D – Morse Code ▬ ● ●
D flag + six numerals – Code flags; Date.
D shacke – Shackle having its sides parallel to one another.
D. F. Bearing – Position line obtained from a directional radio beam.
Dabchick – Diving bird. Particularly applied to the Little Grebe, which is frequently seen near coast.
Dagger – Piece of timber used to support poppets of bilgeways during launching of a vessel.
Dagger Board – A non-pivoting board slotted into a sailing boat’s keel to minimize leeway; it is raised and lowered through a watertight case and can be entirely removed.
Dagger Keel – Deep and narrow drop-keel.
Dagger Knees – Knees placed obliquely, instead of vertically, to give as much uninterrupted stowage space as possible.
Dagger Piece – Name applied to any oblique member in a vessel’s framing.
Dagger Plank – Plank uniting poppets and stepping up pieces of a launching cradle.
Daily Service Tank – One days fuel pumped up from the bunkers in readiness.
Daltonism – Inability of eye to distinguish between red and green colours. A form of colour blindness.
Dalton’s Law – In a mixture of gases each gas exerts its own pressure independently of the others, the pressure of the mixture being the sum total of the constituent pressures.
Dam – A bank built to contain a waterway.
Damp – To damp fires is to reduce the air supply so that combustion goes on very slowly. 2. To damp a gyro is to constrain its movements to a limited amount. Slightly wet.
Damp Air – Atmospheric air when its water content is about 85% of maximum.
Damper – Bread, risen (aerated) by bicarbonate of soda rather than yeast.
Dampier, William – 17th century British seaman, buccaneer, explorer, hydrographer and cartographer recognised as the first European explorer to land on the Western Australian Coast.
Damping – A torque applied to a gyroscope to assist it in settling in the meridian.
Dan Buoy – Pole or spar with ballasting weight at one end and buoyant unit at middle. Mooring rope, with weighted mooring, is attached to middle. Used by trawlers, surveying vessels, minesweepers and others as a temporary sea mark.
Dand –. Sloop or cutter with a jiggermast right aft, on which a small lugsail is set.
Dandy Note – ‘Pricking Note.’
Dandyfunk – Kind of pudding made from crushed ship’s biscuits.
Danforth Anchor – A light duty stowable anchor with plate flukes that swivel.
Danger Angle – A maximum angle set on a sextant over which a vessel will be navigating too close to an obstruction. See HAS and VSA.
Danger Line – A limiting dotted line marked around a charted hazard.
Dangerous Goods – Commodities that seriously endanger the safety of a vessel in which they are carried. Examples are aquafortis, vitriol, naphtha, benzine, gunpowder, lucifer matches, nitroglycerine, petroleum and explosives, but see ‘ I. M. D. G. code.
Dangerous Quadrant – That half of front of a cyclonic storm that is on the side towards which recurvature is to be expected.
Dash – The longer flash or sign in Morse signalling. Is three times the length of the ‘dot’.
Date Line – Line on which time zones —12 hours and+ 12 hours meet. The time is the same on either side, but the dates are one day different; 180°E being a day in advance of 180°W. This line is mainly, but not entirely, on the 180th meridian; varying between 170°E and 172 1/2 °W, to avoid having different dates in a group of islands, or same area of land. A civil modification of the 180º East or West meridian marking the zone where the date on the globe changes from one day to the next.
Datum – A geographic point, line, or area used as a reference in search planning.
Datum Area – Area where it is estimated that the search object is most likely to be located.
Datum Line – A line, such as the distressed craft’s intended track line or a line of bearing, which defines the centre of the area where it is estimated that the search object is most likely to be located.
Datum Point – A point, such as a reported or estimated position, at the centre of the area where it is estimated that the search object is most likely to be located.
Davis Current – Alternative name for Labrador Current.
Davit – Iron or steel (formerly wood) fitting projecting over ship’s side for attachment of tackle for hoisting and lowering boat, accommodation ladder, anchor, stores, etc. Sometimes fitted at hatch.
Davy Jones – Evil spirit of the sea, who lies in wait for seamen. Said to be a corruption of ‘Dufiy Jones’; ‘duffy’ being a negro word for ‘ghost’, and ‘Jones’ being a corruption of ‘Jonah’. Mythical undersea domain of the devil, Davy Jones, in which drowned seamen are confined.
Davy Jones Locker – The bottom of the sea, where Davy Jones holds drowned seamen and foundered ships.
Dawn – Approximate time for first light. See Astronomical, civil and nautical twilight.
Day – Period of time based on Earth’s revolution on its axis. Its duration is based on successive transits of a point of definition at a given place. This point is, in most civilised countries, based on the mean Sun for civil time, and First Point of Aries for sidereal time.
Day Mark – Shape hoisted, in daytime, by vessels in specified circumstances, and in accordance with international rules. 2. Distinguishing characteristic of a light vessel. 3. Navigational beacon that is not observable at night.
Day Shape – Black shapes shown in daylight to indicate the nature of a vessels condition.
Daylight Hours – Between sunrise and sunset. See twilight.
Days of Grace – Time allowed, beyond a time and date specified during which no action will be taken for non-fulfilment of a contract. In the case of money bills the usual period is three days.
Day’s Work – At one time called ‘Day’s works’. Practical methods of deducing ship’s noon position, usually by dead reckoning, and computing course and distance made good and course to be steered.
Day-sailer – A sailing boat with limited accommodation for short passages.
DC (direct current) – Direct current (D. C.) is a form of electricity often supplied by batteries. It is conducted in a constant direction (see polarity).
De Laval Turbine – Uncompounded turbine that is used for driving pumps and dynamos.
De Vries-Smitt Tide Gauge – Submerged tide gauge used by Netherlands Hydrographic Office. Records variations of water pressure due to change in height of water level; gauge being at constant distance from bottom.
Dead Ahead – Exactly AHEAD on the ships fore and aft line.
Dead Astern – Exactly AFT on the ships fore and aft line.
Dead Beat Compass – Magnetic compass in which swing due to quick alterations of course, or liveliness of vessel, is greatly reduced both in time and amplitude. Has short but very strong needles, and comparatively large bowl.
Dead Calm – Perfectly smooth sea and no wind whatever.
Dead Door – Sliding wooden shutter for blanking square window of a cabin.
Dead Flat – Completely calm sea state. The flat-surfaced midship section of a vessel on the sides or bottom.
Dead Freight – Money paid to ship for failure to provide a full cargo promised.
Dead Head – Solid piece of wood used as anchor buoy.
Dead Horse – Performance of work that has already been paid for.
Dead Lights – Plates fitted over portholes to protect them or to prevent lights inside the ship from showing outboard.
