Glossary, A to Z.

Short definitions of the terms used across this site. Each links to the page that covers it in depth, and where our sources define a term differently, the entry says so.

406 MHz beacon: The family of distress beacons (PLB, EPIRB and the aircraft ELT) that alert rescuers through the SARSAT satellite system. In the US every one must be registered with NOAA, and NOAA says registrations expire after two years. (Beacons and MOB gear)
470: A dinghy with a mainsail, jib and spinnaker and one trapeze. It has been an Olympic boat since 1976, the oldest in the current program, and since Paris 2024 has been sailed as a single mixed event. (One-design and Olympic classes)
49er and 49erFX: Olympic skiffs carrying a mainsail, jib and spinnaker, with two trapezes. The 49er has been Olympic since 2000 and the women's 49erFX since 2016. (One-design and Olympic classes)
Abeam: Off either side of the boat, at 90 degrees to the centerline. (Parts of a boat)
AC40: The one-design boat used for the America's Cup preliminary regattas and for the Women's and Youth America's Cup events. (America's Cup)
AC75: The carbon-fiber foiling monohull class whose rule was launched in 2018, raced in the 2021 and 2024 America's Cups and chosen for Naples 2027. Sources differ on the 2027 crew: Protocol coverage from August 2025 says five sailors, at least one of them a woman, while Wikipedia cites six from a May 2025 draft. (America's Cup)
Accidental gybe: An unplanned gybe in which the boom can swing across the boat and hit crew. The USCG Auxiliary names wind shifts and careless steering as common causes, and Sail Magazine adds that squall shifts can trigger one. (Tacking and gybing)
Aft: Toward the stern. (Parts of a boat)
AIS (Automatic Identification System): A system that broadcasts a boat's position and MMSI to other users, from Class A or Class B units. The Coast Guard requires Class A on certain commercial vessels and states no requirement for recreational boats, but a unit that is fitted must broadcast accurate information at all times. (Electronics)
AIS MOB device: A personal beacon that alerts nearby AIS-equipped boats and chartplotters, not satellites. Seas of Solutions stresses that it is not part of COSPAS-SARSAT and should not be called a PLB. Range figures are makers' claims and differ: Ocean Signal says 1 to 2 miles for its unit, Seas of Solutions about 4 miles for another. (Beacons and MOB gear)
America's Cup: The trophy first raced for in 1851 around the Isle of Wight and won by the New York schooner America, and now a match race between a defender and a challenger chosen through the Louis Vuitton Cup. For Naples 2027 the defender is Emirates Team New Zealand. Sources name the original prize differently: the Royal Yacht Squadron calls it the "£100 Cup", while Britannica calls it the Hundred Guinea Cup. (America's Cup; America's Cup history)
American Sailing Association (ASA): A US training body founded in 1983 by Lenny Shabes, a Marina del Rey charter operator, using standards adapted from the Canadian Yachting Association. Its courses are numbered, starting with ASA 101. (Learning to sail)
Apparent wind: The wind felt on the moving boat: the true wind combined with the wind created by the boat's own motion. It is what fills the sails and what telltales and basic wind instruments show. For a stopped boat, apparent and true wind are the same, and an instrument needs a boat-speed input to display true wind. (Apparent wind calculator)
ASA 101: ASA's Basic Keelboat Sailing course, the first in its system. Graduates should be able to skipper a sloop of about 20 to 27 ft by day in winds up to 15 knots, and there is no prerequisite. (Learning to sail)
Asymmetric spinnaker: A spinnaker that tacks to a fixed pole or bowsprit rather than flying from a spinnaker pole. North Sails says it is better for reaching and easier to set and douse, and names asymmetric sails with an "A" (symmetric ones start with "S"). (Sails)
Backstay: A stay in the standing rigging. Where it is adjustable, Quantum Sails says tensioning it bends the mast, flattens the mainsail, reduces forestay sag, and cuts heel and weather helm in a breeze. (Sail trim)
Basic Keelboat: US Sailing's entry-level keelboat certification, meant to prepare graduates to skipper and crew a simple daysailing keelboat in familiar waters in about 5 to 15 knots. US Sailing recommends an 18 to 27 ft tiller-steered sloop for it. (Learning to sail)
Battens: Stiff inserts, usually fiberglass, that help a sail hold its shape, most often in the mainsail's roach. North Sails says full-length battens suit mainsails with a large roach. (Parts of a boat)
Beam: A boat's width at its widest point. (Parts of a boat)
Beam reach: The point of sail with the wind crossing the boat at 90 degrees. (Points of sail)
