Glossary of Nautical Terms

Note that while the glossary may seem like merely a reference tool, it is important to take note of various definitions as they may show up on the test.  Beyond that, the use of correct marine terminology is a sign of professionalism and can help reduce misunderstandings when communicating onboard ships.

A

Abaft – Toward the stern relative to a particular location (eg. “abaft of the starboard davit”)

Abaft the beam – Further aft than the beam in terms of an angle (eg. “two points abaft the starboard beam” refers to an object 22.5 degrees towards the stern from the starboard beam or a relative bearing of 112.5 degrees from the bow)

Abandon ship – A directive to leave the vessel, typically in the event of an imminent loss of the ship.

Abeam – An angle perpendicular to the ships bow (eg. the starboard beam is 90 degrees, port beam is 270 degrees)

Absolute bearing – The bearing of an object relative to either magnetic north or geopositional (true) north

Accommodation ladder – A flight of stairs used for embarking and disembarking from the vessel.

Adrift – Afloat and unattached to a mooring of any kind such that it moves with the wind and current.

Aft – Toward the stern of the vessel

Aground – Indicating that the object or vessel is either wholly or partially resting on land.

Aid to navigation (ATON) – An object external to the vessel whose purpose is to assist navigators in determining the location of safe water. (eg. a buoy, lighthouse, sector light, etc)

Aloft – Overhead or above.

Amidships – Refers to a point halfway between to bow and the stern of the vessel.  Can also refer to the midway point between port and starboard (eg. “the rudder is amidships”)

Anchor ball – A round, black shape designed to be hoisted to indicate to other vessels during daytime that the vessel is at anchor.

Anchor rode – The anchor line (rope, cable, chain, or combination of materials) connecting the anchor to the vessel.

Anchor’s aweigh – Expression used to indicate the anchor has been lifted from the sea floor, typically during the weighing of the anchor.

Arc of visibility – The number of degrees over which a light is visible.  This commonly is used in reference to sidelights, sector lights, and other navigational lights that are visible from anything less than 360 degrees.

Astern – In a direction toward the stern (or rear) of the vessel and beyond.

Athwartships – In a direction perpendicular to the forward-aft line of the ship.

Azimuth – The angle to an object usually measured clockwise from a reference direction (often magnetic or true north).  An observed object with a bearing of true west would have an azimuth of 270 degrees from true north.

B

Bailer – A device used to bail out a boat (remove water from it).

Ballast – Material used to add weight, often low to the hull, in order to increase ship stability.

Ballast tank – A compartment which can be filled with water for the purposes of increasing ship stability.

Barometer – An instrument for measuring air pressure. Used in weather forecasting.

Beacon – A fixed aid to navigation that is usually brightly painted and often equipped with lights.  Examples include lighthouses and range light beacons.

Beam – The width of a vessel at its widest point, or a point alongside the ship at the midpoint of its length.

Beam sea – Waves coming perpendicular to the ship’s course.

Bearing – The horizontal direction of one point relative to another.  This can either be relative or absolute.

Beaufort scale – A scale that categorizes wind speed.  This categorization defines what we might call a “gale force wind” for example as being 34–40 knots of wind speed.  See Beaufort scale.

Belay – An order to halt the execution of a prior order.

Bell rope – A piece of rope (often ornamental) fastened to the clapper of a ships bell for holding onto while ringing the bell.

Bend – A knot used to join two ropes or lines.

Berth – A location in a port or harbor used specifically for mooring vessels while not at sea.  Can also refer to a safe margin of distance to be kept by a vessel from another object, as in “give it a wide berth”

Bight – Generally refers to loose rope but, as in the danger of standing in a bight, also refers to the area that can become dangerous when the rope is tightened.

Bilge – The space at the bottom of the hull.  It’s here that water and other liquids may gather.

Binnacle – The stand dedicated to holding a compass.

Bitt – A post or pair of posts mounted on the ship for fastening ropes or cables.

Bitter end – The last part or loose end of a rope or cable.

Block – A case containing one or more pulleys with sheaves over which a line is roved.

Boat hook – A long pole with a blunt tip and a hook on the end.  Typically used to assist when docking or in trying to reach objects in the water.

Boathouse – A building used to store boats, sheltering them from the elements.

