Nautical terms
A
- Abaft Directions & positions
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Farther aft than some reference point on the boat. "Abaft the mast" means somewhere behind the mast.
- Abaft the beam Directions & positions
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Any direction between straight out to the side (abeam) and straight behind (astern).
It matters in the Rules: a vessel coming up from more than 22.5 degrees abaft another's beam is overtaking.
- Abeam (On the beam) Directions & positions
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Straight out to the side of the boat, at roughly a right angle to the keel: about 090 degrees relative on the starboard beam or 270 degrees on the port beam.
- Abstract of title (A/T) Crew, roles & paperwork
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A record (form CG-1332) that anyone may request from the NVDC for a documented vessel, drawn from the ownership documents, mortgages and lien notices filed there. Buyers order one to check for recorded debts before paying.
- ABYC (American Boat and Yacht Council, American Boat & Yacht Council, ABYC standards, ABYC certified technician) Crew, roles & paperwork
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The American Boat and Yacht Council, which sets the standards for designing, building and repairing recreational boats, and certifies marine technicians trained to them.
Examples of ABYC standards BoatUS highlights: CO detectors must be replaced when they expire, bilge pumps need smooth-walled hose, circuits need proper fuses and breakers, and new boats need an ELCI on shore power.
- Aft (After) Directions & positions
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Toward, near or at the stern of the boat. The "aft cabin" is the cabin at the back.
- Ahead (Dead ahead) Directions & positions
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In front of the boat, in the direction the bow points (a relative bearing of about 000 degrees). "Dead ahead" means exactly straight ahead. The opposite is astern.
- Air draft Navigation & charts
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The height of the highest point of your boat above the waterline, including mast, antennas, radar and lights. You need it to judge whether you fit under bridges and overhead power cables.
The Coast Pilot advises boats with masts or antennas to leave extra room under power lines, since electricity can arc across without contact.
- AIS (Automatic Identification System, Class A AIS, Class B AIS) Electrical & electronics
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A radio system that automatically broadcasts a vessel's identity, type, position, course, speed and status to other ships and shore stations and shows theirs. Vessels required to carry it generally use Class A units; the simpler Class B is allowed for some of them and can be fitted voluntarily.
An AIS must be programmed with the boat's official MMSI and kept on and accurate once installed.
- All-round light (All-around light) Rules of the road
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A light that shows all the way around the horizon (360 degrees). A white all-round light serves as an anchor light, and on power boats under 12 m it may replace the masthead light and sternlight.
- Aloft Directions & positions
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Up in the rigging or up the mast. "Going aloft" means climbing or being hoisted up the mast.
- Alternator (Voltage regulator, Regulator) Electrical & electronics
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The engine-driven generator that charges the batteries while the engine runs. It makes AC internally and converts it to DC; a voltage regulator keeps adjusting its output to the right charging voltage.
- America's Boating Club (United States Power Squadrons, USPS) Crew, roles & paperwork
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A volunteer boating safety organization, also known as the United States Power Squadrons, that works with the Coast Guard: its examiners do free Vessel Safety Checks, and it is one of the groups that issue domestic MMSI numbers.
- Amidships (Midships) Directions & positions
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At, near or toward the middle of the boat, lengthwise and sometimes across.
- Anchor Anchoring & mooring
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A device that digs into or grips the bottom so that, through its resistance to being dragged, it holds a vessel within a limited area. Types suit different bottoms; many boats carry two of different styles.
Federal law does not require an anchor on a recreational boat, but BoatUS Foundation recommends one big enough to hold the boat overnight, and the Coast Guard boat crew handbook advises carrying two.
dco.uscg.mil · higherlogicdownload.s3.amazonaws.com · boatus.org · uscgboating.org
- Anchor bridle (Bridle) Anchoring & mooring
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Two snubber lines joined at the anchor chain and led to cleats on each side of the bow (or hulls of a catamaran). Like a snubber it absorbs shock loads, and it also reduces the boat's tendency to swing back and forth at anchor.
In towing, "bridle" also means a two-legged line spreading a tow's load across two fittings.
- Anchor chain (Proof coil, BBB chain, High-test chain) Anchoring & mooring
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Galvanized steel chain used alone or with nylon line in a rode. Common grades are proof coil (general use), BBB (shorter, thicker links, often used with windlasses) and high-test (hardened, stronger and lighter).
- Anchor light (Riding light) Rules of the road
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An all-round white light shown where it can best be seen by a vessel at anchor, from sunset to sunrise and in restricted visibility. Vessels under 50 m may show a single one.
On inland waters a vessel under 20 m anchored in a Coast Guard special anchorage area need not show one, and a vessel under 7 m anchored away from channels and fairways is also excused (Rule 30).
- Anchorage area (Anchorage, Special anchorage area) Anchoring & mooring
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A customary or officially designated area where vessels may anchor, shown on charts. In Coast Guard special anchorage areas, vessels under 20 m need not show anchor lights or sound anchor signals.
higherlogicdownload.s3.amazonaws.com · navcen.uscg.gov · oceanservice.noaa.gov
- Apparent wind (Relative wind) Directions & positions
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The wind you feel on a moving boat: the true wind combined with the wind made by the boat's own motion.
- Astern (Dead astern) Directions & positions
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Behind the boat (a relative bearing of about 180 degrees). "Going astern" also means moving backward, as in putting the engine in reverse.
- Athwartships (Athwartship) Directions & positions
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Across the boat from side to side, at right angles to the centerline, as opposed to fore-and-aft. A berth that runs athwartships lies crosswise.
- Automatic charging relay (ACR) Electrical & electronics
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A relay that senses voltage and automatically connects two battery banks while a charging source is running, then separates them when charging stops, so both get charged but the house loads cannot flatten the starting battery.
Unlike a diode battery isolator, an ACR has no voltage drop to cause incomplete charging. Blue Sea's version connects the banks after seeing 13.0 volts for 2 minutes and separates them after 12.75 volts for 30 seconds.
- Autopilot (Heading sensor, Fluxgate compass, Rudder sensor) Electrical & electronics
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A system that steers the boat on a set heading or route: a heading sensor (often a fluxgate compass) tells a course computer where the bow points, and a drive moves the rudder to correct any error.
The NMEA warns autopilots can fail and invite complacency; their alarms help, but they do not replace a person keeping watch.
B
- Back and fill (Casting) Docking & boat handling
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Turning a single-screw boat in tight space by alternating short bursts ahead and astern: going ahead with the rudder over to swing the bow, then backing and letting prop walk swing the stern, repeating until turned.
