Boating glossary

A

AGM battery (also AGM)

Absorbent Glass Mat battery — a sealed lead-acid design that holds electrolyte in fiberglass mats. Common for marine starting and house banks; charge with an AGM-capable charger. Related guide

AIS (also Automatic Identification System)

Automatic Identification System — a VHF-based broadcast of vessel identity; position and movement used by ships and some recreational boats for collision awareness. Related guide

All-round light (also anchor light)

A white light visible through 360 degrees. Often used as an anchor light when a vessel is at anchor. Related guide

Anchor rode (also rode)

The line and/or chain that connects the anchor to the boat. Scope is the ratio of rode length to water depth under the bow. Related guide

B

Bay boat

A shallow-draft fishing boat meant for bays and coastal flats; usually with a lower freeboard and console layout for casting. Related guide

Beam

The width of the boat at its widest point. Wider beams usually feel more stable at rest; they also affect trailer width and slip size. Related guide

Bilge

The lowest interior part of the hull where water collects. Keep it clean and make sure the bilge pump and float switch work. Related guide

Bilge pump

An electric or manual pump that removes water from the bilge. Test it before each season and carry a backup on larger boats. Related guide

Bill of sale

The written record of the boat’s transfer: buyer; seller; HIN; price and date. Many states require a specific form for registration. Related guide

Bowrider (also bow rider)

A runabout with seating forward of the windshield in a scooped bow cockpit; aimed at day cruising and watersports. Related guide

C

Capacity label (also capacity plate)

The builder’s plate (on many monohulls under 20 ft) that lists max persons; max weight and max horsepower. Stay within those limits. Related guide

Center console

A boat layout with the helm on a console in the middle of the cockpit so you can walk all around it; popular for fishing. Related guide

Certificate of Number (also registration certificate)

The state registration credential (paper or digital) that must be aboard a numbered vessel. Display numbers and the validation decal as your state requires. Related guide

Channel 16 (also VHF Channel 16)

The international VHF distress; safety and calling channel (156.8 MHz). Hail or call for help here; then switch to a working channel. Related guide

Chartplotter (also MFD)

A multifunction display that shows electronic charts and usually GPS position; often combined with sonar (“fish finder”) on recreational boats.

Clean Drain Dry

The habit of cleaning; draining and drying boats; trailers and gear after each trip to stop invasive species from hitchhiking between waters. Related guide

Cleat

A horned fitting on the boat or dock used to secure dock lines and anchor lines with a cleat hitch. Related guide

Cleat hitch

The standard wrap-and-figure-eight knot used to make a line fast to a cleat so it holds under load but can be cast off quickly. Related guide

COLREGS (also navigation rules, Rules of the Road)

The International Regulations for Preventing Collisions at Sea (and the U.S. inland rules). They set lights; shapes; sound signals and who gives way. Related guide

D

Deadrise

The V-angle of the hull bottom at the transom (in degrees). A sharper V usually rides softer in chop; a flatter bottom planes sooner and drafts less. Related guide

Deck boat

A wide-beam day boat with an open; patio-like deck and usually a square or blunt bow for more seating than a classic bowrider. Related guide

Deep-cycle battery (also deep cycle)

A battery built to be discharged and recharged repeatedly for lights; pumps and electronics — unlike a starting battery made for short; high-current engine cranking. Related guide

Displacement hull

A hull that moves through the water at speeds limited by its waterline length — typical of many trawlers and traditional sailboats. Related guide

Draft

How deep the boat sits in the water from the waterline to the lowest point (often the prop or keel). Shallow draft reaches thinner water; deep draft can handle bigger seas better. Related guide

Dry weight

The builder’s published weight of the boat without engine; fuel; water; gear or passengers. Real trailering weight is always higher. Related guide

DSC (also Digital Selective Calling)

Digital Selective Calling — a VHF feature that can send a digital distress alert with your MMSI and position when the radio is GPS-linked. Related guide

E

E15

Motor gasoline with about 15% ethanol. It is not approved for most boat engines; misfueling can void warranties and damage fuel systems. Related guide

EPIRB

Emergency Position Indicating Radio Beacon — a distress beacon that alerts rescue services by satellite with your position. Register it and keep the battery in date. Related guide

Ethanol fuel (also E10)

Gasoline blended with ethanol (commonly E10). Many marine engines are approved for E10 but not E15; store fuel with stabilizer and keep water out. Related guide

F

Fender (also boat fender)

A soft cushion hung between hull and dock (or another boat) to prevent scrapes and impact damage when coming alongside. Related guide

Freeboard

The height of the hull side from the waterline up to the gunwale or deck edge. Higher freeboard sheds spray better and can feel drier.

