Sailing Terms: A Complete Glossary

A

Abeam: At a right angle to the centerline of the boat — directly to the side. "The lighthouse is abeam to starboard."
Aft: Toward the stern (rear) of the boat. "The cockpit is aft of the companionway."
Anchor watch: A scheduled vigil — either by a person or a GPS alarm — maintained while anchored overnight or in deteriorating conditions to detect if the vessel begins to drag.
Apparent wind: The wind as felt on a moving boat — a combination of the true wind and the boat's forward motion. Apparent wind is always forward of true wind when the boat is moving, and it is what sails are actually trimmed to.
Asymmetric spinnaker: A large downwind sail with an asymmetric cut, flown from a bow pole or bowsprit. Easier to gybe than a symmetric spinnaker; used on beam-to-broad reaches as well as dead downwind.

B

Backing the jib: Holding or sheeting the jib to windward so the wind fills it from the "wrong" side, pushing the bow away from the wind. Used in heaving-to and when stuck in irons.
Backstay: A wire or rod running from the masthead to the stern, providing aft support to the mast. An adjustable backstay can be used to bend the mast and flatten the mainsail.
Batten: A flexible or semi-rigid strip (fiberglass, carbon, or plastic) inserted in a pocket along the leech of a sail to support the roach and maintain sail shape.
Beam: The widest point of a boat, measured athwartships. Also used as a directional reference — "on the beam" means directly abeam.
Beam reach: Sailing with the wind coming directly from the side — perpendicular to the boat's heading. Generally the fastest point of sail for most monohulls.
Bearing away: Turning the bow away from the wind — heading to a broader point of sail. Also called "bearing off" or "falling off."
Block: A nautical pulley — a grooved wheel in a housing through which a line runs to change direction or provide mechanical advantage. Blocks are used throughout the running rigging.
Boom: The horizontal spar at the base of the mainsail, attached to the mast at the gooseneck. Controls the foot of the sail and can cause injury if it swings unexpectedly during a gybe.
Boom vang (vang): A tackle or hydraulic strut running from the boom down to the base of the mast, used to prevent the boom from rising and to control sail twist on downwind points of sail.
Bow: The front of the boat. The forward-most point of the hull.
Broad reach: Sailing with the wind coming from aft of the beam but not directly behind — roughly 120–160 degrees off the bow. A fast, comfortable point of sail.
Bulb keel: A fin keel with a weighted bulb at the bottom, concentrating ballast low to maximize righting moment relative to the keel's weight.

C

Cam cleat: A spring-loaded cleat that grips a line automatically when it's pulled through and releases it with an upward tug. Widely used on jib sheets and control lines for quick adjustment.
Cap shroud: The primary shroud running from the masthead to the chainplates, providing lateral support to the upper portion of the mast.
Chainplates: Strong metal fittings bolted through the hull or deck to which the lower ends of shrouds are attached. A failure point to inspect regularly, especially on older fiberglass boats.
Chop: Short, steep, irregular waves — typically generated by local wind on shallow or confined water. Chop is often more uncomfortable than ocean swell because of its frequency.
Cleat: A fitting with two horns around which a line is secured with a figure-eight hitch. Standard cleats are bolted to the deck; cam cleats and horn cleats serve different functions.
Clew: The lower aft corner of a sail — where the foot and leech meet. The sheet attaches to the clew on a jib; the outhaul attaches to the mainsail clew.
Close-hauled: Sailing as close to the wind as the boat can efficiently go — typically 30–45 degrees apparent wind angle depending on design. The sheets are pulled in tight.
Close reach: A point of sail between close-hauled and beam reach, with the wind coming from forward of the beam but not as far forward as close-hauled.
Clutch: A rope clutch — a locking device on the mast or cabin top that holds a line (halyard, reefing line) under load without a winch, freeing the winch for other tasks.
Code zero: A large, flat-cut upwind-to-reaching sail, typically flown from a furler on a long sprit or bowsprit. Fills the gap between a genoa and a spinnaker in light, reaching conditions.
COG (Course Over Ground): The actual direction of travel across the earth's surface, accounting for current and leeway. May differ significantly from the compass heading (COH).
CPA (Closest Point of Approach): The predicted minimum distance between your vessel and another vessel if both maintain course and speed. AIS displays CPA and TCPA for all tracked targets.
CTS (Course to Steer): The compass heading a vessel must maintain to reach a destination, calculated to account for predicted current set and drift.

