Boat terminology

Abeam means at right angles to the boat’s centerline, straight out from its side.

Directions and lights AmidshipsCenterline

Aft means toward the stern.

Directions and lights ForwardStern

A boat is aground when its keel or bottom is stuck fast on the bottom of the waterway.

Underway UnderwayDraft

Ahead means in a forward direction, in front of the boat's bow.

Underway AsternForwardBow

An all-round white light shows over an unbroken arc of 360 degrees; on the runabout it sits on a pole at the stern.

Parts of the boat Port & starboard page Sternlight

Amidships is the middle of the boat, halfway between bow and stern.

Directions and lights Abeam

An anchor is a device that engages the bottom and, by resisting being dragged, keeps a boat within a given radius.

Lines and docking RodeWindlassMooring

Astern means behind the boat; a boat going astern is moving backward, in reverse.

Underway Stern page AheadAftStern

The backstay is the wire from the top of the mast to the stern that supports the mast from aft.

Sailboat terms Forestay

Beam is the width of a boat at its widest point; US boat regulations measure it between the outer sides, excluding handles and similar fittings.

Dimensions Beam page Length overallFlare

A berth is a place to sleep on a boat; the word also means the place a boat occupies in a harbor.

Aboard CabinCuddyMooring

The bilge is the lowest part of the inside of the hull, where water collects.

The hull Bottom

A bilge pump is a pump that clears out water that collects in the bilge.

Aboard BilgeDrain plug

A bimini top is a canvas top on a metal frame over the cockpit that gives shade and shelter from sun and rain.

Parts of the boat

The body plan is the end view of a lines plan, with the sections forward of amidships drawn on the right and those aft on the left.

Reading a lines plan Hull types page Lines planStation

The boom is the spar that runs aft from the mast along the foot of the mainsail.

Sailboat terms

The bottom is the underside of the hull, which meets the sides at the chines.

The hull Hull types page

The bow is the front, or forward end, of a boat.

Parts of the boat Bow page SternForwardStem

The bow eye is an eye bolt on the stem that gives an attaching point when the boat is on a trailer.

Parts of the boat

The bow pulpit is the metal guardrail at the bow, to which the lifelines are usually connected.

Sailboat terms LifelinesBow rail

The bow rail is a metal guardrail fitted around the bow.

Parts of the boat Bow pulpit

A bowrider has an open seating area in the bow, in front of the helm.

Parts of the boat

A bulb keel is a fin keel with a cigar-shaped bulb of lead at its tip, as the keel-types sheet draws it.

Sailboat terms Keel page Fin keel

A bulbous bow is a rounded swelling of the hull at the bow, below the waterline, found mostly on ships.

The hull Bow page

A bulkhead is a wall or partition inside a boat that divides it into compartments; many add strength or keep water out.

Aboard HullCabin

A buttock line is the shape made by slicing the hull with a vertical fore-and-aft plane, drawn in the sheer plan.

Reading a lines plan Hull types page Sheer plan

A cabin is an enclosed space on a boat, usually a small room where people can live or sleep.

Aboard CuddyBerthGalleyHeadCompanionwayCabin top

The cabin top, or coachroof, is the part of the cabin raised above the deck to give headroom below.

Sailboat terms

A canoe stern comes to a point much like the bow, so the boat is a double-ender with no flat transom.

The hull Stern page Transom

A capacity plate is the label that US regulations require on monohull boats under 20 feet, other than sailboats, canoes, kayaks and inflatables, giving the maximum persons and weight.

Parts of the boat Freeboard page Freeboard

To cast off is to let go of the lines that hold a boat to a dock or mooring so it can leave.

Lines and docking Make fastDock lineUnderway

A catamaran has two hulls side by side joined by a deck or bridge deck, with open water between them.

The hull MultihullMonohullTrimaranBeam

A centerboard is a movable plate, pivoted at its forward end, that is raised or lowered through the keel of a sailboat.

Sailboat terms Keel page Fin keel

The centerline is the line running fore and aft down the middle of the boat.

Directions and lights Keel

The chine is the corner along the hull where the bottom meets the side.

The hull Hull types page Lifting strakesKeelDeadrise

A cleat is a horned fitting on deck that lines are made fast to.

Parts of the boat

A clipper bow’s stem forms a concave curve that projects forward above the waterline in a long overhang.

The hull Bow page Spoon bow

A coaming is a raised edge around a cockpit or hatch opening that helps keep water out.

Parts of the boat Gunwale page Cockpit

The cockpit is the open well of the boat where people sit and from which it is steered.