Fuel stabilizer

An additive mixed into gasoline before storage to slow varnish and gum formation during lay-up. Follow the product and engine-maker directions. Related guide

G

Galvanic isolator

A device in the shore-power ground path that blocks low-level DC stray current that can corrode underwater metals while still allowing AC fault current to flow. Related guide

GFCI (also Ground Fault Circuit Interrupter)

Ground Fault Circuit Interrupter — a device that cuts power quickly if it senses current leaking to ground; helping prevent electric shock drowning around docks. Related guide

Give-way vessel

Under the navigation rules; the vessel that must take early and clear action to keep out of the way of the stand-on vessel. Related guide

GPS

Global Positioning System satellite navigation used for chartplotters; DSC position and many phone apps. A radio’s DSC distress alert is stronger when GPS is linked. Related guide

Gunwale (also gunnel)

The upper edge of the boat’s side where the hull meets the deck. Cleats; rod holders and rub rails often mount here.

GVWR (also Gross Vehicle Weight Rating)

Gross Vehicle Weight Rating — the maximum allowed weight of a vehicle or trailer including its load; set by the manufacturer on the ID label. Related guide

Gybing (also jibing)

Turning a sailboat’s stern through the wind so the boom and sails swing to the other side — control the boom carefully. Related guide

H

Haul-out (also haul out)

Lifting the boat out of the water for storage; bottom work or inspection — often by travelift at a yard. Related guide

HIN verification

Confirming the hull identification number stamped on the boat matches the title; registration and any documentation paperwork before you pay. Related guide

Holding tank

A tank that stores sewage from the head until you can pump it out at a station or (where legal) discharge treated waste through an approved MSD. Related guide

Hull Identification Number (also HIN)

A unique 12-character serial number required on boats made or imported for sale in the U.S.; it should match the title and registration. Related guide

I

Impeller

A rubber pump wheel in many raw-water cooling systems that moves seawater through the engine. Replace it on the maker’s interval and after dry running. Related guide

Inboard (also inboard engine)

An engine mounted inside the hull that drives a shaft or jet; common on ski/wake boats and many cruisers. Related guide

L

Lien

A lender’s legal claim on the boat until the loan is paid. Get a written lien release when you pay off or refinance. Related guide

Lithium marine battery (also LiFePO4)

Usually LiFePO4 chemistry on boats: light weight and deep usable capacity; but needs a proper battery management system and a charger profile the maker specifies. Related guide

Livewell (also live well, baitwell)

A circulating tank that keeps bait or catch alive with pumped water. Check pumps and drains during a sea trial or spring start-up. Related guide

LOA (also length overall)

Length overall — the boat’s full length from the tip of the bow to the end of the stern; builders may also publish a separate length-with-engines figure. Related guide

M

Marine survey

An independent inspection of a boat’s condition (structure; systems; safety) by a marine surveyor; common before buying a used boat or for insurance. Related guide

Marine surveyor

A professional who inspects boats and writes condition and valuation reports. Many buyers look for SAMS or NAMS credentials. Related guide

MAYDAY

The radiotelephone distress signal used only when a vessel or person is in grave and imminent danger and needs immediate help. Related guide

MMSI (also Maritime Mobile Service Identity)

A nine-digit Maritime Mobile Service Identity programmed into a DSC radio (and AIS) so distress and routine digital calls identify your vessel. Related guide

Mooring ball (also mooring buoy)

A permanently set buoy you pick up and secure to instead of dropping your own anchor; often white with a blue stripe in U.S. waters. Related guide

MSD (also marine sanitation device)

Marine sanitation device — onboard equipment that treats or holds sewage. Federal rules set Type I; II and III devices and where untreated discharge is banned. Related guide

N

NASBLA

National Association of State Boating Law Administrators — the group whose boating-education standards many states accept for course reciprocity. Related guide

Navigation lights (also nav lights, running lights)

Required lights shown from sunset to sunrise (and in restricted visibility) so other boats can see your vessel type; size and aspect. Related guide

NMMA

National Marine Manufacturers Association — the industry group behind Discover Boating education content and boat certification programs. Related guide

No Discharge Zone (also NDZ, No-Discharge Zone)

A water body where the discharge of treated or untreated sewage from vessels is banned; you must use a holding tank and pump-out. Related guide

No-wake zone (also no-wake)

An area where boats must go slow enough that they make no more than a minimum wake — often near marinas; docks and swimming areas. Related guide

O

Outboard (also outboard engine, outboard motor)

A complete propulsion unit hung on the transom: engine; gears and propeller in one package that steers by pivoting. Related guide

P

Pan-Pan (also pan pan)

An urgency signal for a serious problem that is not yet a life-threatening distress (for example a breakdown that still needs help). Related guide

PFD (also personal flotation device, life jacket, life jackets, lifejacket)

Personal flotation device — a Coast Guard–approved life jacket or buoyancy aid. Wearable PFDs are sized by person; Type IV throwables are not worn. Related guide

Planing hull (also on plane)

A hull shape meant to rise and skim on top of the water at speed instead of pushing through it like a displacement hull. Related guide