Beating: Working upwind by sailing alternate close-hauled courses on port and starboard tack, a zig-zag on either side of the no-go zone. (Points of sail)
Beaufort scale: A wind scale from Force 0 (calm, under 1 knot) to Force 12 (hurricane, 64 knots and above), devised in 1805 by Francis Beaufort of the Royal Navy. For Force 9 the Met Office uses "Severe gale" rather than "Strong gale". (Beaufort scale)
Beer can racing: Casual weeknight evening racing that puts fun first. Latitude 38 notes that many new sailors try racing for the first time this way. (Getting into racing)
Boom: The horizontal spar running aft from the base of the mast, holding the foot of the mainsail. (Parts of a boat)
Bow: The front of the boat. (Parts of a boat)
Bowline: A fixed loop at the end of a line that will not slip or jam and is easy to untie, used for attaching sheets to sails and many general jobs. (Knots)
Broad reach: A point of sail farther downwind than a beam reach, with the wind coming from behind at an angle. (Points of sail)
Buoyancy aid: A flotation garment that helps a conscious swimmer stay afloat but, unlike a lifejacket, is not designed to turn an unconscious wearer face up. The RYA lists one as essential for dinghy sailing; the ISO level is 50N. (Life jackets)
Capsize: US Sailing says dinghies usually capsize to leeward, when the wind overwhelms the crew's ability to hike or ease the sails. (Capsize recovery)
Cardinal marks: Yellow and black IALA marks with black double-cone topmarks and white lights, the same in both buoyage regions. Their lights differ for each: north continuous quick flashing, east three flashes, south six plus a long flash, west nine. (Navigation)
Catamaran: A boat with two parallel hulls of equal size, which gets its stability from the wide spacing of the hulls rather than from ballast. (Multihulls)
Center of effort: North Sails says a boat is balanced when the sails' center of effort lines up with the hull's center of lateral resistance; moving it aft creates weather helm and moving it forward creates lee helm. (Steering)
Centerboard (centreboard): A fin-like appendage that pivots down out of, and back up into, a slot in the hull. Wikipedia lists retractable centreboards and daggerboards as alternatives to a fixed keel. The USCG Auxiliary says the board goes down upwind, partly down on a reach, and is not needed dead downwind. (Parts of a boat)
Centerline: The imaginary line from bow to stern down the middle of the boat. (Parts of a boat)
Cleat hitch: The knot used to secure dock lines and other lines to a cleat. (Knots)
Clew: The bottom aft corner of a sail, where the sheet or the boom attaches. (Parts of a boat)
Close-hauled: Sailing along the edge of the no-go zone with the sails pulled in as close to the centerline as possible. Wikipedia gives about 45 degrees to the wind as typical. (Points of sail)
Close reach: The point of sail between close-hauled and a beam reach. (Points of sail)
Clove hitch: A quick, adjustable, temporary hitch to a post, rail or stanchion; it can slip. (Knots)
Code 0: A flat, roller-furled reaching sail. Sail Magazine says it works from about 35 to 45 degrees forward to about 115 to 125 degrees aft in 5 to 10 knots, is easy to set and douse, and cannot be partly reefed. (Sails)
COLREGs: The Convention on the International Regulations for Preventing Collisions at Sea, 1972, adopted that year and in force since 15 July 1977. In the US the Inland Navigation Rules apply inside the COLREGS Demarcation Lines, and the USCG says the two sets are very similar apart from Annex V. (Rules of the road)
Cunningham: A downhaul that adjusts the mainsail's luff tension without touching the halyard. Quantum says more tension pulls the draft forward and flattens the sail. (Sail trim)
Cutter: A rig like a sloop but with the mast set farther aft, leaving room for two headsails, a jib and a staysail. (Parts of a boat)
Dacron (woven polyester): DuPont's polyester fiber, sold as Dacron in the US and Terylene in Britain, and used for sailcloth since the 1950s. Yacht says it resists UV and creasing but stretches under load. Sources differ on its life: Sailtrader reports owners getting more than 20 years, while SpinSheet expects about 10 years from a premium cruising sail used about 150 hours a year. (Sails; Technology history)
Day Skipper: An RYA qualification that, per the RYA, prepares a sailor to take charge of a 30 to 45 ft sailing yacht and crew on day trips in familiar waters and makes the holder eligible to apply for an ICC. The practical course runs 5 days, with a minimum age of 16. (Chartering)
Deed of Gift: The 1857 document under which the America's surviving owners gave the cup to the New York Yacht Club, renamed it the America's Cup and made it a perpetual challenge trophy between nations. Wikipedia says it was amended in 1881 and replaced by a new Deed in 1887. (America's Cup history)