- Backfire flame arrestor (Flame arrestor, Flame arrester, BFA) Safety & emergencies
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A device on the air intake of an inboard gasoline engine that stops flame from a backfire escaping into the engine space. Gasoline inboards (not outboards) must have an approved one, secured with a flame-tight connection.
- Backing plate Hull & deck
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A reinforcing plate under the deck behind a cleat, winch or other fitting, which spreads the load so bolts cannot pull through.
The Coast Guard handbook says hardware used for towing should always have backing plates and be through-bolted, not screwed.
- Backstay Sails & rigging
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The stay that runs from the top of the mast down to the stern, keeping the mast from falling forward. On some boats it splits into two legs near deck level.
- Bank effect (Bank suction, Bank cushion) Docking & boat handling
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In a narrow channel or river, water pressure near a steep bank pushes the bow away from it (bank cushion) while the stern is drawn toward it (bank suction), which can suddenly sheer the boat across the channel.
- Barrier coat (Epoxy barrier coat) Maintenance & haul-out
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Several coats of epoxy applied to the bottom under the antifouling paint to cut down water absorption, used to help prevent osmotic blisters or after repairing them.
- Battery bank (House bank, House battery, Starting bank, Starting battery) Electrical & electronics
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A group of batteries wired together. The house bank runs the boat's DC loads; the starting bank is kept for starting the engine. Capacity is rated in amp-hours (what a battery delivers over 20 hours before falling to 10.5 volts); parallel wiring adds amp-hours, series wiring adds voltage.
- Battery charger (Three-stage charging, Multi-stage charger, Float charge) Electrical & electronics
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An AC-powered charger that recharges the batteries. Multi-stage chargers charge in steps, a fast bulk stage first and finally a lower float voltage that keeps a full battery topped up without overcharging.
- Battery switch (Battery selector switch, Paralleling switch, Emergency parallel) Electrical & electronics
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A heavy-duty switch that connects or disconnects the batteries from the boat's circuits. A paralleling switch can tie the house bank to the starting circuit to start the engine in an emergency.
- Beam Hull & deck
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The boat's width at its widest point.
higherlogicdownload.s3.amazonaws.com · oregon.gov · discoverboating.com
- Bearing Navigation & charts
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The direction of one point from another, measured clockwise from 000 degrees, usually from north. You take a bearing on a landmark to fix your position, or on another boat to judge risk of collision.
- Beaufort scale (Beaufort wind force scale) Weather & sea
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A 0 to 12 scale for estimating wind force from what you see on the water, from Force 0 (calm, mirror-like sea) to Force 12 (hurricane, 64 knots or more). For example, Force 4 is 11 to 16 knots with numerous whitecaps; Force 8, 34 to 40 knots, is a gale.
- Bend Lines & knots
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A knot that joins two lines together, such as the sheet bend.
- Bight Lines & knots
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A loop or U-shaped bend formed by doubling a line back on itself without crossing it. The Coast Guard handbook warns never to stand in the bight of a line on deck.
- Bilge (Bilges) Hull & deck
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The lowest part of the inside of the hull, below the floorboards, where water collects. The Coast Guard counts clean bilges as part of keeping a boat in good operating condition.
oregon.gov · discoverboating.com · ionianmarinesurveys.com · uscgboating.org
- Bilge pump (Automatic bilge pump, Manual bilge pump, Float switch) Plumbing, tanks & systems
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A pump that removes water from the bilge. An electric pump can be switched on automatically by a float switch when water rises; manual pumps back it up. Discharge lines often run up through a vented loop before going overboard.
BoatUS Foundation cautions that a bilge pump can hide a leak until it clogs or the battery dies, so find where water is coming from. ABYC standards call for smooth-walled discharge hose rather than corrugated.
- Bill of sale (CG-1340) Crew, roles & paperwork
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The document transferring ownership from seller to buyer. For a documented boat the Coast Guard form CG-1340 is used and filed with the NVDC; in states without boat titles, a bill of sale is key proof of ownership.
- Bitt (Samson post, Sampson post, Mooring bitt) Lines & knots
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A strong vertical post on the foredeck or stern used to secure anchor, mooring or towing lines. A single one at the bow is often called a Samson post.
- Bitter end (Running end) Lines & knots
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The very end of a line. The Coast Guard boat crew handbook uses it for the free end you work with when tying a knot; in anchoring it usually means the inboard end of the rode that must be made fast to the boat.
Many anchors have been lost because the bitter end of the rode was not secured before letting go; BoatUS Foundation lists it as a common anchoring mistake.
- Bleeding the fuel system (Bleeding, Bleed the engine, Lift pump, Air in the fuel) Engines & machinery
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Purging trapped air from a diesel's fuel system, for example after changing filters. On many engines a lift pump pushes fuel through the filters and lines to drive the air out; running the engine several minutes afterward confirms none is left.
- Block (Pulley, Sheave) Sails & rigging
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A pulley in a case. Blocks change the direction of a line or, combined into a tackle, multiply pulling power. The wheel inside that the line runs over is the sheave.
- Blower (Bilge blower, Engine room blower, Powered ventilation) Safety & emergencies
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An exhaust fan that pulls fuel vapors out of an engine or fuel-tank compartment. Gasoline-powered boats need ventilation, and many have a label saying to run the blower at least 4 minutes and sniff the bilge for fumes before starting.
After fueling the Coast Guard advises opening hatches, running the blower at least four minutes and checking by smell for gasoline vapors before starting.
- Boating accident report (Accident report, BAR) Crew, roles & paperwork
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A report the operator or owner must file with the state when a recreational boat is involved in a death, disappearance, injury needing more than first aid, damage of $2,000 or more, or loss of the boat. A death or disappearance must be reported immediately.
State rules can be stricter; check with the state boating law administrator where the accident happened.
- Boating under the influence (BUI) Crew, roles & paperwork
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Operating a boat while impaired by alcohol or drugs, a federal and state offense. Under federal law a blood alcohol content of 0.08 or more (0.10 in some states) brings civil and criminal penalties, and alcohol is the leading known factor in fatal boating accidents.
- Bollard Lines & knots
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A single heavy post on a pier, wharf or large deck to which mooring lines are made fast.
- Bonding system (Bonding, Cathodic protection) Electrical & electronics
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Wiring that connects the underwater metal fittings and engine to each other and to the sacrificial anodes, so they are all protected together. ABYC technicians check this cathodic protection system.
- Boom (Gooseneck) Sails & rigging
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The horizontal spar that holds the bottom edge (foot) of the mainsail. It attaches to the mast at a swiveling fitting called the gooseneck and swings across the boat when tacking or jibing.
