📖 Reference

Maritime Glossary

392 sailing, navigation, VHF radio and yachting terms — written for modern cruising sailors, charter crews and skipper exam candidates. Last updated May 2026.

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A B C D E F G H I J K L M N O P Q R S T U V W Y

A

Aback: A sail that has been trimmed so the wind pushes against the reverse side of the cloth, filling it from behind.
Abeam: Lying on a line perpendicular to the vessel's centerline — directly off her side.
Aboard: On, onto, or inside the vessel.
Adrift: Afloat with no means of propulsion or attachment, carried along by wind, current, or tide.
Aft: Toward, at, or behind the stern.
Aground: The condition of a vessel whose keel or hull is in contact with the seabed.
AIS: Automatic Identification System — a VHF-based transponder network that continuously broadcasts a vessel's identity, position, course, and speed to other AIS-equipped craft and to shore stations, greatly improving collision awareness.
AIS-MOB: A personal AIS man-overboard beacon that, when activated (usually automatically on immersion), transmits the casualty's GPS position as an AIS distress target visible on every nearby AIS receiver.
Alternator: An engine-driven generator that converts mechanical rotation into alternating current, which on a yacht is then rectified to charge the house and starter batteries while the engine runs.
Amidships: At or toward the middle of the vessel, whether fore-and-aft or athwartships.
Anchor windlass: An electric or manual winch mounted on the foredeck that hauls and lowers the anchor chain or rode, typically with a gypsy for chain and a drum for warp.
Apparent wind: The wind actually experienced on board, produced by combining the true wind with the wind caused by the boat's own motion.
ARPA: Automatic Radar Plotting Aid — radar software that tracks targets automatically and computes CPA (closest point of approach) and TCPA (time to CPA) to flag collision risk.
Astern: In the water behind the vessel, or moving backwards.
Asymmetric spinnaker: A downwind sail (also called a cruising chute or gennaker) with a fixed tack but no pole, cut asymmetrically so it can be set and trimmed like a large genoa on a reach.
Athwartships: Running across the vessel from one side to the other, at right angles to the fore-and-aft line.
Autopilot: An electronic self-steering system that uses a heading or GPS input to drive a hydraulic ram, linear drive, or wheel motor, holding the boat on course without a human helm.

B

Back: (1) To haul a sail to windward so the wind fills the wrong side, stopping the boat or driving it astern. (2) Of the wind: to shift anticlockwise.
Backstay: A piece of standing rigging running from the masthead (or partway down) to the stern, resisting the forward pull of the headsail.
Bail: To remove water from inside the vessel, traditionally with a bucket or scoop.
Ballast: Weight — usually carried low in the keel — that lowers the centre of gravity and gives the boat stability and righting moment.
Barometer: A pressure-measuring instrument whose readings are used to monitor and predict weather trends.
Batten: A thin strip of timber, fibreglass, or carbon inserted into a pocket along the leech of a sail to maintain its aerodynamic shape.
Battery monitor: An instrument that integrates current flow over time to report the true state of charge and remaining amp-hours of a battery bank, far more accurately than voltage alone.
Beam: The greatest width of the vessel measured at its widest point.
Beam reach: A point of sail in which the wind blows at roughly 90° to the boat's direction of travel.
Bear away: To steer the bow away from the wind (also called bearing off or falling off).
Bearing: The angular direction of one object from another, expressed in compass degrees.
Beating: Working to windward by sailing a succession of close-hauled tacks.
Below: Any space inside the vessel that is beneath the deck.
Bend: To make fast — attaching a sail to a spar or stay, or tying a line to a sail.
Bight: Any loop or curve formed in a rope between its two ends.
Bilge: The lowest internal part of the hull, where water inevitably drains and collects.
Bilge pump: A manual or electric pump fitted to remove water from the bilge; most cruising yachts carry at least one of each type, with the electric pump often wired to an automatic float switch.
Bimini: A fabric sun awning stretched over a stainless-steel frame above the cockpit to shelter the crew from sun and light rain.
Bitter end: The very last part of a line — the end opposite the working end.
Blanket: To interpose a sail or other object between the wind and another sail so the downwind sail is starved of breeze.
Block: The marine term for a pulley — a sheave in a housing through which a line runs.
Boat hook: A shaft with a hook and a blunt end, used for snagging mooring lines, retrieving overboard items, or fending off.
Boat speed: The speed at which the hull moves through the water, as opposed to speed over ground.
Boltrope: A length of rope sewn inside the foot or luff of a sail so the sail can be slid into a groove on the boom or mast.
Boom: The horizontal spar that extends aft from the mast and carries the foot of the mainsail.
Boom vang: A tackle (also called a kicking strap) running from the base of the mast to the boom, pulling the boom down to flatten the mainsail and control leech twist.
Bottom: The underwater surface of the hull.
Bow: The forward end of the vessel.
Bow line: A mooring line led from the bow of the vessel to the dock or pontoon.
Bowline: A classic knot that forms a secure, non-slipping loop and can still be untied after heavy loading.
Bow Spring: A dockline led from the bow aft along the dock, preventing the boat from surging forward.
Bowsprit: A spar extending forward of the stem (often retractable on modern cruisers) to which an asymmetric spinnaker, code zero, or gennaker tack is attached.
Bow thruster: A small transverse propeller mounted in a tunnel near the bow that pushes the bow sideways at low speed, making close-quarters manoeuvring much easier.
Breastline: A short line led directly from the vessel to the dock, holding the hull close alongside.
Broach: A sudden, unintended round-up into the wind, usually while running or reaching in strong breeze and waves.
Broad reach: A point of sail with the wind coming over the quarter — roughly 135° from the bow.
Bulkhead: An athwartships interior wall that stiffens the hull and subdivides the internal space.
Bulwark: A solid raised extension of the topsides above deck level, providing a barrier against falling overboard.
Buoy: A floating aid to navigation, anchored in position to mark channels, dangers, or stations.
Buoyancy: The upward force exerted by water on a submerged body — the property that lets an object float.
Burdened vessel: The former term (replaced in modern COLREGs usage by 'give-way vessel') for the vessel obliged to keep out of the way in a crossing or overtaking situation.
Bus bar: A heavy copper or brass terminal strip to which multiple battery cables or circuits are connected, providing a single low-resistance junction point.
By the lee: A run in which the wind is coming over the same side of the boat as the boom — a configuration that invites an accidental gybe.