Dead Man – Rope’s end, or small piece of yam or line, when left hanging untidily. 2. Counterbalancing weight that assists guy of derrick.
Dead Men’s Eyes – Early name for ‘Deadeye’.
Dead Neap – Lowest possible high water of a tide.
Dead on End – Said of wind when exactly ahead; and of another vessel when her fore and aft line coincides with observer’s line of sight.
Dead Reckoning – Calculation of a ship’s position by consideration of distance logged and courses steered. Sometimes said to be corruption of ‘deduced reckoning’; but this is very debatable.
Dead reckoning – Estimating a position by plotting a record of courses run and distances sailed.
Dead Rising – Those parts of a vessel’s floor, throughout her length, where floor timbers meet lower futtocks.
Dead Ropes – All ropes, or running rigging, that are not led through a block or sheave.
Dead Slow – Minimum speed that will give steerage way.
Dead Water – Eddy water immediately astern of a sailing vessel or boat.
Dead Wind – Wind directly contrary to ship’s course.
Dead Work – Old name for ‘Freeboard’.
Deadeye – Hard wooden block, pierced with holes, fitted in lower end of shroud to take lanyard for setting up. A block without sheaves.
Deadlights – Metal plate coverings fitted over portholes for greater watertight integrity in heavy weather.
Deadmen – Land based posts that secure the cables of a vehicular cable ferry.
Deadrise – On a body plan of a vessel, the angle between the base or keel line and the turn of the bilge.
Deadweight – Total weight, in tons, of cargo, stores and fuel carried by a vessel at her maximum permitted draught.
Deadweight Cargo – Cargo whose specific gravity is such that a vessel loading it will go down to her marks.
Deadweight Scale – Table, or graph, showing total weight of fuel, stores and cargo, and corresponding mean draught of vessel.
Deadweight Tonnage – It is the difference in displacement in tonnes between the light and loaded conditions. The size of tankers is often given in terms of deadweight tonnage. Ships are usually chartered on the deadweight tonnage.
Deadwood – Flat, vertical surfaces at junction of stem or stern post with keel. Has no buoyant effect.
Deadwood Chock – Blocks of timber, sandwiched and drift bolted together, sawn in the shape of and used as a vertical knee.
Deals – Planks, particularly of fir, 7 to 11 in. in width and 2 to 4 in. thick.
Decca Navigator – A radio aid for fixing positions up to at least 300 miles from the transmitter. A master transmitter ashore controls a chain of other transmitters, designated Slaves. All transmit signals continuously. A ship provided with a special receiver can receive these signals, the phase difference between them being measured by Decometers. The numbers indicated on the Decometers refer to coloured lattice lines printed on special charts. The ship’s position is where the numbered lines cross each other. Now linked with computers to give digital read-out latitude, longitude, course to way points and distance.
Deciles – A score out of ten to indicate ranking.
Deck – Horizontal flooring, or plating, above bottom of vessel. May be continuous or partial. A planked platform on a vessel that provides a surface to stand on.
Deck Beam – Thwartship member that supports a deck and preserves form of a vessel.
Deck Bridge – Former name for a navigating bridge.
Deck Button – A round, steel deck fitting used to guide cables for barge tows.
Deck Cargo – Cargo that must be carried on deck. 2. Cargo that is customarily carried on deck. 3. Cargo actually carried on deck.
Deck Girders – Run longitudinally supporting the deck plating.
Deck Hand – Seaman, other than officer, who serves on deck. Man of 17 years of age, or over, with at least one year’s sea service.
Deck Head – The underside of a deck (your roof when below deck).
Deck Hook – Thwartship frame across apron, to strengthen bow and support fore end of deck. More usually breast hook.
Deck House – A superstructure on the deck of a vessel.
Deck Light – Strong glass bull’s eye fitted in a deck to light a compartment below. 2. A permanent light fitted on a deck.
Deck Line – Horizontal mark, cut in plating of side and painted in a distinct colour, that indicates position of freeboard deck.
Deck Load – Deck cargo.
Deck Log – Log book kept by officer of watch and entered with events, changes of course, weather, log readings, work done and other items occurring during the watch. In harbour, is kept by duty officer.
Deck Nail – Large nail, of diamond section, used for securing deck plank to beam of a wooden ship.
Deck Officer – In general, an officer whose duties are connected with the deck department. Sometimes applied to the duty officer of the deck or watch.
Deck Passage – Voyage of a passenger for whom no accommodation is available. Confined to short voyages and trades, such as the carrying of pilgrims.
Deck Pipe – Navel pipe, through which chain cable passes to chain locker.
Deck Shee –. Studdingsail sheet that leads directly from sail to deck.
Deck Stopper – Formerly, length of very strong rope to which cable could be lashed; one end of a stopper being secured to deck. Name is sometimes given to any fitting on deck for holding cable for a short time.
Deck Transom – Formerly, a horizontal timber under counter of a ship.
Deck Watch – Watch that is used for timing sights taken on deck. Is compared with chronometer before and after sights are taken, so avoiding disturbance of chronometer.
Declination – Angular distance, of a heavenly body, north or south of Equinoctial. 2. Former name for variation of compass.
Declination Circle – Great circle, of celestial concave, that is perpendicular to Equinoctial. Also called hour circle, of circle of Right Ascension.
Declination Inequalities – Variations in heights or intervals of high and low waters of tides when due to variations in declination of Sun and Moon.
Declivity – The slope of a shipway to allow for ease of launching.
Deconsolidation Point – A place where cargo is ungrouped for distribution.
‘Deep’ – Leadsman’s call before naming a sounding in fathoms that is not marked in lead line.
Deep – Navigable channel bounded by shoal water. 2. Applied to frames and stringers that have been widened, by extending plate between angle bars, to give additional strength.
Deep Floor – Any of the floors in the ends of a vessel that, due to the converging sides of ship, become deeper than those in the main body.
Deep Frame – A frame whose transverse dimension is wider than standard.
Deep Sea Lead – 28-lb. lead used for taking soundings by hand in deep water.
Deep Sea Leadline – One-inch cable laid rope, 100 fathoms long, used with deep sea lead. Marked as hand leadline to 20 fathoms, then every 5 fathoms.
Deep Sea Sounding – Ascertaining sea depths beyond reach of hand lead. Also applied to a sounding exceeding 100 fathoms.
Deep Sea trade – The traffic routes of vessels which are engaged on the high seas.
Deep Six – To give it the ‘deep six’; to permanently dispose of something unwanted. (it probably will rest under six fathoms of water).
Deep Stowage – Any cargo stowed in single hold ships.