- Boom vang (Vang) Sails & rigging
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A tackle or strut from the boom down to the base of the mast that pulls the boom downward, controlling the shape and twist of the mainsail, mainly when reaching and running.
- Bottom paint (Antifouling paint, Antifouling, Ablative paint, Hard paint) Maintenance & haul-out
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Paint containing biocides that keeps barnacles, weed and slime off the hull below the waterline. Ablative paints wear away slowly like a bar of soap, exposing fresh biocide, and don't build up; hard paints leach biocide while the film stays mostly in place.
Ablatives need the boat to move to work; many can be hauled and relaunched without repainting. Check compatibility before putting one type over another.
- Bow Hull & deck
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The front end of the boat. Moving toward it is going forward; the front right is the starboard bow and the front left the port bow.
higherlogicdownload.s3.amazonaws.com · oregon.gov · dco.uscg.mil
- Bow line Docking & boat handling
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A dock line led from the bow of the boat to the dock or a piling.
Not to be confused with the bowline knot.
higherlogicdownload.s3.amazonaws.com · boatus.com · ionianmarinesurveys.com
- Bow roller (Anchor roller) Anchoring & mooring
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The roller fitting at the bow over which the anchor rode runs and where many boats stow the anchor. Measure scope from the height of the roller, not from the water surface.
- Bow thruster (Stern thruster, Thruster) Docking & boat handling
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A small propeller, usually in a tunnel through the hull near the bow (or stern), driven by an electric or hydraulic motor, that pushes the bow (or stern) sideways for docking. With both, a boat can move sideways and turn in place.
Electric thrusters lose much of their thrust if battery voltage drops, and many have limited run times; the maker advises keeping the supply voltage up and changing the thruster's anode.
- Bowline Lines & knots
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A classic knot that makes a fixed loop in the end of a line that will not slip or jam and is easy to untie after being loaded.
Not to be confused with the bow line, the dock line that runs from the bow.
- Breaking strength (BS, Tensile strength) Lines & knots
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The load in pounds at which a new line parts. Knots can cut a line's strength by half or more, and a splice keeps more strength than a knot.
- Breast line Docking & boat handling
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A dock line run out sideways from the boat to the dock at roughly a right angle, as opposed to a spring line, which runs at a shallow angle along the boat.
- Broach (Broaching) Docking & boat handling
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When a following sea pushes the stern around so the boat is thrown broadside to the waves or surf.
The Coast Guard handbook advises steering quickly into any sideways movement of the stern in following seas.
- Bulkhead Hull & deck
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An upright wall inside the boat dividing compartments. Many are structural, adding strength, and some are watertight.
higherlogicdownload.s3.amazonaws.com · boatus.com · discoverboating.com
- Bulwark Hull & deck
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An extension of the hull side above the deck forming a solid wall around its edge.
C
- Can buoy (Can) Navigation & charts
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An unlighted buoy whose top is shaped like a cylinder. In the US system cans are green with odd numbers and mark the port (left) side of a channel when returning from sea.
- Capacity plate (Maximum capacity plate) Safety & emergencies
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A label on many smaller boats showing the maximum number of people and weight the boat can safely carry. Do not exceed it; load evenly and keep weight low.
If there is no plate, the Coast Guard suggests asking the builder or a naval architect; its rule of thumb (length times width divided by 15, for 150-pound people) does not account for boat volume.
- Capstan (Rope drum, Warping drum) Anchoring & mooring
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The smooth drum on a windlass used for hauling rope, such as a rope rode or a dock line, by taking turns around it.
- Captain's license (OUPV, Six-pack license, Merchant Mariner Credential, Master license) Crew, roles & paperwork
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A Coast Guard credential needed to carry passengers for hire. The entry-level OUPV ("six-pack") endorsement covers uninspected boats with six or fewer paying passengers; a Master endorsement is needed for inspected vessels carrying more.
No Coast Guard license is needed to run your own boat for pleasure, though states may have boater education rules. OUPV endorsements are not valid on international voyages. Applications go through a Coast Guard Regional Exam Center.
- Carbon monoxide (CO, CO poisoning) Safety & emergencies
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A colorless, odorless poisonous gas in engine and generator exhaust. It can build up in cabins and around the swim platform and rear deck, and it injures or kills boaters every year.
The Coast Guard advises keeping people off the swim platform and away from the rear deck while engines or the generator run, and keeping engines well maintained.
- Cast off (Let go) Lines & knots
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To untie and release the lines holding the boat to a dock or mooring, so it can get underway; also to release a single line on command.
- Catenary Anchoring & mooring
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The natural sag in an anchor chain or rode caused by its own weight. The sag acts like a spring and keeps the pull on the anchor low; in strong winds the chain straightens and that cushioning is lost.
higherlogicdownload.s3.amazonaws.com · practical-sailor.com · vikinganchors.com
- Cavitation (Ventilation) Docking & boat handling
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When a propeller loses grip because low-pressure bubbles form on its blades, or air is drawn in from the surface: the engine races, thrust drops and the prop can be damaged. Easing the throttle and then building speed gradually restores thrust.
- Certificate of Documentation (COD, CG-1270, Recreational endorsement) Crew, roles & paperwork
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The Coast Guard document (form CG-1270) issued for a documented vessel. A recreational boat's certificate carries a recreational endorsement and can be renewed for 1 to 5 years; the original, current certificate must be kept aboard.
- Chafing gear (Chafe gear, Chafe guard) Lines & knots
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Protective material or sleeves placed where a line rubs on a chock, rail or edge, to stop it wearing through.
The Coast Guard handbook calls for chafing gear where an anchor rode passes through the chocks, and snubber tests found lines can fail without warning.
- Chain stopper (Chain compressor, Chain lock) Anchoring & mooring
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A fitting between the windlass and the bow roller that grips the anchor chain and takes the load off the windlass once the anchor is down or stowed.
- Chainplate (Chainplates, Chain plate) Sails & rigging
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A strong metal fitting at deck level, fastened to the boat's structure, where a shroud or stay attaches so the rig's load passes into the hull.
Where chainplates pass through the deck they can leak; BoatUS lists weeping chainplates as a red flag, and hidden corrosion there can lead to rig failure.
usna.edu · icdept.cgaux.org · boatus.com · boatus.org · boatus.com
- Channel 16 (VHF channel 16, 156.800 MHz) Safety & emergencies
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The international VHF-FM distress, safety and calling channel. Boats with a VHF radio switched on should monitor 16 (or channel 9, the recreational calling channel) when not talking; after first contact, move to a working channel.
The Coast Guard asks boaters not to use channel 16 for radio checks or general chat.
