A glossary of nautical terms

Each month, we will add nautical terms to this list in alphabetical order. This is a partial glossary of nautical terms; some remain current, while many date from the 17th to 19th centuries.

A to C - D to F - G to I - J to L - M to O

Jack - 1. A sailor. Also jack tar or just tar. 2. A flag. Typically the flag was talked about as if it were a member of the crew. Strictly speaking, a flag is only a "jack" if it is worn at the jackstaff at the bow of a ship.
Jackass-barque - Sometimes spelled jackass bark, is a sailing ship with three (or more) masts, of which the foremast is square-rigged and the main is partially square-rigged (topsail, topgallant, etc.) and partially fore-and-aft rigged (course). The mizzen mast is fore-and-aft rigged.
Jack Dusty - A naval stores clerk.
Jack Tar - A sailor dressed in 'square rig' with square collar. Formerly with a tarred pigtail.
Jacklines or jack stays - Lines, often steel wire with a plastic jacket, from the bow to the stern on both port and starboard. A crewmember clips his safety harness to a jackline, allowing him to walk along the deck while still being safely attached to the vessel.
Jackstay - Iron rod bolted clear of the mainmast, to which the luff of the mainsail is laced.
Jetty - A man-made wall in open water rising several feet above high tide made of rubble and rocks used to create a breakwater, shelter, erosion control, a channel, or other such purpose.
Jetsam - Debris ejected from a ship that sinks or washes ashore.
Jib - A triangular staysail at the front of a ship. More specifically, one mounted between bowsprit and the head if the mainmast.
Jibboom - A spar used to extend the bowsprit.
Jigger-mast - The fourth mast, although ships with four or more masts were uncommon, or the aft most mast where it is smallest on vessels of less than four masts.
Jollies - Traditional Royal Navy nickname for the Royal Marines.
Jolly boat - On a barge, the ship′s boat used to ferry crew and stores when the barge is moored off.
Joggle - a slender triangular recess cut into the faying surface of a frame or steamed timber to fit over the land of clinker planking, or cut into the faying edge of a plank or rebate to avoid feather ends on a strake of planking. The feather end is cut off to produce a nib. The joggle and nib in this case is made wide enough to allow a caulking iron to enter the seam.
Jonah - A person (either a sailor or a passenger) who carries a jinx, one whose presence on board brings bad luck and endangers the ship.
Junk - 1. Old cordage past its useful service life as lines aboard ship. The strands of old junk were teased apart in the process called picking oakum. 2. A sailing ship of classic Chinese design with characteristic full batten sails that span the masts usually on unstayed rigs.
Jury rig - Both the act of rigging a temporary mast and sails and the name of the resulting rig. A jury rig would be built at sea when the original rig was damaged, then it would be used to sail to a harbor or other safe place for permanent repairs.

