Glossary of Nautical Terms

Summary: A glossary of nautical and sailing terms found in our website.

You may want to check out our Selected Books section under the Learn Sailing and Tactics category for books covering much or all of the information below.



To avoid re-inventing the wheel, and since there are lots of other good sites with nautical definitions out there, we've borrowed from and linked to many of them. 


Definitions without linked references were written by us.


“Here Be Dragons”
An ancient phrase used by mapmakers to denote unexplored territories. It is also the name of Dave’s second boat.

“Douse the jib”

An expression often used referring to dropping or furling the jib or forward triangular sail.

4 Sisters

Coal-fired hydro facility in Mississauga which was a landmark on Lake Ontario.

Accidental jibe
An accidental jibe happens when the boat is steered or the wind shifts such that the stern of the boat accidentally passes through the eye of the wind. This causes that main boom to swing violently to the other side of the boat. Without proper preparation when jibing, the force of the boom's motion can be destructive, injuring the crew and damaging equipment. In strong winds and on large boats this force can dismast the boat and seriously injure crew members hit by the boom. Sometimes a preventer is used to reduce the possibility of an accidental jibe.


Towards, at, or near the stern or back of the vessel.


The center portion of the boat, near the centerline.


A heavy object used to fix the the boat to the seabed.  Anchors can be permanently installed in the seabed as in a permanent mooring, or can be carried with the boat and deployed when needed.  They are commonly made of steel, but lightweight aluminum alloys are also used, as are large concrete block for permanent moorings.


A condition where the jib sheet is made fast on the windward side of the boat rather than the leeward side. This sometimes happens accidentally, but is often used to “heave-to” or to help turn the boat quickly using the force of the wind on the sail to push the bow around.


A piece of standing rigging, commonly stainless steel wire, running from the masthead to the deck at or towards the stern of the vessel.


To attach a line to a cleat, belaying pin, or other fixed object.


(1) A place for a person to sleep.

(2) A place where the ship can be secured.

(3) A safe and cautious distance, such as "We gave the shark a wide berth."


The lowest section of hull in a vessel.  It is the place where water will naturally run and collect to via gravity, and therefore where "bilge pumps" are generally located so that the bilge water can be removed by pumping overboard.


A weather protection covering, usually mounted on a frame over a portion of the cockpit. Can be of fabric, i.e., canvas or hard material, i.e., fiberglass or plastic.


In sailing, a boom is a spar (pole), along the foot (bottom) of a fore and aft rigged sail, that greatly improves control of the angle and shape of the sail. The primary action of the boom is to keep the foot of the sail flatter when the sail angle is away from the centerline of the boat. ...



The forward end of the boat, the pointy end.


A strong wall, commonly of stone, concrete, or steel, that protects a harbour from large open-water waves.


The unplanned turning of a vessel to expose its side to the oncoming waves. In heavy seas this could cause the boat to be knocked down.

Broad reach

A point of sail when the wind comes from behind on either quarter.


Vertical partition in a boat, the walls.


The chine is an angle on the bottom of the vessel where the flair decreases as the hull transitions from the bottom of the vessel to the sides.. A hard chine is where that angle decreases rapidly making a sharp angle. A hard chine kayak has a well defined turn where the "V" comes up to the side. ...


A fitting, secured to the deck, mast, or spar, having two projection horns to which lines are made fast.


The lower, aft corner of a fore-and-aft sail or the two lower corners of a square sail.


Sailing close to the wind with sails pulled in.

Coach roof

The cabin roof, raised above the deck to provide headroom in the cabin.


The location from which the boat is steered, usually in the middle or the rear of the boat.


On a sailboat, generally the main access way into the cabin.


A compass (or mariner's compass) is a navigational instrument for finding directions on the earth. It consists of a magnetized pointer free to align itself accurately with Earth's magnetic field, which is of great assistance in navigation. The cardinal points are north, south, east and west. ...


A crest is the point on a wave with the greatest positive value or upward displacement in a cycle. A trough is the opposite of a crest.

Dead reckoning

A means of estimating a boat’s position by using the course steered, speed of the boat, and the amount of time that has elapsed. Each time the course or speed changes, the new course, speed, and time should be noted. Periodically, the navigator calculates the boat’s DR (dead reckoning) position and marks it on the chart.

Dead run

Sailing directly downwind with the sails out (the jib is sometimes held out with a pole) to either side of the boat. This is also called sailing wing-on-wing.


The surface on the top of the boat that people can stand on.


A small sailboat often raced that can be sailed on and off a beach. Also a tender, either rowed or equipped with power, used to go to and from a larger vessel.


A cover attached to the top of the cabin at the front of the cockpit. Dodgers help shelter the cockpit from wind and water.