C

Cabin: The enclosed interior accommodation of the vessel.
Can: In the IALA Region B buoyage system (USA, parts of the Americas, Japan, Korea, Philippines), an odd-numbered green cylindrical buoy marking the port side of a channel when entering from seaward.
Capsize: To tip a vessel so far that it rolls over onto its side or beyond.
Carbon fibre: A stiff, light composite material widely used for modern masts, booms, rudders, and hulls where strength-to-weight ratio matters.
Cast off: To let go a mooring line when departing a dock, mooring, or other vessel.
Catamaran: A multihull with two parallel hulls connected by a deck, bridgedeck, or trampoline.
Catboat: A simple rig with a single mainsail stepped on an unstayed mast set well forward, with no headsail.
Centerboard: A pivoting keel that can be raised into a trunk to reduce draft and lowered to resist leeway.
Centerline: The imaginary line running down the middle of the vessel from bow to stern.
Chafe: Wear on a rope, sail, or sheet caused by repeated rubbing against another surface.
Chainplates: Heavy metal fittings, through-bolted to the hull structure, that anchor the lower ends of the shrouds and stays.
Channel: A navigable stretch of water — usually marked with buoyage — where depth is sufficient for safe passage.
Chart: A nautical map showing coastlines, depths, aids to navigation, and hazards.
Charter: To hire a vessel for a period — either bareboat (skipper and crew provided by hirer) or crewed.
Chartplotter: An electronic display that overlays the vessel's GPS position on digital charts, and often integrates AIS, radar, sonar, and autopilot data on the same screen.
Chart table: A flat surface (usually below in the navigation station) of roughly half-chart size, fitted with stowage and instruments for passage planning.
Chock: A deck-mounted fairlead, often smoothed or rollered, through which docklines and anchor rode are led cleanly.
Chop: Short, steep, broken waves — typically caused by wind over a shallow or restricted fetch.
Cleat: A deck fitting — most commonly a horned or jam cleat — designed to hold a line under load.
Clew: The aft lower corner of a fore-and-aft sail; on a mainsail it is tensioned by the outhaul, on a jib by the sheets.
Close hauled: The point of sail nearest the wind, with sails sheeted hard in toward the centreline so the boat can work to windward.
Close reach: A point of sail between close-hauled and a beam reach, with the apparent wind about 70° off the bow.
Coaming: A raised lip around the edge of the cockpit or a hatch, designed to keep out water.
Cockpit: The recessed working area of the deck where the helm, sheets, and instruments are usually grouped.
Code Zero: A very flat, large, reaching sail set on a continuous-line furler forward of the forestay; it fills the gap between a genoa and an asymmetric spinnaker in light upwind-to-close-reaching conditions.
Coil: To lay a rope down in neat, uniform loops for storage, or the stored loops themselves.
COLREGs: The International Regulations for Preventing Collisions at Sea (1972, amended) — the body of rules governing rights of way, lights, shapes, and sound signals at sea.
Come about: Synonym for tacking — turning the bow through the eye of the wind.
Companionway: The stairway or ladder leading from the cockpit or deck down into the cabin.
Compass: A magnetic instrument indicating the vessel's heading relative to the Earth's magnetic field.
Compass rose: A printed ring on a chart giving the directions of true and magnetic north and the local variation.
Course: The direction, expressed in degrees, in which the vessel is being steered.
Crew: Everyone aboard besides the skipper who helps sail and run the boat.
Cruising chute: A cruiser-friendly asymmetric downwind sail, simpler to handle than a conventional spinnaker and often used with a snuffer or top-down furler.
Cunningham: A line rigged through a cringle a short way above the tack of the mainsail and pulled down to increase luff tension, flattening the sail's entry.
Current: Horizontal movement of water driven by tide, wind, river flow, or ocean circulation.
Cutter: A single-masted rig carrying both a jib (outer headsail) and a staysail on an inner forestay.