Depowering: Reducing the sails' power when overpowered. Quantum lists lowering the traveler, easing the mainsheet, adding backstay, flattening with the outhaul and adding luff tension; Jobson and Holmes both put reefing after flattening. (Reefing and depowering)
Deviation: The difference between magnetic north and what the boat's compass shows. It depends on the boat and its heading and is read from a deviation card. (Navigation)
Dinghy: A small, open, unballasted sailboat with no cabin, used for recreation, training and tending a larger vessel. ASA's small-boat course defines its scope as centerboard or daggerboard boats of 8 to 20 ft. (Dinghies)
Distress signals: The signals listed in COLREG Rule 37 and Annex IV, including continuous sounding of a fog signal, red rockets or flares, SOS, "Mayday" by radio, orange smoke, slowly raising and lowering outstretched arms, DSC alerts and EPIRB signals. (Rules of the road)
Drysuit: A fully waterproof suit that replaces both mid and outer layers and can be worn over ordinary clothes. All At Sea says they are made of neoprene, which insulates better, or a thinner breathable membrane, which breathes better. (Dinghy clothing)
DSC (Digital Selective Calling): A VHF feature whose red distress button sends a digital alert identifying the vessel and, with GPS, its position, repeating about every four minutes until acknowledged. It only identifies the boat if the radio is programmed with an MMSI. (Electronics)
EPIRB: An emergency position-indicating radio beacon: a 406 MHz beacon mounted on a vessel, larger and more powerful than a PLB. A Category I unit sits in a bracket with a hydrostatic release that frees it and switches it on underwater; a Category II is removed and switched on by hand. (Beacons and MOB gear)
F50: The identical foiling catamaran that every SailGP team races. (SailGP)
Fastnet Race: A biennial offshore race founded in 1925 and organized by the Royal Ocean Racing Club, 695 nautical miles from Cowes around the Fastnet Rock off southern Ireland to Cherbourg. The 1979 race led ORC to strengthen the Offshore Special Regulations. (Offshore races; the 1979 race: Offshore and solo history)
Figure-eight knot: A stopper knot that keeps a line from running out through a block or fairlead and stays easy to untie under load. (Knots)
Fin keel: A keel that is deep but short compared with the hull's length. Wikipedia says most modern monohulls use one, and Practical Sailor calls it the most common type and suited to most sailors. (Keelboats)
Flood, ebb and slack water: NOAA's terms for tidal current: a flood current flows toward land, an ebb current flows toward the sea, and slack water is the brief period of near-zero flow between them. NOAA adds that tidal currents are strongest around full and new moon (spring tides) and weakest around the first and third quarter (neap tides). (Navigation)
Foot: The bottom edge of a sail. (Parts of a boat)
Formula Kite: The Olympic kiteboarding equipment, raced in men's and women's events. Kiteboarding made its Olympic debut at Paris 2024 and stays on the program for LA28. (Olympic sailing)
Freeboard: The height from the water to the top of the hull. (Parts of a boat)
Full keel: The traditional keel type, running half or more of the boat's length. Practical Sailor associates full keels with serious bluewater sailing. (Keelboats)
Furler (headsail): A system for rolling up a headsail: an extruded foil slid over the headstay, a drum at the bottom turned by a furling line, and a swivel at the head. Practical Sailor notes the headstay still carries the rig loads. (Rigging and hardware)
Gale: On the Beaufort scale, Force 8, which the Met Office gives as 34 to 40 knots. The US National Weather Service's Gale Warning covers a wider band, sustained winds or frequent gusts of 34 to 47 knots. (Wind and weather)
Genoa: A jib larger than the foretriangle whose leech overlaps the mainsail (Wikipedia, secondary). Its size is quoted as LP (luff perpendicular, the shortest distance from clew to luff) divided by the boat's J dimension, so UK Sailmakers' example 135% genoa on a 10 ft J has a 13.5 ft LP. (Sails)
Give-way vessel: Under the COLREGs, the vessel required to keep out of the way of another. Rule 16 says it must act early and substantially to keep well clear. (Rules of the road)
Groove: The few-degree band of heading in which a boat sails upwind most efficiently, at steady heel and speed. North Sails says a narrow groove points higher in flat water, while a wider one, helped by a more twisted leech, copes better with waves and gusts. (Steering)
Gybe (jibe): Changing tack by turning the stern through the wind. The USCG Auxiliary and others treat it with more care than a tack because the boom can swing across with force. (Tacking and gybing)
