Boating Terms Glossary: 150 Nautical Terms Explained

October 17, 2026

A to Z boating terms glossary with 150 nautical terms in plain English, from abeam to windward, with links to detailed guides on bow, stern, draft, tides and more.

Nautical terms are the special words boaters use for parts of a boat, directions, weather and rules on the water. This glossary explains 150 boating terms and boat terminology in plain English, from A to Z, so you can follow a dockhand, a marine forecast or a Coast Guard radio call. Where a topic needs more than a line or two, the entry links to a longer Logbook guide.

How to use this glossary

Terms are listed alphabetically in groups. If you are brand new to boats, start with these basics:

Question	Start here
What are the front, back and sides called?	Parts of a boat and port vs starboard
What do depth and width measurements mean?	Draft, beam and freeboard and how deep is a fathom
How do tides work?	Ebb, flood and slack tide
What are the lights at night?	Boat navigation lights
How do I talk on the radio?	VHF marine radio

Rules-based definitions, such as the lights and what counts as a vessel, come from the Inland Navigation Rules (33 CFR Part 83). The definitions of beam and length overall follow the Coast Guard's boat-building rules (33 CFR 183.3).

A to B

Abaft: Toward the stern, behind another point on the boat. "Abaft the beam" means behind the widest part.
Abeam: At a right angle to the boat's centerline, off the side.
Aft: Toward the back of the boat. See parts of a boat.
Aground: Touching or stuck on the bottom. Rule 30 of the Navigation Rules sets special lights for a vessel aground. See boat navigation lights.
Aids to navigation (ATON): Buoys, beacons, lights and daymarks that mark channels and hazards.
Anchor: A heavy device on a rode that grips the bottom to hold the boat in place.
Anchor light: An all-round white light shown by an anchored vessel at night, as set out in Rule 30. See boat navigation lights.
Astern: Behind the boat, or backward.
Athwartships: Across the boat, from side to side.
Ballast: Heavy material low in the hull that adds stability.
Beam: The width of the boat at its widest point. See draft beam freeboard.
Bearing: The direction to an object, usually in degrees from north.
Beaufort scale: A scale of wind force from 0 to 12 based on observed sea and wind effects. See beaufort scale for boaters.
Berth: A place where a boat is docked or moored, or a bunk on board.
Bilge: The lowest inside part of the hull, where water collects. See what is a bilge.
Bilge pump: A pump that removes water from the bilge. See what is a bilge.
Bimini top: A fold-down canvas shade over the cockpit.
Bitter end: The free end of a line or anchor rode.
Boat hook: A pole with a hook for picking up lines, buoys or fenders.
Boom: The horizontal pole that holds the foot of a sail.
Bow: The front of the boat. See parts of a boat.
Bowline: A knot that makes a fixed loop, and also a line at the bow. See boating knots.
Bow thruster: A small propeller in the bow that pushes the boat sideways for docking.
Bridge: The control station of a larger boat, or a structure crossing the water.
Bulkhead: A vertical wall inside the hull that divides space and adds strength.
Buoy: A floating marker that shows a channel, hazard or mooring.

C to D

Cabin: An enclosed living space on a boat.
Capsize: To turn over in the water. See what to do if your boat capsizes.
Cast off: To release the lines holding the boat to a dock.
Catamaran: A boat with two parallel hulls. See types of boats.
Center console: A boat with the helm in the middle of the deck so you can walk around it. See center console boats.
Chart: A nautical map showing depths, hazards and aids to navigation.
Chart datum: The reference level for charted depths. NOAA uses mean lower low water on most charts. See how to read a tide chart.
Chine: The line where the bottom of a hull meets the side.
Chock: A fitting that guides a line over the side of the boat.
Cleat: A fitting with two horns for tying off a line. See boating knots.
Cockpit: The open area at the rear of a boat where the crew sits.
Companionway: A stairway or ladder leading below deck.
Compass: An instrument that shows magnetic direction.
Course: The direction in which a boat is steered.
Cradle: A frame that supports a boat out of the water. See boat storage options.
Current: The horizontal flow of water, caused by tide, wind or a river. See ebb flood slack tide.
Daymark: A fixed sign or shape on a post or structure that marks a channel in daylight.
Davit: A crane on a boat or dock that raises and lowers a dinghy or boat.
Deadrise: The angle between the bottom of the hull and a horizontal line.
Deck: The floor-like surface on top of the hull.
Deep-V: A hull with a steep bottom angle that cuts through waves. See types of boats.
Dinghy: A small boat used as a tender. See inflatable boats and dinghies.
Displacement: The weight of water a boat pushes aside, equal to the boat's weight.
Dock: A structure where boats tie up. Also, to bring a boat alongside one.
Dockage: The fee or space for keeping a boat at a dock. See how much does a boat slip cost.
Draft: How deep a boat sits in the water, from waterline to the lowest point. See draft beam freeboard.
Dry stack: Storage where a boat is kept on a rack on land and launched on request. See boat storage options.

