Reference

Marine glossary

Every nautical term used across our articles, explained clearly. From abaft to working channel.

a b c d e f g h i k l m n o p r s t v w

109 terms

a7 terms

Abaft: Toward the stern (rear) of the boat. Opposite of 'abaft the beam' means behind a line drawn across the boat's widest point.
Abeam: At a right angle to the boat's centerline. An object 'abeam' is directly to your side. Used in navigation to describe relative bearing.
Aft: Toward, near, or in the stern (rear) of the boat. 'Aft cabin' = a cabin toward the back.
AIS: Automatic Identification System. A VHF-based system that broadcasts your vessel's position, course, and speed to other AIS-equipped vesse…
Anchor Rode: The line, chain, or combination connecting the anchor to the boat. Scope is the ratio of rode length to water depth.
Apparent Wind: The wind you feel on a moving boat — a combination of true wind and the wind created by your own motion. Differs from true wind in both s…
Auto Guidance: A chartplotter feature that routes you through water deep enough and under bridges tall enough for your vessel's draft and air draft.

b9 terms

Backing Down: Operating the engine in reverse, typically used when fighting large fish to keep the line from breaking or when maneuvering in tight spaces.
Ballast: Weight placed low in the hull to improve stability. In wake boats, ballast tanks are filled with water to create larger wakes for surfing…
Beam: The widest point of the boat. 'Beam sea' means waves hitting the boat from the side — the most uncomfortable and dangerous angle.
Bearing: The horizontal direction to an object, measured in degrees from north. 'True bearing' uses true north; 'magnetic bearing' uses magnetic n…
Berth: A sleeping area on a boat. Also, a designated spot where a boat is moored ('your berth at the marina').
Bilge: The lowest inner part of a boat's hull where water collects. Bilge pumps remove this water.
Bimini Top: A canvas sunshade mounted on a metal frame, typically over the cockpit or helm. Folds down when not needed. Named after the Bimini island…
Bow: The front (forward) part of the boat. 'Port bow' = front-left; 'starboard bow' = front-right.
Bulkhead: A vertical wall inside the hull that divides the boat into compartments. Bulkheads add structural rigidity and create watertight sections…

c11 terms

Cast Off: To release the lines holding the boat to the dock, preparing to depart. The reverse of 'make fast' or 'tie up'.
Catenary: The curve of an anchor chain caused by its own weight. Catenary helps absorb shock loads and keeps the anchor shank flat.
Chart Datum: The reference water level from which depths are measured on a nautical chart. In U.S. waters, this is usually Mean Lower Low Water (MLLW).
Chine: The intersection of the boat's bottom and sides. A 'hard chine' is a sharp angle; a 'soft chine' is rounded. Chines affect planing behavi…
ClearVü: Garmin's down-scanning sonar technology that produces photo-like images of structure beneath the boat. Operates at 455/800 kHz.
Cleat: A T-shaped fitting on deck used to secure lines. Proper cleat hitch is essential for safe docking.
Clevis Pin: A cylindrical pin with a head used to connect shackles, turnbuckles, and other fittings. Secured with a cotter pin or split ring.
Cockpit: The open area at the stern of a boat, typically where fishing or boarding happens. Not to be confused with the helm.
Cockpit Drain: A scupper or drain that lets water out of the cockpit. Self-bailing cockpits drain by gravity; non-self-bailing require a bilge pump.
Course Over Ground (COG): The actual direction the boat is moving over the earth's surface, accounting for wind, current, and leeway. Differs from heading.
Cuddy Cabin: A small, enclosed cabin in the bow of a boat, typically with a V-berth and minimal headroom. Common on 18-22 ft bowriders and center cons…

d7 terms

Dead Reckoning: Navigating by calculating position from a known starting point, using heading, speed, and time. No GPS or landmarks required.
Deadrise: The angle between the boat's bottom and the horizontal, measured at the transom. More deadrise = smoother ride in rough water but less st…
Depth Sounder: An instrument that measures water depth using sonar. Essential for avoiding groundings in shallow or unfamiliar water.
Displacement Hull: A hull that moves through the water by pushing it aside, rather than planing on top. Slower but more fuel-efficient than planing hulls.
Draft: The minimum water depth a boat needs to float without touching bottom. Critical for navigating shallow areas and inlets.
Drag: The resistance of water against the hull. Minimizing drag (through hull design, bottom paint, and trim) improves speed and fuel efficiency.
DSC (Digital Selective Calling): A VHF radio feature that sends a digital distress alert with your MMSI and GPS position at the push of a button.