Boatswain – Also known as a “Bosun” or “Deck Boss” and is typically the most qualified among the deck crew and responsible for supervising the deck crew.  Specific duties depend on the nature of the vessel and it’s operation.

Bosun’s chair – A short board or heavy canvas, secured in a bridle of ropes, used to hoist a man aloft or over the ship’s side for painting and similar work.

Boatwright – A maker of boats, especially of traditional wooden construction.

Bollard – A substantial vertical pillar to which lines may be made fast.  Often bollards will have horizontal posts coming out of the sides to facilitate securing lines via figure 8 loops.

Boom

1 – A floating barrier for a particular use.  Log booms are often used by tug boats to encircle a large number of logs for towing.  Pollution response booms are used to control the spread of substances at the surface of the water.
2 – The lower spar on a sail that people should be mindful of because of it’s capacity to swing across with substantial force when tacking.

Bowline – A knot used to form a loop that neither slips nor becomes difficult to untie.

Bowpicker – A gillnetter that fishes by deploying gillnets from the bow.

Bowsprit – A spar projecting forward of the bow.

Bow thruster – A propeller mounted underwater near the bow that is useful for lateral maneuvering.  Typically it can be rotated so it can apply its propulsion towards either starboard or port.

Boxing the compass – To state all 32 points of the compass, starting at north and proceeding clockwise.

Breaker – A breaking wave that breaks into foam against the shore, a shoal, a rock or a reef.  Can be a valuable indicator of underwater danger.

Breakwater – A structure used to dampen the effect of wind and waves.

Bridge – The part of the ship’s superstructure from which it is navigated.

Broadside – Refers to one of the sides of the ship, usually as it pertains to the direction of objects relative to the ship’s position in the water. (eg. “The waves were hitting us broadside”)

Bulbous bow – A protrusion at the bow just below the waterline that helps reduce ship drag through the water.

Bulk cargo – Commodity cargo that is transported unpackaged in large quantities.

Bulk carrier – A merchant ship specially designed to transport unpackaged bulk cargo in its cargo holds.

Bulkhead – One of the upright partitions (similar to a wall) dividing a ship into compartments and serving to add structural rigidity and to prevent the spread of leakage or fire.

Bulwark – The exterior part of a ship’s superstructure above the deck.

Bunker fuel – A heavy, viscous fuel oil that is used primarily to power large marine vessels.

Buoy – A floating object, usually anchored at a given position for a specific purpose.

C

Cabin cruiser – A type of powered pleasure craft that provides accommodation for its crew and passengers inside the structure of the craft.

Cable

1 – Wire rope.
2 – A distance equivalent to 1/10 of a nautical mile or 608 feet.

Camber – The lateral curvature of the deck (to facilitate water run off).

Capsize – To list so severely that the vessel rolls over, exposing the keel.

Capstan – A capstan is a round, cylindrical post that is typically hydraulically powered with the capacity to turn in order to haul on line.

Captain – The person lawfully in command of a vessel.

Cardinal – Referring to the four main points of the compass: north, south, east, and west.

Cargo ship – Any ship or vessel that carries cargo, goods, and materials from one port to another.

Catamaran – A vessel with two hulls.

Celestial navigation – Navigation by the position of celestial objects, including the stars, Sun, and Moon.

Centerline – An imaginary line down the center of a vessel lengthwise.

Centerboard – A retractable plate that can be slotted downward through the hull that helps provide lateral stability.

Chafing – Wear that is caused by constant rubbing against another surface.

Chafing gear – Material applied to an object to prevent or reduce the effect of chafing.

Chain locker – A space in the forward part of the ship where the anchor chain is stored when not in use.

Chief Engineer – The senior engineering officer.

Chief Officer – The chief mate or first mate and the second-in-command on a merchant ship.

Chine – The intersection of the bottom and the sides of the hull of a vessel representing a corner in the hull.  Note that this corner on certain vessels can, when at speed, induce what’s called a “chine lock” where the vessel begins to use a chine as though it were a keel thereby keeping a vessel listed at the angle of the chine and resisting a more natural righting lever.

Chock

1 – A shaped support or cradle for a ship’s boat, barrel, etc.
2 – Can be used to describe various metal fittings that act as fairleads or guides for rope, cable, or chain.

Cleat – A metal or wooden object attached to a boat or dock and around which a rope can be tied.