Deep Tank – Ballast tank extending from ‘tween deck to bottom of ship, and from shipside to shipside. Has centre fore and aft bulkhead, with valve between compartments. May be utilised for cargo.
Deep V – A hard chine power boat having a 15 degree or more angle deadrise at the transom.
Deep Waist – Upper deck in a ship with high forecastle and poop.
Deep Waisted – Said of a ship having a deep waist.
Deface – To strip a wooden ship of her planking and leave the ribs bare.
Definition – A measure of the degree of detail on a radar display.
Deflector – Instrument invented by Lord Kelvin for measuring directive force of a compass mounted in a steel or iron ship. Measurements are made with ship’s head on four cardinal points.
Degaussing – Neutralising magnetic effect of steel or iron vessel by encircling her with wires carrying electric current. Used as protection against magnetic mines.
Degree – Originally, arc of Ecliptic travelled by Sun in one day. Now, angle subtended by 1/360th of circumference of a circle.
Degree of Dependence – Measure of probable error in an observation or assessment.
Dekad – Meteorological name for a period of ten days.
Delambre’s Analogies – Formulae for solving spherical triangles in terms of those used for solving plane triangles.
Delta – Triangular area of sediment in mouth of a river, so giving river more than one discharging channel.
Delta Metal – Alloy of copper, zinc and iron. Much used for engineering purposes.
Delta T – The dry bulb temperature less the wet bulb, it shows evaporation rate. Used by farmers for determining spraying conditions.
Demand Respirator – An atmosphere-supplying respirator that admits breathing air to the face piece only when a negative pressure is created inside the face piece by inhalation.
Demi-Culverin – Naval gun of Tudor times. Threw ball of 9-10 Ib.
Demise – Temporary transfer of a vessel to another party under such terms and conditions that the owner ceases to have any control over her for the period of the charter.
Demurrage – Money paid to shipowner, by charterer, when his ship is detained beyond the lay days mentioned in charter party.
Deneb Adige – Star α Cygni. Usually called ‘Deneb’. S. H. A. 50°; Dec. N. 45°.
Deneb Aleet – Old name for star Denebola.
Denebola – Star β Leonis. S. H. A. 183°; Dec. N. 15°; Mag. 2.2.
Density – Mass per unit volume.
Departure – The distance made good due East or West when sailing on any course. The event of a vessel beginning its voyage. The bearing of a coastal object from where a vessel commenced dead reckoning.
Departure Course – Course made good from a point of reference at which a voyage, or stage of voyage, commenced.
Departure Distance – Distance of a ship from a point of reference at which a voyage, or stage of a voyage, commenced.
Deposit Receipt – Acknowledgement of receipt of a sum of money, from a receiver of cargo, when a general average contribution is likely to be claimed.
Deposition – Statement made on oath or affirmation.
Depression – Of horizon, is angular distance of visible horizon, or shore horizon, below sensible horizon. Usually termed ‘Dip’. 2. Atmospheric mass in which barometric pressure is lower than that of surrounding atmosphere. A meteorological low pressure system.
Depression of Wet Bulb – Amount, in degrees, that registration of wet bulb thermometer is less than that of dry bulb. Occasionally there may be a negative depression when temperature is falling quickly. Depression is usually zero in fog or wet mist.
Depth – Of boat, is vertical distance from level of gunwhale to keel. 2. Of flag, measure of its vertical length. More usually termed its ‘breadth’. 3. Of hold, is vertical distance from underside of beam to top of keelson. 4. Of sea, is distance, in fathoms, feet, or metres from level of low water spring tide to sea bed. 5. Of sail, is vertical distance from head to foot of square sail; length of leech of a fore and aft sail.
Depth Charge – Canister of explosive detonated at a required depth by a hydrostatic valve. Used against submerged submarines.
Depth Finder – Lead having a vane attachment that measures depth on the same principle that a towed log measures horizontal distance. See ‘Harpoon Depth Finder’.
Depth Moulded (D) – The vertical distance between the moulded base line and the top of the beams of the uppermost continuous deck measured at the side amidships.
Deratisation – Extermination of all rats aboard a vessel.
Derelict – Floating vessel that has been totally abandoned.
Derrick – Boom or spar used for hoisting or lowering weights. Made of wood or steel, controlled by guys, supported by topping lift, and pivoted at lower end.
Derrick Post – Stump mast used for taking topping lift of a swinging derrick.
Descending Latitude – Decreasing celestial latitude of Moon or planet.
Descending Node – That point in Ecliptic at which Moon passes to South (minus) celestial latitude.
Deserter – One who leaves, or remains away from, his ship without permission and shows no intention of eventual return.
Desertion – Leaving, or remaining away from, a ship without permission and showing no intention of eventually returning.
Despatch – Quickness in performance. 2. To send away.
Despatch Money – Agreed amount paid by shipowner to receiver of cargo when cargo is discharged in less time than that contracted.
Destination – Port to which a vessel is bound, or at which cargo is to be delivered.
Destitute Foreign Seamen – In M. S. A. is applied to certain Asiatics, Africans, South Sea Islanders and foreign seamen of countries who have no Consul in the United Kingdom under M. S. A. 1970.
Destroyer – ‘Torpedo Boat Destroyer.’ Fast, unarmoured, warship armed with torpedoes and guns, capable of attacking large warships with her torpedoes and submarines with depth-charges.
De-Superheater – Appliance for removing excess heat from superheated steam that is to be used for auxiliary machinery. Generally effected by an automatically controlled system of water spraying.
Detention – The holding of a vessel in a port—without resorting to seizure, arrest or capture—by a sovereign power or competent authority.
Determination – Exact ascertainment of position, amount, or other required information.
Detresfa – Immediate SAR required – See distress phase.
Development – A technique where lines representing a curved surface are drawn on a flat sheet.
Deviation – Applied to a voyage, is an unjustified and unnecessary departure from normal course or customary route; delay in sailing, tardiness on voyage, arrival at port other than that intended, or any divergence that makes the voyage other than that intended.
Deviation (of Compass) – Angle that compass needle makes with the magnetic meridian at a place when due to attracting forces in ship or cargo.
Devil – Deck seam between ship’s side and outboard line of planking.
Devil Fish – Large fish of ray family. Has enormous head, and is 3 to 5 ft. In length.
‘Devil to pay and no pitch hot’ – Refers to ‘devil’ deck seam. Means a difficult job to be done and no preparation made.
Devil’s Claw – Two-pronged hook, or claw, that drops over side of link of cable. Attached to deck and used for holding cable temporarily. A securing device to hold the anchor and cable in its stowed condition.