e1 term

EPIRB: Emergency Position Indicating Radio Beacon. A satellite distress beacon that alerts rescue authorities with your GPS position. Registered…

f6 terms

Fairlead: A fitting that guides a line or chain, preventing chafe and keeping it running true. Used on anchor rodes, dock lines, and sailing sheets.
Fairway: The navigable channel of a river or harbor. 'Mid-channel' is the center of the fairway.
Fender: A cushion (usually inflatable) hung over the boat's side to prevent contact with docks, pilings, or other boats.
Ferry Angle: The angle at which you point the bow upwind/current so that the element pushes you sideways toward a dock or destination while maintainin…
Flare: 1. An outward curve of the hull at the bow that deflects spray. 2. A pyrotechnic distress signal — required safety equipment on many vess…
Freeboard: The distance from the waterline to the deck edge. More freeboard = drier ride and less likely to ship water over the side.

g5 terms

Gelcoat: The outermost layer of a fiberglass hull — a pigmented resin that provides color, gloss, and water resistance. Requires periodic compound…
Gimbal Bearing: The pivot point in a sterndrive (I/O) that allows the drive to turn and tilt. A common failure point on older sterndrives.
GPS: Global Positioning System. A satellite-based navigation system that provides position, speed, and time. Standard on all modern chartplott…
Ground Tackle: The collective term for the anchor, rode, chain, and all hardware used to secure the boat to the bottom. 'Good ground tackle' = properly …
Gunwale: The upper edge of the boat's side — the 'rail'. Pronounced 'gun-nel'. Where you mount rod holders, cleats, and railings.

h7 terms

Hailing: Calling another vessel on VHF radio to establish communication. Done on Channel 16, then switch to a working channel.
Halyard: A line used to raise and lower sails, flags, or antennas on a boat. Originally 'haul-yard' — a line to haul a yard arm.
Hatch: An opening in the deck with a cover, providing access to storage or the bilge below. Should be dogged (secured) in rough weather.
Head: The marine toilet (bathroom). 'Going to the head' = using the bathroom. The name comes from the historical placement at the bow (head) of…
Heading: The direction the boat's bow is pointing, in degrees from north. Differs from Course Over Ground (COG) when wind or current push you side…
Helm: The steering station of the boat — where the wheel, throttle, and primary instruments are located. 'Taking the helm' = taking control.
Hull Speed: The theoretical maximum speed of a displacement hull, calculated as 1.34 × √waterline length. Planing hulls exceed hull speed.

i1 term

Inboard: An engine mounted inside the boat, driving a propeller shaft through the hull. Common on wake boats and large cruisers.

k3 terms

Keel: The structural backbone of the boat, running along the bottom from bow to stern. Provides ballast (on sailboats) and prevents sideways sl…
Knot: A unit of speed equal to one nautical mile per hour (1.15 mph or 1.85 km/h). The standard speed unit in marine navigation.
Knotmeter: An instrument that measures the boat's speed through the water using a paddlewheel or ultrasonic sensor. Differs from GPS speed (which me…

l5 terms

Lazarette: A storage compartment in the stern of the boat, typically accessed through a hatch in the cockpit. Used for fenders, lines, and spare equ…
Lee Shore: A shore that the wind is blowing onto — dangerous because the wind pushes you toward the rocks. Always keep a lee shore to leeward.
LiveScope: Garmin's real-time forward-facing sonar that shows fish swimming ahead of the boat in motion. The biggest advance in fishing electronics …
LOA: Length Overall. The maximum length of the boat from the tip of the bow to the end of the stern (including any extensions like pulpits or …
LWL: Length at the Waterline. The length of the boat at the water's surface. Used to calculate hull speed and displacement ratios.

m4 terms

Make Fast: To securely tie a line to a cleat or bollard. 'Make fast the bow line' = tie the bow line securely to the dock cleat.
Mayday: The international distress call for grave and imminent danger. Said three times on VHF Channel 16, followed by vessel info and position.
MMSI: Maritime Mobile Service Identity. A unique 9-digit number that identifies your vessel for DSC calls. Free from BoatUS (U.S.) or FCC (inte…
Mooring: A permanent anchor system (typically a heavy block with a chain and buoy) that boats tie to instead of anchoring. Common in harbors and m…

n2 terms

Nautical Mile: A unit of distance equal to 1,852 meters (1.15 statute miles). Based on one minute of latitude. Speed in knots = nautical miles per hour.
NMEA 2000: A marine networking standard that lets instruments (GPS, sonar, engine, autopilot) share data over a single cable. Plug-and-play between …

o1 term

Outboard: An engine mounted on the boat's transom, combining engine, drive, and steering in one unit. The most common propulsion for small to mid-s…

p7 terms

Pan-Pan: The urgent-but-not-life-threatening distress call. Used for situations like a disabled engine drifting toward a lee shore. Pronounced 'pa…
PFD: Personal Flotation Device. A life jacket. Type I (offshore), Type II (near-shore), Type III (flotation aid), Type IV (throwable), Type V …
Pilothouse: An enclosed helm station with windows, protecting the operator from weather. Common on commercial vessels and cruising boats in cold clim…
Planing Hull: A hull that rises out of the water and skims across the surface at speed. Faster than displacement hulls but less efficient at low speeds.
Port: The left side of the boat when facing forward. Marked with red navigation lights and red channel markers (returning to port).
Prop Walk: The sideways force of the propeller that pushes the stern to one side (usually port in reverse on a right-hand prop). Used to advantage i…
Pulpit: A railing extension at the bow, forward of the deck. The anchor is often mounted on the pulp. Also called a bow pulpit.