PLB (also personal locator beacon)

Personal Locator Beacon — a smaller satellite distress beacon you carry on your person. Register it like an EPIRB. Related guide

Pontoon

A boat with a flat deck on aluminum tubes (pontoons). Stable at rest and roomy for groups; not built for big offshore seas. Related guide

Pump-out (also pump out, pump-outs, pumpouts)

A shoreside fitting that empties a boat’s holding tank into a sewer or treatment system. Many harbors and lakes require pump-outs instead of overboard discharge. Related guide

PWC (also personal watercraft)

Personal watercraft — a vessel you sit or stand on that uses an internal-combustion engine powering a water jet pump. States often set special age and night rules. Related guide

S

Sacrificial anode (also zincs, sacrificial anodes)

A replaceable metal (often zinc; aluminum or magnesium) that corrodes instead of your prop; shaft or stern drive. Check and replace when wasted. Related guide

Scope (also anchor scope)

The ratio of deployed rode length to the depth of water (plus freeboard) under the bow. More scope usually holds better in open conditions. Related guide

Sea trial (also sea trials)

A test run under power before you buy — checking how the boat starts; planes; handles; docks and runs with a realistic load. Related guide

Shore power (also shorepower)

AC electrical power from a dock pedestal through a shore cord into the boat’s AC system. Use marine-rated cords and GFCIs/ELCIs to reduce shock risk. Related guide

Sidelights (also side lights)

Red (port) and green (starboard) running lights that show other boats which side of you they are looking at. Related guide

Ski boat (also inboard ski boat)

A boat set up for waterskiing or barefooting with a flatter wake and strong low-speed pull; often a direct-drive inboard. Related guide

Sound signal (also sound-producing device)

A whistle; horn or other device that can make the sound signals required by the navigation rules and by equipment carriage rules. Related guide

Spring commissioning (also de-winterize)

The spring reverse of winterizing: fluids; batteries; safety gear; systems checks and a short shake-down run before the season. Related guide

Spring line (also spring lines)

A dock line led forward or aft at an angle to stop the boat from surging ahead or astern along the dock. Related guide

Stand-on vessel

Under the navigation rules; the vessel that should hold course and speed while the give-way vessel keeps clear — still ready to act if collision risk remains. Related guide

Starting battery (also cranking battery)

A battery designed to deliver a short burst of high current to start the engine; not meant for deep discharge of house loads. Related guide

Sterndrive (also I/O, inboard/outboard, stern drive)

An inboard engine paired with a steerable outdrive through the transom (also called I/O). Common on runabouts and cruisers. Related guide

T

Tacking

Turning a sailboat’s bow through the wind so the sails fill on the opposite side. Used to progress upwind in a zigzag. Related guide

Throwable PFD (also Type IV PFD, throwable)

A Coast Guard–approved flotation device you throw to someone in the water (cushion or ring) rather than wear. Required on many boats 16 ft and longer. Related guide

Tongue weight

The downward force the loaded trailer coupler puts on the tow-vehicle hitch. Too little or too much hurts stability; makers often target about 5–15% of trailer weight. Related guide

Transom

The flat (or nearly flat) back face of the hull where outboards mount and the HIN is usually stamped. Related guide

Trim tabs

Small adjustable planes on the transom that help level the boat side-to-side or bring the bow down for a better running angle.

Tritoon (also tri-toon)

A pontoon boat with three tubes instead of two; often able to handle more horsepower and weight than a two-tube pontoon. Related guide

U

USCG documentation (also documented vessel, Coast Guard documentation)

Federal vessel documentation through the National Vessel Documentation Center — an option for eligible vessels instead of (or alongside) some state title practices. Related guide

V

VDS (also visual distress signals, visual distress signal)

Visual distress signals — flares; smoke signals or electric lights used to show you need help. Carriage rules depend on boat length; waters and day vs night. Related guide

Vessel Safety Check (also VSC)

A free courtesy exam by the Coast Guard Auxiliary (or Power Squadrons) of required and recommended safety gear. Passing boats can display a decal. Related guide

VHF (also VHF radio, VHF-FM, marine VHF)

Very High Frequency marine radio used for distress; safety and ship-to-ship or ship-to-shore voice (and DSC) on assigned channels. Related guide

W

Wake boat (also wakeboard boat)

A boat designed to shape a large; rideable wake for wakeboarding or wakesurfing; often with ballast and surf systems. Related guide

Windlass

A deck winch that hauls or pays out anchor chain and rode so you do not lift heavy ground tackle by hand. Related guide

Winterizing (also winterize)

Preparing the engine; plumbing; fuel and systems for freezing weather so water does not crack blocks; pumps or tanks. Related guide

Y

Y-valve (also Y valve)

A diverter valve that can send head waste to a holding tank or (where legal) overboard through a treatment device. Many NDZs require it locked to the tank. Related guide