Dew – Particles of water deposited by atmosphere when in contact with a surface whose temperature is below that of dew point.
Dew Point – Lowest temperature to which air can be cooled without condensation of its water vapour. Should temperature fall below this point fog or mist may form.
De-zincification – The common leaching of zinc from the alloy brass in the marine environment that renders it brittle.
Dghaisa – Open boat with greatly extended stem and stem posts. Peculiar to Malta. Two oars are pushed.
Dhobi – Washing clothes.
Dhow – Arab sailing vessel of about 150-200 tons. Has one mast and very large lateen sail.
Diacoustics – Science of direct sound.
Diagonal – Any knee, plank, brace, etc., that is placed diagonally. 2. Line cutting a body plan in an oblique direction.
Diagonal Buil –. Said of wooden boats and vessels in which side planking is made up of two layers at an angle of 45° with keel, upper layer crossing lower layer in opposite directions.
Diamagnetic – Name given to substance whose magnetic permeability is less than unity. 2. A substance which, when magnetised, lies across lines of magnetic force.
Diametral Plane – Great circle of a sphere.
Diamond – Stay to support the mast centre laterally.
Diamond Knot – Fancy bend in two ropes’ ends made by interlacing them. Similar to ‘Carrick Bend’. 2. Knot formed in a rope, somewhat similar to single ‘Turk’s Head’.
Diaphone – Sonic fog-signalling apparatus that gives a high note that descends to a low note of great carrying power. Fitted in light vessels.
Diaphragm – A rubberised membrane that when repeatedly distorted by a reciprocating handle results in positive displacement pumping action.
Diatom – Microscopic phytoplankton.
Diatomic Ooze – Yellowish-brown ooze containing the algae ‘bacillareophyta’. Found at depths from 600 to 2000 fathoms.
Dicrotum – Boat propelled by two oars.
Dielectric – Insulating material that prevents conduction of electricity but allows induction. Used in electrical condensers. Insulating material.
Diesel Engine – Oil engine in which ignition of fuel is caused by compression. Cycle comprises air compression, fuel injection, ignition, and scavenging. Cycle may be completed in two or four strokes.
Difference of Latitude – Angular value of arc of meridian intercepted between parallels of latitude passing through two different positions.
Difference of Longitude – Angle at pole, or intercepted arc of Equator, between two meridians.
Difference of Meridional Parts – North South distance expressed in units of longitude on a Mercator chart.
Differences (Tidal) – Amounts that heights or times of high and low water at a given place differ from the corresponding heights and times at a port of reference.
Differential Block – Wheel with two sets of sprockets around its circumference, one set being on a smaller diameter than the other, and so having less sprockets. Endless chain is laid in each wheel, each having hanging bight. Weight is lifted in bight of larger wheel, power is applied to bight of lower.
Differential Global Positioning System (DGPS) – Refines a ship stations G.P.S. positions by referring those to simultaneously found readings obtained by a shore system with known position. Error in East and West can be calculated from the later and assumed to equally apply to the ship station.
Differentiator – A radar rain clutter control.
Diffusion – The dispersion of a gas or liquid within another. The permeation of battery acid into the active plates surface.
Digital – Display of data presented by numerical digits.
Digital Selective Calling System (DSC) – using digital codes which enables a radio station to establish contact with, and transfer information to, another station or group of stations. Dangerous goods, solid cargoes and containers.
Dikrotos – Ancient Greek vessel similar to bireme.
Dilution of Precision (DOP) – an indication of the quality of the signal being received from the satellite. Dilution of precision can be horizontal, vertical, position and time. These are then combined and given as a GDOP (Geometric Dilution Of Precision). The smaller the number the better. The GPS selects satellites based on GDOP.
Dingbat – Slang term for a small swab made of rope and used for drying decks.
Dinghy – Small boat, about 10-14 ft. long, pulling two oars and fitted with mast and one or two sails. A yachts tender.
Diode – A one way electrical valve, used to rectify AC into DC current.
Dioptric – Applied to lenses and lights when concentration of light rays is obtained by refraction.
Dip – Angular amount that visible horizon is below horizontal plane due to height of observer’s eye. 2. Angle that a freely-suspended magnet makes with horizontal plane when aligned with lines of magnetic force. 3. To lower a flag a small distance, either as salute or signal. 4. To commence to descend in altitude. 5. To pass a rope, end of spar or other article down and under an obstruction. 6. Amount of submergence of a paddle wheel.
Diphda – Star β Ceti. S. H. A. 350°; Dec. S18°; Mag. 2.2.
Dipper – Ladle used for baling a boat. 2. Name is common in U. S. A., and in Britain, for constellation Ursa Major.
Dipping a Light – Sailing away from a navigational beacon light and so causing it to dip below horizon.
Dipping Colours—Ensign – Lowering national colours as a salute.
Dipping Distance – The distance at which an object of known height viewed from a known altitude will disappear below the horizon.
Dipping Lug – Lugsail that has to be lowered a little, when going about, so that throat of sail and end of yard can be dipped round mast.
Dipping Needle – Magnetic needle on horizontal axis; used when measuring inclination of Earth’s magnetic force.
Dipsy – Name sometimes given to deep sea lead. 2. Float on fishing line.
Direct Current – Electrical current flowing in one direction. A is a form of electricity often supplied by batteries. It is conducted in a constant direction (see polarity).
Direct Motion – Movement in space that is in direction of Earth’s rotation and Sun’s apparent motion in heavens. All planets have direct motion. Applied to movement of planet when its right ascension increases.
Direct Tide – Undulation of tide that synchronises with Moon’s transit at a place.
Directing Force – That component, of magnetism of a compass needle, that directs the needle into the magnetic meridian.
Direction – Of wind, is compass point from which it blows. Of current, is direction towards which it sets.
Direction Finder – Instrument for finding the bearing of a transmitting radio station or radio beacon.
Directive Force – ‘Directing Force.’
Dirk – Short sword forming part of R. N. midshipman’s uniform. Also, colloquial name for a seaman’s knife.
Disabled Vessel – One unable to sail efficiently or in a seaworthy state as a result of engine trouble, damage to the hull or ship’s gear.
Disbursement – The paying of money. Sum of money paid out.
Disbursements – Sums of money paid out of a fund credited or allotted.
Disc – Circular face of a solar system body.
Discharge – To put cargo out of a ship and obtain freedom of responsibility for it. 2. To pay off a man, or crew, and relinquish all claims for service. Discharge Book. Continuous record of a seaman’s service at sea. Contains names and particulars of ships served in, rating, reports on character and ability. Held in custody of master while serving in ship.
