Nautical Glossary

Compiled from: <>, and Arthur Ransome's Swallows and Amazons and Swallowdale

Toward the rear of the boat, behind the boat.
At a right angle to the length of the boat.
Off the side, even with the boat.
Admiralty law
The “law of the sea”.
Floating free with the currents and tide, not under control.
Aft, After
Toward the stern (rear) of the boat.
When a boat is in water too shallow for it to float in, i.e: the boat’s bottom is resting on the ground.
Aid to navigation
Any fixed object that a navigator may use to find his position, such as permanent land or sea markers, buoys, radio beacons, and lighthouses.
Anchor locker
A locker used to store the anchor rode and anchor.
Anchor windlass
A windlass used to assist when raising the anchor.
(1) a heavy metal object designed such that its weight and shape will help to hold a boat in its position when lowered to the sea bottom on a rode or chain. (2) The act of using an anchor.
A place where a boat anchors, usually an established and marked area.
A device that measures wind velocity.
Toward the stern of a vessel, or behind the boat.
Athwart, Athwartships
Lying along the ship’s width, at right angles to the vessel’s centerline.
A second method of propelling a vessel. On a sailboat this could be an engine.
To raise an anchor off the bottom.
Backing (wind)
The changing of the wind direction, opposite of veering. Clockwise in the southern hemisphere, counter-clockwise in the northern hemisphere.
A method of weaving the end of a rope to keep it from unraveling.
To remove water from a boat, as with a bucket or a pump.
Weight at the bottom of the boat to help keep it stable. Ballast can be placed inside the hull of the boat or externally in a keel.
A region of shallow water usually made of sand or mud.
The widest part of a boat.
Bear away, bear off
To fall off. A boat falls off the wind when it points its bow further from the eye of the wind. The opposite of heading up.
Beaufort wind scale
Used to gauge wind speed using observations of the winds effects on trees and other objects. LINK TO BEAUFORT SCALE TABLE
(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 mount for the compass, usually located on the wheel’s pedestal.
A sturdy post mounted on the bow or stern to which anchor or mooring lines may be attached.
Bitter end
The end of a line. Also the end of the anchor rode attached to the boat.
Block and tackle
A combination of one or more blocks and the associated tackle necessary to give a mechanical advantage. Useful for lifting heavy loads.
One or more wheels with grooves in them (pulleys) designed to carry a line and change the direction of its travel. A housing around the wheel allows the block to be connected to a spar, or another line. Lines used with a block are known as tackle.
Also bosun, bos’n, bo’s’n, and bo’sun, all of which are pronounced bosun. A crew member responsible for keeping the hull, rigging and sails in repair.
The front of the boat.
A knot used to make a loop in a line. Easily untied, it is simple and strong. The bowline is used to tie sheets to sails.
A wave that approaches shallow water, causing the wave height to exceed the depth of the water it is in, in effect tripping it. The wave changes from a smooth surge in the water to a cresting wave with water tumbling down the front of it.
The room from which a ship is controlled. On a smaller boat this is usually not a room, is outside, and is known as a cockpit.
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.
An interior wall in a vessel. Sometimes bulkheads are also watertight, adding to the vessel’s safety.
A room inside a boat.
The curvature of an object such as a sail, keel or deck. Usually used when referring to an objects aerodynamic or hydrodynamic properties.
Can buoy
A cylindrical buoy painted green and having an odd number used in the United States as a navigational aid. At night they may have a green light. Green buoys should be kept on the left side when returning from a larger body of water to a smaller one.
The person who is in charge of a vessel and legally responsible for it and its occupants.
Cardinal points
The points of North, South, East and West as marked on a compass rose.
Celestial navigation
A method of using the stars, sun and moon to determine one’s position. Position is determined by measuring the apparent altitude of one of these objects above the horizon using a sextant and recording the times of these sightings with an accurate clock. That information is then used with tables in the Nautical Almanac to determine one’s position.
Center line
The imaginary line running from bow to stern along the middle of the boat.
A navigable route on a waterway, usually marked by buoys. Channels are similar to roads where the water is known to be deep enough for ships or boats to sail without running aground.
Chart table
A table designated as the area in the boat where the navigator will study charts and plot courses.