- Chart datum (Sounding datum) Navigation & charts
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The reference water level that chart depths are measured from. On NOAA charts of tidal waters it is Mean Lower Low Water, so most of the time there is more water than charted. The Great Lakes and non-tidal inland waters use a separate Low Water Datum.
Lower-than-average low tides, shown as minus tides in the tide tables, leave less water than the chart shows.
Sources disagree on year mean lower low water became chart datum for all US marine waters — left out rather than guessed. Check your local authority.
nauticalcharts.noaa.gov · tidesandcurrents.noaa.gov · tidesandcurrents.noaa.gov
- Chart scale (Scale) Navigation & charts
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The ratio between a distance on the chart and the real distance: on a 1:10,000 chart, one inch equals 10,000 inches. Large-scale charts show a small area such as a harbor in great detail; small-scale charts cover more area with less detail.
NOAA advises using the largest-scale chart available near shore, because smaller-scale charts may leave out some hazards.
- Chartplotter (Chart plotter) Electrical & electronics
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An electronic navigation display that shows the boat's GPS position on electronic charts, used to plan and follow routes. Many can also overlay radar on the chart.
- Chine (Hard chine, Soft chine) Hull & deck
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Where the bottom of the hull meets the sides. A hard chine is a sharp angle; a soft chine is rounded. Chine shape affects speed and turning.
- Chock (Bow chock, Fairlead chock) Lines & knots
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A smooth, open or closed fitting, usually at the rail, that guides a dock or anchor line over the edge of the deck to reduce chafe and keep the lead fair.
- Chop (Choppy) Weather & sea
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Short, breaking waves. A "choppy" sea is covered with them, even when the waves are not high.
- Circuit breaker (Breaker, Overcurrent protection) Electrical & electronics
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A switch-like device that opens a circuit automatically when current gets too high, protecting the wire from overheating. Unlike a fuse, which melts and must be replaced, a breaker can be reset.
ABYC standards call for the right fuses and breakers so wiring cannot overheat and start a fire.
- Claw anchor (Bruce anchor) Anchoring & mooring
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A one-piece anchor with a scoop of claws that lets the boat swing all the way round without breaking the anchor out. It performs much like a plow anchor at a lower weight.
- Cleat (Horn cleat) Lines & knots
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An anvil-shaped deck or dock fitting with two horns, used to make lines fast. Cam or wedge cleats on sailboats hold a line ready for quick release.
higherlogicdownload.s3.amazonaws.com · boatus.com · usna.edu
- Cleat hitch (Making fast to a cleat) Lines & knots
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The standard way to secure a line to a horn cleat: a full turn around the base, then figure-eights over the horns. The Coast Guard handbook calls for at least three figure-eights when securing a loaded line.
- Clove hitch Lines & knots
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A quick hitch of two turns crossing over each other, used to fasten a line to a rail, spar, ring or post. A slipped version releases fast, which is handy for fenders.
- Coaming Hull & deck
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A raised rim around a cockpit, hatch or other opening that keeps water on deck from running below.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Coast Guard Auxiliary (USCG Auxiliary, CG Aux) Crew, roles & paperwork
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The Coast Guard's uniformed civilian volunteer arm. Members teach boating safety courses, carry out free Vessel Safety Checks and help with patrols and aids-to-navigation checks.
- Coast Guard boarding (Boarding, Heave to for boarding) Crew, roles & paperwork
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The Coast Guard may board any US vessel at any time to check documents and safety equipment. When hailed, a boat underway must stop ("heave to") or maneuver as directed so the team can come aboard; afterward you receive a boarding report.
Other federal, state and local officers may also board and inspect. A boarding officer can end a voyage for especially hazardous conditions such as missing fire extinguishers or a fuel leak.
- Coast Pilot (United States Coast Pilot) Navigation & charts
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NOAA's series of books that add what charts cannot show: navigation regulations, landmarks, channel and anchorage details, dangers, weather, currents, bridges and port facilities for US coastal waters and the Great Lakes.
- Coastal waters forecast (Marine forecast, CWF) Weather & sea
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The NWS forecast for coastal and Great Lakes waters, issued four times a day by local offices, giving wind speed and direction, wave heights, visibility and weather, plus any advisories and warnings.
- Cockpit Hull & deck
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The recessed open deck area, usually aft, from which the boat is handled or where crew and guests sit. A self-bailing cockpit drains overboard through scuppers.
- Coil (Coil down) Lines & knots
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To gather the loose end of a line into neat loops for stowing, usually after making it fast. Three-strand line is often coiled clockwise; coiling in figure-eights avoids kinks.
- Cold front (Front) Weather & sea
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The leading edge of a colder air mass pushing in and replacing warmer air. A front in general is the boundary between two air masses of different temperature.
- Cold water immersion (Cold shock, Cold incapacitation) Safety & emergencies
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What happens in the first minutes after falling into cold water: an uncontrolled gasp and rapid breathing (cold shock) that can cause drowning, then, within about 10 minutes, loss of useful movement in hands, arms and legs, well before hypothermia sets in.
This is a key reason to wear a life jacket rather than just carry one.
- Companionway Hull & deck
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The entryway and steps leading from the deck or cockpit down into the cabin.
- Compass rose Navigation & charts
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The circle printed on a chart, marked in degrees clockwise from 000, used to measure directions. Each rose also shows the local magnetic variation, the year it applies to, and its annual change.
dco.uscg.mil · oceanservice.noaa.gov · nauticalcharts.noaa.gov
- Compression test Maintenance & haul-out
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A test of how well each cylinder holds pressure, used in engine surveys, particularly on older engines, to show whether seals need replacing or the cylinders and pistons have problems.
- Constrained by her draft (CBD, Vessel constrained by her draft) Rules of the road
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International Rules only: a power-driven vessel so deep for the available depth and width of water that it can barely leave its track. It may show three all-round red lights in a vertical line or a cylinder, and others should avoid impeding it.
The Inland Rules have no such category; the definition is marked "reserved" there.
- Cored hull (Core, Balsa core, Cored deck, Sandwich construction) Hull & deck
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Construction with a lightweight core, commonly end-grain balsa or foam, sandwiched between two fiberglass skins to make a stiff, light deck or hull.
Water leaking in around deck hardware can soak and rot the core, often without visible signs at first; surveyors look for it with moisture meters and hammer sounding.
- Course Navigation & charts
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The direction a boat is steered, or intended to be steered, through the water, measured in degrees from north (true or magnetic, so say which).
- Course over ground (COG, Track) Navigation & charts
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The direction you are actually moving over the bottom, as shown by GPS, after wind and current have had their effect. It can differ from both your heading and your steered course.