Discharge Book – Record of a seaman’s service.
Discipline – Due and honest rendering of service and obedience. Equitable coordination of duties and responsibilities for the common benefit. Maintenance of proper subordination.
Discrimination – Radar ability to show targets which are close together as separate identities.
Disembark – To come out of a ship. To put out of ship and put ashore.
Disengaging Gear – Applied to fittings, to boat and falls, that release a boat from her falls simultaneously and rapidly.
Dismast – Carry away, or remove, the mast or masts of a vessel.
Dispatch – ‘Despatch.’
Dispatch Money – ‘Despatch Money.’
Dispatch Note – ‘Despatch Note.’
Displacement – Amount of water displaced by a floating vessel in a given condition. May be expressed in tons, or volume in cubic feet; tons being weight of vessel and contents, volume being that of immersed part of vessel.
Displacement as a Mass – This equals the quantity of water displaced and as the kilogram is the unit of mass and 1000 kg = 1 tonne this is the unit which is used when referring to the size of a ship.
Displacement as a Volume (▼) – This is the size of the hole in the water occupied by the ship measured in cubic metres. There is no density correction.
Displacement as a Weight. (▲) – This is the weight of water displaced by the ship and equals the volume displaced multiplied by a constant representing the density of water.
Displacement Hull – A type of hull that plows through the water, displacing a weight of water equal to its own weight, even when more power is added.
Displacement Tonnage – This represents the amount of water displaced by a ship, expressed in tonnes. (1 tonne = 1000 kg). The size of ships is always given in terms of displacement tonnage.
Display – Visual presentation of received radar signals. Relative Display. The observer’s position remains stationary and the movement of targets (coastline, ships, etc.) is thus relative to the observer. Stabilised Display in which the heading marker and bearings of targets are stabilised by a transmitting compass. True-motion Display. The observer’s position moves across the display in accordance with his ship’s course and speed. Movements of targets are thus in their proper direction and at their proper speed.
Disrating – Degrading from one rank or rating to a lower. Withdrawal of a rating given to a man.
Distance – A separation of between one point and another expressed in units of length, for navigational purposes these being divisions of a nautical mile (equal to 1852 metres).
Distance of Visible Horizon – Varies with height of observer’s eye. Can be found, in miles, from product of square root of height of eye, in feet, and constant factor of 1.15.
Distance Recorde –. In general, any log or log mechanism that records distance.
Distant Signals – System of shapes used between ships when far apart in daytime, and colours of flags were indistinguishable.
Distiller – Combined condenser and aerator used when converting steam to drinking water.
Distortion of Charts – See ‘Chart Distortion’
Distraint – Legal seizure of ship or goods in satisfaction of a debt.
Distress – In a state of danger and in need of assistance. Also alternative name for ‘Distraint’.
Distress Phase – A situation wherein there is reasonable certainty that a vessel or other craft, including an aircraft or a person, is threatened by grave and imminent danger and requires immediate assistance.
Distress Signal – A flag, sound, light, or radio signal meaning a vessel is threatened by grave and imminent danger and requires immediate assistance.
Distress Signals – Customary and statutory indications that a vessel, or her personnel, are in danger and in need of assistance.
Distressed Seaman – Seaman, who, through no fault of his own but through some event in his employment, is in need of assistance, to maintain himself and to return home or to a proper return port.
Distributor – A rotating mechanism for internal combustion engines, to distribute high tension electricity to the spark plugs. It houses the cam operated breaker points for the primary circuit.
Ditch – Colloquial name for the sea. To ditch is to throw overboard.
Ditcher – Name given to a small light draught vessel that can navigate narrow, shallow channels.
Ditching – The forced landing of an aircraft on water.
Ditty Bag – Small canvas bag in which a seaman keeps his small stores and impedimenta.
Ditty Box – Small wooden box, with lock and key, in which seamen of R. N. keep sentimental valuables, stationery and sundry small stores.
Diurnal – Daily. Occurring once a day.
Diurnal Aberration – Apparent error in position of heavenly body due to light rays from the body being received by an observer who is being moved by Earth’s diurnal rotation.
Diurnal Arc – Apparent arc made in the sky, by a heavenly body, when due to Earth’s diurnal rotation.
Diurnal Circle – Circle in celestial concave in which a heavenly body, when viewed from Earth, seems to move.
Diurnal Components – Those tidal components whose maximum values are attained once a day approximately.
Diurnal Inequality of Tides – Difference, in time or height, between two successive semidiurnal tides when a diurnal factor has affected one tide differently from the other.
Diurnal Liberation – Parallactic effect due to Earth’s rotational movement, in which we see a little around western side of Moon when she is rising, and a little around eastern side when she is setting.
Diurnal Motion – Measure of arc through which a solar system body moves in celestial concave during a day. Also applied to apparent movement of heavenly bodies when due to Earth’s rotation on axis.
Diurnal Parallax – Difference between position of heavenly body, when viewed from a point on surface of Earth, and its position when viewed from centre of Earth. Difference varies throughout day.
Diurnal Tide – Tide that has one high water and one low water in each day.
Diurnal Variation of Barometer – Small rise of barometric pressure between 4 a. m. and 10 a. m., then fall until 4 p. m., followed by rise till 10 p. m. and fall to 4 a. m.
Diver – One who goes under water. Particularly applied to man who goes under water in a special dress in which he can be supplied with air. 2. Long-necked bird that dives into ocean in search of fish.
Diver’s Palsy – ‘Caisson Disease.’
Dividers – Instrument for measuring distance on a chart with two legs connected at one end by a movable joint.
Divisions – Daily morning muster of ship’s company in R. N. Men muster by divisions and proceed to prayers. Introduced by Kempenfeldt, 1780.
Dock – Artificial excavation or construction in which ships can be placed for loading, unloading, fitting out, or repairing. Principal types are wet, dry and floating docks.
Dock Dues – Money paid for use of a dock and its equipment.
Dock Pass – Receipt for dock dues paid, and authorisation for ship to leave dock and proceed to sea. Authorisation for a person to leave or enter a dock area.
Dock Rent – Charges made for storage of goods in a dock warehouse.
Dock Warrant – Receipt given by dock warehouseman for goods deposited with him.
Docket – Label or document giving particulars of goods to which it refers.
Dockinaster – Official in charge of a dock.
Docking – Placing of a vessel in dock. 2. Overhaul of a vessel in dock.
Docking Bridge – Small thwartship bridge on poop, to give clear view to officer in charge aft when docking a ship.
Docking Keel – Name sometimes given to bilge keel.
Docking Light – A light near the bow of a vessel used to guide the operator when mooring or docking, not used for a navigation light.