Coaming – Any vertical surface on a ship designed to deflect or prevent entry of water.  Often found around hatches, skylights, and various other points of entry on a vessel.

Cofferdam – An insulating space between two watertight bulkheads or decks.

Commanding Officer – The captain on a ship, also referred to as the CO or skipper.

Companionway – A hallway on a ship.

Complement – A collective term for all of the persons in a ship′s crew, including officers.

Conn – To direct a ship or submarine from a position of command. While performing this duty, an officer is said to “have the conn”.

Coxswain – The helmsman or crew member in command of a boat.  Often the name given to the person in charge of a smaller or subordinate vessel.

D

Davit – A crane, often found working in pairs and usually made of steel, used to lower things over the side of a ship, including lifeboats.

Dead ahead – Directly ahead or in front.

Deadhead – A partially submerged log in the water who’s buoyancy has been affected such that it floats vertically in the water.  Deadheads represent hazards to navigation as they are difficult to see and yet can damage vessels and their gear underwater upon impact.

Deadlight – A strong shutter fitted over a porthole or other opening that can be closed in bad weather.

Dead reckoning – A method of navigation that estimates a ship’s position from the distance run measured by the log and the course steered.

Deckhead – The underside of the deck above or what might be considered a compartment’s ceiling.

Derrick – A derrick is a lifting device composed of a guyed (supported by cables) mast and boom that can be articulated by adjusting its guys.

Devil’s claw – A type of chain stopper often used to secure an anchor and its chain in its hauled up position.  Consists of a two-pronged hook that fits over a link of chain and a turnbuckle that is fastened to a strong point.

Dipping the eye – A method of attaching more than one fixed loop to a bollard so that each can be lifted off without disturbing the others. The second loop is passed upwards through the eye of the first before being secured over the bollard.

Displacement – The weight of water displaced by the immersed volume of a ship’s hull, exactly equivalent to the weight of the whole ship.

Displacement hull – A hull designed to travel through the water, rather than planing over it.

Double bottom tank – A double bottom tank on a ship is a structural feature that consists of an additional layer or compartment located beneath the main hull of the vessel. This additional layer forms a secondary bottom or inner bottom within the hull structure, providing enhanced protection against hull damage.

Downflooding – The entry of water through any opening into the hull or superstructure of an undamaged vessel, possibly through an open door or porthole, loose or open hatch, ventilator opening, etc.

Drogue – Also known as a sea anchor or drift anchor, a drogue is often deployed from the bow of a vessel in heavy weather to prevent a vessel from turning broadside to the waves while adrift.  It is typically shaped like a cone or parachute capable of providing drag as it is pulled through the water.

Dry dock – is an enclosed area that can be flooded to allow a load to be floated in, then drained to allow that load to come to rest on a dry platform.  Typically used for the repair and maintenance of vessels.

Dunnage – Inexpensive material used to secure or support cargo and various objects during transportation.  Old, wooden 4×4 inch beams could be used as dunnage under a large stack of plywood for example.

E

Eye splice – A closed loop or eye at the end of a rope or cable that is made by weaving the working end back into the standing portion of the line.

F

Fairlead – A device usually found near the hull of the ship designed to safely control the movement of a line that is passed through it.  Fairleads can be partially open or fully enclosed.

Fairway – The usual course taken by vessels through a harbor or coastal waters.  Commonly used courses like these may contain fairway buoys that help separate incoming from outgoing traffic along this course.

Fantail – A type of overhanging stern found on some ships.

Fathom – A unit of length equal to 6 feet (1.8 m), roughly measured as the distance between a man’s outstretched hands.  Typically used during sounding.

Fender – A flexible bumper used on the outside of boats to prevent damage near docks or other vessels.

Fetch – The distance across water that wind and waves have traveled.  Useful to consider when trying to predict the sea state of a particular location as the fetch length combined with wind speed and wind duration will help determine the size of waves in the area.

Fid – A tapered tool used for separating the strands of rope during splicing.

Flake – Most commonly used to describe the process of laying out a line in such a way as it can be payed out without the possibility of introducing twists or knots.

Fluke – The wedge shaped part of an anchor’s arms that digs into the sea floor.

Following sea – Waves travelling in the same direction as the ship.

Forecastle – The upper and forward most part of the ship.