D

Daysailer: A small open or lightly decked sailboat intended for short pleasure sails rather than overnight cruising.
Dead downwind: Sailing directly with the wind astern, 180° from its source.
Deck: The mostly horizontal upper surface of the hull.
De-power: To reduce the drive produced by the sails, by (1) pinching into the wind so the sails luff, (2) easing sheets to let the sails flutter, or (3) over-trimming so airflow detaches and stalls.
Depth sounder: An electronic instrument (also called an echo sounder) that measures depth below the transducer by timing an ultrasonic pulse's reflection from the seabed.
DGPS: Differential GPS — a GPS that uses correction signals from ground or satellite-based reference stations to refine accuracy from metres to sub-metre.
Dhow: A traditional Arabian sailing craft, typically single- or twin-masted and carrying lateen sails, still seen throughout the Red Sea and western Indian Ocean.
Dinghy: A small boat, sailed or rowed, used for pleasure or as a yacht's tender.
Dinghy davits: A stern-mounted arch or pair of arms fitted with tackle so a tender can be lifted clear of the water for passage-making.
Displacement: The total weight of the vessel, equal to the weight of water she pushes aside when floating.
Dock: A quay, pontoon, or berth where a vessel ties up — and also the act of bringing her alongside.
Dockline: A mooring line used to secure the vessel to a dock, pontoon, or piling.
Dodger: A fabric and framework spray hood forward of the cockpit that shelters the crew from wind and spray.
Downhaul: A line on some rigs that pulls down a sliding gooseneck to tension the luff of the mainsail, performing the same job as a Cunningham.
Draft: The vertical distance from the waterline to the deepest part of the keel — the minimum water depth the vessel needs to float.
Drogue: A long cone or series of small cones streamed on a bridle from the stern in very heavy weather to slow the boat, keep her stern-to the seas, and prevent broaching. Distinct from a sea anchor.
DSC: Digital Selective Calling — a feature of modern VHF and SSB radios that allows a pre-formatted digital distress alert, including the boat's identity and GPS position, to be transmitted at the press of a button.
Dyneema: A brand of ultra-high-molecular-weight polyethylene (UHMWPE) fibre; as strong as steel wire but a fraction of the weight, now widely used for halyards, sheets, and even standing rigging.

E

Ease: To let a sheet, halyard, or other line run out in a controlled manner.
Ebb: The outgoing phase of the tide, when water level is falling and the flow runs seaward.
ECDIS: Electronic Chart Display and Information System — a type-approved electronic charting system accepted as the primary means of navigation on many commercial vessels, using ENC vector charts.
EPIRB: Emergency Position Indicating Radio Beacon — a self-contained 406 MHz satellite distress beacon registered to the vessel, activated manually or by a hydrostatic release, which alerts the global Cospas-Sarsat system.

F

Fairlead: A fitting — often a block, ring, or slotted plate — that redirects a line with minimum friction and chafe.
Fairway: The centre portion of a navigable channel.
Fake (flake): To lay a rope down in wide, overlapping loops so it can run out without snagging.
Fall off: To alter course away from the wind (see also head down and bear away).
Fast: Secured — held in place, tied off.
Fathom: A legacy unit of depth equal to six feet (1.8288 m).
Fender: An inflated plastic or rubber buffer hung over the side to protect the hull when alongside a dock or another vessel.
Fend off: To push the vessel clear of an obstacle by hand, foot, or boat hook.
Fetch: The distance of open water, to windward, over which the wind has blown — the longer the fetch, the larger the waves.
Fid: A tapered hardwood or metal spike used to open the strands of a rope when splicing.
Fire extinguisher: A portable pressure-charged bottle used to fight fire on board; yachts typically carry Class A, B, and E/C types to cover solids, liquids, and electrical fires respectively.
Flare: A pyrotechnic distress signal — handheld red flares are for close-range visibility, parachute red flares for long-range, and orange hand smokes for daylight surface signalling.
Flood: The incoming phase of the tide, when water level is rising and the flow runs landward.
Following sea: A wave train overtaking the vessel from astern.
Foot: The lower edge of a sail.
Fore: Forward, or toward the bow.
Forepeak: The compartment in the bow below deck — in cruising yachts often a cabin, in older designs a stowage void.
Foresail: A collective term for a jib or genoa — any sail set forward of the mast.
Forestay: Standing rigging running from the bow (or stemhead) up to the mast, to which the foresail is hanked or furled.
Forward: Toward the bow.
Fouled: Tangled, jammed, or caught up.
Foul weather gear: Waterproof clothing — jacket, trousers (salopettes), sea boots — for sailing in wet or heavy conditions.
Fractional rig: A rig in which the forestay meets the mast below the masthead (e.g. 7/8 or 9/10 of mast height), common on modern performance cruisers.
Freeboard: The vertical distance from the waterline to the deck edge.
Full: A sail drawing properly, filled with wind and not luffing.
Furl: To roll or gather up a sail so it stows neatly on a boom, stay, or inside a spar.
Furling line: The continuous control line led back to the cockpit that drives a headsail, code zero, or in-mast mainsail furler.
Furling mainsail: A mainsail designed to roll up inside the mast (in-mast) or inside the boom (in-boom), allowing stepless reefing from the cockpit.

