A

Aback
Wind on the wrong side of the sails.

Abaft
Toward the rear of the boat, behind the boat.

Abeam
At a right angle to the length of the boat.

Abreast
Off the side, even with the boat.

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.

Admeasure
Formal measurement of a boat for documentation.

Admiralty law
The "law of the sea".

Adrift
Floating free with the currents and tide, not under control.

Aerodynamic
Having a shape that that is not adversely affected by wind flowing past it.

Aft, after
Toward the stern (rear) of the boat.

After bow spring line
A mooring line fixed to the bow of the boat and leading aft where it is attached to the dock. This prevents the boat from moving forward in its berth. Its opposite, the forward quarter spring line, is used to keep the boat from moving aft in its berth.

Agonic line
The line around the earth where there is no magnetic deviation between magnetic north (as measured by a compass) and true north.

Aground
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.

Alee
To the leeward side (downwind).

Aloft
Above the boat, in its rigging.

Amas
The outboard hulls of a trimaran.

Amidships
In the center of the boat.

Anchor bell
A bell required to be rung at certain times when at anchor during fog, according to the navigation rules.

Anchor bend
A type of knot used to fasten an anchor to its line.

Anchor chain
A chain attached to the anchor. The chain acts partially as a weight to keep the anchor lying next to the ground so that it can dig in better. Chain is also not damaged as much as line when lying on rocks. The weight of the chain also helps to absorb changes in the boat's position due to waves.

Anchor light
A white light, usually on the masthead, visible from all directions, used when anchored.

Anchor locker
A locker used to store the anchor rode and anchor.

Anchor rode
The line or chain attached to the anchor and secured to the boat.

Anchor roller
Also called bow roller. A fitting with a small wheel that allows the anchor and chain to roll over when dropping or raising the anchor. Some anchor rollers also have a provision to store the anchor as well.

Anchor watch
A watch kept when the boat is at anchor in case the anchor starts to drag.

Anchor windlass
A windlass used to assist when raising the anchor.

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. See kedge, lightweight, mushroom, and plow anchors.
(2) The act of using an anchor.

Anchorage
A place where a boat anchors, usually an established and marked area.

Anemometer A device that measures wind velocity. Aneroid barometer
A mechanical barometer used to measure air pressure for warnings of changing weather.

Antifouling
Poisonous paint used on the bottom of the boat to prevent barnacles and other organisms from growing on the ship's bottom.

Apparent wind
The apparent direction of the wind, which is affected by a boat's motion. The apparent wind is only the same as the true wind if the boat is stopped.

Astern
Toward the stern of a vessel, or behind the boat.

At the dip
A flag hoisted half way up a flagpole. Also see close up.

Athwart, athwartships
Lying along the ship's width, at right angles to the vessels centerline.

Atmospheric pressure
Also called barometric pressure. The weight of the atmosphere, an average of 1013.2 millibars or 29.2 inches of mercury at sea level. Measuring the changes in atmospheric pressure can help predict weather.

Autopilot
A device used to steer a boat automatically, usually electrical, hydraulic or mechanical in nature. A similar mechanism called self steering gear may also be used on a sailing vessel.

Auxiliary
A second method of propelling a vessel. On a sailboat this could be a engine.

Aweigh
To raise an anchor off the bottom.

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B

Backing (wind)
The changing of the wind direction, opposite of veering. Clockwise in the southern hemisphere, counter-clockwise in the northern hemisphere.

Backsplice
A method of weaving the end of a rope to keep it from unraveling.

Backstay
A stay (line or cable) used to support the mast. The backstay runs from the masthead to the stern and helps keep the mast from falling forward.

Backwinded
When the wind pushes on the wrong side of the sail, causing it to be pushed away from the wind. If the lines holding the sail in place are not released, the boat could become hard to control and heel excessively.

Bail
To remove water from a boat, as with a bucket or a pump.

Ballast
A weight at the bottom of the boat to help keep it stable. Ballast can be place inside the hull of the boat or externally in a keel.

Bar
A region of shallow water usually made of sand or mud, usually running parallel to the shore. Bars are caused by wave and current action, and may not be shown on a chart.

Barge
A long vessel with a flat bottom used to carry freight on rivers. Barges are usually not powered, being pushed or towed by a tugboat instead.

Barograph
An instrument used to keep a record of atmospheric pressure, such as on a paper drum.

Barometer
An instrument used to measure atmospheric pressure, usually measured in inches of mercury or millibars. Inches of mercury are used because some barometers use the height of mercury in a sealed tube as a measuring device.

Barometric pressure
Atmospheric pressure as measured by a barometer.

Batten down
Also batten the hatches. To put away all loose objects on the ship and to close all openings, such as ports and hatches, in preparation for heavy weather. Hatches used to be secured with battens.

Batten pockets
Pockets in a sail where battens can be placed to stiffen the sail.

Batten the hatches
Also batten down. To put away all loose objects on the ship and to close all openings, such as ports and hatches, in preparation for heavy weather. Hatches used to be secured with battens.

Batten
(1) A thin strip of hard material, such as wood or plastic.
(2) Battens are attached to a sail to stiffen it to a more preferred shape. They are placed in pockets sewn into the sail called batten pockets.
(3) Battens also used to be used to secure hatches.

Bay
An enclosed body of water with a wide mouth leading to the sea.

Beam reach
Sailing on a point of sail such that the apparent wind is coming from the beam (side) of the boat at about a 90° angle. A beam reach is usually the fastest point of sail. A beam reach is a point of sail between a broad reach and a close reach.

Beam
(1) The widest part of a boat.
(2) Abeam, at right angles to the length of the boat.
(3) Sturdy wooden timbers running across the width of a boat . Used to support the deck of a wooden 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.

Bearing
The direction of an object from the observer. "The lighthouse is at a bearing of 90 degrees."

Beat
To sail on a tack (direction) toward the wind.

Beating
Tacking. To sail against the wind by sailing on alternate tacks directions).

Beaufort wind scale
A method of measuring the severity of the force of wind, named after Admiral Beaufort who created the system. 0 is no wind, whereas 12 would be a hurricane.

Becket
A loop at the end of a line.

Bedding compound
A material used to join two objects completely. Usually used to create a water tight or very secure joint.

Bend on
To attach a sail and prepare it for use.

Bend
A type of knot used to connect a line to a spar or another line. Also the act of using such a knot.

Berth
(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."

Bight
The center of a slack line. (i.e: where it sags). Also a small indented curve in a shoreline.

Bilge pump
A mechanical, electrical, or manually operated pump used to remove water from the bilge.

Bilge
The lowest part of the interior of the boat where water collects.

Bimini
A cover used to shelter the cockpit from the sun.

Binnacle
The mount for the compass, usually located on the wheel's pedestal.

Binocular
A pair of small telescopes, one for each eye, used to magnify distant objects.

Bitt
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.

Block
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.

Boarding ladder
A ladder used to board the vessel. Boarding ladders may be designed to be useful from either the water or a dock and are usually stowed when not in use.

Boarding wave
A wave that breaks over the deck of the boat.

Boat hook
A pole with an attached hook at the end, used for either retrieving objects or fending them off.

Boat
A small vessel used to travel on the water, powered either by wind, power or oars. Also any small vessel carried on a larger ship. Also an abbreviation for; “Break Out Another Thousand”.

Boatswain
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.

Bollard
A large pillar, usually made of concrete or steel, to which a boat's mooring lines can by tied.

Bolt rope
A line (rope) sewn into the luff of a sail. The bolt rope fits in a notch in the mast or other spar when the sail is raised.

Boom vang
Any system used to hold the boom down. This is useful for maintaining proper sail shape, particularly when running or on a broad reach.

Boom
A spar that is used to secure the bottom of a sail, allowing more control of the position of a sail.

Bosun’s chair
A chair traditionally made from a plank and rope, used to hoist workers aloft to maintain the rigging.

Bosun’s locker
A locker where tools for maintaining the deck, rigging and sails are kept.

Bosun
Also boatswain, 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.