- Cross-track error (XTE, XTK) Navigation & charts
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How far you are to port or starboard of the straight line between two waypoints, as shown by a GPS, plotter or autopilot, usually with an arrow showing which way to steer back.
Starting a new "Go To" redraws the line from your present position, so a zero cross-track error may no longer mean you are on the safe track you planned.
- Crossing situation Rules of the road
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Two power-driven vessels crossing with risk of collision: the one that has the other on her own starboard side keeps out of the way and, if possible, avoids crossing ahead of her (Rule 15).
A quick check the Coast Guard gives: if you see another vessel's red sidelight on your starboard side at night, you are the give-way vessel.
- Cutless bearing (Cutlass bearing, Strut bearing) Engines & machinery
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A sleeve bearing with a grooved rubber lining that supports the propeller shaft, usually in the strut (the bracket under the hull) or at the end of the shaft tube. Water flowing through the grooves lubricates it and flushes out grit.
Cutless is a registered trade name of Duramax Marine; "cutlass" is the common spelling. Surveyors check struts and bearings at haul-out.
duramaxmarine.com · higherlogicdownload.s3.amazonaws.com · practical-sailor.com · boatus.com
- Cutter (Cutter rig) Sails & rigging
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A single-masted sailboat like a sloop but with the mast farther aft, leaving room for two headsails set one behind the other.
D
- Danger signal (Doubt signal, Five short blasts) Rules of the road
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At least five short, rapid blasts on the whistle, sounded when you do not understand another vessel's intentions or doubt it is doing enough to avoid a collision (Rule 34(d)). It may be backed up with five or more short, rapid flashes.
- Day shape (Shapes) Rules of the road
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Black balls, cones, diamonds or cylinders hoisted by day to show a vessel's status, the daytime match for special lights. Examples: one ball forward at anchor, a cone point-down when motor-sailing, two balls when not under command.
- Daybeacon (Daymark, Dayboard) Navigation & charts
-
An unlighted aid fixed on a post or piling, carrying a dayboard whose shape and color show which side to pass: green squares with odd numbers mark the left side and red triangles with even numbers the right side when returning from sea.
nauticalcharts.noaa.gov · pdept.cgaux.org · dco.uscg.mil · uscgboating.org
- Dead reckoning (DR) Navigation & charts
-
Working out your position from your last known position plus the course steered, speed and time run, without outside references. Comparing a DR position with a fix shows how much current and wind have moved you.
- Deadrise (Deep-V, Modified-V) Hull & deck
-
The angle of the V in a hull's bottom, usually measured at the transom of planing powerboats. A deep-V hull has sharp deadrise, typically more than 20 degrees; a modified-V has less than 20; a flat-bottom boat has little or none.
- Deep-cycle battery (Deep cycle) Electrical & electronics
-
A battery built with thick plates so it can be discharged deeply and recharged over and over, as house batteries are.
- Delamination (Voids) Maintenance & haul-out
-
Separation of the layers of a fiberglass laminate, which weakens the structure. Surveyors treat it, with structural rot and a separating hull-to-deck joint, as a potential deal-breaker.
- Demarcation line (COLREGS demarcation line) Rules of the road
-
A line, printed on charts and listed in 33 CFR 80, that divides the high seas from US harbors, rivers and other inland waters. It decides whether the Inland Rules or the International Rules apply where you are.
- Dense fog advisory Weather & sea
-
An NWS marine advisory for fog cutting visibility to a regionally set limit, never more than 1 nautical mile.
- Depth sounder (Echo sounder, Depth finder, Fishfinder, Transducer) Electrical & electronics
-
An instrument that measures water depth by timing a sound pulse from a transducer on the hull to the bottom and back. Fishfinders use the same sonar to show fish and bottom structure.
A through-hull transducer is a hole in the boat; BoatUS Foundation warns removable ones must be locked in place or they can work loose and sink the boat.
- Deviation (Compass deviation) Navigation & charts
-
The error in your own boat's compass caused by magnetic influences close to it. It changes as the boat turns, so after the compass is adjusted the boat is "swung" through different headings to record the leftover error in a deviation table.
Total compass error is variation and deviation added together.
- Dew point Weather & sea
-
The temperature to which air must cool to become saturated. Cool the air further and the moisture condenses as dew, or over water as fog.
- Diesel engine (Diesel) Engines & machinery
-
An engine built much like a gasoline engine but with no carburetor or spark ignition: an injection pump meters fuel at high pressure to injectors in the cylinders. Its precision fuel parts need clean, water-free fuel.
BoatUS Foundation cites repair data blaming about 90 percent of diesel problems on contaminated fuel, which is why filters and tank care come first.
- Digital selective calling (DSC, DSC distress button) Electrical & electronics
-
A digital feature of modern VHF and HF radios that can "dial" and "ring" other radios directly and, with one button, send an automatic distress alert with the boat's identity and, if a GPS is connected, its position.
It works only with an MMSI programmed in; the Coast Guard recommends connecting the GPS to the radio. Hold the red distress button about 5 seconds, then continue on channel 16.
- Displacement Hull & deck
-
The weight of a boat, equal to the weight of the water it pushes aside when floating. Light displacement excludes fuel, water, gear and people; loaded displacement includes them.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Displacement hull Hull & deck
-
A hull that always moves through the water, pushing it aside, rather than climbing on top. Trawlers typically have one. Adding power beyond hull speed takes excessive power for little gain.
- Distress flag (Orange distress flag) Safety & emergencies
-
An orange flag at least 3 by 3 feet with a black square and a black ball, marked as meeting Coast Guard requirements. It counts as a day-only visual distress signal and is most visible waved on a boat hook or flown from a mast.
- Distress signals (Annex IV signals) Rules of the road
-
The signals listed in Annex IV of the Rules that mean "in distress and need help": a continuous fog signal, red flares, orange smoke, SOS, "Mayday" by radio, a DSC distress alert, an EPIRB signal, and slowly raising and lowering outstretched arms, among others.
Using any of these signals except in real distress is prohibited. Inland rules also recognize a high-intensity white light flashing 50 to 70 times a minute.
- Dock lines (Mooring lines) Lines & knots
-
The lines that hold a boat to a dock, pier or slip: bow line, stern line, spring lines and sometimes breast lines. Nylon is common because its stretch absorbs surges.
boatus.com · higherlogicdownload.s3.amazonaws.com · boatus.org
- Documentation (USCG documentation, Federal documentation, Documented vessel) Crew, roles & paperwork
-
Federal registration of a boat by the Coast Guard's National Vessel Documentation Center, an alternative to state numbering. The boat must measure at least 5 net tons and be owned by a US citizen. It proves nationality abroad and allows a preferred ship mortgage.