The location where the deck joins the hull of the boat.
Small, steep disorderly waves.
A fitting to which lines can be easily attached.
Compass course
The course as read on a compass. The compass course has added the magnetic deviation and the magnetic variation to the true course.
Compass rose
A circle on a chart indicating the direction of geographic north and sometimes also magnetic north. Charts usually have more that one compass rose. In that case the compass rose nearest to the object being plotted should be used as the geographic directions and magnetic variations may change slightly in different places on the chart.
Coordinated Universal Time (UTC)
The international time standard. It is the current term for what was commonly referred to as Greenwich Meridian Time (GMT). Zero (0) hours UTC is midnight in Greenwich England, which lies on the zero longitudinal meridian. Universal time is based on a 24 hour clock, therefore, afternoon hours such as 4 p.m. UTC are expressed as 16:00 UTC (sixteen hours, zero minutes). Since a day is 24 hours long, the world may be split into 15 degree wide longitudinal bands (360 degrees/24 hours). Each band represents one hour. As an example, Huntsville Alabama is located at approximately 90 degrees west longitude, hence, local time lags UTC time by 6 hours (90/15, assuming Central Standard Time, 5 hours in Central Daylight Time). So, if the universal time is 14:30 UTC, United States Central Standard Time would be 8:30 am CST. <>
The movement of water, due to tides, river movement and circular currents caused by the motion of the earth.
A device that projects beyond the side of the boat to raise objects from the water. Typically a single davit is used on the bow of a vessel to raise an anchor, and a pair are used on the side or stern of the vessel to raise a dinghy.
Dead ahead
A position directly in front of the vessel.
Dead reckoning
A method of determining position by making an educated guess based on last known position, speed and currents.
The underside of the deck, viewed from below (the ceiling.)
Depth sounder
An instrument that uses sound waves to measure the distance to the seafloor.
Displacement speed
Also hull speed. The theoretical speed that a boat can travel without planing, based on the shape of its hull. This speed is 1.34 times the length of a boat at its waterline. Since most monohull sailboats cannot exceed their hull speed, longer boats are faster.
The weight of a boat measured as a the weight of the amount of water it displaces. A boat displaces an amount of water equal to the weight of the boat, so the boat’s displacement and weight are identical.
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.
In the direction the wind is blowing.
An electrical depth sounder that uses sound echoes to determine water depth. It does so by timing how long it takes a sound pulse to leave the instrument travel to the seafloor and return to the receiver on the ship.
Fall off
Also bear away or bear off. A boat falls off the wind when it points its bow farther from the eye of the wind. The opposite of heading up.
The distance that wind and seas (waves) can travel toward land without being blocked. In areas without obstructions the wind and seas can build to great strength, but in areas such as sheltered coves and harbors the wind and seas can be quite calm.
Debris floating on the water surface.
Following sea
Sea with waves approaching from the stern of the boat.
Toward the bow (front) of the vessel.
Also fo’c’sle or fo’csle. Pronounced fo’csle. The most forward below decks area of a vessel.
A storm with a wind speed between 34 to 40 knots.
The kitchen area on a boat.
Global Positioning System
GPS for short. A system of satellites that allows one’s position to be calculated with great accuracy by the use of an electronic receiver.
Great circle route
A course that is the shortest distance between two points. the center of a great circle is the center of the earth.
Greenwich Meridian Time (GMT)
A time standard that is not affected by time zones or seasons. Now called Coordinated Universal Time (UTC).
Ground swells
Swells that become shorter and steeper as they approach the shore due to shallow water.
To attempt to contact another boat or shore, either by voice or radio.
Hand rail
Hand hold. Usually along the cabin top or ladder.
The individual who is in charge of a harbor.
A sliding or hinged opening in the deck, providing people with access to the cabin or space below.
Haul out
Remove a boat from the water.
Hawse hole
A hole in the hull for mooring lines to run through.
A rope that is very large in diameter, usually used when docking large vessels.
An object that might not allow safe operation. A group of rocks just under the water or a submerged wreck could be a navigational hazard.
Head seas
Waves coming from the front of the vessel.
Head up
To turn the bow more directly into the eye of the wind. The opposite of falling off.