Bow & beam bearings
A set of bearings taken from an object with a known position, such as a landmark, to determine the ship's location. A type of running fix.

Bow
The front of the boat.

Bowditch
A reference book named after the original author, Nathaniel Bowditch. Updated versions contain tables and other information useful for navigation.

Bowline
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.

Bowsprit
A pole extending from the bow of a boat. The bowsprit is used to attach the headstay forward of the front of the boat's deck. This allows added sail area for the head sail.

Brace
A guy. A line used to control the movement of the object at the other end, such as a spar.

Braided line
A method of making lines that allows for greater strength and durability when using modern materials.

Breakers
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.

Breaking seas
With sufficiently strong wind, large waves can form crests even in deep water, causing the wave tops to tumble forward over the waves.

Breakwater
A structure build to improve a harbor by sheltering it from waves.

Breast line
A line attached laterally from a boat to a dock, preventing movement away from the dock.

Bridge
(1) 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.
(2) A man made structure crossing a body of water, usually for the use of automobiles or train. A boat intending to pass under a bridge needs to make sure it has sufficient vertical clearance unless it is a swinging bridge or a drawbridge.

Brightwork
Pieces of varnished wood or polished metal on a vessel.

Bristol fashion
A term used to describe a clean and orderly ship.

Broach to
An undesirable position in which a vessel is turned to expose its side to the oncoming waves.

Broaching
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 on the beam
The position of an object that lies off to one side of the vessel.

Broad reach
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.

Bulkhead
An interior wall in a vessel. Sometimes bulkheads are also watertight, adding to the vessel's safety.

Buntline hitch
A type of knot used to attach a line to a shackle.

Buoy
A floating device used as a navigational aid by marking channels, hazards and prohibited areas.

Burdened vessel
The vessel responsible for moving out of another vessels path according to the navigation rules. Also known as the give way vessel.

Burgee
A type of flag used to identify a boater's affiliation with a yacht club or boating organization.

By the lee
A point of sail similar to running where the wind is coming over the quarter of the sailboat on the same side that the main sail and boom are on. This point of sail is considered dangerous because of the possibility of an accidental jibe.

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C

Cabin
A room inside a boat.

Cam cleat
A mechanical cleat used to hold a line automatically. It uses two spring loaded cams that come together to clamp their teeth on the line, which is place between them. Also see jam cleat.

Camber
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. Nun buoys mark the other side of the channel. Also see green and red daymarks

Canal
A manmade waterway used to connect bodies of water that do not connect naturally. Canals use locks to raise and lower boats when connecting bodies of water that have different water levels. The Panama and Suez canals are two of the most famous.

Canoe stern
A pointed stern, such as those on a canoe.

Canvas
Tightly woven cloth used for sails, covers, dodgers and biminis. Typically made from cotton, hemp or linen. Modern sails are made out of synthetic materials generally known as sailcloth.

Capsize
When a boat falls over in the water so that is no longer right side up.

Capstan
A rotating drum used to haul heavy lines and chains. Similar to a winch, but mounted vertically.

Captain
The person who is in charge of a vessel and legally responsible for it and its occupants.

Car
A sliding fitting that attaches to a track allowing for the adjustment of blocks or other devices attached to the car.

Carbon fiber
A synthetic material consisting of fibers glued together with epoxy that is very strong for its weight.

Cardinal points
The points of North, South, East and West as marked on a compass rose.

Carlins
Structural pieces running fore and aft between the beams.

Carrick bend
A knot used to tie two lines together.

Cast off
To detach mooring lines as when leaving a dock.

Catamaran
A twin hulled boat. Catamaran sailboats are known for their ability to plane and are faster than single hulled boats (monohull) in some conditions.

Catboat
A sailboat rigged with one mast and one sail.

Catenary
The sag in a line strung between two points.

Caulking
Material used to seal the seams in a wooden vessel, making it watertight.

Cavitate, cavitation
A type of drag on a propeller caused by air bubbles forming near the tips of a propeller that is spinning too fast. This causes inefficiencies and unnecessary wear and tear on the propeller.

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.

Celestial sphere
An imaginary sphere surrounding the globe that contains the sun, moon, stars and planets.

Center line
The imaginary line running from bow to stern along the middle of the boat.

Centerboard
A device similar to a keel, except that it is usually either removable or can pivot. Also see daggerboard. The centerboard is used like a keel to reduce the unwanted sideways motion of a boat.

Certificate
A legal paper or license of a boat or its captain.

Chafe
Wear caused by the friction of parts moving past each other.

Chafing gear
Tape, cloth or other materials placed on one or more parts that rub together. By using chafing gear, hopefully the chafing gear will wear rather than the parts that it is protecting.

Chain locker
Storage for the anchor chain.

Chain
Metal links that are locked together to make a strong and flexible line. Chains are typically used for anchors and other places where high loads may be exerted on the line, particularly in large vessels.

Chainplates
Plates on the deck to which lines and stays are attached.

Chandlery
A store that sells nautical gear.

Channel marker
A buoy or other mark used to mark a navigable path through a waterway.

Channel
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 datum
The water level used to record data on a chart. Usually the average low tide water level.

Chart table
A table designated as the area in the boat where the navigator will study charts and plot courses.

Chart
Maps for boaters are known as charts. Charts are usually issued by government agencies and include information on channels, navigational aids, water depth and hazards.

Cheek block
A block with one end permanently attached to a surface.

Chine
The location where the deck joins the hull of the boat.

Chock
A fitting that a line can pass through and be controlled.

Chockablock
When a line is pulled as tight as is can go, as when two blocks are pulled together.

Chop
Small, steep disorderly waves.

Chronometer
An accurate clock that is used for navigation.

Classes
Groups of boats organized for racing. Boats compete against others in the same class, assuming that their performance will be similar.

Cleat hitch
A figure eight pattern used to tie a line to a cleat.

Cleat
A fitting to which lines can be easily attached.

Clevis pin
A metal pin used to attach fittings to each other or their mounts.

Clew
The lower aft corner of a sail.

Close hauled
Sailing with the sails hauled tight, sailing the boat towards the wind as much as possible.

Close Reach
Sailing with the wind coming from the direction forward of the beam of the boat. A close reach is the point of sail between a beam reach and close hauled.

Close up
A flag hoisted to the top of a flagpole. Also see at the dip.

Close winded
A boat that is able to sail well into the wind.

Clove hitch
A type of knot typically used when mooring. It is easily adjustable, but it may work loose.

Club footed
A jib or staysail that utilizes a small boom.

Club
A boom on a jib or staysail.

CNG
Compressed natural gas. A type of compressed gas used as fuel for stoves and heaters. CNG is stored in metal cylinders prior to use. CNG is considered safer than other types of fuel such as propane (LPG) because it is lighter than air and may rise into the sky in the event of a leak. Caution should still be used as CNG can collect near the cabin ceiling, potentially causing an explosion. Propane is available in more areas around the world than CNG so CNG is not often used outside of North America.

Coaming
A small wall to prevent water from entering the cockpit.

Coast Pilots
Books covering information about coastal navigation, including navigational aids, courses, distances, anchorages and harbors.

Coast
The region of land near the water.

Coastal navigation
Navigating near the coast, allowing one to find one's position by use of landmarks and other references.

Cock
A valve used to regulate the flow of water or gas.

Cockpit sole
Sole (floor) of the cockpit.

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

Code
Any method of passing messages, such as visual or electronic Morse code, code flag pennants and semaphore.

Cold front
Used in meteorology to describe a mass of cold air moving toward a mass of warm air. Strong winds and rain typically accompany a cold front.

Cold molding
A method of bending a material into an appropriate shape without heating or steaming to soften the material first.

Collision bulkhead
A watertight forward bulkhead designed to keep the boat from sinking in the event of a collision.

Colors
The national flag and or other flags.

COLREGS
A term for the international rules designed to prevent collisions between boats.

Come about
To tack. To change a boat's direction, bringing the bow through the eye of the wind.

Companionway
The entryway into the cabin from the deck.