D

Danbuoy: A tall buoy with a flag on a pole, thrown overboard when a crew member falls in. Marks the MOB position visually from a distance while the crew maneuvers to recover.
Dead downwind: Sailing with the wind coming from directly behind — 180 degrees. On a monohull this is often slower than a broad reach; risk of an accidental gybe is highest here.
Deviation: The error in a magnetic compass caused by the boat's own magnetic field — engine, electronics, metal fittings. Deviation varies with heading and is corrected by a deviation table specific to each compass.
Draft: The depth of the hull below the waterline — how much water the boat needs to float. A boat with a 6-foot draft cannot enter an anchorage that's 5 feet deep at low tide.
DSC (Digital Selective Calling): A digital function built into VHF radios that allows a sailor to send an automated distress signal with GPS coordinates to the Coast Guard and nearby vessels by pressing a single button.

E

EPIRB (Emergency Position Indicating Radio Beacon): A satellite-linked distress beacon that, when activated, transmits the vessel's position to rescue services via COSPAS-SARSAT satellites. Registered to a specific vessel and owner; requires registration with NOAA (in the US).

F

Fairlead: A fitting that guides a line in a specific direction without significant friction — controlling the angle at which a jib sheet or other line reaches a winch or cleat.
Fathom: A unit of depth equal to 6 feet (1.83 meters). Older charts and many anchoring guides still express depths in fathoms.
Fetch: The unobstructed distance over open water across which wind can blow and build waves. A long fetch produces larger waves; an anchorage exposed to a long fetch is uncomfortable in a blow.
Fin keel: A narrow, deep keel projecting below the hull, providing lateral resistance and ballast. Most modern performance sailboats use fin keels for their efficiency.
Foot: The bottom edge of a sail — running from tack to clew. On a mainsail, the foot typically runs along the top of the boom.
Forestay: The wire or rod running from the masthead (or intermediate point) to the bow, supporting the mast from forward. The jib or genoa is typically hanked on or furled around the forestay.
Freeboard: The height of the hull from the waterline to the deck — how much boat is above water. Higher freeboard means a drier boat in a seaway but more windage.
Full keel: A long keel running much of the length of the hull, providing directional stability and protection for the rudder. Traditional cruising designs; less maneuverable than fin-keel boats.
Furling: A system for rolling a sail around a stay (headstay furling for jibs) or a boom or mast (in-boom or in-mast furling for mainsails). Allows rapid sail area reduction without dropping the sail.

G

Genoa: An overlapping jib whose clew extends aft of the mast — typically expressed as a percentage of the foretriangle. A 150% genoa overlaps the mast by half the foretriangle length. More powerful than a non-overlapping jib in light air.
Gennaker: A hybrid sail between a spinnaker and a genoa — flown like an asymmetric spinnaker but designed for reaching rather than pure downwind work. Often used without a spinnaker pole.
Gybe (or jibe): Turning the stern through the wind so that the wind changes from one side to the other — the downwind equivalent of a tack. An accidental gybe in strong wind can be violent and dangerous.