Docking plan – A detailed plan and profile of the lower hull structure required to correctly position a vessel in a slipping operation.
Docking Stresses – Particular stresses set up in a ship in dry dock. Due to lack of water support. Most important are compressive stresses on bottom, shearing stresses in decks, tensile stresses at upper edges of floors.
Docks Regulations – Rules and regulations governing ships when in a dock.
Docks Regulations – Those sections of the Factory Act 1961 that apply to the loading, unloading, handling and moving of goods in a ship or dock, or on wharf or quay.
Dockyard – Enclosed space containing docks, storehouses and workshops, and having facilities for the fitting, refitting and repair of ships.
Doctor – Usual nickname for a ship’s cook.
Dodger – Small piece of canvas spread as wind screen for man on watch.
Dog – Frequently used to denote something small e. g. dog watch 2 hours instead of 4. Also found in gripping closing or holding e. g. dog shore, dog clips.
Dog Clips – Fastenings on a watertight door or watertight hatch.
Dog Shores – The last supports knocked away during the launch of a ship.
Dog Star – Sirius, α Canis Majoris.
Dog Vane – Small piece of bunting stopped to shroud, when under sail, to indicate wind direction to helmsman.
Dog Watch – One of the two-hour watches between 4 p. m. and 8 p. m., introduced to effect changes in watches kept on consecutive days.
Dogger – Dutch fishing vessel, with two masts, employed on Dogger Bank.
Dogging – A particular form of whipping applied to the working ends of a splice.
Doghouse – Enclosure for weather protection and controls at after end of cabin.
Dog’s Lug – Projection of boltrope of sail, between earing cringle and reef cringle, when sail is reefed.
Dog-watches – Half watches of two hours each, from 4 to 6 and 6 to 8 pm.
Doldrums – Comparatively windless zone, along Equator, that separates the prevailing winds of north and south latitudes.
Dolly – A heavy tool held against and supporting a rivet head, while the rivet shank is shaped by repeated hammer blows.
Dolphin – Mammalian marine creature that frequently sports around ships’ bows at sea. 2. Iron or wood structure, in harbours, for mooring of ships. 3. Moored spar to which a ship can be moored. 4. Plaited cordage formerly put around mast, immediately below jaws, to support yard if lifts were shot away.
Dolphin Striker – Spar vertically below end of bowsprit to give downward lead to martingales of jib boom and flying jib boom.
Dominical Letter – Letter that Sundays will have in a given year when January 1 is A and days are successively lettered from A to G.
Donkey – Short form of ‘Donkey Boiler’, ‘Donkey Engine’ or ‘Donkeyman’.
Donkey Boiler – Small boiler, often vertical, used for generating steam for winches and other machinery used in harbour.
Donkey Engine – Small steam winch used in sailing ships to reduce number of men required when weighing anchor, pumping, or working cargo.
Donkey Topsail – ‘Jack Topsail’.
Donkeyman – Rating who tends a donkey boiler, or engine, and assists in engineroom.
Donkey’s Breakfast – Merchant seaman’s name for his bed or mattress. Which until the 1930’s was a bag of straw.
Dorade Ventilator – A ventilator in a box. A projecting pipe stands above the deck level so that water entering the box flows past but air is directed into the cabin.
Dory – Flat-bottomed boat with sharp ends, and sides sloping upward and outward. An advantage is that they stow one inside the next. 2. Edible fish sometimes found in British waters. Has spiny rays along back and and on lower side.
Dot – Short flash in Morse signalling. One-third length of ‘dash’.
Double – To alter course round a point of land.
Double Altitude – Two altitudes of one heavenly body, with an elapsed interval; or approximately simultaneous altitudes of two bodies. Taken to obtain position lines.
Double Bank – To put two men to pull one oar.
Double Banked – Said of a boat in which two oars are pulled on one thwart. Said of an oar pulled by two men.
Double Block – Pulley block having two sheaves on the same pin.
Double Bottom – The space between the inner and outer bottom plating of a vessels hull, mainly used as water or oil storage tanks.
Double Chronometer – Name given to the finding of a ship’s position by Sumner’s Method, and using two heavenly bodies sufficiently distant from the meridian.
Double Clewed Jib – Four-sided jib with two clews. Introduced by Sopwith in ‘Endeavour’, 1934, to take place of jib and jib top sail.
Double Compound Engine – Reciprocating engine consisting of two engines having h. p. and l. p. cylinders.
Double Diagonal – Double diagonal or cold moulded – uses strips of plywood or solid wood veneers laid over the hull in layers of opposite diagonals, glued together, most often with epoxy.
Double Ender – A boat with a pointed or canoe stern.
Double Headsail – Two sails forward of the mast as in a cutter.
Double Luff – Purchase having two double blocks with standing part of rope made fast at head of one block.
Double Pole Switch – A safety switch that simultaneously isolates both the active (positive) and neutral (negative) conducting wires of the electrical circuit.
Double Sheetbend – Used to securely join ropes of the dissimilar sizes. It can be held under strain while being tied.
Double Skin – Double watertight hull construction.
Double Summer Time – See ‘Summer Time’.
Double Tide – Occurrence of two high waters in one semidiurnal period. Noticeable at Portland, Southampton and other places.
Double Topsail – Two topsails, without reefs, that take the place of a large topsail that can be reefed. Sail area is reduced by furling upper topsail.
Double Up. (Moorings.) – To double a vessel’s mooring lines.
Double Whip – See ‘Whip’.
Doubler – A steel plate placed over existing for added strength under deck fittings or for damage repair.
Doubling – Sailing round a point of land. 2. Extra strip of canvas stitched to sail for strengthening. 3. Turned in edge of sail that takes boltrope. 4. Piece of timber on after side of wooden bitts. 5. Additional timber fastened to outer skin of vessel when working amongst floating ice. 6. Generally applied to any lap of plate, planking or canvas.
Doubling Angle on Bow – Method of finding distance from a fixed point, or object, by measuring distance run from a point where its angle on bow has certain value, to another point where the angle on bow of same object, is double the value of the first. Distance run between bearings will be equal to
Doublings – Those parts of a built mast where the upper end of one mast lies abaft the lower part of a mast extending above it.
Douglas Protractor – Square, transparent, protractor with a graticule of squares, and degrees marked on the edges.
Douglas Sea and Swell Scale – International scale for recording state of sea by a figure between 0 and 9; and swell by figures between 00 and 99, upper and lower figures inclusive.
Douse – To put out a small fire. To put out a light. To lower a sail quickly and suddenly.