Compass card
A card labeling the 360° of the circle and the named directions such as north, south, east and west.

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 error
Magnetic deviation. The difference between the reading of a compass and the actual magnetic course or bearing due to errors in the compass reading. These errors can be caused by metals, magnetic fields and electrical fields near the compass. Prior to using a compass, magnetic deviation should be recorded for many different points on the compass as the error can be different at different points. The act of checking for magnetic deviation is called swinging.

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.

Compass
(1) An instrument that uses the earth's magnetic field to point to the direction of the magnetic north pole.
(2) A device used to draw circles.

Composite construction
An object made with more than one type of material.

Compressed natural gas
CNG for short. A type of compressed gas used as fuel for stoves and heaters. CNG is stored in metal cylinders prior to use. CNG is considered safer than other types of fuel such as propane (LPG) because it is lighter than air and may rise into the sky in the event of a leak. Caution should still be used as CNG can collect near the cabin ceiling, potentially causing an explosion. Propane is available in more areas around the world than CNG so CNG is not often used outside of North America.

Continent
A large land mass, such as Africa, Antarctica, Asia, Australia, Europe, North America, and South America.

Continental shelf
A region of relatively shallow water surrounding each of the continents.

Coordinated universal time
A time standard that is not affected by time zones or seasons. Time measured in coordinated universal time labeled with the term Zulu. It is used so that people around the world can communicate about time without regard to individual time zones.

Cordage
Any rope or line.

Cotter pin
A small metal pin used to keep other parts from changing their position, such as to keep a nut from turning or a clevis pin from falling out.

Counter
The part of the stern aft of where it leaves the waterline.

Course
(1) The direction the boat is traveling or intends to travel.
(2) A path which racing boats are to follow.

Courtesy flag
A smaller version of the flag of the country being visited. It is flown from the starboard spreader.

Cove
A small sheltered recessed area in the shoreline.

Cowls
Scoop like devices used to direct air into a boat.

CQR anchor
Also called a plow anchor. Short for coastal quick release anchor. An anchor that is designed to bury itself into the ground by use of its plow shape.

Cradle
A frame to support a vessel when out of water.

Crest
(1) The top of a wave.
(2) The act of reaching the top of a wave.

Crew
One or more people that aid in the operation of a boat.

Cringle
A fitting in a sail that allows a line to fasten to it.

Crossing situation
When two vessels approach each other and their paths are crossing. The boat with the other boat on its starboard side is the give way vessel and must yield.

Crosstrees
Spreaders. Small spars extending toward the sides from one or more places along the mast. The shrouds cross the end of the spreaders, enabling the shrouds to better support the mast.

Cruising guides
Books that describe features of particular sailing areas, such as hazards, anchorages, etc.

Cunningham
A line used to control the tension along a sail's luff in order to maintain proper sail shape.

Current
The movement of water, due to tides, river movement and circular currents caused by the motion of the earth.

Cutter
A sailboat with one mast and rigged a mainsail and two headsails. Also see sloop.

Cutwater
The front edge of the boat.

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D

Dacron
A synthetic polyester material.

Daggerboard
Similar to a centerboard, except that it is raised vertically. Like a keel, daggerboards are used to prevent a sailboat being pushed sideways by the wind.

Danforth anchor
A brand of lightweight anchor. It has pivoting flukes that dig into the ground as tension is placed on the anchor. It does not have a stock.

Davit
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.

Daybeacon, daymark
A navigational aid visible during the day. In the United States and Canada, square red daybeacons should be kept on the right and triangular green daybeacons should be kept on the left when returning from a larger to smaller body of water. Also see can and nun buoys.

Daysailer
A small boat intended to be used only for short sails or racing.

Dayshape
Black diamond, ball, and cone shapes hoisted on vessels during the day to indicate restricted movement ability or type. For example three balls means aground.

Dead ahead
A position directly in front of the vessel.

Dead astern
A position directly behind the vessel.

Dead before
Running with the wind directly behind the boat.

Dead reckoning
A method of determining position by making an educated guess based on last known position, speed and currents.

Deadlight
Fixed ports that do not open, placed in the deck or cabin to admit light.

Deadrise
The measurement of the angle between the bottom of a boat and its widest beam. A vessel with a 0º deadrise has a flat bottom, high numbers indicate deep V shaped hulls.

Deck stepped
A mast that is stepped (placed) on the deck of a boat rather than through the boat and keel stepped. The mast of a deck stepped boat is usually easier to raise and lower and are usually intended for lighter conditions than keel stepped boats.

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

Deckhead
The underside of the deck, viewed from below (the ceiling.)

Depth sounder
An instrument that uses sound waves to measure the distance to the bottom.

Deviation
See magnetic deviation or compass error.

Dinghy, dink
A small boat used to travel from a boat to shore, carrying people or supplies. Also known as a dink or tender.

Dismast
The loss of a mast on a boat. Generally this also means the loss of some or all of the ability of the boat to sail.

Displacement hull
A type of hull that only floats, even when in motion, as opposed to a type of hull that allows a boat to skim across the surface of the water. See planing hull.

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.

Displacement
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.

Distress signals
Any signal that is used to indicate that a vessel is in distress. Flares, smoke, audible alarms, electronic beacons and others are all types of distress signals.

Ditty bag
A small bag.

Dive flag
(1) A red flag with a white stripe.
(2) The alpha flag is the legal requirement for boats with divers in the water. Boats should probably display both flags when they have divers in the water.

Dividers
A navigational tool used to measure distances on a chart.

Dock
(1) A platform where vessels can make fast. The act of securing a boat in such a place. Docks are often subdivided into smaller areas for docking known as slips.
(2) The act of entering a dock.

Documentation
Licenses or registration papers for a vessel. Types of documentation vary depending on the country, vessel size and purposes.

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

Dolphin
A playful sea mammal. Also a type of fish. Also a group of piles used for mooring or as a channel marker.

Dorade vent
A type of vent designed to let air into a cabin and keep water out by the use of baffles.

Double-braid
A line consisting of a braided inner core and a braided outer sheath.

Double-ender
A boat with a pointed stern. Known as a double-ender because the stern may look very similar to the bow.

Douse
(1) To drop a sail quickly.
(2) To extinguish a candle, lamp, or fire.

Down helm
To steer a sailboat toward the wind.

Downhaul
A line used to pull down on a spar or sail.

Downwind
In the direction the wind is blowing.

Draft
(1) The depth of a boat, measured from the deepest point to the waterline. The water must be at least this depth or the boat will run aground.
(2) A term describing the amount of curvature designed into a sail.

Drag
The resistance to movement.

Dragging
Description of an anchor that is not securely fastened to the bottom and moves.

Draw
Draft. The depth of water that a boat requires to stay off the bottom. A vessel "draws" a certain amount of water.

Drawbridge
A bridge that can be raised vertically to allow boats to pass underneath.

Drift
The velocity of a current.

Drogue
Any object used to increase the drag of a boat. Typically shaped like a parachute or cone opened underwater, drogues slow a boat's motion in heavy weather. Also see sea anchor.

Dry dock
A dock where a boat can be worked on out of the water. The boat is usually sailed into a dry dock and then the water is pumped out.

Dry rot
Used to describe the decay of wood. A misnomer, dry rot is actually caused by moist conditions in fresh water.

Dry storage
Storing on land. Many small boats are placed in dry storage over the winter.

Ducts
Tubes used to move air, such as to ventilate an enclosed area.

DWL
Design waterline. Also length waterline or load waterline (LWL). This is the length of the boat where it meets the water when loaded to its designed capacity.

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E

Ease the sheets
To loosen the lines that control the sails.

Ease
To slowly loosen a line while maintaining control, such as when loosening the sails.

East wind, easterly wind
A wind coming from the east.

East
One of the 4 cardinal compass points. East is at 90° on a compass card.

Ebb, ebb tide
The falling tide when the water moves out to the sea and the water level lowers.

Echo sounder
An electrical fish finder or depth sounder that uses sound echoes to locate the depth of objects in water. It does so by timing the sound pulses.