Parts of the boat Cockpit soleCoaming

The cockpit sole is the floor of the cockpit; the drawings set it below the deck.

Parts of the boat Cockpit

The companionway is the entrance and steps from the cockpit down into the cabin.

Sailboat terms

The console is the cabinet at the helm that holds the steering, the engine controls and the instruments.

Parts of the boat Helm

A counter stern extends aft above the waterline in a long overhang.

The hull Stern page Transom

A cruiser stern is rounded, with a convex profile, and shows less flat surface at the back than a transom stern.

The hull Stern page Canoe stern

A cuddy is a small cabin or shelter on a boat.

Aboard CabinBerth

Deadrise is the angle between the bottom of the hull and a horizontal line, seen in a cross-section.

Dimensions Deadrise page BottomChine

The deck is the horizontal surface that closes in the top of the hull and forms the boat’s outside floor.

Parts of the boat

A deep-V hull keeps a steep V along the whole bottom; BoatUS and industry guides usually describe it as having more than 20 degrees of deadrise at the transom.

The hull V-hullModified-V hullDeadrise

Depth is the height of the hull from the keel to the deck.

Dimensions Freeboard page DraftFreeboard

Displacement is the mass of the water a boat pushes aside while floating.

The hull Planing

Dock lines, also called mooring lines, are the lines that tie a boat to a dock, pier or float.

Lines and docking Spring lineCleatFenderMake fastCast off

Draft is how deep the hull sits: the vertical distance from the keel to the surface of the water.

Dimensions Draft page FreeboardDepthWaterline

The drain plug is a plug or valve low in the transom that controls the draining of water from the hull.

Parts of the boat Transom page

A fathom is a unit of length used for water depth and rope, equal to 6 feet, about 1.83 meters.

Underway Nautical mileDraft

A fender is a portable bumper hung over the side to cushion contact between the hull and a dock or another boat.

Lines and docking Rub railDock line

A fin keel is a deep, thin, fixed fin under a sailboat’s hull that resists the sideways push of the wind on the sails.

Sailboat terms Keel page KeelFull keelBulb keel

Flare is the outward slope of the hull sides as they rise from the waterline.

The hull Hull types page

A flat-bottom hull has a bottom that is flat, or nearly so, from side to side, meeting the sides at a hard chine.

The hull V-hullChineDeadrise

The forefoot is the part of the bow where the stem meets the keel.

The hull Bow page StemKeel

The forestay is the wire that runs from the mast forward to the bow; the jib is set on it.

Sailboat terms BackstayShrouds

Forward, or fore, means toward the bow.

Directions and lights AftBow

Freeboard is the height of the boat’s side above the water: the depth of the hull minus its draft.

Dimensions Freeboard page DraftDepthTopsides

A full keel runs along much of the bottom of the hull, with the rudder hung on its after end, as the keel-types sheet draws it.

Sailboat terms Keel page Fin keel

The galley is the kitchen on a boat.

Aboard CabinHead

The gunwale, pronounced “gunnel”, is the upper edge of the boat’s side.

Parts of the boat Gunwale page SheerRub railTopsides

The half-breadth plan is the view from above; it shows the waterlines, and only one side because the hull is symmetric.

Reading a lines plan Hull types page Lines planWaterline

A halyard is the line used to hoist and lower a sail.

Sailboat terms SheetMastLine

A hardtop is a rigid top fixed over a boat's cabin top or console that shelters the driver, and sometimes passengers, from the weather.

Aboard T-topBimini topConsoleHelm

A hatch is an opening in the deck to the space below, and the cover, often watertight, that closes it.

Aboard DeckCoamingCompanionway

The head is the toilet on a boat.

Aboard CabinGalley

Heel is a temporary lean of the boat to one side, caused by wind, waves or a fast turn.

Underway ListTrimWindward

The helm is the wheel or tiller that steers the boat, and by extension the place it is steered from.

Parts of the boat ConsoleWindshield

The hull is the body of the boat, including the part below the waterline.

The hull Hull types page

Hull speed is a rule of thumb for displacement hulls: 1.34 times the square root of the waterline length in feet, in knots.

The hull Waterline lengthDisplacement

The hull-to-deck joint is where a separately molded hull and deck are joined; the drawing puts it at the gunwale, under the rub rail.

Parts of the boat Gunwale page

The jib is the triangular sail set forward of the mast, on the forestay.

Sailboat terms MainsailForestay

To jibe, or gybe, is to turn the stern through the wind, so the wind comes from the other side and the sails swing across.

Sailboat terms TackBoomMainsail

The keel is the backbone of the hull, running fore and aft along the centerline at the bottom.