G

Gaff: On a four-sided fore-and-aft sail, the spar that supports the sail's upper (head) edge.
Galley: The cooking area below decks, typically containing a gimballed stove, sink, refrigeration, and lockers.
Galvanic isolator: A device fitted in the shore-power earth conductor to block low-voltage galvanic currents that would otherwise corrode underwater metals while connected to a marina.
Galvanic series: A ranking of metals by their tendency to corrode in a given electrolyte (typically seawater); used to choose compatible fasteners, fittings, and sacrificial anodes.
Gennaker: A hybrid between a genoa and a spinnaker — an asymmetric downwind sail flown from a bowsprit or tack line, easier to handle than a symmetric kite.
Genoa: A large headsail whose clew overlaps the mast, giving extra upwind drive compared with a working jib.
Give way vessel: Under the COLREGs, the vessel that is required to keep out of the way of another when risk of collision exists.
GMDSS: Global Maritime Distress and Safety System — the integrated network of satellite and terrestrial radio services (VHF-DSC, MF/HF-DSC, Inmarsat, EPIRB, SART) that coordinates maritime distress alerting and search and rescue.
G.M.T.: Greenwich Mean Time — the mean solar time at the prime meridian in Greenwich, London. Now superseded by UTC (Coordinated Universal Time).
GNSS: Global Navigation Satellite System — the umbrella term covering all satellite positioning constellations: GPS (USA), GLONASS (Russia), Galileo (EU), and BeiDou (China).
Gooseneck: The articulated fitting that joins the forward end of the boom to the mast, allowing the boom to swing and pivot.
GPS: Global Positioning System — the US satellite constellation whose signals let a receiver compute its position, heading, and speed over ground almost anywhere on Earth; today typically combined with other GNSS signals for better accuracy.
Grab bag: A watertight bag pre-packed with survival essentials (flares, water, food, EPIRB, handheld VHF, passports, etc.) that is grabbed on the way to the liferaft in an abandon-ship emergency.
Great Circle: The shortest path between two points on the Earth's surface — an arc of a circle whose plane passes through the centre of the Earth. Used for long ocean passages.
GRIB file: A compact binary weather-data format (Gridded Binary) used to download forecast wind, pressure, waves, and currents for display on board in GRIB-capable navigation software.
Grommet: A reinforced ring — usually brass or stainless — set into a sail or cover to accept a line or fastening.
Ground tackle: The collective name for the anchor and its rode (chain, warp, swivels, and shackles).
Gudgeon: A ring-shaped fitting on the transom into which a rudder's pintle pin drops, allowing the rudder to swing.
Gunwale: (Pronounced 'gunnel') The top edge of the hull where deck meets topsides.
Gybe: See jibe — a turn in which the stern passes through the wind.

H

Halyard: A line used to hoist, hold up, or lower a sail.
Hank: A piston or snap hook used to attach the luff of a foresail at intervals along the forestay.
Hard a-lee: (Also 'helm's a-lee', 'lee-oh', 'lee-ho') The skipper's command telling the crew that the helm is going down and the boat is about to tack.
Hard over: Turning the helm, tiller, or wheel as far as it will go in one direction.
Hatch: A large, usually closable opening in the deck or coachroof for access, ventilation, or light.
Haul in: To tighten or pull in a line.
Head: The upper corner of a sail; also, the marine toilet.
Headboard: A small reinforcing plate built into the head of a sail to spread halyard load.
Head down: To bear away — to alter course away from the wind.
Headed: A windshift in which the wind moves forward on the boat, forcing the helm to bear away or the sheets to be eased.
Heading: The direction the bow is pointing, expressed in degrees.
Heading sensor: A solid-state (usually fluxgate or MEMS) compass providing a fast-updating digital heading to the autopilot, radar, and chartplotter.
Head off: Synonym for head down.
Headsail: Any sail set forward of the mast — jib, genoa, staysail, or code zero — typically attached to the forestay.
Headstay: See forestay — the standing rigging from bow to masthead.
Head to wind: The moment when the bow is pointing directly into the wind — for instance, the centre of a tack.
Headway: Forward movement through the water.
Heave: To throw — usually a line.
Heave to: To balance the boat almost stationary by backing the headsail, lashing the helm to leeward, and trimming the main so the rig and rudder cancel each other out.
Heavy weather: Conditions of strong wind and significant sea state.
Heel: The sideways lean of the hull caused by wind pressure on the sails.
Helm: The steering control — tiller or wheel.
Helmsman: The crew member steering the boat at a given moment.
Holding ground: The character of the seabed in an anchorage — e.g. mud, sand, weed, rock — which determines how well an anchor will set.
Holding tank: An on-board tank that stores sewage from the heads until it can be pumped out ashore or, where permitted, discharged outside coastal limits.
Hove to: Describing a vessel that has completed the heaving-to process and is sitting more or less stationary with backed jib, eased main, and helm held to leeward.
Hull: The main body of the vessel, excluding the rig, spars, sails, and appendages.
Hull speed: The theoretical maximum displacement speed of a monohull sailboat, approximated by 1.34 × √(waterline length in feet), in knots.
Hydrogenerator: A towed or transom-mounted propeller-driven generator that extracts electrical energy from the boat's forward motion, useful for long passages.

I

Inboard: Located inside the rail or within the hull of the boat.
In irons: Stalled head-to-wind with insufficient way to steer — neither on one tack nor the other.
In-mast furling: A reefing system in which the mainsail is rolled onto a vertical spindle inside a hollow mast, controlled by a line from the cockpit.
Inverter: An electronic device that converts the boat's 12/24 V DC supply into 120/230 V AC mains for running domestic appliances off the battery bank.
Iridium: A global satellite network (e.g. Iridium Go!, Iridium Certus) widely used by offshore sailors for voice, SMS, weather downloads, and low-bandwidth email anywhere on Earth.