Book a Course

Kaep - a type of Proa native to Palau.
Kedge - A technique for moving or turning a ship by using a relatively light anchor known as a kedge. The kedge anchor may be dropped while in motion to create a pivot and thus perform a sharp turn. The kedge anchor may also be carried away from the ship in a smaller boat, dropped, and then weighed, pulling the ship forward.
Keel - The central structural basis of the hull.
Keelhauling - Maritime punishment: to punish by dragging under the keel of a ship.
Keelson - A baulk of timber or steel girder immediately above the keel that forms the backbone of a wooden ship. Chine keelson of more modest proportions are fitted at the junction of the floors and frames.
Kentledge - Weights (often scrap or pig iron) used as permanent high-density ballast.
Ketch - A two-masted fore-and-aft rigged sailboat with the aft mast (the mizzen) mounted (stepped) afore (in front of) the rudder.
Killick - A small anchor. A fouled killick is the substantive badge of non-commissioned officers in the RN. Seamen promoted to the first step in the promotion ladder are called 'Killick'. The badge signifies that here is an able seaman skilled to cope with the awkward job of dealing with a fouled anchor.
Kicking strap - 1. A rope, tackle or hydraulic ram running from the mast at or just above deck level to a point part-way along the boom of a yacht's mainsail or mizzen. Its function is to pull the boom down, flattening the sail in strong winds, reducing twist and preventing the boom from kicking up when running. 2. A chain rigged from the rudder to quarter, tightened when anchored, it relieve the pressure on the gudgeon pin,
King plank - The centerline plank of a laid deck. Its sides are often recessed, or nibbed, to take the ends of their parallel curved deck planks.
Kingston valve - A type of seacock (q.v.) designed so that sea pressure keeps it closed under normal operating conitions, but which can be opened from the inside of the ship, allowing seawater to enter internal fuel, water, or ballast tanks. Kingston valves can be opened to scuttle a ship.
Kissing the gunner's daughter - Bending over the barrel of a gun for punitive beating with a cane or cat.
Kitchen rudder - Hinged cowling around a fixed propeller, allowing the drive to be directed to the side or forwards to manoeuvre the vessel.
Knee - 1. Connects two parts roughly at right angles, e.g. deck beams to frames. 2. A vertical rubber fender used on pushboats or piers, sometimes shaped like a human leg bent slightly at the knee.
Knighthead - 1. A mitred backing timber which extends the after line of the rabbet in the stem to give extra support to the ends of the planks and the bowsprit. 2. A bollard or bitt. 3. Either of two timbers rising from the keel of a sailing ship and supporting the inner end of the bowsprit.
Knockdown - The condition of a sailboat being pushed abruptly to horizontal, with the mast parallel to the water surface.
Knot - A unit of speed: 1 nautical mile (1.8520 km; 1.1508 mi) per hour. Originally speed was measured by paying out a line from the stern of a moving boat; the line had a knot every 47 feet 3 inches (14.40 m), and the number of knots passed out in 30 seconds gave the speed through the water in nautical miles per hour. Sometimes "knots" is mistakenly stated as "knots per hour," but the latter is a measure of acceleration (i.e., "nautical miles per hour per hour") rather than of speed.
Know the ropes - A sailor who 'knows the ropes' is familiar with the miles of cordage and ropes involved in running a ship.