The hull Keel page Fin keelChineBottom

A knot is a unit of speed equal to one nautical mile per hour, about 1.15 statute miles per hour.

Underway Nautical mileHull speed

A lazarette is a storage or service compartment in the after part of a boat, often beneath the cockpit or aft deck.

Aboard SternCockpitHatch

Leeward, said “loo-ard”, is the direction the wind blows toward, and the side of the boat away from the wind.

Underway WindwardHeel

Length overall is a straight horizontal line from the foremost to the aftermost part of the boat, leaving out fittings such as bow sprits, rudders and motor brackets.

Dimensions Beam page Waterline lengthBeam

Lifelines are the wires around the deck edge, held up by stanchions, that help keep people aboard.

Sailboat terms Bow pulpit

Lifting strakes are narrow ridges running fore and aft along the bottom of a planing hull, as the drawings show them.

The hull Hull types page ChineBottom

Aboard a boat, rope is called line unless a piece has a name of its own, such as a halyard or a sheet.

Lines and docking Dock lineHalyardSheetRodeCleat

A lines plan draws a hull in three views: the sheer plan from the side, the half-breadth plan from above and the body plan from the end.

Reading a lines plan Hull types page Body planHalf-breadth planSheer plan

A list is a lasting lean to one side caused by weight that is unevenly placed.

Underway HeelTrim

The mainsail is the boat’s principal sail, set on the mast and along the boom.

Sailboat terms JibBoomTraveler

To make fast is to secure a line to a cleat, bitt or similar fitting so that it can neither slip nor jam.

Lines and docking CleatCast offDock line

The mast is the upright spar that carries the sails.

Sailboat terms MastheadBoom

The masthead is the top of the mast.

Sailboat terms

A modified-V hull has a V bottom with less deadrise at the transom than a deep V, somewhere between a flat bottom and a deep V.

The hull V-hullDeep-V hullDeadrise

A monohull is a boat with a single hull. US boat regulations define it as a boat whose waterline forms a single closed curve.

The hull MultihullCatamaran

A mooring is the line or chain that holds a boat to a fixed object, such as a dock or a weight on the bottom.

Lines and docking Dock lineAnchorBerth

A motor cut-out is a lowered section of the transom’s top edge where an outboard motor is mounted.

Parts of the boat Transom page SplashwellTransom

A multihull is a boat with more than one hull side by side, such as a catamaran or trimaran; a single-hulled boat is a monohull.

The hull MonohullCatamaranTrimaran

A nautical mile is exactly 1,852 meters, about 1.15 statute miles, and is based on one minute of latitude.

Underway KnotFathom

An outboard motor is a self-contained engine, gear case and propeller unit mounted on the transom.

Parts of the boat Transom

PFD stands for personal flotation device; in US regulations (33 CFR 175.13) it means a flotation device approved by the Coast Guard. A wearable PFD, such as a life jacket, is worn on the body; a throwable PFD is thrown to a person in the water.

Aboard

Planing is the mode in which a boat’s weight is carried mostly by hydrodynamic lift instead of buoyancy.

The hull DisplacementHull speed

A plumb bow has a stem that runs straight up and down, at or near vertical.

The hull Bow page Raked bowStem

Under 33 CFR 173.3, a pontoon boat has a broad, flat deck fixed on top of closed cylinders that keep it afloat.

The hull TritoonCatamaranDeck

Port is the left side of the boat when you face the bow.

Directions and lights Port & starboard page StarboardSidelights

A propeller is a hub with radiating blades set in a helical pattern that drives the boat when it turns in the water.

Aboard Outboard motorRudderStern

A raked bow has a straight stem that slopes forward as it rises.

The hull Bow page Plumb bow

To reef is to reduce a sail's area by folding or rolling part of it away.

Sailboat terms MainsailBoom

A reverse transom leans forward at the top, so the stern slopes forward from the waterline up to the deck.

The hull Stern page Transom

The rode is the anchor line, of rope, chain or both, that connects the anchor to the boat.

Lines and docking AnchorWindlassLine

A round-bottom hull turns from bottom to side in a curve instead of a hard chine.

The hull BilgeChineDisplacement

The rub rail is a permanent protective strip along the outside of the hull, often running its whole length, that does the job of a fender.

Parts of the boat Gunwale page GunwaleHull-to-deck joint

The rudder is the blade under the stern that turns to steer the boat.

Sailboat terms TillerFin keel

The sheer is the topmost line of the boat’s side, seen from the side as a curve from bow to stern.