The toilet and toilet room in a vessel.
The forward motion of a vessel through the water.
Heaving to
To slow or stop the forward motion of the boat, such as when in heavy seas.
Heavy seas
When the water has large or breaking waves in stormy conditions.
Heavy weather
Stormy conditions, including rough, high seas and strong winds.
High tide
The point of a tide when the water is the highest. The opposite of low tide.
A knot used to attach a line to a cleat or other object.
Where the water and sky or ground and sky appear to intersect.
The main structural body of the boat, not including the deck, keel, mast, or cabin. The part that keeps the water out of the boat.
A strong tropical revolving storm of force 12 or higher. In the northern hemisphere. hurricanes revolve in a clockwise direction. In the southern hemisphere they revolve counterclockwise and are known as typhoons.
(1) toward the center of the boat. (2) an engine that is mounted inside the boat.
A dinghy or raft that can be inflated for use or deflated for easy stowage.
A flat surface built into the bottom of the boat to reduce the leeway caused by the wind pushing against the side of the boat. A keel also usually has some ballast to help keep the boat upright and prevent it from heeling too much.
(1) a speed of one nautical mile per hour. (2) a method of attaching a rope or line to itself, another line or a fitting.
Land breeze
A wind moving from the land to the water due to temperature changes in the evening.
A line attached to a tool.
To tie something with a line.
(1) to put a boat in the water. (2) a small boat used to ferry people to and from a larger vessel.
Lead line
A line with a weight on the end used to measure depth. The lead is dropped into the water and marks on the line are read to determine the current water depth. The lead usually has a cavity to return a sample of the bottom type (mud, sand, etc.)
Three nautical miles.
The direction away from the wind. Opposite of windward.
The sideways movement of a boat away from the wind, usually unwanted. Keels and other devices help prevent a boat from having excessive leeway.
Life jacket
A device used to keep a person afloat. Also called a life preserver, life vest, PFD or personal flotation device.
Life raft
An emergency raft used in case of serious problems to the parent vessel, such as sinking.
(1) a device used to measure the distance traveled through the water. The distance read from a log can be affected by currents, leeway and other factors, so those distances are sometimes corrected to a distance made good.
Imaginary lines drawn through the north and south poles on the globe used to measure distance east and west. Greenwich England is designated as 0 with other distances being measured in degrees east and west of Greenwich.
Magnetic north
The direction to which a compass points. Magnetic north differs from true north because the magnetic fields of the planet are not exactly in line with the north and south poles. Observed differences between magnetic and true north is known as magnetic variation.
Make fast
To attach a line to something so that it will not move.
Make way
Moving through the water.
A pointed tool used to separate the strands of a rope or wire.
A small line used to pull a heavier line or cable. The messenger line is usually easier to throw, lead through holes or otherwise manipulate than the line that it will be used to pull.
A place on a boat where its beam is the widest.
Nautical miles
Distance at sea is measured in nautical miles, which are about 6067.12 feet, 1.15 statute miles or exactly 1852 meters. Nautical miles have the unique property that a minute of latitude is equal to one nautical mile (there is a slight error because the earth is not perfectly round.) Measurement of speed is done in knots where one knot equals one nautical mile per hour.
To attach a boat to a mooring, dock, post, anchor, etc.
Mooring line
A line used to secure a boat to an anchor, dock, or mooring.
A place where a boat can be moored. Usually a buoy marks the location of a firmly set anchor.
Nautical mile
Distance at sea is measured in nautical miles, which are about 6067.12 feet, 1.15 statute miles or exactly 1852 meters. Nautical miles have the unique property that a minute of latitude is equal to one nautical mile (there is a slight error because the earth is not perfectly round.) Measurement of speed is done in knots where one knot equals one nautical mile per hour. A statute mile is used to measure distances on land in the United states and is 5280 feet.
Navigation lights
Lights on a boat help others determine its course, position and what it is doing. Boats underway should have a red light visible from its port bow, a green light on the starboard bow and a white light at its stern. Other lights are required for vessels under power, fishing, towing, etc.
On the side of the hull that the water is on. Outboard engines are sometimes just called outboards.
Pad eye
A small fitting with a hole used to guide a line.