H

Halyard: A line used to raise (hoist) a sail. The main halyard raises the mainsail; jib, spinnaker, and staysail halyards raise their respective sails. Halyards run from the sail head to a winch or clutch at the base of the mast.
Harness: A load-bearing vest worn offshore to which a tether is attached, keeping a sailor connected to the jackline or a fixed point on deck if they fall or are washed overboard.
Head: The top corner of a sail — where the luff and leech meet. The halyard attaches to the head. Also the nautical term for a marine toilet.
Header: A wind shift that causes the boat to be headed — forces the bow further away from the rhumb line when sailing upwind. The opposite of a lift. On a tack, a persistent header is a signal to tack.
Heading up: Turning the bow toward the wind — moving to a closer point of sail. "Luffing up" or "coming up."
Heave-to: A technique for stopping the boat in a stable, nearly stationary position by backing the jib and lashing the tiller to leeward. Used to ride out heavy weather, for crew meals, or to wait for a harbor entrance to open.
Horseshoe buoy: A U-shaped ring buoy thrown to a man overboard to provide flotation. Typically mounted in brackets at the stern, with an attached light and drogue.

I

In irons: The condition of being head-to-wind with no forward motion — the boat is stalled and cannot be steered off onto either tack. Happens when a tack is executed too slowly. Backing the jib breaks the stall.
Inflatable PFD: A personal flotation device that inflates automatically on immersion or manually by pulling a cord. Provides high buoyancy when inflated; must be serviced annually to ensure the CO₂ cylinder and auto-inflate mechanism are functional.
Intermediate shroud: A shroud that runs from a point partway up the mast (spreader tip) to the chainplates, providing support to the middle section of the mast on taller rigs with multiple sets of spreaders.

J

Jackline: A length of webbing or wire strung fore-and-aft along the deck to which sailors clip their safety tethers offshore. Allows movement from bow to cockpit without unclipping.
Jib: A headsail set forward of the mast that does not overlap the mast. A working jib is typically 100% of the foretriangle; anything larger is a genoa.
Jiffy reef (slab reef): A reefing system where the luff and leech of the mainsail are pulled down and secured at reef points, reducing sail area. The quickest and most reliable reefing method for offshore use.

K

Kedge: A secondary anchor — typically lighter than the main hook — used for kedging off (freeing a grounded boat by setting the anchor away from the boat and winching toward it) or as a stern anchor in a Med moor.
Keel: The structural and hydrodynamic element below the hull that provides ballast and prevents the boat from sliding sideways through the water (leeway). Common types: full keel, fin keel, and bulb keel.
Knot: A unit of speed equal to one nautical mile per hour (1.15 mph / 1.85 km/h). A boat doing 7 knots covers 7 nautical miles in one hour. Never say "knots per hour."

L

Leech: The trailing (aft) edge of a sail — from the clew to the head. Leech shape is controlled by the leech line (a drawstring inside the leech) and by batten tension.
Lifelines: Stainless steel wires strung between stanchions around the deck perimeter to prevent crew from falling overboard. Required by offshore racing rules; should be inspected regularly for crevice corrosion at swaged ends.
Lift: A favorable wind shift that allows the boat to point higher toward its destination when sailing upwind. The opposite of a header. When you get a persistent lift, hold the tack to take advantage of it.
Luff: The leading (forward) edge of a sail. Also the action of a sail when it flutters or collapses because the boat is pointed too close to the wind or the sail is eased too much.
Luffing: Either the act of heading up toward the wind (often done to slow the boat or to slow a boat to windward in a racing context) or the fluttering of a sail that hasn't been trimmed in far enough for the current point of sail.
Lull: A temporary decrease in wind speed. After a lull, the wind often fills back in from a slightly different direction.

M

Magnetic bearing: A bearing measured relative to magnetic north rather than true north. Magnetic north differs from true north by a variable amount called variation, which changes by geographic location and year.
Mainsail: The primary sail on a sloop or cutter, set on the mast and boom. The largest sail on most monohulls; trimmed by the mainsheet and traveler.
Mainsheet: The line that controls the angle and trim of the boom and mainsail. Often runs through a multi-part purchase system to a cam cleat in the cockpit.
Man overboard (MOB): The emergency situation when a crew member falls into the water. Immediate actions: throw the horseshoe buoy and danbuoy, mark the GPS position, detail one person to keep eyes on the victim, and begin the recovery maneuver.
Mast: The vertical spar that supports the sails. On a sloop, there is a single mast. On a ketch, yawl, or schooner, there are two. The mast is supported by the standing rigging (shrouds and stays).
Mayday: The internationally recognized voice distress call, spoken three times ("Mayday Mayday Mayday") on VHF Channel 16. Used only for grave and imminent danger to life or vessel. Triggers a full Coast Guard and nearby vessel response.
MMSI (Maritime Mobile Service Identity): A unique 9-digit number assigned to a vessel's DSC radio and EPIRB. Registered with NOAA (US) or Transport Canada so rescue services can immediately identify the vessel from a distress signal.