Documented boats still follow federal equipment rules and may still owe state fees, taxes or a state use decal.
- Double-braid line (Braid-on-braid, Double braid) Lines & knots
-
Rope made of a braided core inside a braided cover. Double-braided nylon is strong and elastic, and the Coast Guard handbook prefers it for lines that bear a load.
- Draft (Draught) Hull & deck
-
How deep the boat reaches below the waterline, measured to the lowest point of the keel, or of the propeller, rudder or skeg if they hang lower. It is the least depth of water the boat can float in.
Draft is not fixed: it changes with how the boat is loaded and trimmed.
higherlogicdownload.s3.amazonaws.com · oregon.gov · discoverboating.com
- Dragging (Dragging anchor) Anchoring & mooring
-
When the anchor fails to hold and slides across the bottom, letting the boat drift. Signs include bearings or ranges to shore changing while the boat should only be swinging.
- Drift (Drift of current) Weather & sea
-
The speed of a current, in knots; also the distance a boat is carried by current and wind. A boat left drifting moves with wind and current without control.
- Dripless shaft seal (Dripless seal, PSS seal, Face seal, Mechanical shaft seal) Engines & machinery
-
A shaft seal that does not drip, used in place of a stuffing box. A common type presses a stainless collar fixed to the shaft against a carbon face held on the shaft tube by a rubber bellows.
One maker (PSS) advises replacing the bellows every six years and says boats faster than about 12 knots need a water feed to the seal; slower boats can simply vent it above the waterline.
E
- Ebb (Ebb current, Ebb tide) Weather & sea
-
The tidal current flowing away from shore or down a river or estuary, as the tide goes out.
- ELCI (Equipment leakage circuit interrupter) Electrical & electronics
-
A device on a boat's shore power system that interrupts the circuit when AC current leaks from it, guarding against stray AC in the water that can cause electric shock drowning. ABYC standards require one on new boats.
- Electronic visual distress signal device (eVDSD, Electric distress light, Distress light) Safety & emergencies
-
A battery-powered light that automatically flashes SOS and is certified to Coast Guard or RTCM standards. It meets the night-time visual distress signal requirement without the fire risk of flares.
A plain high-intensity white strobe is recognized as a distress signal on inland waters, but it does not satisfy the carriage requirement.
- Engine cut-off switch (ECOS, Kill switch, Engine cut-off switch link, Lanyard) Safety & emergencies
-
A switch, usually with a lanyard clipped to the operator, that stops the engine if the operator is thrown from the helm. On boats under 26 feet that have one, federal law requires the operator to use it when running on plane or above displacement speed.
- Engine hours (Hour meter, Hours, Elapsed time meter) Engines & machinery
-
The total running time recorded by the engine's hour meter. Engine manuals set service intervals (oil, filters, impeller, injectors) in hours, so the meter and the maintenance log together show what is due.
- Engine survey (Mechanical survey) Maintenance & haul-out
-
A separate inspection of propulsion and generator engines by a mechanic trained on that make, covering controls, electrical, cooling and exhaust systems and engine mounts, with temperature and compression checks and usually oil samples.
BoatUS notes most general surveyors are not qualified to run in-depth engine diagnostics, so hire a specialist when engines are a big part of the boat's value.
- EPIRB (Emergency Position Indicating Radio Beacon, 406 MHz EPIRB) Safety & emergencies
-
A marine distress beacon that sends a coded 406 MHz signal via satellite to rescue authorities, often with a GPS position, plus a homing signal and strobe. Category I units float free and switch on automatically if the boat sinks; Category II are manual.
US-coded 406 MHz beacons must be registered with NOAA (free) and the registration renewed every two years. Mount a Category I unit outside the cabin where it can float free.
- Exhaust elbow (Mixing elbow, Water-injected exhaust elbow, Wet exhaust, Muffler) Engines & machinery
-
The fitting on the exhaust manifold where raw cooling water is sprayed into the hot exhaust, cooling it so it can run through rubber hose and a muffler and out of the boat.
Westerbeke calls for checking its passages for carbon and corrosion; BoatUS Foundation notes backfires and corrosion can hole mufflers and let water into the boat.
- Eye splice (Eye) Lines & knots
-
A permanent loop worked into the end of a line by tucking the strands back into it. A splice keeps much more of the line's strength than a knot and is the usual eye on dock lines and anchor rodes.
F
- Fairlead Lines & knots
-
Any fitting, such as a block, chock, ring or roller, that changes a line's direction and guides it smoothly, reducing chafe and friction.
- Fake down (Flake, Flake down) Lines & knots
-
To lay a line out on deck in long, flat loops or figure-eights so it can run out freely without kinks or tangles, for example before anchoring.
- Fathom Navigation & charts
-
A unit of depth equal to six feet. Some charts give soundings in fathoms, so always check which unit a chart uses.
- Fender (Bumper) Docking & boat handling
-
A cushion hung over the side to protect the hull from the dock, pilings or another boat. The Coast Guard handbook says never to fend off by hand or foot; use a fender.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · boatus.org
- Fetch Weather & sea
-
The stretch of open water over which the wind blows from one direction, and its length. Wind blowing over a long fetch builds bigger seas than the same wind over a short one.
- Fiberglass (FRP, GRP, Glass-reinforced plastic) Hull & deck
-
The material most production boats are built from: glass fibers, woven or chopped, set in resin and laid up in a mold. The structure is built from layers called laminates.
- Figure-eight knot (Figure eight, Stopper knot) Lines & knots
-
An overhand knot with an extra twist, tied in the end of a line to stop it running out through a block or fairlead.
- Fin keel (Full keel, Long keel) Hull & deck
-
A sailboat keel shaped like a fish's fin: shorter fore-and-aft and deeper than a full (long) keel, which runs much of the hull's length.
- Fire extinguisher (Portable fire extinguisher) Safety & emergencies
-
Boats with closed living spaces, closed compartments where fuel or flammables are stored, unsealed double bottoms or permanent fuel tanks must carry Coast Guard-approved, marine-type hand-portable extinguishers: 5-B or 20-B for boats built 2018 and later. The number required depends on length.
Boats of model year 2017 or older may keep B-I or B-II extinguishers until they are no longer serviceable. Non-rechargeable units expire 12 years from the date stamped on the bottom.