J

Jackstay / Jackline: A wire, webbing strap, or spliced rope run fore-and-aft along each sidedeck, to which a safety harness tether can be clipped so the crew stays attached when moving around.
Jib: The small triangular headsail set forward of the mast, tacked to the stemhead and hanked, bolted, or furled onto the forestay.
Jibe: (Also 'gybe') To change tack by turning the stern through the wind, allowing the mainsail and boom to swing across.
Jibe oh: The skipper's command warning the crew that the mainsail is about to swing — the command to execute the gybe.
Jiffy reef: See slab reefing — a rapid reefing method where a fixed reef point is pulled down to the boom and the extra cloth gathered and tied off.
Jury rig: An improvised, temporary repair or substitute — for example, replacing a broken mast with a spinnaker pole lashed upright.

K

Kedge: A secondary anchor, smaller than the bower, carried for manoeuvring or for kedging the boat off a grounding.
Kedge off: To refloat a grounded vessel by laying a kedge anchor in deeper water and hauling the boat toward it.
Keel: The weighted vertical fin beneath the hull that resists leeway and, through its ballast, keeps the boat upright; modern variants include fin, bulb, winged, lifting, swing, and twin keels.
Ketch: A two-masted rig whose shorter mizzen mast stands forward of the rudder post and is shorter than the main mast.
Kevlar: An aramid fibre used in high-performance laminate sails and safety gear; it is strong and resists stretch, but degrades with UV exposure.
Knockdown: A severe knock in which the boat is blown onto her side far enough that a spreader dips into the water.
Knot: One nautical mile per hour — the standard unit of speed at sea.

L

Laminate sail: A sail made of composite panels — typically film-over-fibre (e.g. Dacron, polyester, Kevlar, or carbon) laminated together — offering better shape-holding than woven cloth.
Land breeze: A night-time wind caused by land cooling faster than the sea, drawing air from shore out to sea.
Lash: To bind or secure with line or webbing.
Lay: To sail a course that will clear a mark or obstacle without an additional tack.
Lazarette: A stowage locker let into the cockpit sole, seats, or afterdeck.
Lazy jacks: A network of light lines running from the upper mast down to the boom that cradles the mainsail as it is lowered, stopping it from spilling onto the deck.
Lazy sheet: The jib sheet on the windward side that is slack while the leeward sheet takes the load.
Lead: To route a line through a block, fairlead, or similar fitting.
Leech: The aft edge of a fore-and-aft sail.
Lee helm: A boat's tendency to turn her bow away from the wind if the helm is released — generally undesirable.
Lee shore: Shoreline lying downwind of the boat; a hazard because the wind will steadily push a disabled vessel toward the beach.
Leeward: The side or direction away from the wind — where the wind is blowing toward.
Leeward side: The side of the boat or sail opposite the wind.
Leeway: The sideways slippage of the hull to leeward caused by the sail's horizontal force component.
Lifeline: A wire or rope rigged on stanchions around the edge of the deck to help prevent crew from falling overboard.
Life raft: A self-inflating, canister- or valise-packed survival craft launched in an abandon-ship situation; modern ISO-standard rafts carry water, flares, a sea anchor, and other survival gear.
Lifesling: A buoyant horseshoe-shaped sling on a floating line, deployed to trail astern during a man-overboard recovery so the casualty can be reached and hauled alongside.
Lift: (1) The aerodynamic or hydrodynamic force generated by a sail or keel that drives the boat through the water. (2) A windshift that lets the boat head up higher than before.
Line: The generic term at sea for any rope in use.
Lithium-ion battery (LiFePO4): A modern lithium iron phosphate house battery offering far greater usable capacity, deeper cycling, faster charging, and longer life than lead-acid, at higher purchase cost and with specific charging and BMS requirements.
LOA: Length Overall — the maximum fore-and-aft hull length, excluding bowsprits and pulpits unless specifically included.
Lubber line: A fixed reference line on a compass card housing that represents the boat's heading, read against the rotating compass card.
Luff: (1) The leading edge of a sail. (2) The fluttering of a sail caused by pointing the boat too close to the wind or easing the sheet too far.
Lull: A short-lived dip in wind speed.
LWL: Length Waterline — the fore-and-aft length of the hull measured at the waterline; a major factor in hull speed.