Halyard (halliard): The line that raises or lowers a sail. Quantum says more halyard tension moves the draft forward and flattens the sail. (Parts of a boat)
Handicap racing: Racing in which finish times are adjusted by formula (giving a corrected time) so that different designs can compete together. Under IRC, for example, corrected time is elapsed time multiplied by the boat's TCC. PHRF, ORC and the Portsmouth Yardstick are other systems. (Handicap systems)
Harness and tether: Gear that keeps a crew member attached to the boat. The Offshore Special Regulations require them to meet ISO 12401, with tethers no longer than 2 m and self-closing hooks, and US Sailing's Safety at Sea Committee calls wearing them whenever on deck "the real solution" to crew overboard. (Life jackets)
Head: The top corner of a sail. (Parts of a boat)
Header: A wind shift that forces a boat sailing upwind to point lower; the opposite of a lift. Mike Ingham (Sailing World) notes a shift's effect is doubled, because the alternative to tacking on a header is sailing in it. (Racing tactics)
Heel: The boat leaning over under wind pressure. North Sails says extra heel increases weather helm, and the USCG Auxiliary says modern boats sail best with little or no heel. (How sailing works)
Hiking: Leaning the crew's weight out over the side to keep a dinghy flat. A Sailing World study by Loe and Smith measured legs-out hiking producing more righting torque than legs-in styles, and found hiking matters most when the boat is nearly flat. (Dinghy technique)
IALA buoyage: The international system of buoys and marks, in two regions. In Region A (Europe, Africa, Australia, New Zealand and others) port-hand marks are red and starboard-hand marks green; Region B (the Americas, Japan, the Republic of Korea and the Philippines) reverses the colors. (Navigation)
ICC (International Certificate of Competence): Also called the International Certificate for Operators of Pleasure Craft: a certificate created under UN Resolution 40 and issued only by agents in signatory countries; the RYA issues it in the UK. The US is not a signatory, so there is no US agent, and requirements vary by country. (Chartering)
ILCA: The single-handed dinghy formerly sold as the Laser, designed by Bruce Kirby and unveiled in January 1971. It has one hull and three rigs: ILCA 7 (men's Olympic boat since 1996), ILCA 6 (women's Olympic boat since 2008) and ILCA 4. The name changed after a trademark dispute. (One-design and Olympic classes; Technology history)
IMOCA 60: A racing keelboat class used in the Vendée Globe and in The Ocean Race, including the 2027 round-the-world edition. Semi-foiling IMOCA 60s first started the Vendée Globe in 2016. (Offshore races; Technology history)
In irons: Stopped while pointing into the wind, in the no-go zone, with the sails luffing and the boat hard to steer (US Sailing). (Points of sail)
Inflatable life jacket: A life jacket inflated by a CO2 cylinder, fired automatically by a water-soluble bobbin, by water pressure (hydrostatic) or by a manual pull. Under US rules one counts only with a full cylinder and working status indicators, and Oregon's boating agency says the Coast Guard does not approve inflatables for users under 16. (Life jackets)
IPC (International Proficiency Certificate): A certificate for US sailors chartering abroad, where the ICC may not be available to them. ASA issues one that requires ASA 101, 103 and 104; US Sailing issues one to members with Bareboat Cruising certification, valid for five years. (Chartering)
iQFOiL: The Olympic windfoil, which replaced the RS:X windsurfer at Paris 2024. From January 2025 the men's sail went from 9 to 8 square metres and the women's from 8 to a new 7.3 square metre sail. (Olympic sailing)
IRC: A measurement-based rating owned by the Royal Ocean Racing Club and France's UNCL. A boat's rating is a single Time Corrector Coefficient (TCC) calculated from its data, not from race results, and the formula is unpublished. (Handicap systems)
ISO 12402: The international lifejacket standard, in parts by buoyancy: Part 5 for 50N buoyancy aids, Part 4 for 100N, Part 3 for 150N and Part 2 for 275N. The RYA says all new lifejackets and buoyancy aids sold in the UK or Europe must meet it. (Life jackets)
Jib: A triangular headsail sheeted from its clew. Non-furling jibs are usually hanked onto the forestay. (Parts of a boat)
Keel: The backbone of the hull. On a sailboat the word also covers the added underwater area that resists leeway, producing sideways lift in the water that balances the sails' sideways force. (Parts of a boat)