s14 terms

Scope: The ratio of anchor rode length to water depth (plus bow height). 7:1 is the standard for overnight anchoring; 5:1 for lunch; 3:1 only in…
Scupper: A drain in the deck or cockpit that lets water flow overboard. Self-bailing decks have scuppers that drain by gravity.
Seacock: A valve on a through-hull fitting that can be closed to prevent water entering the boat. Must be accessible and maintained — a failed sea…
Sécurité: A safety warning broadcast to other vessels about a navigational hazard (floating debris, etc.). Pronounced 'say-cure-ih-tay'.
Shackle: A U-shaped metal fitting with a pin, used to connect lines, chain, and hardware. The clevis pin shackle is the most common on recreationa…
SideVü: Garmin's side-scanning sonar that images structure up to 500 feet to either side of the boat. Operates at 455/800/1000 kHz.
Skeg: A fixed fin below the hull that protects the propeller and provides directional stability. Also called a 'skeg guard' on outboards.
Sound Signal: A horn or whistle signal used to communicate intentions in fog or restricted visibility. One short blast = altering to starboard; two = p…
Splice: To join two lines (or a line to itself) by weaving the strands together, rather than tying a knot. A splice is stronger than a knot and r…
Spring Line: A docking line run from a midship cleat to the dock, used to pivot the boat against the dock using engine power. The most important docki…
Standing Rigging: The fixed wires and cables that support the mast on a sailboat — forestay, backstay, and shrouds. Contrast with running rigging.
Starboard: The right side of the boat when facing forward. Marked with green navigation lights and green channel markers.
Stern: The rear of the boat. 'Aft' and 'stern' are often used interchangeably, though 'aft' is a direction and 'stern' is a location.
Sterndrive: An inboard engine connected to an outboard-like drive unit through the transom. Also called I/O (inboard/outboard). Common on bowriders.

t7 terms

Tachometer: An instrument that displays engine RPM. Essential for matching prop to engine and monitoring engine health. 'Tach' for short.
Tide Range: The vertical distance between high and low tide at a given location. Ranges from inches (inland waters) to 40+ feet (Bay of Fundy). Affec…
Topping Lift: A line that supports the outboard end of a boom when the sail is lowered. Also used on outboard motor brackets to tilt the engine.
Transom: The flat (or slightly curved) rear surface of the boat. The transom holds the outboard(s) or sterndrive on most planing boats.
Trim: 1. The bow-up or bow-down attitude of a planing boat, adjusted with trim tabs or engine trim. 2. To adjust sails for optimal angle to the…
Trim Tabs: Adjustable metal planes on the transom that redirect water flow to lift the bow or correct list. Essential for ride quality in rough water.
Trolling Motor: An electric motor used for slow, precise positioning — primarily for fishing. Bow-mounted (hand or foot controlled) or transom-mounted. P…

v3 terms

V-Berth: A V-shaped sleeping berth in the bow of a boat, where the hull narrows. The most common forward berth on cruisers and cuddy cabins.
Vang: A line or hydraulic ram that pulls the boom down to control sail shape. 'Preventer vang' prevents accidental jibes. Essential on racing s…
VHF: Very High Frequency radio. The primary communication and distress device on boats. Channel 16 is monitored by the Coast Guard for hailing…

w5 terms

Wake: The waves created by the boat as it moves through the water. 'No wake zone' = idle speed only. Large wakes cause shore erosion and dock d…
Waterline: The line where the water surface meets the hull. 'Above the waterline' = visible; 'below the waterline' = submerged. Growth below the wat…
Waypoint: A saved GPS position used for navigation. Waypoints can mark fishing spots, route turns, or hazards. Routes are sequences of waypoints.
Windlass: A motorized winch used to raise and lower the anchor. Essential on boats with heavy all-chain rodes. Should not be used to pull the boat …
Working Channel: A VHF channel used for routine communication after hailing on Channel 16. Common working channels: 68, 69, 71, 72, 78.

r4 terms

Raw Water: Water drawn from outside the boat (lake or ocean) for cooling engines, flushing toilets, or washdown systems. Must be filtered to prevent…
Rode: Short for 'anchor rode' — the line, chain, or combination connecting the anchor to the boat.
Rubrail: A protective strip along the gunwale that absorbs contact with docks and pilings. Usually made of rubber, vinyl, or metal-over-rubber.
Running Rigging: Lines and tackle that are adjusted while sailing — halyards, sheets, outhauls. Contrast with 'standing rigging' (the fixed wires that sup…

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