N

Nautical mile: A unit of distance equal to one minute of latitude — 1,852 meters or approximately 1.15 statute miles. Used in all marine navigation; speed in nautical miles per hour is expressed in knots.

O

On the wind: Sailing close-hauled or on a close reach — with the sails sheeted in and the boat working to windward. The opposite of off the wind (reaching or running).

P

Pan-pan: An urgency call on VHF Channel 16 — one level below Mayday — indicating a serious situation that does not yet require immediate rescue. Used for medical issues, mechanical failures, or vessels in difficulty but not in immediate danger.
PLB (Personal Locator Beacon): A personal distress beacon similar to an EPIRB but worn by an individual. When activated, it transmits the person's position to search-and-rescue satellites. Registered to a person, not a vessel.
Port: The left side of the boat when facing forward. Marked with a red light at night. Memory aid: "port" and "left" both have four letters.
Preventer: A line rigged from the boom to a forward point on the boat (bow or chainplate) to prevent the boom from swinging across the boat in an accidental gybe. Essential when sailing downwind in any kind of breeze.
Puff: A brief, localized increase in wind speed — often visible on the water as a darker patch. Proper sail trim requires anticipating and responding to puffs by easing the mainsheet slightly to prevent excessive heel.

R

Reefing: Reducing the effective area of a sail by folding or rolling part of it up. Slab (jiffy) reefing pulls the luff and leech cringle down to reef points; roller furling partially rolls the headsail around the forestay.
Roach: The curved, convex area of sail that extends beyond a straight line from head to clew on the leech of a mainsail or between the two clews of a spinnaker. Battens support the roach.
Rudder: The underwater foil controlled by the tiller or wheel that steers the boat by deflecting water flow. Most modern sailboats have a separate rudder aft of or below the keel.
Running: Sailing downwind — with the wind generally behind the boat. Includes both dead downwind and broad reach angles.

S

Sea state: The general condition of the ocean surface — described in terms of wave height, period, and direction. The Beaufort scale describes wind force and its associated sea state, from calm (0) to hurricane (12).
Securite: A safety announcement broadcast on VHF Channel 16 to warn other vessels of a navigational hazard — shoal, debris, disabled vessel, or similar — that does not require emergency assistance.
Set and drift: The direction (set) and speed (drift) of a current. Knowing the set and drift allows a navigator to calculate the course to steer to arrive at a waypoint despite the current pushing the boat sideways.
Sheet: A line used to control the angle of a sail relative to the wind — distinct from a halyard, which raises and lowers sails. Jib sheets run from the clew through fairleads to winches in the cockpit.
Shrouds: Wire or rod stays running from the mast to the sides of the boat, providing lateral support. Cap shrouds go to the masthead; intermediate shrouds support the mast at a lower point.
SOG (Speed Over Ground): The actual speed of the vessel relative to the earth's surface, accounting for current. Differs from boat speed through the water (BSP) when a current is present.
Spinnaker: A large, parachute-like downwind sail flown from a halyard at the masthead. A symmetric spinnaker requires a pole; an asymmetric spinnaker (or gennaker) does not. Used for reaching and running in light-to-moderate conditions.
Spreaders: Horizontal struts extending from the mast at one or more heights, pushing the shrouds outboard to increase their angle of support. Wider spreaders provide stiffer rig support but limit how close the boat can sail to the wind.
Stanchions: Vertical posts mounted at the deck edge that support the lifelines. Stanchion bases are a common point of deck leaks on older boats.
Starboard: The right side of the boat when facing forward. Marked with a green light at night. A vessel on starboard tack has the right of way over one on port tack.
Staysail: An inner forestaysail on a cutter or ketch — set between the mast and the jib. In heavy weather, a storm staysail can be set alone or with a deeply reefed main for a balanced, manageable sail plan.
Stern: The rear of the boat. "Making sternway" means the boat is moving backward.
Storm jib: A small, heavy-weather headsail made from thick cloth — designed for winds above 35–40 knots. Set on the inner forestay or on a removable stay, not on the roller-furling headstay.
Swell: Long-period waves generated by distant weather systems, which travel far from their origin. Swell is usually more regular and less steep than locally generated chop; it can make sailing uncomfortable even in no local wind.
Symmetric spinnaker: A traditional spinnaker designed for sailing dead downwind or on a broad reach. Set on a spinnaker pole to windward; gybing requires moving the pole from one side to the other.