Keelboat: A sailboat with a keel and ballast that help keep it upright, typically with a cabin. UKSA says the fixed keel makes it more stable than a dinghy and lowers the risk of capsize. (Keelboats)
Keep clear: In the racing rules, a boat keeps clear when the right-of-way boat can sail her course without taking avoiding action and, when overlapped, can also change course either way without immediate contact. (Racing rules)
Ketch: A rig with a second, shorter mast (the mizzen) aft of the mainmast and forward of the rudder post. (Parts of a boat)
Laminate and membrane (sailcloth): Sailcloth made of fibers laid along the load paths and bonded between films such as Mylar. Yacht says laminates hold their shape longer than woven cloth but eventually fail by delaminating. A membrane is a laminate whose fibers are laid while the sail itself is built (Sailtrader), and Yacht calls membranes the lightest and most costly construction. (Sails)
Layline: The course from which a boat can just fetch the mark on its current tack. David Dellenbaugh says boats tacking through about 80 to 90 degrees reach it when the mark sits slightly forward of abeam, and advises staying off laylines until late. (Racing tactics)
Lee helm: A boat's tendency to turn away from the wind. Practical Boat Owner says it is acceptable in light air but not wanted in stronger winds. (Steering)
Leech: The aft, trailing edge of a sail. (Parts of a boat)
Leeward: Pronounced "loo-ard": the side away from the wind, and the low side when the boat heels. In the racing rules, of two overlapped boats on the same tack, the one on the other's leeward side is the leeward boat. (Parts of a boat)
Leeway: The sideways slip of a boat through the water, which the keel or centerboard resists. (Parts of a boat)
Level (life jacket): The US performance-level labels (50, 70, 100, 150 and 275) that replaced the old Types, where the number is the minimum buoyancy in newtons. They replace the old Type I to V labels; the Coast Guard no longer approves new Type-labeled products, but existing ones stay legal while serviceable. Sources disagree on Level 100: the Coast Guard boating site says it is for sheltered water, while Boating Magazine describes it as for offshore and coastal use. (Life jackets)
Life jacket (lifejacket, PFD): A personal flotation device. In RYA usage a lifejacket is one designed to turn the wearer face up even if unconscious. US federal rules require a Coast Guard-approved wearable PFD for each person aboard. (Life jackets)
Lift: Two meanings. On a sail, the force from the pressure difference between its windward and leeward sides, which drives and heels the boat (How sailing works). In tactics, a wind shift that lets a boat sailing upwind point higher toward the mark (Racing tactics).
Line honours: Being the first boat to finish, as distinct from winning on corrected time. The Sydney Hobart awards both, with the overall winner taking the Tattersall Cup, and Transpac's Barn Door Trophy goes to the first monohull to finish. (Offshore races)
Louis Vuitton Cup: The America's Cup challenger series, which picks the challenger to meet the defender; the event history traces it to 1983. Under the 2027 Protocol its semi-final is first to 5 wins and its final first to 7. (America's Cup)
Luff: The forward, leading edge of a sail, attached along a mast or stay. As a verb, a sail luffs when its leading edge loses smooth flow and flutters, and to luff up is to steer closer to the wind. (Parts of a boat)
Mainsail: A fore-and-aft sail whose foot is usually attached to a boom. (Parts of a boat)
Mainsheet: The sheet that mainly controls the boom's angle and so the mainsail's trim. Quantum says tightening it adds leech tension, and easing opens the sail. (Sail trim)
Mark-room: Room to sail to and round a mark, owed under rule 18. Since 2025, if boats are overlapped when the first reaches the zone, the outside boat gives mark-room; if not, the boat that reached the zone first is owed it. The 2025 definition also includes room to leave the mark astern. (Racing rules)
Mast: The tall vertical spar that supports the sails. (Parts of a boat)
MMSI: A nine-digit Maritime Mobile Service Identity that a DSC radio must be programmed with so responders know who is calling. BoatUS issues them for US recreational boats that stay in US waters; international cruising needs an FCC-issued number, which ends in zero. (Electronics)
Multihull: Catamarans and trimarans. Wikipedia says multihulls are lighter and faster than monohulls but harder to tack and harder to right after a capsize. (Multihulls)
Nacra 17: The catamaran used for the mixed multihull Olympic event, introduced at Rio 2016. Its updated version at Tokyo 2020 was the first foiling boat in the Olympics, per US Sailing. (One-design and Olympic classes; Technology history)