Forepeak – The hold of the ship within its bow.

Founder – To fill with water and sink.

Freeboard – The distance from the waterline to the upper deck, measured at the lowest point where water can enter the vessel.

Freeing ports – Openings in the bulwarks above deck to allow large excesses of water to drain overboard.

G

Gangway – A passage through the side of a ship through which it may be boarded.

Give-way vessel – In a situation where two vessels are approaching one another so as to involve a risk of collision, the give way vessel is the one directed to keep out of the way of the other.  See Collision Regulations.

Gunwale – The top edge of the hull, often stiffened or reinforced.  Also called the gunnel.

H

Hard eye – An eye splice with a thimble fitted inside.

Hawsepipe – The shaft or hole in a vessel’s bow through which the anchor chain passes.

Head

1 – The forwardmost or uppermost portion of the ship.
2 – The toilet on a vessel.

Head sea – Waves travelling in an opposite direction of the ship.

Heading – The direction in which the nose of a vessel is pointing.  This is different from both it’s course and the direction over land it may be moving.

Heave to – (also hove to) Stopping forward propulsion.

Heaving line – A line with a soft, weighted end that is meant to be used for throwing.  Typical uses include tying to mooring line and throwing to a person on a dock or tying to a towing line and throwing to a vessel needing a tow.

Heel – The sideways tilt of a ship as a result of environmental and propulsion forces.  This is different from listing which is a sideways tilt due to a ship’s weight distribution.

Helm – The ship’s steering mechanism.

Helmsman – A member of the crew responsible for steering the ship.

Hitch – A knot used to tie a line to a fixed object.

Hogging – The stress a ship experiences that causes the center of the ship to bend upward (and subsequently, the bow and stern to bend downward).  The opposite of sagging.

Hull speed – The maximum efficient speed of a displacement-hulled vessel.

Hydrofoil – A boat with wing-like foils mounted on struts below the hull, lifting the hull entirely out of the water at speed and therefore greatly reducing water resistance.

Hydroplaning – When a vessel is supported by the planing forces of it’s speed across the surface of the water as opposed to it’s buoyancy forces.

Hydrostatic release – A type of fastener that is often used to secure liferafts.  It has the feature of automatically breaking when submerged in sufficient water which, in the case of a life raft, would allow the raft to float free to the surface in the event a ship sinks.

I

J

Jack – Informally refers to a flag flown by a ship.  The term “Jack flag” refers to one flown on a short jackstaff at the bow indicating its nationality or particular seagoing service.

Jacob’s ladder – A flexible hanging ladder consisting of vertical ropes or chains supporting horizontal rungs, used to allow access over the side of a ship.

K

Kedge – To move (a ship) by means of a line attached to a small anchor dropped at the distance and in the direction desired.  A kedge anchor would refer to an anchor used for this purpose.

Keel – The bottom-most longitudinal structural element on a vessel.

Knot

1 – A unit of speed equivalent to 1 nautical mile (1.8520 km) per hour.
2 – A fastening made by tying together lengths of material, such as rope.

L

Lang lay – Refers to rope or cable that has it’s strands laying the same direction as the fibers or wires.

Leadline – A device used to measure water depth using a marked line with a lead weight at the bottom.

Lee side – The side of a ship that is sheltered from the wind.  Opposite of windward side.

Lifeboat – A small boat kept onboard a ship to be used in the event of the ship being abandoned.  Rescue lifeboats refer to ones launched from shore to rescue people and vessels in distress.

Liferaft – An inflatable boat to be used as a last resort in the event that the ship is lost.  Liferafts are typically meant to float to the surface in the event the ship sinks and are usually inflated by pulling the painter line attached to raft.

Line – A rope, cable, or other cordage having an understood purpose (ie. spring lines, bow line, stern line, tag line, etc.)

List – When a vessel tilts sideways due to imbalanced weight.

M

Magnetic north – The direction towards the north magnetic pole.  Varies slowly over time.

Magnetic bearing – An absolute bearing using magnetic north.

Making way – When a vessel is moving under its own power.

Man overboard – An emergency call indicating someone has fallen overboard and must be rescued.

Manifest – A document listing the cargo, passengers, and crew of a ship for the use of customs and other officials.

Marlinspike – A tapered marine tool commonly used for untying knots, separating strands of rope, tightening or loosening threaded shackles, and a variety of other marine purposes.