M

Magnetic: Referring to the magnetic north pole rather than true geographic north.
Mainmast: The taller (main) mast on a vessel with more than one mast.
Mainsail: The principal sail set on the (main) mast of a sloop, cutter, ketch, or yawl.
Mainsheet: The control line that trims the mainsail in and out, running through a block system on the boom and a track or traveller.
Marlinspike: A tapered metal spike used to loosen knots, open rope lays, and work splices.
Mast: The vertical spar — originally timber, today commonly aluminium or carbon — from which the mainsail is hoisted.
Masthead: The top end of the mast, often carrying a wind instrument, anchor light, VHF antenna, and sheave for the main halyard.
Maststep: The fitting (on deck or on the keel) into which the foot of the mast is stepped.
MFD: Multi-Function Display — a large chartplotter screen able to show radar, AIS, sonar, engine data, camera feeds, and charts, usually linked by NMEA 2000 or Ethernet.
Mizzen: The small sail set on the mizzenmast of a ketch or yawl.
Mizzenmast: The shorter mast stepped aft of the mainmast on a ketch or yawl.
MMSI: Maritime Mobile Service Identity — a unique nine-digit number issued to each DSC-VHF/HF radio, EPIRB, or AIS transponder, used to identify the vessel in digital distress and routine calls.
MOB button: A dedicated button on a GPS, chartplotter, or autopilot that marks the current position the instant a person goes overboard, giving an immediate waypoint to navigate back to.
Mooring: A permanent ground tackle — anchor, chain, and buoy — to which a vessel can secure instead of deploying her own anchor.
MPPT charge controller: Maximum Power Point Tracking charge controller — an electronic regulator that continuously matches a solar panel's output to the battery, extracting 20–30 % more energy than a simple PWM controller.

N

Nautical mile: The standard unit of distance at sea, 1852 m or 6076 ft, originally defined as one minute of latitude.
Navigation rules: The body of law — internationally the COLREGs — designed to prevent collisions at sea.
NMEA 0183: A legacy serial data standard defined by the US National Marine Electronics Association, used to send sentences (e.g. GPS position, heading, depth) between instruments at 4800 baud.
NMEA 2000: A modern CAN-bus data network for marine electronics, allowing plug-and-play interconnection of GPS, wind, depth, engine, autopilot, and MFDs on a single backbone.
No-go zone: The sector of directions into the wind — roughly ±45° — where a sailing vessel cannot make forward progress; crossing it is the purpose of tacking.
Nun: In the IALA Region B system, a red even-numbered conical buoy marking the starboard side of a channel when entering from seaward, usually paired with green cans on the opposite side.

O

Offshore: Away from land, or out of sight of it.
Offshore wind: A wind blowing from the shore out toward open water.
Off the wind: Sailing on any point of sail broader than close-hauled.
On the wind: Close-hauled — sailing as near the wind as the boat will efficiently go.
Outboard: Outside the rail, or toward or beyond the sides of the boat.
Outhaul: The control line attached to the clew of the mainsail, tensioning the foot along the boom.
Overpowered: Heeling excessively because the boat is carrying too much sail for the wind strength.

P

Painter: The line permanently attached to the bow of a dinghy or tender.
Parasailor: A proprietary symmetric downwind sail with a horizontal aerofoil slot through the middle, giving lift and stability and making shorthanded downwind passages easier.
Pay out: To let out or surrender a line in a controlled way.
P.F.D.: Personal Flotation Device — a lifejacket, buoyancy aid, or similar wearable buoyancy.
Pinching: Sailing too close to the wind, resulting in a stalled luff and reduced boat speed.
Pintle: The pin of a rudder fitting that drops into a gudgeon on the transom, allowing the rudder to swing freely.
PLB: Personal Locator Beacon — a small 406 MHz satellite distress beacon registered to an individual (not a vessel), carried on a lifejacket or harness for personal survival use.
Point: (1) To sail close to the wind. (2) A legacy unit of compass direction equal to 11¼° (32 points in 360°).
Points of sail: The classification of a boat's course relative to the wind — close-hauled, close reach, beam reach, broad reach, and run.
Port: (1) The left side of the boat when facing forward. (2) A harbour. (3) A small window or opening in a cabin or hull.
Port tack: Sailing with the wind coming over the port side; under the COLREGs, a port-tack vessel normally gives way to a starboard-tack vessel.
Prevailing wind: The statistically dominant wind direction for a region or season.
Puff: A short-lived increase in wind strength.
Pulpit: A stainless-steel safety rail around the bow (or stern, where it is usually called a pushpit).

Q

Quarter: The part of the boat's side close to the stern — port quarter and starboard quarter.

R

Radar: A microwave ranging system that bounces a rotating pulse off targets and displays their bearing and range; modern broadband/pulse-compression radars resolve close targets at very low power, often with MARPA/ARPA target tracking.
Rail: The outer edge of the deck, where the deck meets the topsides.
Rake: The fore-and-aft tilt of the mast relative to vertical.
Range: The line of sight formed when two marks ashore line up, showing the centre of a channel or a transit bearing.
Reach: A point of sail with the wind forward of, abeam, or aft of the beam but not dead astern — close, beam, or broad reach.
Ready about: Skipper's command warning the crew to prepare for a tack.
Ready to jibe: Skipper's command warning the crew to prepare for a gybe.
Reef: To reduce effective sail area in strong wind by rolling, folding, or partly lowering a sail.
Reeve: To lead a line through a block, ring, or eye.
Rhumb line: A course line crossing all meridians at the same angle — a straight line on a Mercator chart, suitable for passages up to a few hundred miles; for longer distances a Great Circle is shorter.
Rig: The spars, standing rigging, and sail plan collectively — or the act of rigging the boat for sea.
Rigging: The wires (standing rigging) and lines (running rigging) supporting and controlling the spars and sails.
Roach: The curved extension of a sail's area aft of a straight line drawn from head to clew.
Rode: The whole line-and-chain assembly linking the anchor to the boat.
Roller-furling: A mechanical system allowing the headsail (or mainsail) to be rolled away around the stay or inside the mast/boom from the cockpit.
Rudder: The underwater steering foil hinged at the stern (or on a skeg) that, swung to port or starboard, alters the boat's heading.
Run: A point of sail with the wind coming from dead astern.
Running rigging: All lines used to hoist, lower, and trim sails — halyards, sheets, reefing lines, outhaul, vang, and so on.