Moving in the same direction as the wind.


Short form for “dead reckoning”.

Even keel

When the draft of a vessel fore and aft is equal. In other words: the ship's keel is parallel to the ship's waterline.


Simply put, the vessel is floating level - not leaning over to either side.


Protective devices placed alongside the freeboard to protect the hull. Old tyres, sponges, rolled nets, hawsers were all called defenders, thus fender.


Distance over which wind acts on the water surface to generate waves.

Fin keel

A keel shaped like the fin of a fish that is shorter and deeper than a full-length keel.

Fish finder

A generic term used for electronic units, generally sonar, that identify fish and outline the bottom of a body of water.


1) Safety equipment - an unsteady glaring light produced by an incendiary device,

2) The rise of a boat hull that flares out from the water line to the deck, usually at the bow.


Towards the bow (of the vessel).


Forward part of the main deck, ahead of the superstructure.



On a sailing vessel, a forestay is a piece of standing rigging which keeps a mast from falling backwards. It is attached either at the very top of the mast, or in fractional rigs between about 1/8 and 1/4 from the top of the mast. The other end of the forestay is attached to the bow of the boat.



The kitchen area on a boat.


Genoa - A genoa (pronounced like the city, or as jenny) is a type of large jib-sail used on Bermuda-rigged craft, commonly the single-masted sloop and twin-masted boats such as yawl and ketch. ...


A system of inner and outer rings with pivots arranged for an object, such as a gyro compass, to remain level as the ship moves around. (See Gyroscope).


Gimbals can also be set up to work in one dimension only - probably the most common example of this is the stove, which is usually set up in a fixed fore/aft position but is able to swing freely as the boat heals to port or starboard so that pots on the stove stay level.


An acronym for: Global Positioning System. It is a method to determine geographical coordinates and local time coordinates on Earth using calibrating signals from a network of satellites. ...


The line used to hoist a sail, generally attached to the head and running down the mast to where it can be used to tension the luff.

Hardening a sail

A term used to mean hauling in on a sail’s sheet in order to put more tension on it and pull it closer in. Generally, this is done when trying to sail closer to the wind.


An opening in a boat's deck fitted with a watertight cover.


The head (or heads) is a ship's water closet or toilet.


To position the sails of a vessel so as to cause them to counteract each other, thus inhibiting the vessel’s forward motion.


When a boat tilts away from the wind, caused by wind blowing on the sails and pulling the top of the mast over. Some heel is normal when under sail.


The wheel or tiller controlling the rudder.


A helmsman is a person who steers a ship. In the merchant marine this is usually an able seaman. In the Navy it is a seaman or a quartermaster. Mao Zedong is commonly known as the "Great Helmsman".

Often shortened to 'Helm', the person steering the boat. In a Laser 2 the Helmsman generally holds the tiller and mainsheet, controlling both the mainsail and the steering of the boat.


A slang term for the anchor. A lightweight, easily deployed, and thus not terribly secure anchor is often referred to as a “lunch hook” – basically an anchor suitable for short stops in fair weather with people remaining on board that can keep an eye on it.


Past tense of Heave-to.


The main body of a ship excluding the masts, rigging and internal fittings. ; it displaces water, allowing the vessel’s buoyancy.


Strong lines, commonly of stainless steel cable or nylon webbing, run along each side of the boat from bow to stern, used by sailors wearing safety harnesses to clip on to and secure themselves to the boat. They can help prevent a person from falling overboard, and if a person does fall overboard, they help ensure they stay tethered to the boat to make rescue easier.


A jib is a triangular staysail set ahead of the foremost mast of a sailing boat. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast. Jibs and spinnakers are the two main types of headsails on a modern yacht.


The act of moving the sails from one side of the boat to the other by bringing the stern of the boat through the wind so that the wind strikes it on the opposite side. This can also be done manually when running directly down wind – the sails are just pulled by hand to the other side.


See Accidental Jibe.


The fin attached to the underside of the hull. It is filled with lead ballast to provide upright stability and prevent side-slipping by countering the lateral force of the wind.

Keep on

The “Keep on” or “Stand on” vessel is the one, when two vessels are approaching each other, that is “privileged” or has the right to maintain its course according to the rules of the road. Of course, if the other vessel involved does not alter course, the “Keep on”/privileged vessel is obligated to take early and decisive action to avoid a collision.


A boat with a two-masted rig in which the larger, or mainmast, is forward, and the smaller mizzenmast is stepped aft, but forward of the rudder and usually, of the helm.