No-go zone: The arc around the wind direction where a sailboat cannot sail effectively. ASA and Discover Boating describe about 90 degrees in total; Wikipedia gives roughly 45 degrees either side of the wind, typically 30 to 50 degrees depending on the boat. (Points of sail)
Offshore Special Regulations (OSR): World Sailing's safety and equipment rules for offshore racing, maintained under licence from ORC. They define race categories 0 (trans-oceanic) to 6 (inshore dinghy racing with rescue boats). An April 2026 notice says they were amended for 2026-2027, but the new wording was not available to us. (Offshore races)
One-design: A class in which all boats are identical or nearly so, so no handicap is needed and the first boat across the line wins. (One-design and Olympic classes)
Optimist: A youth dinghy designed in 1947 by Clark Mills in Florida, 2.31 m long, and one of the world's largest classes. A 2012 article says the International Sailing Federation approved it exclusively for sailors under 16. (Getting into racing)
ORC: The Offshore Racing Congress (founded in 1969 as the Offshore Rating Council) and its measurement-based rating, which uses a Velocity Prediction Program to predict boat speed across wind speeds and angles. ORC International needs full measurement; ORC Club accepts partly declared data. (Handicap systems)
Outhaul: The control line at the mainsail's clew, which shapes the lower part of the sail: tighter to flatten it in a breeze, eased for a fuller shape in light air. (Sail trim)
Overlap: In the racing rules, two boats overlap when neither is clear astern of the other. A boat is clear astern when she is behind a line abeam from the aftmost point of the other boat's hull and equipment, and the other boat is then clear ahead. (Racing rules)
Overtaking: Under COLREG Rule 13, approaching another vessel from more than 22.5 degrees abaft its beam. The overtaking vessel keeps clear, even a sailboat overtaking a powerboat. (Rules of the road)
Penalty turns: The penalties in rule 44.1: a Two-Turns Penalty for a possible breach of a Part 2 rule, or a One-Turn Penalty for touching a mark. Each turn includes one tack and one gybe, and taking one is not an admission of fault. The sailing instructions or notice of race may replace the turns with a Scoring Penalty. (Racing rules)
PHRF: Performance Handicap Racing Fleet, a handicap system based on observed performance and set by local fleets, which issue the certificates. Wikipedia (secondary) says ratings are in seconds per mile, with lower numbers meaning faster boats; US Sailing gives a time-on-time correction formula instead. (Handicap systems)
Pinching: Sailing too close to the wind, which costs speed and efficiency. (Points of sail)
PLB: A personal locator beacon: a 406 MHz beacon carried by a person, switched on by hand and held out of the water to transmit. Its alert goes to a Rescue Coordination Centre, not to nearby boats. (Beacons and MOB gear)
Point of sail: A boat's heading described by its angle to the wind. Discover Boating names five: close-hauled, close reach, beam reach, broad reach and running. (Points of sail)
Port: The left side of the boat when facing forward. (Parts of a boat)
Port tack, starboard tack: On port tack the wind comes over the port side and the sails are out to starboard; starboard tack is the reverse. The racing rules fix a boat's tack by her windward side, and COLREG Rule 12 defines the windward side as the one opposite the mainsail. (Points of sail)
Portsmouth Yardstick: A handicap system based on how boats perform against the boats they race with, run by clubs and needing no measurement. The RYA publishes the UK lists each year; the US version is the Dixie-Portsmouth Number (Wikipedia, secondary). (Handicap systems)
Preventer: A line North Sails recommends rigging to guard against an accidental gybe, released when a planned gybe begins. (Tacking and gybing)
Puff: A patch of stronger wind, which Moose McClintock (Sailing World) says usually shows as darker water. He calls an expanding dark oval at a gust's leading edge a "fan puff", and says flat water with no ripples signals a lull. (Wind and weather)
Racing Rules of Sailing (RRS): World Sailing's rulebook for racing, revised every four years after each Olympics. The 2025-2028 edition runs from 1 January 2025 to 31 December 2028, and national authorities add their own prescriptions. (Racing rules)
Reef: To reduce sail area by lowering part of the sail and securing the extra cloth. North Sails advises reefing early, and says a reefed sail must be flat, with the load on the reef tack and reef clew. (Reefing and depowering)
Right of way (racing): The Part 2 rules for boats that meet: a port-tack boat keeps clear of a starboard-tack boat (rule 10); on the same tack the windward boat keeps clear if overlapped (rule 11) and the boat clear astern keeps clear if not (rule 12); and a boat tacking keeps clear until close-hauled (rule 13). (Racing rules)
