DAGGERBOARD - Similar to the centerboard, except it is raised and lowered vertically rather than pivoted.


DANGER ZONE – The sector extending from dead-ahead to two points abaft the starboard beam


DATUM – A reference level from which heights and depths are measured


DAVIT – A curved metal spar fitting in a socket on deck and projecting over the side or stern for handling a boat or weights.  Sometimes used forward for bringing an anchor aboard.


DAVY JONES’ LOCKER – The bottom of the sea


DAYBEACON - A fixed navigation aid structure used in shallow waters upon which is placed one or more daymarks.


DAYMARK - A signboard attached to a daybeacon to convey navigational information presenting one of several standard shapes (square, triangle, rectangle) and colors (red, green, orange, yellow, or black). Daymarks usually have reflective material indicating the shape, but may also be lighted.


DEAD AHEAD - Directly ahead.


DEAD ASTERN - Directly aft.


DEAD LIGHT – A heavy circular glass lens set flush and permanently into decks of bulkheads for admitting light or permitting observation


DEAD RECKONING - A calculation of determining position by using course speed last known position


DEAD WATER – The eddy of a vessel’s wake under the counter


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.


DEADEYE - A block with three hole in use to receive the lanyard of a shroud or a stay to adjust tension.


DEADEYE WATCH - 4 a.m. to 8 a.m.


DEADHEAD - a log or heavy timber floating nearly vertical but with little of it’s bulk above the surface


DEADWOOD - Heavy longitudinal timbers fastened over the keelson  The timbers of the bow and stern are fastened to the deadwood.


DECK - A permanent covering over a compartment, hull or any part thereof.


DECK LOG – A book in which the conduct of the vessel is recorded


DECK PLATE - a metal plate fitting on the deck that can be opened to take on fuel or water


DECLINATION – The angular interval of a celestial body north or south of the celestial equator along an Hour Circle


DEEPS – The fathoms of a lead line which are not marked


DEEP SIX - To discard something, specifically to throw it in the water. Water depth is measured in fathoms, six feet to a fathom. The term "deep six" comes from the throwing of the lead to determine water depth and indicates a depth "over six fathoms."


DEPTH OF HOLD - The measurement from beneath the deck to the bottom of the hold; the vertical space in the cargo hold.


DEGREE – A unit of angular measurement


DELAMINATION – A condition in which layers of fiberglass separate from each other


DEPARTURE – An accurate fix or other position on a chart from which a course is laid


DEVIATION – The angular difference between magnetic north and compass north


DINGBAT - Slang term for a small swab made of rope and used for drying decks.


DINGHY - A small open boat. A dinghy is often used as a tender for a larger craft.


DIP – A position of a flag when hoisted part way of the hoist; to lower a flag part way and then hoist it again


DISCHARGE CURRENT – The water expelled by the propeller


DISPLACEMENT - The weight of water displaced by a floating vessel, thus, a boat's weight.


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 SPEED (HULL SPEED) - The theoretical speed that a boat can travel without planing. This speed is 1.34 times the length of a boat at its waterline.


DISTANCE MADE GOOD - The distance traveled after correction for current, leeway and other errors that may not have been included in the original distance measurement.


DISTRESS SIGNALS - International signals which indicate that a boat is in danger. For example, in American waters: the sudden appearance of lawyers, the pointing of fingers, and repression of memories; in Italian waters: moaning, weeping, and wild gesticulations; in French waters: fistfights, horn blowing, and screamed accusations; in Spanish waters: boasts, taunts, and random gunfire; in Irish waters: rhythmic grunting, the sound of broken glass, and the detonation of small explosive devices; in Japanese waters: shouted apologies, the exchange of calling cards, and minor self-inflected wounds; and in English waters: doffed hats, the burning of toast, and the spilling of tea.


DITTY BAG - a small bag for carrying or stowing all personal articles.


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.


DOCK - A protected water area in which vessels are moored. The term is often used to denote a pier or a wharf


DOCKING – The procedure for coming alongside and securing to a dock, wharf or jetty


DODGER - A wrap-around awning in front of the cockpit to protect the crew from weather


DOG WATCH - Half watches of two hours each, from 4 to 6 and from 6 to 8 P.M..


DOGS RUNNING BEFORE THEIR MASTER - The heavy swell in advance of a hurricane.


DOLPHIN - A group of piles driven close together and bound with wire cables into a single structure.


DONKEYMAN - Rating who tends a donkey boiler, or engine, and assists in engine-room.


DONKEY'S BREAKFAST - Merchant seaman's name for his bed or mattress.


DORADE - A horn type of vent designed to let air into a cabin and keep water out.


DORY - Small, flat-bottomed rowing boats manned by one or two fishermen. Used for cod fishing off Newfoundland. The name is derived from the Portuguese pescadores meaning fishermen


DOUBLE-ENDER – A boat having a pointed stern


DOUBLE SHEETBEND - Join small to medium size rope.


DOUSE - To drop a sail quickly


DOWNHAUL - A rope used to haul down jibs, staysails and studding sails


DOWNWIND – To leeward


DRAFT (DRAUGHT) - The depth of water a boat draws.


DRIFT – The speed of a current.  Material floating at random.  The distance a vessel is moved by a current.  To move idly without propulsive force of engine or sail


DUMB COMPASS – A sighting instrument used for taking bearings (A Pelorus)


DUNNAGE  - Belongings.


DUTCH COURAGE - Fearlessness brought on by strong drink


DYING MAN'S DINNER - Food quickly prepared during an emergency