E to G

Ebb: The falling tide, when water moves away from shore. See ebb flood slack tide.
EPIRB: Emergency Position Indicating Radiobeacon, a satellite distress beacon. See what to do if your boat capsizes.
Fairway: A navigable channel, or open water used by vessels.
Fathom: A unit of depth equal to 6 feet. See how deep is a fathom.
Fender: A cushion hung between a boat and a dock or another boat. See boat fenders.
Fetch: The distance wind blows over water, which affects wave size.
Flood: The rising tide, when water moves toward shore. See ebb flood slack tide.
Flotation: Buoyant material in a hull that keeps a small boat afloat when swamped.
Following sea: Waves coming from behind the boat.
Fore: Toward the front of the boat.
Freeboard: The height of the side above the waterline. See draft beam freeboard.
Fuel dock: A dock where boats buy fuel.
Galley: The kitchen on a boat.
Gelcoat: The glossy outer layer on a fiberglass hull.
Give-way vessel: The vessel that must keep clear of another under the Navigation Rules.
GPS: Global Positioning System, a satellite navigation system.
Ground tackle: The anchor, rode and related gear.
Gunwale: The upper edge of the side of a boat, pronounced "gunnel." See parts of a boat.
Gybe: To turn a sailboat so the stern passes through the wind.

H to L

Hatch: An opening in the deck, usually with a cover.
Head: The marine toilet, or the room that holds it.
Heading: The direction the bow points at a given moment.
Headway: Forward movement through the water.
Heel: The sideways lean of a sailboat caused by wind.
Helm: The steering station or wheel.
Hitch: A knot that ties a line to an object. See boating knots.
Hull: The watertight body of the boat. See parts of a boat.
Idle speed: The slowest speed that maintains steerage. Florida rules use "Idle Speed No Wake." See no wake zones.
Inboard: An engine mounted inside the hull. See inboard vs outboard.
Intracoastal Waterway (ICW): A chain of protected channels along the Atlantic and Gulf coasts. See intracoastal waterway florida texas.
Jib: A triangular sail set in front of the mast.
Jon boat: A flat-bottomed aluminum boat with a square bow. See jon boats.
Keel: The structural spine along the bottom of the hull. See parts of a boat.
Knot (speed): One nautical mile per hour. Convert with the knots to mph tool.
Knot (rope): A fastening made in a line. See boating knots.
Latitude: Distance north or south of the equator, measured in degrees.
Lee: The side sheltered from the wind.
Leeward: The direction away from the wind.
Length overall (LOA): The length of the boat from end to end. The Coast Guard definition excludes attachments such as bowsprits and outboard brackets. See draft beam freeboard.
Life jacket: A wearable flotation device, also called a PFD. See coast guard approved life jackets.
Line: Rope used on a boat once it has a job. See boating knots.
Lock: A chamber that raises or lowers boats between water levels.
Longitude: Distance east or west of the prime meridian, measured in degrees.

M to O

Mainsail: The principal sail on a sailboat.
Marina: A facility with docks, slips and services for boats.
Mast: A vertical pole that holds sails, lights or antennas.
Masthead light: A white light shown over the centerline. It covers 225 degrees under Rule 21. See boat navigation lights.
Mayday: The spoken distress call for immediate danger. See VHF marine radio.
MMSI: Maritime Mobile Service Identity, a nine-digit number for a radio. See VHF marine radio.
Mooring: A permanent anchor and buoy that a boat ties to.
Nautical mile: A distance of 1,852 meters, used in navigation.
Neap tide: A tide with a small range, near the first and third quarter moon. See how to read a tide chart.
No wake: A zone where boats must slow so they make little or no wake. See no wake zones.
Outboard: An engine mounted on the transom, outside the hull. See inboard vs outboard.
Outdrive: A drive unit on the transom connected to an engine inside the hull, also called stern drive. See inboard vs outboard.