Dousing Chocks – Pieces of wood laid across apron of wooden ship, and extended to knight heads.
Dow – ‘Dhow.’
Dowel – Small circular piece of wood let into deck plank to cover countersunk head of fastening bolt.
Dowelling – Joining wood spars by making shaped projections, on one of the parts, fit into corresponding cut-out portions in the other part, then securing with dowels or treenails.
Down – Said of a tiller when it is put to leeward while sailing.
Downburst – Violent or damaging downdraught of wind during a thunderstorm.
Downhaul – Rope rove for hauling down purposes. Especially applied to rope by which jib, staysail, jaw of gaff, or flag are hauled down.
Downton Pump – Double-acting pump in which piston is solid, and valves are so placed as to be easily accessible for clearing. Used for pumping bilges, or for sea suction.
Downwind – In the direction that the wind is moving. In a position that is further away from the source of the wind than another vessel or feature.
Dowse – ‘Doused
Drabler – Strip of canvas laced to bonnet of square sail to increase its area.
Draco – Winding constellation between Lyra and Ursa Minor.
Draft – To draw a plan. American spelling of draught.
Drag – To draw an anchor along the bottom. 2. Difference between propeller speed and ship’s speed through water when ship is going faster than propeller’s speed. 3. Alternative name for ‘Drogue’.
Drag Anchor – Old name for ‘Drogue’ or ‘Sea Anchor’.
Drag Net – Net dragged along the bottom by fishing vessel.
Drag Sheet – Sail laced to a spar that is weighed at foot, and used as a drogue.
Dragon – 1. Norse Longship of about 900 A. D. of largest size. The biggest had a keel 148 ft. long and rowed 68 oars. Named from its figurehead. 2. Northern constellation ‘Draco’.
Dragon Boat – A decorated many paddled canoe used for racing.
Drail – A lead weighted fish-hook and line for dragging below the surface.
Drain Well – A sump that collects water seepage for pump out.
Draught – The distance between the lowest part of a vessel and her waterline. Fullness of sail created by sail maker, called camber or draught. It can be altered by bending middle of mast forward and bending boom downwards.
Draught extreme (TE) – This is obtained by adding to the draught moulded the distance between the moulded base line and a line touching the lowest point of the underside of the keel. This line is continued to the FP and AP, where it is used as the datum for the sets of draught marks.
Draught Guage – Draught Indicator.
Draught Indicator – Instrument fitted inside a ship to indicate draught at which she is floating.
Draught Marks – Figures cut into stem and sternpost and painted. Used for ascertaining draught at any moment and for finding trim.
Draught moulded (T) – – The draught measured to any water-line, either forward or aft, using the moulded base line as a datum.
Draught, load – Draft at load displacement.
Draught, mean – The average between bow and at stern marks.
Draughts – Old name for charts or plans.
Draw – To submerge hull a specified distance. To require a stated depth of water to be afloat. 2. Sail is said to draw when filled with wind and straining at sheets and attachments to ship. 3. To draw a jib is to shift it to leeward when aback. 4. To draw a splice is to withdraw the spliced strands.
Drawback – Money paid back. More especially applied to refund of import duties when goods are re-exported; and to remission of excise duties on goods of home manufacture, when consigned to a port abroad.
Drawee – Firm or persons responsible for redeeming a bill of exchange or money order.
Drawknife – A two handed carpentry tool similar to a large spokeshave used to shape spindles, shafts and barrel staves.
Dredge – To remove material (sand, gravel or shellfish) from the sea floor. To manoeuvre a vessel across a tidal stream by paying out anchor cable with the helm hard over, hence driving the vessel from one side of a river to the other.
Dredged Channel – A channel that has been artificially widened or deepened for the safe passage of vessels etc.
Dredger – A vessel that removes material from the sea floor in order to provide a deeper navigable channel.
Dredging – Manoeuvring a vessel in a tideway by dragging an anchor on bottom and using difference in speed, between rate of current and speed over ground, for steerage purposes.
Dress Ship – To pay compliment or respect by hoisting flags at mastheads, bow and stern. To dress ship overall is to hoist ensigns at mastheads and a continuous line of flags from stem to fore masthead, between mastheads and from after masthead to stern.
Dressing Line – Line to which flags are stopped when preparing to dress ship.
Dressing ship – To display flags from bow to stern (over the mast) in celebration.
Drier – A refrigerator component that removes water from the refrigerant.
Driers – Pastes or liquids mixed with oil paints to accelerate the solidifying of the oil.
Drift – Name given to ocean current that is generated and maintained by a more or less constant wind. 2. To be carried along by a current. 3. Distance a current flows in a given time. 4. Tapered steel tool of circular section. Used for fairing rivet holes.
Drift Anchor – Sea anchor. Drogue.
Drift Angle – Difference between course steered and course made good when due to action of current.
Drift Bolt – A joining rod that is driven into timber using a sledge hammer.
Drift Current – A surface current set in motion by a constant wind.
Drift Error (De ) – SAR term for the displacement in position over time of a searched object due to the wind and current it experiences.
Drift Ice – Ice in an area containing several small pieces of floating ice, but with total water area exceeding total area of ice.
Drift Lead – Hand lead dropped on bottom, and with end of line made fast inboard, to indicate if an anchored vessel commences to drag anchor.
Drift Net – Fishing net about 120 ft. long by 20 ft. deep. Buoyed with cork along head. Several of these are joined to form a very long net; so that nets may extend a considerable distance to windward of the drifter to which they are attached.
Drift Piece – Upright or curved timber connecting plank sheer with gunwale of wooden ship.
Drift Pin – Conical tapered pins driven into sheets with rivet holes that are not fair in order to force them into line.
Drift Sail – Sail used as a drogue.
Drifter – Fishing boat that streams very long buoyed nets, and rides to the leeward end of them. Now seldom seen in European waters.
Drifts – In sheer draught, are where rails are cut, and ended with scroll iron.
Drip Loop – A low spot in an electrical conduit for the purpose of collecting and draining off condensation.
Drip Tray or Pan – A pan placed under a piece of machinery to contain leaks. Also called a save all.
Drive – To carry too much sail. To run before a gale. To press a vessel with high speed for the conditions. To carry much sail in a heavy wind. The entire mechanism connecting the engine to the propeller, i.e., inboard-outboard drive, reduction-gear drive, direct drive, etc.
Drive Ratio – The ratio of diameters between a driving and driven pully.
Drive Train – All the mechanical equipment from the gearbox to the propeller including for example the propeller shaft, bearing, and couplings.
Driver – Alternative name for a spanker. 2. Foremost spur in bilgeways of a vessel on the stocks. Heel is fayed to foreside of foremost shore.