Lace - To attach a sail to a spar by passing a rope through eyelet holes and around the spar or its jackstay.
Ladder - On board a ship, all "stairs" are called ladders, except for literal staircases aboard passenger ships. Most "stairs" on a ship are narrow and nearly vertical, hence the name. Believed to be from the Anglo-Saxon word hiaeder, meaning ladder.
Lagan - Debris that has sunk to the seabed.
Laid up - To be placed in reserve or mothballed. The latter usage is used in modern times and can refer to a specific set of procedures used by the US Navy to preserve ships in good condition.
Laker - Great Lakes slang for a vessel which spends all her time on the five Great Lakes.
Land lubber - A person unfamiliar with being on the sea.
Landmark - An object ashore that is visible from sea and recognizably distinct that is marked on nautical charts for the purpose of fixing position while at sea.
Landsman - A military rank for a naval recruit, used in the United Kingdom in the eighteenth century and first half of the nineteenth century and in the United States in the nineteenth century and in the early twentieth century.
Lanyard - A rope that ties something off.
Larboard - Obsolete term for the left side of a ship. Derived from "lay-board" providing access between a ship and a quay, when ships normally docked with the left side to the wharf. Replaced by port side or port, to avoid confusion with starboard.
Lateen sail or Latin-rig - A fore-and-aft triangular sail set on a long yard mounted at an angle to the mast.
Lateral system - A system of aids to navigation in which characteristics of buoys and beacons indicate the sides of the channel or route relative to a conventional direction of buoyage (usually upstream).
Launch - 1. Traditionally, a launch was the largest ship's boat carried by a warship. 2. In modern usage, a large motorboat. 3. To dispatch a ship down a slipway, prior to fitting-out and commissioning.
Lay - To come and go, used in giving orders to the crew, such as "lay forward" or "lay aloft". To direct the course of vessel. Also, to twist the strands of a rope together. To make it to a mark, buoy, or harbor, such as "We will lay the mark".
Lay day - An unexpected delay time during a voyage often spent at anchor or in a harbor. It is usually caused by bad weather, equipment failure or needed maintenance.
Laying down - Laying the keel of a ship in a shipyard to begin her construction.
Lazaret (also Lazarette or Lazaretto) - 1. A small stowage locker at the aft end of a boat. 2. A ship or building used for quarantine of sick patients. 3. An area on some merchant ships where provisions are stored. 4. In modern shipbuilding and on powerboats of all sizes, the location of the steering gear equipment for the vessel.
Lazy jacks, lazyjacks - A network of cordage rigged to a point on the mast and to a series of points on either side of the boom that cradles and guides the sail onto the boom when the sail is lowered.
Leach - The after edge of a sail.
Lead - 1. A plummet or mass of lead attached to a line, used in sounding depth at sea. 2. In former usage, to estimate velocity in knots.
Leadline (also sounding line) - An instrument used in navigation to measure water depth; the line attached to a lead.
Leadsman - A sailor who takes soundings with a lead, measuring the depth of water.
League - A unit of length, normally equal to three nautical miles.
Lee helm - The tendency of a sailboat to turn to leeward in a strong wind when there is no change in the rudder's position. This is the opposite of weather helm and is the result of a dynamically unbalanced condition. See also Center of lateral resistance.
Lee side - The side of a ship sheltered from the wind (cf. weather side).
Lee shore - A shore downwind of a ship. A ship which cannot sail well to windward risks being blown onto a lee shore and grounded.
Leeboard - A large fan shaped wooden board or fin mounted in pairs on the side of a boat. They can be lowered on the lee side of the ship to reduce leeway (similarly to a centerboardon a dinghy).
Leeboard irons - The iron bars that run from the mainmast case to the head of each leeboard, which they support.
Leeboard pendant - A wire connecting the fan of the leeboard, to a winch on the barges quarter. They control the fall of the leeboard.
Leech - The aft or trailing edge of a fore-and-aft sail; the leeward edge of a spinnaker; a vertical edge of a square sail. The leech is susceptible to twist, which is controlled by the boom vang, mainsheet and, if rigged with one, the gaff vang.
Lee-oh or hard-a-lee - The command given to come about (tack through the wind) on a sailing boat.
Leeward - In the direction that the wind is blowing towards.
Leeway - The amount that a ship is blown leeward by the wind. Also the amount of open free sailing space available to leeward before encountering hazards. See also weatherly.
Leg - In navigation, a segment of a voyage between two waypoints.
Length between perpendiculars, also p/p, p.p., pp, LPP, LBP or Length BPP - The length of a vessel along the waterline from the forward surface of the stem, or main bow perpendicular member, to the after surface of the sternpost, or main stern perpendicular member. Believed to give a reasonable idea of the vessel's carrying capacity, as it excludes the small, often unusable volume contained in her overhanging ends.
Length overall, or LOA - The maximum length of a vessel's hull measured parallel to the waterline, usually measured on the hull alone, and including overhanging ends that extend beyond the main bow and main stern perpendicular members. For sailing vessels, this may exclude the bowsprit and other fittings added to the hull, but sometimes bowsprits are included.
Let go and haul - An order indicating that the ship is now on the desired course relative to the wind and that the sails should be trimmed ('hauled') to suit.
Letter of marque and reprisal or just Letter of marque - A warrant granted to a privateer condoning specific acts of piracy against a target as a redress for grievances.
Liberty - A relatively short period when a sailor is allowed ashore for recreation.
Lie to - To have the ship's sails arranged so as to counteract each other. A ship in this condition or in the process of achieving this condition is lying to.
Lifebelt, lifebuoy, lifejacket, life preserver, personal flotation device - A device such as a buoyant ring or inflatable jacket which keeps a person afloat in the water.
Lifeboat - 1. Shipboard lifeboat, kept on board a vessel and used to take crew and passengers to safety in the event of the ship being abandoned. 2. Rescue lifeboat, usually launched from shore, used to rescue people from the water or from vessels in difficulty.