S

Sail ties: Short lengths of line or webbing used to lash a lowered sail to its boom or to bundle the surplus cloth of a reefed sail.
SART: Search and Rescue Transponder — an emergency device that, when triggered by an X-band radar pulse, replies with a 12-dot signature on a searching vessel's radar screen, guiding rescuers to the liferaft.
Schooner: A two- (or more) masted rig in which the foremast is equal to or shorter than the mainmast.
Scope: The ratio between the length of anchor rode paid out and the depth of water (plus bow height), e.g. 5:1 all-chain, 7:1 chain-and-warp.
Scull: To propel a boat with a single oar worked side-to-side through a notch or rowlock in the transom.
Scupper: A drain hole or outlet that removes water from the cockpit or deck.
Sea anchor: A large parachute-like drogue streamed from the bow on a long rode in survival conditions to hold the vessel head-to-sea and dramatically slow any drift. Distinct from a stern drogue.
Sea breeze: A daytime onshore wind caused by the land heating faster than the sea, drawing cool air in from the water.
Seacock: A through-hull valve that can be opened or closed to admit water to, or prevent water from entering, the boat through engine, heads, galley, or cockpit drain fittings.
Secure: To tie down, lash, or make fast.
Self-tacking jib: A small headsail fitted with a track across the foredeck so the sheet travels automatically from side to side when the boat tacks, eliminating the need to trim headsails on each tack.
Set: (1) The direction (usually in degrees true) in which a current flows. (2) To trim or adjust the sails.
Shackle: A U-shaped metal fitting closed by a threaded pin (D-shackle, bow shackle, snap shackle etc.), used to connect a line to a sail, chain, or fitting.
Shake out: To undo a reef and restore full sail area.
Sheave: The grooved wheel inside a block or at the head of a mast over which a line runs.
Sheet: A line used to trim a sail — e.g. mainsheet, jib sheet, spinnaker sheet.
Shoal: A patch of shallow water, often sand or mud, representing a hazard.
Shore power: 120/230 V AC supplied from a marina pedestal through a dedicated inlet and cable, used to run onboard AC appliances and to drive the battery charger while alongside.
Shroud: A piece of standing rigging running from a chainplate to the upper mast or spreader tip, supporting the mast laterally.
Singlehanded: Sailing the boat entirely alone.
Skeg: A fixed vertical fin ahead of the rudder, protecting and supporting it.
Slab reefing: A traditional reefing method (also called jiffy reefing) in which the tack and clew reef cringles are pulled down to fixed points on the mast and boom, and the surplus cloth is gathered.
Sloop: A single-masted rig with a mainsail and a single headsail — the commonest modern configuration.
Snuffer (spinnaker sock): A fabric tube with a hoop that slides down over an asymmetric or symmetric spinnaker, smothering the sail from the top to make hoisting and dousing safe and manageable shorthanded.
Solar panel: A photovoltaic array — rigid glass, semi-flexible, or flexible — that converts sunlight to DC current to charge the house bank, commonly 100–400 W on cruising yachts.
Sole: The floor of a cockpit or cabin.
Spar: Any pole that supports a sail — mast, boom, gaff, sprit, yard, whisker pole, or spinnaker pole.
Spinnaker: A large, light downwind sail, symmetric or asymmetric, flown from a halyard rather than a stay and used on broad reaches and runs.
Splice: A permanent joining of two ropes, or a rope's end into itself, by interweaving the strands.
Spreader: A horizontal strut projecting from the mast that redirects the shrouds outboard, increasing the staying angle and lateral stiffness of the rig.
Spring line: A dockline led fore or aft along the hull to the dock to stop the boat moving forward or back along the berth.
Squall: A fast-moving, short-lived storm cell producing sudden strong winds and often heavy rain.
SSB radio: A marine MF/HF single-side-band transceiver that, under the right conditions, can reach thousands of miles — historically used for ocean weather nets, email (e.g. via Pactor modem) and long-range distress; now largely superseded by satellite for cruising sailors.
Stack pack: A zippered mainsail cover fixed to the boom and combined with lazy jacks, so the mainsail is caught and covered in a single step when lowered.
Stanchions: Vertical metal posts bolted to the deck edge that support the lifelines.
Standing rigging: The permanent wires (stays and shrouds) that support the mast — forestay, backstay, cap shrouds, lowers, and diagonals.
Starboard: The right side of the boat when facing forward.
Starboard tack: Sailing with the wind coming over the starboard side; under COLREGs, a starboard-tack sailing vessel normally has right of way over a port-tack vessel.
Starlink: A low-Earth-orbit satellite broadband system widely adopted on cruising and commercial vessels since the mid-2020s for high-speed internet at sea, replacing older geostationary Fleet and V-SAT services on many yachts.
Stay: A piece of standing rigging supporting a mast in the fore-and-aft direction.
Staysail: On a cutter, the inner headsail set on an inner forestay between the bow and the mast; more generally, any sail set on a stay.
Steerage way: The minimum speed through the water at which the rudder produces enough flow to steer the boat.
Stem: The forwardmost structural member of the hull — the bow's leading edge.
Stern: The aft end of the vessel.
Stern Spring: A dockline led from the stern forward along the dock, preventing the boat surging astern.
Storm jib: A small, extra-heavy, high-visibility foresail set in survival conditions — ideally on a removable inner stay — to balance the rig under trysail or triple-reefed main.
Stow: To put away neatly and securely.
Swamped: A vessel filled with water but still floating.

