Marine and Naval Architecture terms have special meaning. Persons studying ship construction, working on board ship, or dockyard will find these pages useful.

	HARD AGROUND	A ship which has gone aground and is not able to move under her own power.
	HATCH BATTENS	Flat bars which are wedged against hatch coamings to secure tarpaulin
	HATCH BEAM	Portable beam across a hatch to support hatch covers
	HATCH OR HATCHWAY	An opening in a deck through which cargo and stores are loaded or unloaded
	HAWSE PIPE	Tube through which anchor chain is led overboard from the windlass on the deck
	HAWSER	Strong rope or steel cable used for securing or mooring ships
	HEEL	The inclination of a ship to one side (See list)
	HELM	Steering wheel installed on the bridge or wheelhouse of a ship to turn the rudder during manoeuvering and navigation
	HOGGING	Straining of the ship that tends to make the bow and stern lower than the middle portion (See Sagging)
	HOISTING ROPE	Flexible wire rope for lifting purposes, generally being of six strands with 19 wires in each strand and in most cases having a hemp rope at the center. Also called wire rope
	HOLD	The large spaces below deck for the stowage of cargo
	HULL	Body of a ship which floats on the water
	INERT GAS SYSTEM	A system of filling the space above the cargo oil in tankers with carbon dioxide from the boiler exhaust so as to prevent explosion.
	INTERCOASTAL	Domestic shipping routes serving more than one coast.
	INTERCOSTAL	Made in separate parts; between floors, frames or beams, etc; the opposite of continuous
	INTERNATIONAL LOAD LINE CERTIFICATE	A certificate issued after the vessel has been surveyed and load lines marked on her sides.
	INTERNATIONAL TONNAGE CERTIFICATE	A certificate issued by a government department in accordance with the International Convention of Tonnage Measurement of Ships stating the gross and net tonnages
	INTERNATIONAL WATERWAYS	International straits, inland and interocean canals and rivers separating the territories of two or more nations which are can be navigated by both merchant ships and warships with no restrictions
	INTRACOASTAL	Domestic shipping routes along a single coast.
	KEEL	The principal fore-and-aft component of a ship's framing located along the centerline of the bottom and connected to the stem and stern frames
	KEEL BLOCKS	Heavy wood or concrete blocks on which ship rests during construction or drydocking
	KEEL, FLAT PLATE	The horizontal, centerline, bottom shell strake constituting the lower flange of the keel
	KNEE, BEAM	Bracket between a deck beam and frame
	KNOT	Unit of speed in nautical mile (6,080 feet or 1,852 meters) per hour.
	L/T	Long tons (2,240 lbs.).
	LAKER	Type of ship which trades only in the Great Lakes of North America. The cargo is usually grain and ore.
	LASH	Lighter Aboard Ship: A ship designed to carry floating containers or lighters.
	LENGTH BETWEEN PERPENDICULARS	The length of a ship between the forward and after perpendiculars
	LENGTH, OVERALL	The extreme length of a ship measured from the foremost point of the stem to the aftermost part of the stern
	LIFEBOAT	A boat which is used when the ship is in danger and has to be abandoned
	LIGHT WEIGHT	(See Displacement, light)
	LIGHTER	A flat-bottomed boat for transporting cargo between ship and shore.
	LIGHTER ABOARD SHIP	See LASH
	LIGHTERS	Small barges for carrying cargo between ship and shore
	LIMBER HOLE	A small drain hole or slot in a frame or plate for the purpose of preventing water or oil from collecting
	LINER	A cargo ship which sails between regular ports of call on a schedule
	LINES (PLAN)	The plans that show the shape or form of the ship
	LIST	When the centerline plane of a ship is not vertical, the ship is said to list, or to heel
	LNG CARRIER	Liquefied natural gas carrier.
	LOAD LINE	The line on a ship which indicates the maximum depth to which it can sink when loaded with cargo. Also known as marks.
	LOAD WATERLINE	The line on the lines plan of a ship, representing the intersection of the ship's form with the plane of the water surface when the ship is floating at the summer freeboard draft or at the designed draft. Also called marks
	LONG TON	2,240 pounds.
	LONGITUDINALS	Fore-and-aft structural shape or plate members attached to the underside of decks, flats, or to the inner bottom, or on the inboard side of the shell plating.
	LPG	Liquefied Petroleum Gas
	M.V.	Motor Vessel or Diesel Engine driven ship
	M/T	Metric tons (2,250 lbs.).
	MAIN DECK	The continuous deck of a ship running from fore to aft. The freeboard is measured from this deck.
	MARGIN BRACKET	A bracket connecting a side frame to the margin plate at the bilge
	MARGIN LINE	A line, not less than 3 in below the top of the bulkhead deck at side, defining the highest permissible waterplane in the final condition of sinkage, trim and heel
	MAST	A tall vertical or raked structure, usually of circular section, located on the centerline of a ship and used to carry navigation lights, radio antennas and cargo booms
	MASTHEAD LIGHT	A white light situated on the fore and aft centerline of a ship
	METACENTER	The intersection point of a vertical line drawn through the line of buoyancy of a slightly listed vessel which intersects the centerline plane
	METACENTRIC HEIGHT	The distance from the metacenter to the center of gravity of a ship. If the center of gravity is below the metacenter the vessel is stable
	MIDSHIP SECTION	A drawing showing a typical cross section of the hull and superstructure at or near amidships and giving the scantlings of the principal structural members
	MOLD LOFT	A floor space used for laying down the full size lines of a ship for making templates for construction
	MOORING	Securing a ship at a dock or elsewhere by ropes or cables
	MOORING LINE	A cable or rope used in securing a ship
	MULTIPURPOSE SHIP	A ship designed for carrying different types of cargoes requiring different methods of handling. See OBO ship