Eddy
Water or air currents flowing in circular patterns.

Electronic navigation
The use of echo sounders, radio, and various electronic satellite and land based position finders to determine a boat's location.

Emergency tiller
A tiller that is designed to be used in the event that wheel steering fails.

Ensign
The national flag of a boat's home nation.

EPIRB
Emergency Position Indicating Radio Beacon. An emergency device that uses a radio signal to alert satellites or passing airplanes to a vessel's position.

Equator
An imaginary line around the center of the world at 0° of latitude.

Estimated position
A position based on dead reckoning estimations of a boat's position using estimated speed, currents, and the last known position (fix) of the boat.

Eye of the wind
The direction that the wind is blowing from.

Eye splice
A splice causing a loop in the end of a line, by braiding the end into itself or similar methods. It may or may not be reinforced by a metal fitting known as a thimble.

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F

Fair
In good condition.

Fairlead
A fitting designed to control the direction of a line with minimal friction.

Fall off
Also bear away or bear off. A boat falls off the wind when it points its bow further from the eye of the wind. The opposite of heading up.

Fastening
An item such as a nail, screw, rivet or other device used to fasten objects together.

Fathom
A nautical measurement equaling 6 feet (182 cm). Usually used to measure depth.

Fathometer
A brand name for a depth measuring device.

FCC Rules
Federal Communications Commission Rules governing radio equipment and operation in the United States.

Feathering
A propeller that can have the pitch of its blade changed to reduce drag when not in use. Also see folding and variable pitch propellers.

Feet
More than one foot. A foot is a unit of measurement used primarily in the United States. 1 foot equals 30.48 centimeters.

Fend off
To push a boat away from another boat or dock by hand.

Fender
A cushion hung from the sides of a boat to protect it from rubbing against a dock or another boat.

Fetch
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. Fetch is also used to describe the act of sailing to a location accurately and without having to tack.

Fiberglass
A construction method using layers of woven glass mats that are bonded together with an epoxy (glue).

Fid
A tool used in splicing and working with rope.

Fiddle
A small rail on tables and counters used to keep objects from sliding off when heeled or in heavy seas.

Fiddle Block
A block with two sets of sheaves (sometimes three), one above the other.

Figure-eight
A type of knot that can be used to stop a line from passing through a block or other fitting.

Fin keel
A keel that is narrow and deeper than a full keel.

Finger pier
A small pier that projects from a larger pier.

Fisherman anchor
Kedge anchor. A traditionally shaped anchor having flukes perpendicular to the stock of the anchor and connected by a shank. These are less common than modern anchors such as the plow and lightweight anchors.

Fix
An accurate position of the vessel, as determined by any reasonably accurate method, such as by taking visual bearings.

Flake
To fold a sail in preparation for storage.

Flame arrester
A device used to prevent or stop unwanted flames.

Flare
A device which burns to produce a bright light, sometimes colored, and usually used to indicate an emergency.

Flashing
Used to describe a light that blinks on and off in regular patterns.

Flemish
To coil a line flat on the deck in spirals.

Flinders bar
An iron bar mounted on or near the compass to correct for magnetic deviation in steal hulled ships.

Flood tide
The incoming tide where the water comes in from the sea, lowering the water level.

Flotsam
Debris floating on the water surface.

Fluke
(1) The broad flat parts of an anchor that are designed to grab and hold in the bottom.
(2) Also a fin on a whale.

Flush deck
A deck that is not obstructed by a cabin.

Flying bridge
A high position from which to steer a boat.

Folding
A propeller having blades that fold up when not in use to reduce drag. Also see feathering and variable pitch propellers.

Following sea
A sea with waves approaching from the stern of the boat.

Foot
(1) The bottom edge of a sail.
(2) sailing slightly more away from the wind than close hauled to increase the boat speed.
(3) A unit of measurement used primarily in the United States. 1 foot equals 30.48 centimeters. Units of more than 1 foot are known as feet.

Fore and aft sail
The more common position of the sail with its length running along the ship's length as opposed to a sail such as a square sail which is mounted across the width of the vessel.

Fore and aft
Running along the length of the boat.

Fore
Toward the bow (front) of the vessel.

Forecabin
The cabin towards the front of the vessel.

Forecast
A weather prediction.

Forecastle
Also fo'c'sle or fo'csle. Pronounced fo'csle. The most forward below decks area of a vessel.

Foredeck
The forward part of the deck.

Foremast
The forward mast of a two or more masted vessel.

Forepeak
The furthermost forward storage area of a vessel.

Foresail
A sail placed forward of the mast, such as a jib.

Forestay
A line running from the bow of the boat to the upper part of the mast designed to pull the mast forward. A forestay that attaches slightly below the top of the mast can be used to help control the bend of the mast. The most forward stay on the boat is also called the headstay.

Forestaysail
A sail attached to the forestay as opposed to a jib which is attached to the headstay.

Foretriangle
The space between the mast, the deck, and the headstay.

Forward quarter spring line
A mooring line running forward from the stern of the boat. The forward quarter spring line prevents the boat from moving backward while moored. The after bow spring line does the opposite.

Forward
Toward the bow (front) of the boat.

Foul
When a line ends up somewhere it does not belong and becomes jammed. Lines can foul on blocks, winches and other objects on a boat.

Founder
Used to describe a boat that is having difficulty remaining afloat. "The boat foundered and then sank."

Fractional rig
A type of rig where the jib attaches below the top of the mast.

Freeboard
The distance between the top of the hull and the waterline.

Freeing port
An opening in the rail (bulwarks) along the deck to allow water to drain.

Freestanding mast
A mast made out of exotic materials so that it can support itself without the use of stays. See fully stayed mast.

Fronts
Used in meteorology to describe bounderies between hot and cold air masses. This is typically where bad weather is found.

Full and by
Sailing as close to the wind as possible with full sails.

Full keel
A keel that runs the length of the boat. Full keels have a shallower draft than fin keels.

Fully battened
A sail having battens that run the full horizontal length of the sail.

Fully stayed
A mast supported by the use of lines known as stays and shrouds.

Furl
To lower a sail. Sails are sometimes partially furled to reduce the amount of sail area in use without completely lowering the sail. This is usually known as reefing.

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G

Gaff rigged
A type of traditional working boat using four sided gaff sails that are hoisted on gaffs.

Gaff sail
A four sided sail used instead of a triangular main sail. Used on gaff rigged boats.

Gaff
(1) A spar that holds the top of a four sided gaff sail.
(2) A pole with a hook at the end used to get a fish on board.

Gale force winds
Wind speeds strong enough to qualify the storm as a gale.

Gale
A storm with a wind speed between 34 to 40 knots.

Galley
The kitchen area on a boat.

Gallows frame
A frame used to support the boom.

Gasket
Ties used to tie up the sails when they are furled.

Gennaker
A large sail that is a cross between a spinnaker and a genoa. Hoisted without a pole, the tack is attached at the bottom of the headstay.

Genoa
A large jib that overlaps the mast. Also known as a jenny.

Geographic north
The direction toward the top point of the line about which the earth rotates (between Canada and Russia in the Arctic Ocean.) See also magnetic north.

Geographic position
The position of a boat on a chart.

Gimbals
Hinges for objects such as lamps, compasses and stoves so that they can remain upright as the boat rolls.

Give way vessel
The vessel that must yield to another vessel according to the navigation rules. Also known as the burdened vessel.

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.

Globe
A map of the earth drawn on a sphere so that both its distances and angles are accurate.

GMT
Time measured in Greenwich Mean Time. Coordinated universal time is a newer standard. A time standard that is not affected by time zones or seasons.

Go about
To tack.

GPS
Global Positioning System. A system of satellites that allows one's position to be calculated with great accuracy by the use of an electronic receiver.

Grab rail
See hand rail.

Granny knot
A bad knot that was probably tied in error, will not necessarily hold fast, and may be difficult to untie.