Liferaft - An inflatable, covered raft, used in the event of a vessel being abandoned.
Lift - An enabling wind shift that allows a close hauled sailboat to point up from its current course to a more favorable one. This is the opposite of a header.
Light irons - Iron bars mounted near the main shrouds which support the navigation lights.
Light screens - Boards on which the navigation lights are hooked, that shield the direction that the red or green light shows.
Lighter - A flat-bottomed barge used to transfer goods and passengers to and from moored ships, traditionally unpowered and moved and steered using "sweeps" (long oars), with their motive power provided by water currents.
Lightering - The process of transferring cargo from one vesel to another to reduce the draft of the first vessel. Done to allow a vessel to enter a port with limited depth or to help free a grounded vessel.
Lightvessel or lightship - A permanently anchored vessel performing the functions of a lighthouse, typically in a location where construction of the latter is impractical. These have largely been replaced by buoys or, as construction techniques have improved, actual lighthouses.
Line - The correct nautical term for the majority of the cordage or "ropes" used on a vessel. A line will always have a more specific name, such as mizzen topsail halyard, that specifies its use.
Line astern - In naval warfare, a line of battle formed behind a flagship.
Liner - 1. During the Age of Sail, a ship-of-the-line, a major warship capable of taking its place in the main battleline of fighting ships. 2. Any cargo or passenger ship running scheduled service along a specific route with published ports of call, excluding ferries and other vessels engaged in short-sea trading. When referring to cargo ships, liner in this sense contrasts with tramp, which refers to a ship engaged in spot-market trade that does not follow a regular schedule or make regular calls at specific ports. When referring to passenger ships, liner in this sense refers to ships providing scheduled transportation between regular ports of call and excludes cruise ships, which voyage merely for recreational purposes and not primarily as a form of transportation between ports. 3. Ocean liner: Any large and prestigious passenger ship, including cruise ships.
List - A vessel's angle of lean or tilt to one side, in the direction called roll. Typically refers to a lean caused by flooding or improperly loaded or shifted cargo (as opposed to 'heeling', which see).
Lizard - short length of rope with an eye, used to hold another rope in position.
Loaded to the gunwales - Literally, having cargo loaded as high as the ship's rail; also means extremely drunk.
Lofting - The technique used to convert a scaled drawing to full size used in boat construction.
Loggerhead - An iron ball attached to a long handle, used for driving caulking into seams and (occasionally) in a fight. Hence: 'at loggerheads'.
Lolling - An uncontrollable list caused by inadequate transverse stability in the upright condition.
Long stay - The relative slackness of an anchor chain; this term means taut and extended.
Longboat - 1. In the Age of Sail, a double-banked open boat carried by a sailing ship, rowed by eight or ten oarsmen, two per thwart, although designed also to be rigged for sailing; more seaworthy than a cutter or dinghy and with a beam greater than that of a gig. Eventually supplanted by the whaleboat. 2. The largest, and thus the most capable, of boats carried on a ship.
Longship - A type of ship invented and used by the Vikings for trade, commerce, exploration, and warfare, evolving over several centuries and appearing in its complete form between the 9th and 13th centuries.
Lookout - A member of the crew specifically assigned to watch surrounding waters for other vessels, land, objects in the water, hazards, threats, etc. Lookouts usually have duty stations high on a vessel's superstructure or in her rigging in order to enhance their field of view.
Loose cannon - An irresponsible and reckless individual whose behavior (either intended or unintended) endangers the group he or she belongs to. A loose cannon, weighing thousands of pounds, would crush anything and anyone in its path, and possibly even break a hole in the hull, thus endangering the seaworthiness of the whole ship.
Loose footed - A mainsail that is not connected to a boom along its foot.
Lower deck - 1. The deck of a ship immediately above the hold. - 2. In British usage, those members of a ship's company who are not officers, often used in the plural (the lower decks).
Lowers - The lower brails on the mainsail.
Lubber's hole - A port cut into the bottom of a masthead or top (crow's-nest) allowing easy entry and exit. It was considered "un-seamanlike" to use this method rather than going over the side from the shrouds, and few sailors would risk the scorn of their shipmates by doing so (at least if there were witnesses). In practice, it is actually quicker and easier for a fit sailor to climb outside the masthead rather than through the lubber's hole.
Lubber's line - A vertical line inside a compass case indicating the direction of the ship's head.
Luff - 1. The forward edge of a sail. 2. Process of pointing a sailing vessel closer to the wind.
Luff and touch her - To bring the vessel so close to wind that the sails shake.
Luff up - To steer a sailing vessel more towards the direction of the wind until the pressure is eased on the [sheet].
Luffing - 1. When a sailing vessel is steered far enough to windward that the sail is no longer completely filled with wind (the luff of a fore-and-aft sail begins to flap first). 2. Loosening a sheet so far past optimal trim that the sail is no longer completely filled with wind. 3. The flapping of the sail(s) which results from having no wind in the sail at all.
Lying ahull - Waiting out a storm by dousing all sails and simply letting the boat drift.
Lumber hooker - A Great Lakes ship designed to carry her own deck load of lumber and to tow one or two barges. The barges were big old schooners stripped of their masts and running gear to carry large cargoes of lumber.
Lugger - A small sailing vessel with lug sails set on two or more masts and perhaps lug topsails, widely used as traditional fishing boats, particularly off the coasts of France, England and Scotland.
Lug sail - A four-sided fore-and-aft sail supported by a spar along the top that is fixed to the mast at a point some distance from the center of the spar.

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