Roach: The sail area outside a straight line from the head to the clew, supported by battens (North Sails). (Sails)
Rode: The line and chain between boat and anchor. Discover Boating describes a typical rode as chain at the anchor end with nylon line to the boat, and Cruising World recommends nylon for its shock-absorbing stretch. (Anchors and ground tackle)
Roll tack: A dinghy tack that uses heeling and flattening to reduce speed loss by cutting the time the sail has no power. Racing rule 42.3(b) allows the extra rolling only if the boat comes out no faster than it would have without it. (Dinghy technique)
Rudder: A movable fin, usually at the stern, that steers the boat by redirecting the water flowing past it. (Parts of a boat)
Rule 12 (COLREGs): The rule for two sailing vessels meeting: with the wind on different sides, the one with the wind on its port side keeps clear; on the same side, the windward vessel keeps clear; and a port-tack vessel that cannot tell the other's tack keeps clear. (Rules of the road)
Running: Sailing directly downwind, at 180 degrees to the wind, where the sails work mainly by drag. (Points of sail)
Running rigging: The lines that work the sails, including the halyard, which raises or lowers a sail, and the sheet, which trims it. (Parts of a boat)
RYA (Royal Yachting Association): The UK national governing body for dinghy, motor and sail cruising, sail racing, windsurfing and more, founded in 1875 as the Yacht Racing Association. It runs the UK's dinghy and cruising training schemes. (Governing bodies)
SailGP: An annual global league of national teams racing identical F50 foiling catamarans inshore, in harbor venues. Wikipedia (secondary) says it was founded in 2018 by Larry Ellison and Russell Coutts. (SailGP)
Sailing vessel: Under COLREG Rule 3, any vessel under sail with any engine not in use. A sailboat motoring counts as a power-driven vessel. (Rules of the road)
Schooner: A rig whose mainmast is taller than its foremast; there may be more than two masts. (Parts of a boat)
Scope: The length of anchor rode let out relative to the depth. Sources differ on the ratio: ASA and Discover Boating use 7:1 (ASA counts the bow's height above the water in the depth), Boating Magazine starts at about 8:1, and a UK Sailmakers cruiser uses 5:1 normally. (Anchoring)
Sea breeze: An onshore wind that forms when land is warmer than the water: heated land lowers the pressure and air flows in from the sea, more strongly with a bigger temperature difference (Ed Adams, Sailing World). (Wind and weather)
Sheet: The line that sets a sail's angle to the wind, its trim. (Parts of a boat)
Shrouds: The standing rigging that supports the mast from side to side, usually stainless steel wire running from the mast to the sides of the boat. (Parts of a boat)
Sloop: A rig with one mast and two sails, usually a mainsail and one headsail; the most common modern rig. (Parts of a boat)
Sound signals: Signals defined in COLREG Rules 32 to 35. A short blast lasts about 1 second and a prolonged blast 4 to 6 seconds; in restricted visibility a sailing vessel under way sounds one prolonged and two short blasts at least every 2 minutes. (Rules of the road)
Spinnaker: A sail for sailing off the wind. A symmetric spinnaker is the same on both sides and flies from a spinnaker pole; North Sails says it is better at deep angles but harder to rig, fly and douse than an asymmetric. (Sails)
Squall: A sudden wind increase. Sail Magazine cites NOAA's definition: a rise of at least 16 knots, sustained at 22 knots or more for at least a minute. (Wind and weather)
Stall: What happens when a sail's angle of attack is too large: the airflow separates from the sail (ASA). Sailing World says a stalled leeward telltale is never acceptable. (How sailing works)
Stand-on vessel: Under COLREG Rule 17, the vessel that keeps its course and speed while the give-way vessel acts. It may act once it is clear the give-way vessel is not, and must act if collision cannot otherwise be avoided. (Rules of the road)
Standing rigging: The rigging that holds the mast up: shrouds for side-to-side support and stays for fore-and-aft support. (Parts of a boat)
Starboard: The right side of the boat when facing forward. (Parts of a boat)
Stern: The back of the boat. (Parts of a boat)
Sydney Hobart: The Rolex Sydney Hobart Yacht Race, first held in 1945 and organized by the Cruising Yacht Club of Australia with the Royal Yacht Club of Tasmania, over 628 nautical miles. (Offshore races)
Tack: Two meanings. The bottom forward corner of a sail, near the mast (Parts of a boat). And the maneuver of changing direction by turning the bow through the wind (Tacking and gybing).