Great circle route
A course that is the shortest distance between two points, following a great circle. Great circle routes usually do not look like the shortest route when drawn on a flat map due to deviations caused by trying to draw a flat map of a round object such as the earth.

Great circle
Any circle drawn around the earth such that the center of the circle is at the center of the earth. The shortest distance between any two points on the earth lies along a great circle.

Green buoy
A 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. Nun buoys mark the other side of the channel. Also see green and red daymarks.

Green daymark
A navigational aid used in the United States and Canada to mark a channel. Green triangular daymarks should be kept on the left when returning from a larger to smaller body of water. Red daymarks mark the other side of the channel. Also see can and nun buoys.

Green water
A solid mass of water coming aboard instead of just spray.

Greenwich Mean Time
GMT for short. Coordinated universal time is a newer standard. A time standard that is not affected by time zones or seasons.

Grommet
A ring or eyelet normally used to attach a line, such as on a sail.

Ground swells
Swells that become shorter and steeper as they approach the shore due to shallow water.

Ground tackle
The anchor and its rode or chain and any other gear used to make the boat fast.

Gudgeon
The hole in which the pin from a stern mounted rudder fits. The pin is known as a pintle.

Gunkholing
Cruising in shallow water and spending the nights in coves.

Gunnel, gunwale
Pronounced gunnel. The rail around the edge of a boat. Smaller versions are called toe rails.

Guy
Also called a brace. A line used to control the movement of the object at the other end, such as a spar.

Gybe
Usually spelled jibe. To change direction when sailing in a manner such that the stern of the boat passes through the eye of the wind and the boom changes sides. Prior to jibing, the boom will be very far to the side of the boat. Careful control of the boom and mainsail is required when jibing in order to prevent a violent motion of the boom when it switches sides. Jibing without controlling the boom properly is known as an accidental jibe. Tacking is preferred to jibing because the boom is not subject to such violent changes. Jibing is usually needed when running with the wind and tacking is used when close hauled.

Gypsy
A windlass or capstan drum.

Gyres
A large circular ocean current.

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H

Hail
To attempt to contact another boat or shore, either by voice or radio.

Half hitch
A simple knot usually used with another knot or half hitch.

Halyard
A line used to hoist a sail or spar. The tightness of the halyard can affect sail shape.

Hand bearing compass
A small portable compass.

Hand lead
A weight attached to a line used to determine depth by lowering it into the water.

Hand rail
A hand hold. Usually along the cabin top or ladder.

Hand
Someone who helps with the work on a boat.

Handsomely
To do something carefully and in the proper manner, such as when stowing a line.

Handy-billy
A movable block and tackle.

Hanging locker
A locker big enough to hang clothes.

Hank
(1) Clips used to fasten a sail to a stay.
(2) Using such slips to attach a sail to a stay.

Harbor
An anchorage protected from storms either naturally or by man-made barriers.

Harbormaster
The individual who is in charge of a harbor.

Hard over
To move all the way in one direction, such as when turning the wheel.

Hard-a-lee
A command to steer the boat downwind.

Hard-chined
A hull shape with flat panels that join at sharp angles.

Hatch
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.

Haul
Pulling on a line.

Hauling part
The part on the object which is hauled upon.

Hawse hole
A hole in the hull for mooring lines to run through.

Hawsepipes
Pipes to guide lines through the hawse hole. On large vessels anchors are stored with their shanks in the hawsepipes.

Hawser
A rope that is very large in diameter, usually used when docking large vessels.

Hazard
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 to wind
A position with the boat's bow in the direction that the wind is coming from. This will probably stop the boat and place it in irons.

Head up
To turn the bow more directly into the eye of the wind. The opposite of falling off.

Head
(1) The front of a vessel.
(2) The upper corner or edge of a sail.
(3) The top or front of a part.
(4) The toilet and toilet room in a vessel.

Heading
The actual course of the vessel at any given time.

Headsail
Any sail forward of the mast, such as a jib.

Headstay
The furthest forward of all the stays on the boat.

Headway
The forward motion of a vessel through the water.

Heave
To throw or pull strongly on a line.

Heaving line
A light line used to be thrown ashore from which a larger rope can then be pulled.

Heaving to
Arranging the sails in such a manner as 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. Probably uncomfortable or dangerous.

Heel, heeling
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.

Heeling error
The error in a compass reading caused by the heel of a boat.

Helm’s alee
A warning from the helmsman that the boat is about to tack.

Helm
The wheel or tiller of a boat.

Helmsman
The person who is steering the boat.

Hemisphere
Half of a sphere. On the globe hemispheres are used to describe the halves of the earth north or south of the equator.

High tide
The point of a tide when the water is the highest. The opposite of low tide.

High
A location of higher barometric pressure than the surrounding area of a weather system.

Hiking stick
An extension to the tiller allowing the helmsman to steer while hiking. This may be desired for improved visibility or stability.

Hiking
Moving the crew's weight to or past the windward rail to counteract the heeling of a boat. Typically seen when boats are racing.

Hitch
A knot used to attach a line to a cleat or other object.

Hoist
(1) To raise a sail.
(2) To raise anything up.

Holding ground
The type of bottom that the anchor is set in. "Good holding ground."

Holding tank
A storage tank where sewage is stored until it can be removed to a treatment facility.

Homing
Using a radio direction finder to steer toward a source of radio signals.

Horizon
Where the water and sky or ground and sky appear to intersect.

Horizontal angle
The angle measured between two fixed objects (usually on shore) to aid in finding a boats position by determining the arc of a circle on which the boat must lie.

Horseshoe buoy
A floatation device shaped like a U and thrown to people in the water in emergencies.

Hull speed
Also displacement speed. The theoretical speed that a boat can travel without planing, based on the shape of its hull. This speed is about 1.34 times the square root of the length of a boat at its waterline. Since most monohull sailboats cannot exceed their hull speed, longer boats are faster.

Hull
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.

Hurricane
A strong tropical revolving storm of force 12 or higher in the northern hemisphere. Hurricanes revolve in a clockwise direction. In the southern hemisphere these storms revolve counterclockwise and are known as typhoons.

Hydrodynamic
A shape designed to move efficiently through the water.

Hydrofoil
A boat that has foils under its hull onto which it rises to plane across the water surface at high speed. See displacement and planing hulls.

Hydrography
The study of the earth's waters.

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I

ICW
Short for Intercoastal Waterway. A system of rivers and canals along the Atlantic and Gulf Coasts of the United States allowing boats to travel along them without having to go offshore.

In irons
A sailboat with its bow pointed directly into the wind, preventing the sails from filling properly so that the boat can move. It can be very difficult to get a boat that is in irons back under sail. An old square rigger could take hours to get underway again.

Inboard cruiser
A motorboat with an inboard engine.

Inboard
(1) Toward the center of the boat.
(2) An engine that is mounted inside the boat.

Inch
A unit of measurement used primarily in the United States equal to 2.54 centimeters.

Inches of mercury
A unit used when measuring the pressure of the atmosphere. 33.86 millibars. Inches of mercury are used because some barometers use the height of mercury in a sealed tube as a measuring device.

Inflatable
A dinghy or raft that can be inflated for use or deflated for easy stowage.

Inland Rules
Rules for the operation of vessels in harbors, rivers and lakes.

Inland
Away from large bodies of water, surrounded by land. See offshore.

Inlet
A bay or cove along a river, sea or lake coast line. A stream or bay leading inland. A narrow passage between to bodies of land.

Intercoastal Waterway
A system of rivers and canals along the Atlantic and Gulf Coasts of the United States allowing boats to travel along them without having to go offshore.

International Code of Signals
A set of radio, sound, and visual signals designed to aid in communications between vessels without language problems. It can be used with Morse Code, with signal pennants, and by spoken code letters.

Irons
In irons. A sailboat with its bow pointed directly into the wind, preventing the sails from filling properly so that the boat can move. It can be very difficult to get a boat that is in irons back under sail. An old square rigger could take hours to get underway again.

Isobars
Lines drawn on a weather map indicating regions of equal pressure. When the lines are close together, this indicates a rapid change in air pressure, accompanied by strong winds.