The hull Gunwale page GunwaleFreeboard

The sheer plan is the side view of a lines plan, with the buttock lines projected onto it.

Reading a lines plan Hull types page Lines planButtock line

A sheet is the line, fastened to a sail's lower aft corner or to its boom, that controls the angle of the sail.

Sailboat terms HalyardWinchTravelerLine

Shrouds are the wires from each side of the boat to the mast that hold it up sideways.

Sailboat terms SpreadersForestay

Sidelights are the navigation lights on each side of the bow: red on the port side, green on the starboard side.

Parts of the boat Port & starboard page SternlightPortStarboard

The splashwell, or motorwell, is the walled area just inside the transom that stops water coming through the motor cut-out from reaching the passenger area.

Parts of the boat Transom page Motor cut-out

A spoon bow is an overhanging bow whose underside is curved like the bowl of a spoon.

The hull Bow page Clipper bow

Spreaders are the struts that stick out from each side of the mast and hold the shrouds away from it.

Sailboat terms ShroudsMast

A spring line runs forward or aft at a sharp angle between the boat and the dock, unlike a breast line, which runs straight across.

Lines and docking Dock lineCleat

Starboard is the right side of the boat when you face the bow.

Directions and lights Port & starboard page PortSidelights

A station is a cross-section of the hull: a curve in the body plan and a straight line in the other two views.

Reading a lines plan Hull types page Body plan

The stem is the forward end of the hull, rising from the keel to the top of the hull at the bow.

The hull Bow page BowForefoot

The stern is the back, or aft end, of a boat.

Parts of the boat Stern page BowTransomAft

Stern eyes are the eye bolts low on the transom, drawn here as attaching points for a boat on a trailer.

Parts of the boat Transom page

A sternlight is a white light at the stern that shows aft over an arc of 135 degrees.

Parts of the boat Port & starboard page SidelightsAll-round white light

The swim platform is a low platform at the stern for getting on and off the boat from the water.

Parts of the boat

Industry guides usually describe a T-top as a frame fixed to a center console that holds a canvas or hard top over the helm.

Aboard HardtopBimini topConsole

To tack is to turn the bow through the wind, so the wind blows on the sails from the other side.

Sailboat terms JibeWindwardSheet

A tender, often a dinghy, is a small boat that carries people and supplies between a larger boat and the shore.

Aboard MooringAnchor

The tiller is the lever attached to the rudder that is moved to steer the boat.

Sailboat terms Rudder

Topsides are the sides of the hull between the waterline and the gunwale.

The hull Freeboard page FreeboardGunwale

The transom is the surface across the stern of the boat that faces aft.

Parts of the boat Transom page SternTransom heightMotor cut-out

Transom height is measured from the lowest point along the top of the transom where water could come in, down to a line extending the bottom of the hull at the centerline.

Dimensions Transom page TransomFreeboard

A traveler is a rod or track across the deck along which a fitting slides; on the sloop it carries the lower end of the mainsheet.

Sailboat terms

Trim is a boat's fore-and-aft angle, down by the bow or by the stern; trimming the sails means adjusting their angle.

Underway HeelListDraftSheet

A trimaran has three hulls side by side: a main hull in the middle and a smaller outer hull, or float, on each side.

The hull MultihullCatamaran

A tritoon is a pontoon boat built on three rows of floats rather than two.

The hull Pontoon boatTrimaran

In the Inland Navigation Rules, underway means a vessel is not at anchor, made fast to the shore or aground; it need not be moving.

Underway AgroundAnchorMake fast

A V-hull's bottom forms a V in cross-section, with its point at the keel and a chine where it meets each side.

The hull DeadriseChineDeep-V hullModified-V hullFlat-bottom hull

The wake is the track of disturbed water that a moving boat leaves astern.

Underway AsternPlaning

The waterline is the line where the surface of the water meets the hull.

The hull Draft page DraftWaterline length

Waterline length is the length of the hull along the waterline, which changes as load and trim move the waterline.

Dimensions Beam page Length overallWaterlineHull speed

A winch is a deck machine for pulling on a rope or wire, used to hoist sails and adjust the sheets and rigging.

Sailboat terms

A windlass is a winch used to haul in and let out the anchor line or chain.

Lines and docking AnchorRodeWinch

The windshield is the clear glass or plastic screen in front of the helm that shelters the people behind it from the wind.

Parts of the boat

Windward is the direction the wind blows from, and the side of the boat facing the wind.

Underway LeewardHeel

A wing keel is a shallow fin with wings at its foot that spread the ballast sideways, as the keel-types sheet draws it.

Sailboat terms Keel page Bulb keel