1000 meters; 0.6214 statute miles; 0.54 nautical miles


A gauge, that displays a vessel’s speed through the water. It is often driven by a paddle wheel or a water pressure sensing device. It measures in Nautical Miles per hour, otherwise referred to as knots.


This is the unit of measurement for gauging a vessel's speed at sea - 1 knot = 1.85 km/hour = 1.15 statute miles/hour.


Short form of knots.


(nautical) a line used for extending or fastening rigging on ships.


The old name for the left hand side of a ship. It was officially changed to 'port' in 1844.


The location north or south in reference to the equator, which is designated at zero (0) degrees. Parallel lines that circle the globe both north and south of the equator. The poles are at 90 degrees North and South latitude.

The distance north or south of the equator of a point on the earth's surface. This distance is measured in degrees, minutes, and seconds. Lines (parallels) of latitude circle the earth horizontally and are parallel to one another. One minute of latitude equals one nautical mile.


The part of a vessel or body that the wind strikes last.  On a body of water, the wind strikes the windward side first, crosses the water, and then strikes the leeward side.  The Lee shore is the one upon which the wind and waves act most strongly.  Therefore being near a lee shore during a storm can be very dangerous - the waves are largest there and the wind is pushing you towards the shore.


Conversely being "in the lee" or "to the lee" of something means to be on the side of the object that is protected by the wind.


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 and mainsheet.


The direction or side of an object that faces away from the wind.

To the lee. Pronounced something like "loow'rd".


Length overall.


Length on deck .


The distance, measured in degrees, east or west of the prime meridian at Greenwich, England.

The location east or west in reference to the Prime Meridian, which is designated as zero (0) degrees longitude. The distance between lines of longitude are greater at the equator and smaller at the higher latitudes, intersecting at the earth's North and South Poles. ...


1) To alter course more nearly into the wind;

2) The forward edge of a sail.

The rippling effect on a sail caused when, in this condition, the sail begins to spill its wind.


(pronounced “mains'l”) the principal fore-and-aft sail on a boat.


The mast of a sailing ship is a tall vertical pole which supports the sails. Larger ships have several masts, with the size and configuration depending on the style of ship.



The internationally recognized voice radio signal for ships and people in serious trouble at sea. Made official in 1948, it is an anglicizing of the French “m'aidez”, "help me".


A unit of length, equivalent to 39.37 inches.


Linear measurement equaling 5,280 feet, 1,760 yards, 1,609 kilometers, or 8 furlongs. Note, a nautical mile is equal to 6,080 feet.


The sail of a ketch, yawl, or three-masted schooner on the aft mast.


Nautical miles.


A radio signal for ships and people in trouble at sea, advising marine authorities that there is a problem, but lives are not presently at risk. The authorities would then monitor the vessel until such time as they are told that the problem is contained or it has been upgraded to “Mayday”.


“Personal Floatation Device” – less buoyant than a bulky lifejacket, but much more comfortable to wear. This is the standard device for everyday wear aboard small boats.

Pilot house

The enclosed space on the navigating bridge from which a ship is controlled when under way.


Pintle and Gudgeon - Most commonly used as a means of attaching a stern-hung rudder to the rudder post.  Gudgeons are brackets with a cylindrical shape (often attached to the rudder post)  that will allow the rod-shaped part of the pintle bracket (often attached to the rudder) to fit inside it, connecting the rudder to the rudder post.  Two or three pintles/gudgeons spaced along its length are required for the rudder to be securely fastened to the rudder post.


The left side of the boat when you are looking forward. ; identified by the colour red on running lights.


An object with two or more twisted blades that is designed to propel a vessel through the water when spun rapidly by the boat's engine.


When a boat is sailing close-hauled and is healing to a strong breeze, it will often be able to dip its “rails” into the water. This is a slang term referring to the edge of the boat on deck where the stanchions and lifelines are found.


Reefing is a sailing manoeuvre intended to reduce the area of a sail on a sailboat or sailing ship, to improve the ship's stability and reduce the risk of capsizing, broaching or damaging sails or boat hardware in a strong wind. ...


The wires, lines, halyards and other items used to attach the sails and the spars to the boat. The lines that do not have to be adjusted often are known as standing rigging. The lines that are adjusted to raise, lower and trim the sails are known as running rigging.


Similar to a roller reefer in function except that a system that furls only, can deploy a sail fully, or roll it up fully, but doesn’t operate with the sail partially deployed or reefed. The terms are mostly interchangeable these days though, as just about every unit sold now can act as a reefer.


Sometimes referred to as roller-furler. Used to roll a sail on a wire attached to a mast. The sail is rolled and unrolled from the pilot house, requiring less work from the captain or crew; the sail does not have to be put on and taken off each time it is required. Rolling the sail does limit the ability to reef the sails somewhat in that the shape of a partially rolled sail becomes less efficient.