- Fire extinguisher ratings (Class A fire, Class B fire, Class C fire, 5-B, 20-B) Safety & emergencies
-
The letter shows the kind of fire an extinguisher is for: A for ordinary combustibles (wood, paper, trash), B for flammable liquids like fuel, oil and grease, C for energized electrical equipment. The number shows how much agent it holds; a higher number is bigger.
Boats must carry Class B marine-type extinguishers; a multipurpose "A:B:C" unit is fine if its B rating and Coast Guard approval meet your boat's requirement.
- Fix (Position fix) Navigation & charts
-
A position found without relying on a previous one, for example where two or more lines of position cross, or a latitude and longitude from GPS.
- Fixed fire extinguishing system (Engine room fire system, Automatic fire extinguisher) Safety & emergencies
-
A Coast Guard-approved extinguishing system permanently installed to protect the engine compartment. Having one reduces the number of portable extinguishers the boat must carry.
- Flare (Pyrotechnic distress signal, Aerial flare, Hand-held flare) Safety & emergencies
-
A pyrotechnic visual distress signal: hand-held or aerial red flares (day and night), parachute flares and red meteors, or orange smoke (day only). If you rely on pyrotechnics you need at least three for day and three for night; some combination flares count for both.
Pyrotechnics expire 42 months after manufacture; expired ones may be kept as extras but do not count. Store them cool and dry, and handle aerial launchers with care.
- Flemish (Flemish down, Flemishing) Lines & knots
-
To coil a line flat on the deck in a tight spiral, like a mat, for a neat appearance. It is for tidiness, not for a line that must run out quickly.
- Float plan Safety & emergencies
-
A written note, left with a responsible person ashore, of who is aboard, a description and photo of the boat, where you are going and when you expect to be back, so they know when and where to have a search started.
- Flood (Flood current, Flood tide) Weather & sea
-
The tidal current flowing toward shore or up a river or estuary, as the tide comes in.
- Fluke (Flukes) Anchoring & mooring
-
The flat, pointed parts of an anchor that dig into the bottom and give it holding power.
- Fluke anchor (Danforth anchor, Lightweight anchor) Anchoring & mooring
-
A lightweight anchor with two long, flat, pivoting flukes that bury in the bottom. It holds very well for its weight and works best in hard sand or mud.
- Flybridge (Flying bridge) Hull & deck
-
A raised, second-level helm station on top of a powerboat's cabin, above the main helm, giving the operator a better view.
A flybridge adds height, so check your air draft for bridges.
- Fog (Advection fog, Radiation fog) Weather & sea
-
A cloud of tiny water droplets at the surface cutting visibility below about half a nautical mile. Advection fog forms when moist air moves over colder water; radiation fog forms on calm, clear nights and usually clears after sunrise.
- Fog signals (Sound signals in restricted visibility) Rules of the road
-
Rule 35 signals in or near restricted visibility, at intervals of no more than 2 minutes: one prolonged blast for a power-driven vessel making way; two when stopped; one prolonged and two short for sailing, fishing, towing, NUC or RAM vessels.
At anchor, ring a bell rapidly for about 5 seconds each minute. Boats under 12 m need not use these exact signals but must make some other efficient sound signal at least every 2 minutes.
- Following sea (Following seas) Docking & boat handling
-
Waves coming from astern, moving the same way as the boat. They can lift the stern, make steering hard and lead to broaching.
The Coast Guard handbook notes a transom stern gives these waves a large surface to push on.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Forward (Fore) Directions & positions
-
Toward the bow, or at the front part of the boat. "Go forward" means walk toward the bow.
- Forward of the beam Directions & positions
-
Any direction between straight out to the side (abeam) and straight ahead.
Rule 19 speaks of fog signals heard "forward of the beam": if you hear one and have not ruled out risk of collision, slow to the least speed that keeps you on course.
- Freeboard Hull & deck
-
The height of the boat's side above the water, from the waterline up to the deck or gunwale. High freeboard and superstructure give the wind more to push on, which affects handling at low speed.
higherlogicdownload.s3.amazonaws.com · oregon.gov · discoverboating.com
- Freshwater cooling (Closed cooling, Coolant, Antifreeze, Coolant recovery tank) Engines & machinery
-
The sealed loop of coolant (antifreeze and water) that circulates through the engine and the heat exchanger. A recovery tank lets the coolant expand and return as it heats and cools without loss.
Westerbeke recommends a 50-50 mix of antifreeze and distilled water all year, stronger if the local winter requires it.
- Fuel filter (Fuel filter/water separator, Primary filter, Secondary filter, Water separator) Engines & machinery
-
Diesels use two stages: a primary filter/water separator between tank and engine, often with a clear bowl that shows water and dirt, and a finer secondary filter on the engine. Change them on the engine maker's schedule or when dirty.
BoatUS Foundation: water in the bowl means water in the tank, and a clogged primary filter is often the first sign of tank sediment stirred up in rough water.
- Fuel injector (Injector, Injection pump, Fuel injection pump) Engines & machinery
-
On a diesel, the injection pump pressurizes and times the fuel, and an injector in each cylinder sprays it in. Both are precision parts that need clean, water-free fuel and specialist service.
Westerbeke calls for testing injectors at about 750 hours and warns owners not to open the pump. BoatUS Foundation notes a drop of water reaching a cylinder can blow the tip off an injector.
- Fuel polishing (Diesel bug, Fuel algae, Fuel biocide) Maintenance & haul-out
-
Pumping the fuel out of a tank and circulating it through filters to remove water, sediment and microbial growth, then returning it. Microbes (algae and fungi) grow where water sits in diesel, so fuel should be kept dry and treated with a biocide.
BoatUS Foundation suggests drawing a sample from the very bottom of the tank every couple of years; keeping tanks topped off reduces condensation.
G
- Gale warning Weather & sea
-
An NWS warning of sustained winds or frequent gusts of 34 to 47 knots (39 to 54 mph), forecast or occurring, not directly tied to a tropical cyclone.
- Galvanic corrosion (Galvanic series, Dissimilar metals) Electrical & electronics
-
Corrosion that happens when two different metals are electrically connected in water: the less noble metal (lower on the galvanic series) acts as the anode and wastes away, protecting the more noble one.
Boaters often call this "electrolysis", but that term strictly means chemical change caused by an electric current.
- Galvanic isolator Electrical & electronics
-
A device wired into the green grounding wire of the shore power cord that blocks small DC galvanic currents from flowing through the shore ground wire, while still letting AC fault current pass. Most are a pair of diodes.
An isolation transformer does a similar job by coupling shore power to the boat magnetically, with no direct wire connection to the dock.