Masthead – A small platform partway up the mast, just above the height of the mast’s main yard.

Master – A term that was used to describe the person responsible for navigation but that wasn’t in command during combat.

Midships – see amidships.

Monkey’s fist – A knot commonly tied on the end of a heaving line to add weight to the line.

Mousing – Several turns of light line used to secure an object.  Common uses include securing the pin of a shackle or mouth of a hook.

Muster station – A specific location on a vessel planned as a gathering place during an emergency or a muster drill.

N

Nautical mile – A unit of length corresponding to approximately one minute of latitude (along a meridian arc), 1,852 meters, or 1.151 miles.

O

Oiler – The job title of a seaman holding a junior position in a ship’s engineering crew.

Overtaking sea – Waves moving in the same direction as the ship and with a speed greater than the ship’s.

P

Painter – A rope attached to the bow of a vessel.

Parbuckle – A method of using two ropes to lift (by way of rolling) a person or cylindrical object.

Pilot boat – A type of boat used to transport maritime pilots between land and the inbound or outbound ships that they are piloting.

Pitchpole – To capsize a boat stern over bow, rather than by rolling over.

Point – An angle equivalent to 1/32nd of a circle or 11.25 degrees.

Purchase – A system of pulleys and ropes used to multiply the force applied to lift a heavy load.

Q

Quarter – The aft 90 degrees to either port or starboard.

Quartering sea – Waves approaching from approximately the middle of either the port or starboard quarter.

R

Radar – An electronic system designed to transmit radio signals and receive reflected images of those signals in order to determine their bearing and distance away. The term is an acronym for Radio Detection and Ranging.

Radar reflector – A device added to vessels or aids to navigation in order to increase their radar cross section, making them more visible to radar systems.

Red to red – The passing of ships where they leave each other on their port side (referred to in this way because the color of the port sidelight is red).

Reeve – To pass (something, such as a rope) through a hole or opening.  Commonly used in reference to passing a rope through a block.

Rode – A line used to attach an anchor to a boat.  Refers to the entire length of connecting equipment between the boat and the anchor.

Rubbing strake – A protective strip or molding typically installed along the hull of a boat or ship. Its primary purpose is to provide added protection to the vessel’s hull from damage caused by abrasion, impact, or contact with other boats, docks, piers, or structures.

S

Sagging – The stress a ship experiences that causes the center of the ship to bend downward (and subsequently, the bow and stern to bend upward).  The opposite of hogging.

Scope – The length of a vessel’s anchor rode in relation to the depth of the water.

Scuppers – Openings in the ships hull near the waterline that are meant to drain water that accumulates on deck.

Sea anchor – See drogue.

Sheave – The grooved wheel inside a block that moves as the line inside it is roved.

Sheer – The longitudinal curvature of the main deck.

Shoal – A shallow place in a body of water.

Single up – To reduce the number of mooring lines attached to its mooring (typically to one bow and one stern line) in preparation for departure.

Slack tide – The period of time inbetween the ebb and flood during which the tide is neither rising nor falling.

Sling – Ropes, cables, or straps, commonly with an eye in either end.  Used for hoisting operations.

Soft eye – An eye splice without a thimble fitted.

Sounding – Measuring the depth of the water.

Snatch block – A block that, either by being open or having a hinge allowing it to open, can have a line put into the sheave without using the free end of the line.

Stand-on vessel – In a situation where two vessels are approaching one another so as to involve a risk of collision, the stand-on vessel refers to the one with right of way.  See Collision Regulations.

Stem – The forwardmost edge of the ship’s hull.

Spurling pipe – The pipe between the chain locker and the anchor windlass on deck.

T

Trim –  The trim refers to the position of the ship as it is described by it’s forward and aft drafts.

True bearing – An absolute bearing using true north.

True north – The direction of the geographical north pole.

U

V

W

Warp – To move a vessel by hauling on a line attached to a reliably fixed position attachment point (anchor, dock, etc.)

Weigh anchor – To haul up an anchor.

Windage – The wind resistance of a boat as it travels.

Windlass – A machine with a drum, usually on a horizontal axis, that is used for hauling on lines.

Windward – In the direction the wind is coming from.  The windward side of the boat is the side that is facing into the wind.

X

Y

Z