Isogonic lines
A line connecting points of equal magnetic variation on a map.

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J

Jack line, jack stay
A strong line, usually of flat webbing, or a wire stay running fore and aft along the sides of a boat to which a safety harness can be attached.

Jacobs’s ladder
A rope ladder.

Jam cleat
A cleat designed to hold a line in place without slipping. It consists of two narrowing jaws with teeth in which the line is placed. Also see cam cleat.

Jaws
A fitting holding a boom or gaff to the mast.

Jenny
A genoa jib. A large jib that overlaps the mast.

Jetty
A man made structure projecting from the shore. May protect a harbor entrance or aid in preventing beach erosion.

Jib netting
A rope net to catch the jib when it is lowered.

Jib sheets
A sheet (line) used to control the position of the jib. The jib has two sheets, and at any time one is the working sheet and the other is the lazy sheet.

Jib stay
The stay that the jib is hoisted on. Usually the headstay.

Jib topsail
A small jib set high on the headstay of a double headsail rig.

Jib
A triangular sail attached to the headstay. A jib that extends aft of the mast is known as a genoa.

Jibe
Also spelled gybe. To change direction when sailing in a manner such that the stern of the boat passes through the eye of the wind and the boom changes sides. Prior to jibing the boom will be very far to the side of the boat. Careful control of the boom and mainsail is required when jibing in order to prevent a violent motion of the boom when it switches sides. Jibing without controlling the boom properly is known as an accidental jibe. tacking is preferred to jibing because the boom is not subject to such violent changes. Jibing is usually needed when running with the wind and tacking is used when close hauled.

Jiffy reefing
A method of lowering the sail in sections so that it can be reefed quickly.

Jigger
A small sail on the mizzen mast of a yawl or a ketch.

Junction buoy
Also known as a preferred channel buoy. A red and green horizontally striped buoy used in the United States to mark the separation of a channel into two channels. The preferred channel is indicated by the color of the uppermost stripe. Red on top indicates that the preferred channel is to the right as you return, green indicates the left. Also see can and nun buoys.

Jury rig
A temporary repair using improvised materials and parts.

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K

Kedging
(1) To kedge off. A method of pulling a boat out of shallow water when it has run aground. A dinghy is used to set an anchor, then the boat is pulled toward the anchor. Those steps are repeated until the boat is in deep enough water to float.
(2) A traditionally shaped anchor having flukes perpendicular to the stock of the anchor and connected by a shank. These are less common than modern anchors such as the plow and lightweight anchors.

Keel stepped
A mast that is stepped (placed) on the keel at the bottom of the boat rather than on the deck. Keel stepped masts are considered sturdier than deck stepped masts.

Keel
A flat surface built into the bottom of the boat to prevent the 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. There are several types of keels, such as fin keels and full keels.

Keelson
A beam attached to the top of the floors to add strength to the keel on a wooden boat.

Ketch
A sailboat with two masts. The shorter mizzen mast is aft of the main mast, but forward of the rudder post. A similar vessel, the yawl, has the mizzen mast aft of the rudder post.

King plank
The center plank on a wooden deck.

King spoke
The top spoke on a wheel when the rudder is centered.

Knees
Supporting braces used for strength when two parts are joined.

Knocked down
A boat that has rolled so that she is lying on her side or even rolled completely over. A boat with appropriate ballast should right herself after being knocked down.

Knot
(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.

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L

Labor
Heavy rolling or pitching while underway.

Lacing
A line used to attach a sail to a spar.

Laid up
A boat in a dry dock.

Land breeze
A wind moving from the land to the water due to temperature changes in the evening.

Landlocked
Surrounded by land.

Landmark
A distinctive reference point that can be used for navigation.

Lanyard
A line attached to a tool.

Lash
To tie something with a line.

Lateral resistance
The ability of a boat to keep from being moved sideways by the wind. Keels, daggerboards, centerboards, and leeboards are all used to improve a boat's lateral resistance.

Latitude
Imaginary lines drawn around the world and used to measure distance north and south of the equator. 90° north is the North Pole and 90° south is the South Pole, and the equator is at 0°. Also see longitude.

Launch
(1) To put a boat in the water.
(2) A small boat used to ferry people to and from a larger vessel.

Lay line
An imaginary line on which a sailboat can sail directly to its target without tacking.

Lay up
To prepare a boat for winter storage.

Lay
(1) The position of an item.
(2) The direction in which a stranded rope is twisted.

Lazarette
A small aft storage space for spare parts and other items.

Lazy guy
A line attached to the boom to prevent it from accidentally jibbing.

Lazy jacks
Lines running from above the main sail to the boom to aid in the lowering of the sail, keeping the sail flaked and off of the deck.

Lazy sheet
A line led to a sail, but is not currently in use. The line currently in use is known as the working sheet. Usually the working and lazy sheets change when the boat is tacked.

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.)

Leading lights
Lights that are separated in distance so that when they are lined up with one behind the other they provide a bearing. Usually used to enter a harbor or navigate a channel.

Leading marks
Unlit navigational aids for use during the day. Like leading lights, they mark a bearing to a channel when they are lined up one above the other.

League
3 nautical miles.

Lee helm
The tendency, if any, for a sailboat to want to steer away from the direction of the wind. The opposite condition is known as weather helm.

Lee shore
The shore that the wind is blowing toward. It is important to keep distance from the lee shore because the boat will be blown toward it if control of the vessel is lost.

Lee
The direction that the wind is blowing toward. The direction sheltered from the wind.

Leeboards
(1) Boards projecting into the water from the lee side of a vessel to help keep it from slipping sideways in the water when traveling across the wind, similar in intent to a keel.
(2) A board placed on the side of a berth to keep the occupant from falling out.

Leech line
A line used to tighten the leech of a sail, helping to create proper sail shape.

Leech
The aft edge of a fore and aft sail.

Leecloths
Cloths raised along the side of a berth to keep the occupant from falling out.

Leeward
The direction away from the wind. Opposite of windward.

Leeway
The sideways movement of a boat away from the wind, usually unwanted. Keels and other devices help prevent a boat from having excessive leeway.

Licensed pilot
A pilot with a license stating that they are qualified to guide vessels in a particular area.

Lie
(1) Where an object is.
(2) To put an object in place.

Life boat
A small boat used for emergencies such as when the parent boat is sinking.

Life jacket
A device used to keep a person afloat. Also called a life preserver, life vest, PFD or personal floatation device.

Life preserver
A device used to keep a person afloat. Also called a life jacket, life vest, PFD or personal floatation device.

Life raft
An emergency raft used in case of serious problems to the parent vessel, such as sinking.

Life vest
A device used to keep a person afloat. Also called a life jacket, life preserver, PFD or personal floatation device.

Lifeline
A line running between the bow and the stern of a boat to which the crew can attach themselves to prevent them from being separated from the boat.

Light list
A list of lights arranged in geographical order.

Light
A lit navigational aid such as a lighthouse that can be used at night or in poor visibility.

Lighthouse
A navigational light placed on a structure on land. The supporting structure was a house in which the person that maintained the light lived. Most modern lighthouses no longer have living areas.

Lightship
A light placed on a ship. The ship remained in a fixed position. Most lightships have been replaced by lit buoys or other structures.

Lightweight anchor
Danforth anchor. It has pivoting flukes that dig into the ground as tension is placed on the anchor. It does not have a stock.

Limber hole
A hole in between compartments in the bottom of the boat to allow water to flow into the bilge where it is sent overboard.

Line
On a boat most ropes are called lines.

Linestoppers
A device used to keep a line from slipping, such as a jam cleat.

Liquid petroleum gas
LPG or propane for short. Propane is a common fuel used for cooking and heating. CNG (natural gas) is considered safer because propane is heavy than air and will sink into the bilge if it leaks, creating the potential for an explosion. Propane is more easily available throughout the world than CNG however, so it is used for most boats outside of North America.