T

Tack: (1) To turn the bow through the eye of the wind so the boat changes from one close-hauled course to the other. (2) The forward lower corner of a fore-and-aft sail.
Tackle: An arrangement of blocks and line that provides mechanical advantage.
Tail: To hold, and keep tension on, the free end of a line while a winch grinder takes turns on the drum.
Telltales: Short strands of wool or ribbon on a sail (or shrouds) showing airflow — a practical guide to sail trim.
Tether: A two- or three-hook safety line attaching a crew member's lifejacket/harness to a jackline or strongpoint, preventing separation from the boat if they fall or are washed down.
Through-hull: A fitting that passes through the hull to admit or discharge water (for engine cooling, heads, sinks, etc.), almost always fitted with a seacock.
Throwbag / Throw line: A buoyant floating line packed in a sock and thrown to a person in the water as a recovery aid.
Tide: The periodic vertical rise and fall of the sea surface caused by the gravitational pull of the Moon and Sun.
Tiller: A horizontal handle (or extension) fixed to the rudder stock, used to steer a smaller yacht.
Toe rail: A low continuous rail around the outer edge of the deck, giving the crew something to brace their feet against.
Topping lift: A line from the masthead (or a backstay bridle) supporting the aft end of the boom when the mainsail is down or being reefed.
Topsides: The outer sides of the hull between the waterline and the deck.
Transom: The flat — or nearly flat — after face of the stern.
Trim: To adjust a sail's controls to produce optimum drive and lift.
Trimaran: A three-hulled vessel: a central hull (vaka) flanked by two amas.
True wind: The actual wind speed and direction relative to the ground — what a stationary observer at the boat's location would feel.
Trysail: A small, heavy, triangular storm sail that replaces the mainsail on its own track or separate track in survival conditions when the boom is inadvisable or unsafe.
Tune: To adjust the tension and alignment of the standing rigging so the mast stands straight and the sails set correctly.
Turnbuckle: (Also 'bottlescrew') A threaded fitting at the lower end of a stay or shroud that allows precise rig tuning.

U

Underway: Under international rules a vessel is 'underway' whenever she is not at anchor, moored, aground, or made fast to the shore — even if she is not currently moving through the water.
Upwind: Toward the wind's source.
USCG: United States Coast Guard — the US federal service responsible for maritime safety, security, and SAR.
U.T.C.: Coordinated Universal Time — the modern reference time (replacing GMT) used for navigation, celestial sights, weather, and radio schedules worldwide.

V

Vang: See boom vang — the tackle or rigid strut that pulls the boom down to control mainsail twist.
Veer: Of wind: a clockwise shift in direction (opposite of 'back').
Vessel: Any craft — sail, power, or other — used or capable of being used as a means of transport on water.
VHF radio: A line-of-sight very-high-frequency marine radio, usually with DSC, used for routine, safety, urgency, and distress traffic; range is typically 20–40 NM between ships, further to a high coast station.

W

Wake: The disturbed water and trailing waves left behind a moving vessel.
Waterline: The line on the hull where it meets the water surface at the design load.
Watermaker: A reverse-osmosis desalinator that forces seawater through a semi-permeable membrane at high pressure to produce drinking-quality fresh water on board.
Waypoint: A position — latitude and longitude — stored in a GPS or chartplotter and used as a step in a planned route.
Weather helm: The boat's tendency to turn into the wind if the helm is released; some is desirable for feel and safety, but excessive weather helm signals an overpowered or mis-trimmed rig.
Weather routing: The practice — today usually software-assisted using GRIB forecasts and the boat's polars — of choosing a passage track that optimises for weather, sea state, and ETA.
Weather side: See windward side — the side of the boat the wind strikes first.
Whip: To bind the strands at the end of a rope with a tight wrapping of twine to prevent unravelling.
Whisker pole: A light spar temporarily set between the mast and the clew of a poled-out jib to hold it square and keep it drawing when running.
Winch: A drum with a handle (manual) or motor (electric/hydraulic) that provides mechanical advantage when sheeting or hoisting; self-tailing winches feed the line off automatically.
Wind generator: A mast- or pole-mounted propeller-driven turbine that converts apparent-wind energy into battery charging current — complementary to solar on extended cruising yachts.
Windward: Toward the source of the wind.
Windward side: The side of the boat facing the wind.
Wing-and-wing: A downwind configuration in which the mainsail is set on one side and the headsail (often poled out) on the opposite side.
Working sails: The mainsail plus the standard (working) jib — the boat's all-round sail wardrobe for moderate conditions.
Working sheet: The leeward sheet carrying load — the one actually trimming the sail at that moment.

Y

Yawl: A two-masted rig similar to a ketch but with the (smaller) mizzenmast stepped aft of the rudder post; the mizzen is used mainly for balance rather than drive.

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