Driver Boom – Spanker boom.
Driver Spanker – Sail that is also called ‘Driver’ and ‘Spanker’.
Drizzle – Precipitation of very small rain drops.
Drogher – 1. An 18th century boat used in catching and curing herrings. 2. West Indian coasting vessel. 3. A slow heavy vessel, e. g. timber drogher.
Drogue – Drag anchor. Sea anchor. 2. Square piece of wood attached to harpoon line of whaler, to check speed of whale.
Dromon – Ancient Byzantine warship with twin banks of oars.
Dromoscopic Card – Compass card having two graduations, the outer giving true bearings, the inner one giving magnetic bearings. Could be used only in one locality, and for a limited time.
Drop – The depth of a sail measured on its middle line. 2. Machine for lowering a coal waggon from a staith to a position just above hatch of a ship. Used to avoid breakage of coal while loading.
Drop Anchor – To let go anchor.
Drop Astern – To fall astern.
Drop Keel – Metal plate keel that can be withdrawn into a water-tight box over a slot in bottom of boat. Has obvious merits when working in shoal water, or beaching.
Drop Strake – A discontinuous strake in the bow or stern sections. See stealer.
Drought – Prolonged deficiency of precipitation (rain).
Drum Head – Head of a capstan.
Drummer’s Plait – Simple plait made by passing bight of rope through each preceding loop.
Dry – Not wet. Free from rain.
Dry Adiabatic Lapse Rate (DALR) – is approx. 9.8º C per kilometre being the temperature change of unsaturated air on rising or falling.
Dry Bulk – Cargoes shipped in a dry state and in bulk; e.g., grain, cement, ore.
Dry Card Compass – Mariner’s compass having no liquid in bowl.
Dry Cargo Ship – Vessel which carriers all, excluding liquid in bulk.
Dry Compass – Dry card compass.
Dry Dock – Excavated dock, fitted with watertight entrance, from which water can be pumped to allow work to be done on underwater portion of a docked ship. Floating dry docks are usually called ‘floating docks’.
Dry Docking – To remove the vessel from the water by placing it in a walled enclosure and pumping it dry. The vessel is supported from the localised pressure on its keel and chine by “chocks” and “side shores”.
Dry Exhaust – An exhaust system or part of an exhaust system that is uncooled or cooled by air currents. Dry exhaust systems operate at higher temperatures than water cooled.
Dry Rot – The decay of timber caused by fungi, usually initiated under moist unventilated conditions, but not cured by drying out.
Dry-Bulb Temperature – The shade temperature of a mercury thermometer.
Drying Features – Underwater obstructions that appear as tide recedes, but are covered as tide rises.
Drying Height – Height that a drying feature is above level of chart datum.
Du Boulay Roller Jib – Works on principle of roller blind. Luff of sail is attached to hollow spar through which passes fore stay. Bottom of spar carries a grooved wheel to which furling-reefing line is attached. Hauling on this line furls, or reduces area of, sail. Invented by Captain E. du Boulay.
Dub – To shape a smooth and even surface on a spar or timber.
Dubhe – Star α Ursa Majoris. S. H. A. 195°; Dec. N62°; Mag. 2.0.
Ducer – Second steward.
Duck – Flax fabric that is lighter and finer than canvas. 2. To dip into the sea.
Duck Lamp – Small oil container with an inclined spout that holds wick. Burns colza oil. Was used in bunkers by coal trimmers.
Ducking (a Sail) – Tricing, or clearing it, so that helmsman’s view is not obstructed.
Duct – A conduit through which piping or cabling is routed.
Duct Keel – Longitudinal conduit forming a boxed keel structure through which piping or cabling is routed.
Duct Keel – Twin centre girders with space between them. Increases longitudinal strength and allows bilge and ballast piping to lie in the space and be easily accessible.
Ductility – The property malleability (the opposite of brittle) of some metals, allowing them to bend or drawn into wire without fracturing, i.e. copper.
Dumb Barge – Barge with no sail, engine or rudder and unable to move except by towing or, to a limited degree, by sweeps.
Dumb Compass – Compass card that has no needle, but is adjustable by hand. A pelorus.
Dumb Fastening – Short screw fastening that holds a strake until a through fastening is passed.
Dumb Lighter – Lighter with neither means of propulsion nor rudder.
Dummy Gantline – Rope rove through a block to act as a reeving line for a gantline.
Dummy Piston – Disc on shaft of a reaction turbine. Steam impinges on this disc, so reducing end thrust.
Dune – A low sand hill.
Dungarees – Working overalls.
Dungiyan – One-masted Arabian sailing vessel.
Dunnage – Any material, permanent or temporary, that is used to ensure good stowage, and protect cargo during carriage.
Dunstos Rudder Brake – Fitting for preventing sudden snatches on rudder chains during heavy weather. Thwartship wire, with ends secured on either side of ship, passes around a sheave on tiller. At normal speed of rudder, the sheave ‘rolls’ along wire;with sudden stresses, wire temporarily grips sheave, so absorbing stress that would, otherwise, come on engine and steering chains.
Duplicating Pipe – A tube used to print rivet hole layout from template to plate surface.
Duration of Tide – Time interval between occurrence of low water and the following high water, or between high water and following low water.
Dust storm – A storm carrying dust often high into the atmosphere.
Dutchman – An infilling piece used to cover up open joints caused by poor workmanship. A vessel from the Netherlands, most famous of which is the ghost ship the Flying Dutchman.
Dutchman’s Log – Piece of wood thrown overboard, well forward and used for ascertaining speed of ship by timing its passage between two marks, of known distance apart, on ship.
Duty – Service or work that should rightly be rendered. 2. Tax or custom charge imposed by a government on goods imported, exported or consumed.
Duty Free – Exempted from customs duty.
Dwarf Star – One of small mass and low candle power, but of enormously high density. Dwarf star companion of Procyon weighs about 250 tons per cubic inch.
Dygogram – Geometrical construction representing the direction and amount of each force acting on a magnetic compass.
Dyke – An embankment.
Dynamical Mean Sun – Imaginary body moving along Ecliptic and travelling from perigee to perigee at a constant speed and in the same time as that taken by true Sun. Not considered in navigation.
Dynamical Stability – Of a ship, is amount of work necessary to heel the vessel through a given angle.
Dynamo – Machine that converts mechanical energy into direct electric current. Effected by revolution of an armature in a magnetic field.
Dyne. C. G. S – unit of force, representing amount necessary to produce or accelerate, velocity of one gramme mass by one centimetre per second.
Dysa, Dyso, Diso – ‘Dghaisa.’