List
A leaning to one side when not underway. Usually the result of an improperly loaded boat. Heeling is different from a list because it is caused by the forces of wind acting upon a sailboat that is underway. When a boat changes tacks, the direction of the heel will change sides, whereas a list is a continual leaning to the same side under any condition.

LOA
Length overall. The total length of a boat including bowsprits or other items projecting from the bow or the stern of the boat.

Lock
A device that allows boats to pass between bodies of water having different water levels, such as in a canal. A boat enters a lock, then large doors close behind it. The water level is then either raised or lowered until a second set of doors can be opened and the boat can pass through.

Locker
Any storage place on a boat. See also chain locker, hanging locker, and wet locker.

Log
(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. Logs can be electronic devices or paddle wheels mounted through the hull of the boat or trailed behind it on a line.
(2) A written record of a boat's condition, usually including items such as boat position, boat speed, wind speed and direction, course, and other information.

Logbook
A book in which the boat's log is kept. Each entry usually contains the time and date of the entry, weather conditions, boat speed and course, position and other information and observations.

Long splice
A method of splicing two lines of identical thickness by unwrapping strands and braiding the lines back together. Long splices have the advantage of being able to fit through blocks and other devices, but are not as strong as other methods of joining lines.

Longitude
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. For example the center of California, USA is approximately 120° west and the center of Australia is around 135° east. Also see latitude.

Lookout
A person designated to watch for other vessels and hazards.

Loose footed
A sail whose foot (bottom) is not attached to a boom or other rigid object. The opposite of club footed.

LORAN
An electronic instrument using radio waves from various stations to find one's position. The LORAN system is being replaced by the GPS system and will be obsolete in a few years. Many LORAN stations have already stopped providing service.

Low tide
The point of a tide when the water is the lowest. The opposite of high tide.

Low
Used in meteorology to describe an area of low atmospheric pressure.

LPG
Liquid petroleum gas or propane. Propane is a common fuel used for cooking and heating. CNG (natural gas) is considered safer because propane is heavy than air and will sink into the bilge if it leaks, creating the potential for an explosion. Propane is more easily available throughout the world than CNG however, so it is used for most boats outside of North America.

Lubber line
A mark on a compass used to read the heading of a boat.

Luff rope
Bolt rope. A rope in the luff of a sail. The luff rope is usually used to attach the sail to a mast.

Luff
(1) The edge of a sail toward the bow of a boat.
(2) A term used to describe that edge when the airflow around it stalls. (see luffing)

Luffing
A description of a flapping motion along the luff (leading edge) of a sail. A sail begins to luff when the air flow stalls when traveling across the sail. Luffing is a sign that the sail is not properly trimmed or that the boat is trying to sail too close to the eye of the wind (pinching.)

Lugs
Metal or plastic pieces attached to a sail's luff that slide in a mast track to allow easy hoisting of the sail.

Lull
A period of no wind. Lulls may be followed by a significant change of wind speed and direction.

LWL
Load waterline or length waterline. Also design waterline (DWL.) This is the length of the boat at the waterline when loaded to its designed capacity.

Lying ahull
A boat that is letting herself be subjected to prevailing conditions without the use of sails or other devices. Lying ahull is usually not preferred to other actions because a boat may tend to lie with her beam to the waves and the wind (parallel to the waves.) This can cause a boat to roll excessively and even become knocked down.

Lying to
A boat that is almost stopped with her bow into the wind, probably with the aid of a sea anchor.

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M

Magnetic bearing
The bearing of an object after magnetic variation has been considered, but without compensation for magnetic deviation.

Magnetic course
The course of a vessel after magnetic variation has been considered, but without compensation for magnetic deviation.

Magnetic deviation
Compass error. The difference between the reading of a compass and the actual magnetic course or bearing due to errors in the compass reading. These errors can be caused by metals, magnetic fields and electrical fields near the compass. Prior to using a compass, magnetic deviation should be recorded for many different points on the compass as the error can be different at different points. The act of checking for magnetic deviation is called swinging.

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.

Magnetic variation
The difference between magnetic north and true north, measured as an angle. Magnetic variation is different in different locations, so the nearest compass rose to each location on a chart must be used.

Main mast
The tallest (or only) mast on a boat.

Main topsail
A topsail on the main mast.

Mainsail
The main sail that is suspended from the main mast.

Mainsheet
The line used to control the mainsail.

Make fast
To attach a line to something so that it will not move.

Make way
Moving through the water.

Marina
A place where boats can find fuel, water and other services. Marinas also contain slips where boats can stay for a period of time.

Mark
(1) Marks used on a lead line or anchor rode indicating the length of the line at that point.
(2) A buoy or other object used to mark a location.

Marl
To wrap a small line around another.

Marline
A small line used for whipping, seizing, and lashing.

Marlinespike
A pointed tool used to separate the strands of a rope or wire.

Mast boot
A protective cover wrapped around the mast at the deck on a keel stepped boat to prevent water from entering the boat.

Mast box
A box where a deck stepped mast is stepped.

Mast partners
Supporting structures to take the load of the mast at the deck.

Mast step
The place that supports the bottom of the mast. The mast step usually has a built in pattern fitting a matching pattern on the bottom of the mast, enabling the mast to be accurately positioned.

Mast track
A track or groove in the back of the mast to which the sail is attached by means of lugs or the bolt rope.

Mast
Any vertical spar on the boat that sails are attached to. If a boat has more than one mast, they can be identified by name.

Master
The person in charge of a vessel. The captain.

Masthead light
Also known as a steaming light. The masthead light is a white light that is visible for an arc extending across the forward 225° of the boat. When lit the masthead light indicates that a vessel under power, including sailboats with engines running. Masthead lights are usually located halfway up the mast rather than at the top.

Masthead
The top of a mast. Wind direction indicators and radio antennas usually collect on the masthead.

Mate
An assistant to the captain.

MAYDAY
An internationally recognized distress signal used on a radio to indicate a life threatening situation. Mayday calls have priority over any other radio transmission and should only be used if there is an immediate threat to life or vessel. Mayday comes from the French "M'aidez" which means "help me." For urgent situations that are not immediately life threatening there is the PAN PAN identifier. Less urgent messages such as navigational hazards should send a SECURITE message.

Mean low water
A figure representing the average low tide of a region.

Mean lower low water
In an area with two tides, this figure represents the average of the lowest of the low tides.

Mean
Average.

Measured mile
A course marked by buoys or ranges measuring one nautical mile. Measured miles are used to calibrate logs.

Mediterranean berth
A method of docking with a boat's stern to the dock.

Mercator
A type of projection of the globe used when making charts. Since the world is a sphere, it is impossible to draw accurate charts on flat paper. A Mercator projection shows all of the meridians as straight vertical lines rather than lines that would intersect. This is the type of projection used on a typical world map, but the distances become very distorted near the poles.

Meridian
A longitude line. Meridians are imaginary circles that run through both poles.

Messenger
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.

Meteorology
The study of weather.

Midchannel buoy
A red and white vertically striped buoy used in the United States to mark the middle of a channel. Midchannel buoys may be passed by on either side. Also see nun and can buoys.

Midships
A place on a boat where its beam is the widest.

Mile
(1) 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.
(2) A statute mile is used to measure distances on land in the United states and is 5280 feet.

Millibar
A unit of pressure used to measure the pressure of the atmosphere. 1 millibar equals 0.03 inches of mercury.

Minute
(1) When used to measure location a minute is one sixtieth of one degree. One minute of latitude is equal to one nautical mile. Each minute is divided into sixty seconds.
(2) When measuring time a minute is one sixtieth of one hour.

Mizzen mast
A smaller aft mast on a ketch or yawl rigged boat.

Mizzen sail
The sail on the aft mast of a ketch or yawl rigged sailboat.

Mizzen staysail
A small sail that is sometimes placed forward of the mizzen mast.

Monkey fist
A large heavy knot usually made in the end of a heaving line to aid in accurate throwing.

Monohull
A boat that has only one hull, as opposed to multihull boats such as catamarans or trimarans.

Moor
To attach a boat to a mooring, dock, post, anchor, etc.

