment made to a ship, by a
consignee of cargo, to cover a pending General Average claim.

 Average Deposit Receipt. 

Receipt for a General Average Deposit.

Average Loss.

‘General Average Loss’.

Average Statement. 

Document, drawn up by General Average adjus-
ter, stating liabilities of the various interests concerned in making good a General Average loss.

 Average Unless General.

Denotes that insured goods are not covered by policy when subject to general average.


Water washing over.


To windward. Towards, or on, that side of ship on which wind blows.


Said of an anchor immediately it is broken
out of the ground when cable is up and down.


Said of a flag when stopped in middle to form a wheft.


Canvas spread above a deck to give protection from sun and rain.

Awning Curtain. 

Canvas screen coming downward from side of
awning, and with lower edge stopped to eyeplates in deck.


Light deck erected above upper deck, or main deck as protection against sun and rain.

 Awning Deck Vessel. 

First introduced for conveyance of natives
between Eastern ports. Has large ventilation openings in top side plating. Has full scantlings to second deck; space between second and
upper decks being in nature of a superstructure.

Awning Hitch.

Name sometimes given to ‘Roband hitch’; this being appropriate hitch for securing edge of awning to jackstay when spread.

Awning Shackle.

Elongated D shackle having a roller fitted at abouthalf length.


Plural of ‘Axis’. Intersection of two axes in a
plane, or three axes in space, define a point that is termed the ‘origin’.


Axle, or hinge. In a plane figure is that straight line about which either part may rotate and generate the same solid. In a solid, is that line
about which the solid is symmetrically disposed.

Axis of Earth. 

That diameter around which daily rotation takes place.

Axis of Great Circle. 

That diameter, of a sphere, that passes perpen-
dicularly through a given great circle of the sphere.

Axis of Heavens. 

That diameter, of celestial sphere, around which the daily rotation of the heavens appear to be made. As this apparent rotation is due to Earth’s rotation, axis of heavens usually coincides with Earth’s axis prolonged indefinitely. Astronomical latitude and longitude assume an axis perpendicular to Ecliptic.

Axis of Small Circle. 

That diameter of a sphere that passes perpen-
dicularly through a small circle of the sphere. It is, therefore, axis of a great circle parallel to the small circle.

Axis of Symmetry. 

Straight line that divides a plane figure into two
similar parts.

‘Aye, Aye, Sir’. 

Customary acknowledgement of an order. Means that the order is understood and will be carried out.


Intercepted arc of horizon between observer’s meridian and a vertical circle passing through an observed object.

Azimuthal Projection.

Alternative name for ‘Zenithal’ projection.
Altitude Azimuth Instrument. ‘Alt-Azimuth Instrument’.

Azimuth Circle.

Instrument similar to ‘Azimuth Mirror’, but is not
pivoted at centre; an outer ring, encircling bowl, keeping it centred.

Azimuth Compass. 

Compass fitted to carry an instrument for taking
azimuths at any altitude. Placed so that there is a minimum of obstructions to observations.

Azimuth Mirror.

Instrument for obtaining azimuth of observed
objects by observing object’s reflection in a mirror, or prism, pivoted in centre of glass over compass card. Preceded azimuth circle. Invented by Lord Kelvin.

Azimuth of Heavenly Body. 

Intercepted arc of horizon between meridian and vertical circle passing through body. Generally reckoned from elevated pole through 180° East or West.

Azimuth Prism. 

Alternative name for ‘Azimuth Circle’ or ‘Azimuth Mirror’.

Azimuth Tables. 

Precomputed quantities that give azimuth corresponding to a given time, a given latitude and a known declination.

Azores Anticyclone

Atlantic part of a more or less permanent zone of
anticyclonic weather that girdles Earth in 30° N approximately.