A flat surface attached behind or underneath the stern used to control the direction that the boat is traveling.


A large piece of fabric designed to be hoisted on the spars of a sailboat in such a manner as to catch the wind and propel the boat. (2) The act of using the wind to propel a sailboat.

Sail bag

A tough bag used to store a sail which is not on rigging or masts.


Sailing is the skillful art of controlling the motion of a sailing ship or sailboat, across a body of water. The force of the wind on the sails propels sailing vessels.

Sailing with the apparent wind coming across the quarter of the ship. A broad reach is a point of sail between a beam reach and running.


Traditionally the mess rooms for deck officers. Contemporarily, it is used by yachtsmen to describe the lounging area aboard a small boat. Usually is equipped with dining table and settee berths.

Dave: People also commonly use the term "salon" as a synonym. Personally, I think of a salon as a place where women go to get their hair and nails done – thus my boat only has a saloon!

Sea cock

A through hull valve, a shut off on a plumbing or drain pipe between the vessel's interior and the sea.


In sailing, a sheet is a line (rope, cable or chain) used to control the moveable corner(s) of a sail.

Shorten Sail

To reduce sail by taking it in.

- See Reefing


On a sailboat, the shrouds are pieces of standing rigging which hold the mast up from side to side. There is frequently more than one shroud on each side of the boat. ...


Any flat protrusion on the outside of the hull that is used to support another object such as the propeller shaft or rudder.


A large sail flown from the bow of a boat that is only connected to the boat at the sails three corners (the clew, tack, and head). Spinnakers are generally used for downwind sailing, and can be difficult to control. ...


Vertical poles that stand on the outer edge of the deck to hold the lifelines.


The right side of the ship when facing the bow. Identified by the color green on running lights.


A staysail is a fore-and-aft rigged sail whose luff is affixed to a stay running forward (and most often but not always downwards) from a mast to the deck, the bowsprit or to another mast. ; pronounced “stays’l”


The back of a vessel; astern—backwards or behind.


The brand name of a tough, acrylic, material which is commonly used to make covers for sails while they are on the boom. The material seems impervious to sun and water damage.


The wave activity occurring on a beach inshore of the point at which incoming waves break. Generally, surf consists of waves that have broken and therefore have air to some degree mixed in with the water.

Surf / surfing is also used as a verb to describe a sailboat semi-planing down the front of a large wave.


Large smooth waves that do not crest. Swells are formed by wind action over a long distance.


1) The lower corner of a jib where it attaches to the deck;
2) A type of ship’s biscuit, often referred to as hard-tack;
3) The act of turning the bow of a sailboat through the wind so that the wind strikes it on the opposite side;
4) Sharp objects that Joshua Slocum spread on deck to prevent unwanted people from boarding his boat while he slept!

Through-hull fitting

Generally a bronze or plastic pipe with a flange on one end that is inserted into a hole in the hull to prevent water from getting in around it and allowing a hose or pipe to be attached to it inside the boat. These are used for engine water intakes, sink drains, bilge pump outlets, etc.


An arm attached to the top of the rudder to steer a small boat. If the helmsman wants to steer to starboard he pushes the tiller to port. Larger boats usually use a wheel instead of a tiller.


The bottom of a wave, the valley between the crests.


In the direction from which the wind is blowing.


Vang - A block and tackle running from near the base of the mast to a point on the underside of the boom, usually forward of mid-boom, used by racing sailors to control the shape of the sail, and by cruising sailors to prevent the boom from lifting when running down wind.

VHF - Very high frequency; a bandwidth designation commonly used by marine radios.

Very High Frequency radio waves. (2) A radio that transmits in the VHF range. VHF radios are the most common communications radio carried on boats, but their range is limited to "line of sight" between the transmitting and receiving stations.


One of a number of horizontal lines on the hull of a ship indicating the surface of the water when the ship is under various loads.


i) A ridge of water between two depressions, ii) a long body of water curling into an arched form and breaking on the shore.


A mechanical device used to pull in a line or chain that may have a heavy load on it, i.e. an anchor line or a sheet attached to a sail under pressure, using a gear ration winding movement.


The direction or side of an object that faces the prevailing wind; opposite of leeward.

Basically, the side of the boat that the wind hits first is the windward side. The other side is leeward.


Sailing directly downwind with the sails out (the jib is sometimes held out with a pole) to either side of the boat.

"Belle Argo" sailing Wing-on-Wing.

Note that her jib is on a boom, being carried to port.




© Copyright 2008 David S. Malar and Angelika Jardine. All rights reserved.
Home -

Website Design and SEO (Search Engine Optimization) by