Mooring buoy
A buoy marking the location of a mooring. Usually attached to an anchor by a small pendant.

Mooring line
A line used to secure a boat to an anchor, dock, or mooring.

Mooring
A place where a boat can be moored. Usually a buoy marks the location of a firmly set anchor.

Morse code
A code that uses dots and dashes to communicate by radio or signal lights.

Motor sailor
A boat designed to use its motor for significant amounts of time and use the sails less often than a normal sailboat.

Motor
(1) An engine.
(2) The act of using an engine to move a boat.

Mount
(1) An attachment point for another object.
(2) The act of putting an object on its mount.

Mouse
A line used to reeve lines.

Multihull
Any boat with more than one hull, such as a catamaran or trimaran.

Mushroom anchor
A type of anchor with a heavy inverted mushroom shaped head. Mushroom anchors are used to anchor in mud and other soft ground.

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N

Natural gas
Short for compressed natural gas or CNG. A type of compressed gas used as fuel for stoves and heaters. CNG is stored in metal cylinders prior to use. CNG is considered safer than other types of fuel such as propane (LPG) because it is lighter than air and may rise into the sky in the event of a leak. Caution should still be used as CNG can collect near the cabin ceiling, potentially causing an explosion. Propane is available in more areas around the world than CNG so CNG is not often used outside of North America.

Nautical Almanac
An annually published book that contains information about the position of the sun, moon, planets and stars. This information is used for celestial navigation.

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.

Nautical
Having to do with boats, ships, or sailing.

Navigable water
Water of sufficient depth to allow a boat to travel through it.

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.

Navigation Rules
The rules concerning which vessel has the right of way if there is a possibility of collision between two or more boats. The United States Inland Rules of the Road and International Rules of the Road are slightly different.

Navigation
The act of determining the position of a boat and the course needed to safely move the boat from place to place.

Navigational aid
Any fixed object that a navigator may use to find his position, such as permanent land or sea markers, buoys, radio beacons, and lighthouses.

Navigator
The person responsible for navigating a boat.

Neap tide
The tide with the least variation in water level, occurring when the moon is one quarter and three quarters full. The lowest high tide and the highest low tide occur at neap tide. The opposite is the spring tide.

Noon sight
A sighting taken for celestial navigation at noon, when the sun is at its highest point in the sky.

North Pole
The "top" point of the line about which the earth rotates.

North Star
Polaris, the North Star, is visible in the northern hemisphere and indicates the direction of north. In the southern hemisphere the Southern Cross is used to find the direction of south.

North wind, northerly wind
Wind coming from the north.

North
One of the 4 cardinal compass points. North is the direction toward the North Pole and is at 0° on a compass card.

Notices to Mariners
Official notices reporting changes to charts and other navigational and safety items.

Nun buoy
A conical buoy with a pointed top, painted red, and having an even number, used in the United States for navigational aids. At night they may have a red light. These buoys should be kept on the right side of the boat when returning from a larger body of water to a smaller one such as a marina. Can buoys are used on the opposite side of the channel. Also see green and red daymarks.

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O

Oar
A stick with a blade at the end used to row a rowboat. Oars are different than paddles because they have a provision to be secured to the rowboat for rowing, such as an oarlock.

Oarlock
A device to attach oars to a rowboat, allowing the operator to row rather than paddle the boat.

Observed position
A position or fix determined by observing landmarks or other objects to find the position.

Occulting lights
A navigational light which turns on and off in a regular pattern, but is on more than it is off. The opposite of a blinking light.

Ocean
(1) The large body of salt water covering seven tenths of the earth.
(2) The Atlantic, Pacific, Indian, and Arctic Oceans.

Off the wind
Sailing with the wind coming from the stern or quarter of the boat.

Offshore wind
Wind that is blowing away from the land, towards the water.

Offshore
Away from land, toward the water. See inland.

On the beam
To the side of the boat at right angles, abeam.

On the bow
To the bow of the boat, forward of the beam.

On the quarter
To the stern of the boat, aft of the beam.

On the wind
Sailing close hauled. Sailing toward the wind as much as possible with the wind coming from the bow.

Open
A location that is not sheltered from the wind and seas. An open location would not make a good anchorage.

Out of trim
Sails that are not properly arranged for the point of sail that the boat is on. The sails may be luffing or have improper sail shape, or the boat may be heeling too much. These conditions will slow the boat down.

Outboard engine
An engine used to power a small boat. Outboard engines are mounted on a bracket aft of the stern of the boat.

Outboard
On the side of the hull that the water is on. Outboard engines are sometimes just called outboards.

Outhaul
A line used to tension the foot of a sail, used to maintain proper sail shape.

Outrigger
A floatation device attached to one or both sides of the hull to help prevent a capsize.

Overall length
The total length of the boat, including any object protruding from the bow or the stern. Also known as LOA.

Overboard
In the water outside of the vessel.

Overfall
Dangerously steep and breaking seas due to opposing currents and wind in a shallow area.

Overhang
The area of the bow or stern which hangs over the water.

Override
A line that becomes improperly wrapped over itself and fouls a winch.

Owner’s flag
A boat owner's private pennant.

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P

Pad eye
A small fitting with a hole used to guide a line.

Paddle
(1) A stick with a blade in the end of it used to propel a small boat through the water.
(2) The act of using a paddle to propel a boat.

Painted waterline
A painted line on the side of a boat at the waterline. The color usually changes above and below the waterline as the boat is painted with special antifouling paint below the waterline.

Painter
A line attached to the bow of a dinghy and used to tie it up or tow it.

Palm
A tool worn on the hand with a thimble shaped structure on it and used when sewing sails.

PAN PAN
An urgent message used on a radio regarding the safety of people or property. A PAN PAN message is not used when there is an immediate threat to life or property, instead the MAYDAY call is used. PAN PAN situations may develop into MAYDAY situations. As with a MAYDAY, PAN PAN messages have priority on the radio channels and should not be interrupted. In the case of a less urgent safety message, such as a hazard to navigation, the appropriate signal to use is SECURITE.

Parachute flare
An emergency signal flare that will float down on a parachute after launch, hopefully improving its visibility.

Parachute
Sometimes used to describe a spinnaker.

Parallax error
Error that can be introduced when not reading an instrument directly from its front, due to the separation of the indicator and the scale being read.

Parallel rules
A navigational tool used to move a line on a chart from one location to another without changing its angle, such as when moving a plotted course to a compass rose. Parallel rules are two straight edges that are mechanically connected such that both edges always remain parallel. Lines can then be "walked" across a flat chart.

Parallels
Latitude lines.

Parcel
Material wrapped around a line to prevent chaffing.

Parrot beak
A clip at the end of a spinnaker pole to hold the guy.

Partners
Supporting structures used to support areas where high loads come through openings in the deck, such as at the mast boot.

Passage
A journey from one place to another.

Patant log
A type of log that uses a counter attached to a rotor on a line which is towed behind the boat to help measure distance and speed.

Pay out
To let out.

Pedestal
The column that the wheel is mounted on.

Pylorus
A card marked in degrees and having sightings on it that is used to take bearings relative to the ship, rather than magnetic bearings as taken with a compass.

Pendant
A small line attached to a mooring chain. Also sometimes called a pennant.

Pennant
(1) A small flag, such as can be used for signaling. Flags can be used together to spell words or individually as codes, such as the quarantine flag.
(2) A small line attached to a mooring chain, sometimes called a pendant.

Personal floatation device
PFD for short. A device used to keep a person afloat. Also called a life jacket, life preserver or life vest.

PFD
Personal Floatation Device. A device used to keep a person afloat. Also called a life jacket, life preserver or life vest.

Pier
A place extending out into the water where vessels may dock. Usually made out of wood or cement.

Pile, piling
A pole embedded in the sea bottom and used to support docks, piers and other structures.

Pilot
An individual with specific knowledge of a harbor, canal, river or other waterway, qualified to guide vessels through the region. Some areas require that boats and ships be piloted by a licensed pilot.

Pil