Telltales: Ribbons on a sail that show the airflow: streaming straight back means smooth, attached flow, while fluttering or drooping means poor flow. Practical Sailor says drooping leeward telltales mean the sail is over-trimmed. (Sail trim)
The Ocean Race: A crewed round-the-world race that began in 1973 as the Whitbread Round the World Race, became the Volvo Ocean Race in 2001 and took its current name in 2019 (Wikipedia, secondary). The 2027 edition starts from Alicante in IMOCA 60s. (Offshore races; Offshore and solo history)
Tiller: A bar attached to the top of the rudder, used to turn it. (Parts of a boat)
Traveler: A mainsheet control whose car moves to set the boom's angle. Dave Flynn (Sailing World) uses the mainsheet for coarse adjustment and the traveler for fine, and Quantum says lowering it in a breeze depowers without adding excess twist. (Sail trim)
Trimaran: A multihull with a central hull and two outrigger hulls. (Multihulls)
Turtle: A capsized boat turned fully upside down. US Sailing's 2012 entrapment report says the most serious capsize risk is a sailor trapped in or under a turtled hull, and that turtling can happen in light winds. (Capsize recovery)
Twist: How far a sail's leech falls open. Sources use different reference battens upwind: Dave Flynn (Sailing World) sets the top batten parallel to the boom, Rupert Holmes (Sail Magazine) the second batten from the top. (Sail trim)
US Sailing: The US national governing body for sailing, organized in 1897 as the North American Yacht Racing Union. It trains race officials and instructors, runs keelboat and Safety at Sea courses, issues all US IRC certificates and processes ORC certificate data for US boats. (Governing bodies)
Vang (kicker): The control that holds the boom down. Quantum says it matters most when the sheet is eased on reaches and runs, because without it the boom lifts and the leech twists open. (Sail trim)
Variation: The difference between true and magnetic north, which depends on location and time and is shown on the chart's compass rose with its annual change. (Navigation)
Vendée Globe: A single-handed, non-stop, unassisted race around the world every four years, starting and finishing at Les Sables d'Olonne. The first edition was in 1989; Charlie Dalin set the race record of 64 days 19 hours 22 minutes 49 seconds in 2024-25. (Offshore races; Offshore and solo history)
VHF radio: The line-of-sight marine radio. A Coast Guard Auxiliary author gives 5 W for handhelds and 25 W for fixed sets, with range set mainly by antenna height; the Coast Guard keeps a voice watch on channel 16 and a DSC watch on channel 70. (Electronics)
Visual distress signals: Flares and other signals that US federal rules require on coastal waters, the Great Lakes and connected waters, with night-only signals for some small open sailboats. Pyrotechnic signals expire 42 months after manufacture. (Safety requirements)
Weather helm: A boat's tendency to turn into the wind, so the tiller has to be held to windward to keep course. North Sails says the goal is a little weather helm. (Steering)
Wetsuit: Neoprene clothing the RYA recommends for dinghy sailing. Thickness is given as body/limb millimetres, and PBO says a 3/2 suits water of about 15 to 20°C. Styles include full-length steamers, shorties and sleeveless long johns. (Dinghy clothing)
Winch: A drum that lines are wrapped around to multiply pulling force. West Marine says self-tailing winches grip the line on their own and calls them essential for shorthanded sailing. (Rigging and hardware)
Windward: The side the wind is blowing from. COLREG Rule 12 defines a vessel's windward side as the one opposite the side carrying the mainsail. (Parts of a boat)
Winged keel: A short, shallow keel with weighted wings (Wikipedia, secondary). Ben Lexcen's winged keel on Australia II, the first challenger to win the America's Cup in 1983, had beaten conventional keels in secret tests. (Parts of a boat; America's Cup history)
World Sailing: The world governing body for sailing, recognized by the IOC, which manages Olympic sailing and writes the Racing Rules of Sailing. It began as the International Yacht Racing Union, became ISAF in 1996 and World Sailing in 2015; its own history page dates the IYRU both to the 1906 London conference and to Paris in October 1907. (Governing bodies; Birth of yachting)
Yawl: A rig like a ketch, but with the mizzen aft of the rudder post, where it mainly helps balance the helm. (Parts of a boat)
Zone: In the racing rules, the area around a mark within three hull lengths of the boat nearer to it; a boat is in it when any part of her hull is inside. Rule 18 mark-room is triggered by boats reaching the zone. (Racing rules)

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