T

Tack (noun): The lower forward corner of a sail — where the luff and foot meet. The tack of a jib attaches to the bow fitting or tack pin; the tack of the main attaches at the gooseneck.
Tack (verb): To turn the boat through the wind so the bow crosses the eye of the wind, shifting the sails from one side to the other. The opposite of a gybe.
TCPA (Time to Closest Point of Approach): How long until the closest point of approach with another vessel occurs. A small CPA combined with a short TCPA demands immediate action to avoid a collision.
Tether: A short line (typically 6 feet or less) connecting a sailor's safety harness to the jackline or a cockpit strong point. Offshore racing rules require short tethers to prevent a crew member from going over the side before the line catches.
Tiller: A lever connected directly to the top of the rudder post, used to steer the boat. Simple, direct, and reliable — push the tiller to port to turn to starboard. Common on boats under 35 feet.
Topping lift: A line from the masthead to the boom end that supports the boom when the sail is down. When sailing, it's typically eased to allow the vang to control boom height.
Traveler: A track mounted athwartships in the cockpit or on the cabin top on which the mainsheet block slides, allowing the angle of the boom to be adjusted without changing sheet tension. Moving the traveler to leeward opens the leech; to windward closes it.
True wind: The actual wind speed and direction as measured by a stationary observer. A boat in motion experiences apparent wind, which is always shifted forward of true wind.
Trysail: A small, triangular storm sail set in place of the mainsail in extreme conditions. Made from heavy cloth and not dependent on the boom — the trysail is sheeted independently to control the clew.
Turning block: A block (pulley) mounted on deck that redirects a line — typically a jib sheet or control line — to a more convenient angle for running to a winch or cleat.

V

Variation: The difference between true north and magnetic north at a given location — caused by the earth's magnetic field not aligning precisely with geographic north. Variation is printed on chart compass roses and changes slowly over years.
VMG (Velocity Made Good): The component of a boat's speed in the direction of the destination or next mark. VMG to windward is maximized not by pointing as high as possible but by balancing height and speed — typically slightly lower than close-hauled.

W

Waterline: The line where the hull meets the water surface. Length at waterline (LWL) is an important determinant of hull speed — longer waterlines generally allow higher theoretical maximum hull speeds.
Waypoint: A specific geographic position — defined by latitude and longitude — entered into a GPS chartplotter as a navigation target. Routes are sequences of waypoints.
Wheel: A steering wheel connected to the rudder via cables, a hydraulic system, or a rack-and-pinion mechanism. Standard on boats over 35–40 feet; gives better mechanical advantage and helm feel in heavy air than a tiller.
Winch: A cylindrical drum with an internal ratchet mechanism, used to create mechanical advantage when tailing sheets, halyards, or reefing lines. Larger boats use electric or hydraulic winches; most cruisers use manual two-speed winches.

Y

Yawl: A two-masted sailboat rig where the mizzen mast is stepped aft of the rudder post — typically smaller than on a ketch. Allows a mizzen staysail to be flown for light-air reaching; the mizzen helps balance helm in heavy weather.