P to R

Pan-Pan: The spoken call for an urgent situation that is not yet a distress. See VHF marine radio.
Pier: A structure extending from shore for tying up boats.
Piling: A post driven into the bottom, used to support a dock or tie a boat.
Plane: To ride on top of the water instead of through it. See no wake zones.
Port: The left side of the boat when facing forward. See port vs starboard.
Port tack: A sailboat with wind coming over the port side.
Propeller: The spinning blades that push the boat. See boat propellers.
Reef: To reduce the area of a sail. Also, a shallow ridge of rock or coral.
Rode: The line or chain connecting the anchor to the boat.
Rudder: A flat blade that steers the boat.
Running lights: Another name for navigation lights. See boat navigation lights.

S

Sailboat: A boat powered by wind in its sails. See types of boats.
Scope: The ratio of anchor line length to water depth.
Sheet: A line that controls a sail.
Sidelights: Red and green lights on the sides of a boat. Each covers 112.5 degrees under Rule 21. See boat navigation lights.
Skeg: A fin below the stern that protects the propeller and helps tracking.
Skiff: A small, open boat, often used for shallow water. See skiff bay boat flats boat.
Slack water: The brief period when the tide stops flowing. See ebb flood slack tide.
Slip: A berth for a boat between two piers or pilings. See how much does a boat slip cost.
Small craft advisory: A weather product warning of winds or seas hazardous to small boats. See special marine warning vs small craft advisory.
Sounding: A measurement of water depth. See how deep is a fathom.
Spring tide: A tide with a large range, near the new and full moon. See how to read a tide chart.
Squall: A sudden short burst of strong wind, often with rain.
Stand-on vessel: The vessel that keeps its course and speed when another must give way.
Starboard: The right side of the boat when facing forward. See port vs starboard.
Steerageway: The minimum speed at which a boat can be steered. See no wake zones.
Stern: The back of the boat. See parts of a boat.
Sternlight: A white light at the stern. It covers 135 degrees under Rule 21. See boat navigation lights.
Swamp: To fill with water from waves or rain. See what to do if your boat capsizes.

T to Z

Tack: To turn a sailboat so the bow passes through the wind.
Tender: A small boat used to carry people to a larger boat. See inflatable boats and dinghies.
Tide: The regular rise and fall of the sea. See how to read a tide chart.
Tiller: A lever attached to the rudder or outboard for steering.
Transom: The flat panel across the stern. See parts of a boat.
Trim: The angle of the boat, or an adjustment to a sail or outdrive.
Trim tabs: Adjustable plates on the transom that change the boat's running angle.
Underway: Moving through the water and not at anchor, tied to shore or aground.
Vessel: Every kind of watercraft used or able to be used for transport on water, as defined in the Navigation Rules.
VHF: Very high frequency, the radio band used for marine communication. See VHF marine radio.
Wake: The waves a boat leaves behind. See no wake zones.
Waterline: The line where the hull meets the surface of the water. See draft beam freeboard.
Windward: The direction the wind comes from.

Where to practice the words

The fastest way to learn the vocabulary is on the water. Marinalo lists Florida boat ramps, Texas boat ramps and Florida fuel docks, plus tide times for reading tide tables, and a nautical miles to miles converter.

FAQ

What are the most important boating terms for beginners?

Bow, stern, port, starboard, draft, wake, fender, cleat, line, helm and anchor. They cover most dock and ramp conversations.

What is the difference between a rope and a line?

Rope is the material. Once it is on a boat and has a job, it is usually called a line, such as a dock line or a sheet.

Why do boats use knots instead of miles per hour?

A knot is one nautical mile per hour. Nautical miles are based on the earth's geometry and are used on charts. A nautical mile is 1,852 meters.

What does "underway" mean?

The boat is not at anchor, made fast to the shore or aground. A boat drifting with the current is still underway.

What is a fathom?

A fathom is 6 feet, a unit used for depth. Our guide explains where it comes from.

Sources

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