A line attached to the bow of a dinghy and used to tie it up or tow it.
Lines of latitude
Pay out
To let out a line.
Personal Flotation Device, a device used to keep a person afloat. Also called a life jacket, life preserver or life vest.
Pile, piling
A pole embedded in the sea bottom and used to support docks, piers and other structures.
Poop deck
A boat’s aft deck.
(1) the left side of the boat from the perspective of a person at the stern of the boat and looking toward the bow. The opposite of starboard. (2) A porthole. A window in the side of a boat, usually round or with rounded corners. Sometimes portholes can be opened, sometimes they are fixed shut. Also see hatches
A port, a window in the side of a boat, usually round or with rounded corners. Sometimes portholes can be opened, sometimes they are fixed shut.
A type of dinghy with a flat bow.
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.
The part of the bow forward of where it leaves the waterline.
A sturdy railing around the deck on the bow.
The side of a boat aft of the beam. There are both a port quarter and a starboard quarter.
Quartering sea
A sea which comes over the quarter of the boat.
Sleeping areas on the boat.
Radio detection and ranging. An electronic instrument that uses radio waves to find the distance and location of other objects. Used to avoid collisions, particularly in times of poor visibility.
Radio beacon
A navigational aid that emits radio waves for navigational purposes. The radio beacon’s position is known and the direction of the radio beacon can be determined by using a radio direction finder.
Leading a line through a block or other object.
Rhumb line
A line that passes through all meridians at the same angle. When drawn on a Mercator chart, the rhumb line is a straight line. However the Mercator chart is a distortion of a round globe on a flat surface, so the rhumb line will be a longer course than a great circle route.
Traditionally a line must be over 1 inch in size to be called a rope.
Rudder post
The post that the rudder is attached to. The wheel or tiller is connected to the rudder post.
Safety harness
A device worn around a person’s body that can be attached to the ship to prevent the person from being separated from the ship.
Sampson post
A strong post used for to attach lines for towing or mooring.
A propeller.
An opening through the toe rail or gunwale to allow water to drain back into the sea.
Sea cock
A valve used to prevent water from entering at a through hull.
To make fast. To stow an object or tie it in place.
A covering to protect the bottom of a boat.
A knot used to temporarily shorten a line.
Snatch block
A block that can be opened on one side, allowing it to be place on a line that is already in use.
The place where two lines are joined together end to end.
The right side of the boat from the perspective of a person at the stern of the boat and looking toward the bow.
Steerage way
In order for the rudder to be able to properly steer the boat, it must be moving through the water. The speed necessary for control is known as steerage way.
The forward edge of the bow. On a wooden boat the stem is a single timber.
The aft part of a boat. The back of the boat.
Stern line
Line running from the stern of the boat to a dock when moored.
To put something away.
Stuffing box
A fitting around the propeller shaft to keep the bearing lubricated and to keep water out of the boat.
A rotating fitting used to keep a line from tangling.
A hinged support for the bottom of a mast so that the mast can be lowered easily when passing under bridges.
Lines used with blocks in order move heavy objects.
A small line free to flow in the direction of the breeze. It is attached to sails, stays in the slot, and in other areas, enabling the helmsman and crew to see how the wind is flowing.
Also athwartships. Across the width of a boat.
Toe rail
Small rail around the deck of a boat. The toe rail may have holes in it to attach lines or blocks. A larger wall is known as a gunwale.
The sides of the hull above the waterline and below the deck.
The time steaming from port to the study site and vice versa.
Under way
A vessel in motion is under way.
To windward, in the direction of the eye of the wind.
Waves generated in the water by a moving vessel.
(1) a division of crew into shifts. (2) The time each watch has duty.
The line where the water comes to on the hull of a boat. Design waterline is where the waterline was designed to be, load waterline is the waterline when the boat is loaded.
To bind the strands of a line with a small cord.
Wind scoop
Funnel used to force wind in a hatch and ventilate the below decks area.
A mechanical device used to pull in cable or chain, such as an anchor rode.
Swinging off course, usually in heavy seas. The bow moves toward one side of the intended course.
Used to indicated times measured in Coordinated Universal Time, a successor to Greenwich Mean Time. A time standard that is not affected by time zones or seasons.