- Garbage placard (MARPOL placard, Waste management plan) Crew, roles & paperwork
-
Federal rules (MARPOL Annex V) ban dumping plastic anywhere and any garbage in US navigable waters. Ocean-going boats 40 feet and longer with a galley and berths also need a written waste management plan naming the person in charge.
- Gelcoat (Gel coat) Hull & deck
-
The smooth, colored outer layer of resin on a fiberglass boat, applied first in the mold. It gives the shine and some protection, but water can slowly pass through it.
- Generator (Genset) Engines & machinery
-
A separate gasoline or diesel engine driving an electric generator, used for AC power away from the dock.
BoatUS notes engine surveys cover generator engines as well as propulsion engines. Generator exhaust carries carbon monoxide like any engine's.
- Give-way vessel Rules of the road
-
The vessel the Rules require to keep out of the way of another. Rule 16 says it must act early and substantially so that it stays well clear.
The Coast Guard stresses that the Rules do not grant rights, they impose responsibilities, so it avoids the phrase "right of way".
- Global Positioning System (GPS) Navigation & charts
-
The US satellite system that gives a receiver its position, speed and time anywhere, in any weather. Chartplotters use it to show your position, and a DSC radio connected to GPS sends your position with a distress alert.
nauticalcharts.noaa.gov · oceanservice.noaa.gov · icdept.cgaux.org · uscgboating.org
- Glow plug (Glow plugs, Preheat) Engines & machinery
-
A small electric heater in each cylinder of many small diesels that warms the combustion chamber for starting. It is switched on with the preheat button before and during cranking; overusing it can burn the plugs out.
- Gray water (Graywater, Drain water) Plumbing, tanks & systems
-
Used water from sinks and showers, as distinct from toilet waste (sewage). On many boats it drains overboard through its own through-hulls or is pumped from a sump.
- Ground tackle Anchoring & mooring
-
All the gear used to anchor: the anchor, its chain and line (the rode), and the shackles, swivels and fittings that join them and fasten them to the boat.
- Gunwale (Gunnel) Hull & deck
-
The upper edge of the boat's side, where hull meets deck. Pronounced "gunnel".
higherlogicdownload.s3.amazonaws.com · oregon.gov · boatus.com
- Gust Weather & sea
-
A sudden, brief increase in wind speed followed by a lull. NWS uses the term when peaks and lulls differ by 10 knots or more.
- Gypsy (Wildcat, Chainwheel) Anchoring & mooring
-
The windlass wheel with shaped pockets that grip the chain links as it hauls or lets out the rode. Each gypsy fits one chain size, and some are made to handle both rope and chain.
Replacement chain must be the size the gypsy is made for.
H
- Hailing port Crew, roles & paperwork
-
The US place name that a documented vessel shows with its name on the hull, usually on the stern, in letters at least 4 inches high.
- Halyard (Main halyard, Jib halyard) Sails & rigging
-
A line used to hoist a sail (or a flag) up the mast and to lower it.
- Hatch Hull & deck
-
An opening in the deck with a cover, for access, light or ventilation. Deck hatches should seal watertight when closed.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Haul-out (Short haul, Quick haul, Haul out) Maintenance & haul-out
-
Lifting a boat out of the water, usually in the slings of a lift, for bottom painting, repairs, storage or inspection. A short (quick) haul takes an hour or less, long enough for a surveyor to check the bottom.
At haul-out a surveyor looks for water intrusion, delamination and blisters and checks props, anodes, struts, rudders, thrusters and trim tabs.
- Hawsepipe (Hawsehole, Hawse pipe) Hull & deck
-
A pipe or opening through the deck or bow through which the anchor rode runs, usually down into the chain or rope locker below.
higherlogicdownload.s3.amazonaws.com · ionianmarinesurveys.com · discoverboating.com
- Head sea (Head seas) Docking & boat handling
-
Waves coming from ahead, against the boat's course.
- Head-on situation (Meeting situation) Rules of the road
-
Two power-driven vessels meeting on opposite or nearly opposite courses with risk of collision. Each turns to starboard so they pass port side to port side (Rule 14). At night you would see the other's masthead lights in line and both sidelights.
- Heading Navigation & charts
-
The direction the bow is actually pointing at a given moment, in degrees. Wind and current can make your heading differ from the path you actually travel over the bottom.
- Headway Docking & boat handling
-
Forward movement of the boat through the water. The opposite is sternway.
- Heat exchanger Engines & machinery
-
A tank of small tubes in which raw water flowing through the tubes carries heat away from the engine coolant flowing around them, so seawater never circulates inside the engine itself.
Westerbeke calls for removing, cleaning and pressure-testing it about every 1,000 hours (sooner in silty or tropical water) and checking the zinc pencil inside monthly.
- Heave to (Heaving to, Hove to) Docking & boat handling
-
To stop or nearly stop the boat and hold it roughly in place. The Coast Guard uses it to mean stopping when hailed for a boarding; sailors also heave to by setting the sails so the boat makes little headway, to wait or ride out a storm.
- Heaving line Lines & knots
-
A light line, weighted at the end, thrown across to a dock or another boat so a heavier mooring or tow line can be pulled over with it.
- Heel Docking & boat handling
-
A temporary lean to one side caused by wind on the sails, waves, or a hard turn at speed.
- HELP position (Heat Escape Lessening Posture, H.E.L.P.) Safety & emergencies
-
Heat Escape Lessening Posture: in cold water with a life jacket on, draw your knees to your chest and hug your arms across it to protect the areas that lose the most heat. Groups in the water should huddle together.
- High water (High tide, HW) Weather & sea
-
The highest level reached by a rising tide. The actual level can be raised or lowered by wind and weather as well as the predicted tide.
- Hitch (Half hitch) Lines & knots
-
A knot that ties a line to an object such as a post, ring, rail or another line under strain. Examples are the clove hitch, rolling hitch and two half hitches.
- Holding ground (Bottom type) Anchoring & mooring
-
How well the bottom holds an anchor. The Coast Guard handbook rates firm sand and dense clay as excellent, sticky mud good, soft mud or loose sand fair or questionable, and rock, coral and grass as poor. Charts show bottom type.
- Holding tank (Type III MSD tank, Waste tank) Plumbing, tanks & systems
-
A tank that stores toilet waste (a Type III MSD) until it is pumped out ashore or, where legal, discharged more than 3 nautical miles offshore. Federal rules require a way to tell when it is more than three-quarters full.
The pumpout deck fitting should be labeled "Waste" so it isn't confused with the water or fuel fill. Clogged vent lines make pumping out hard and can over-pressurize the tank.
- Hose clamp (Double clamping, Hose clamps) Plumbing, tanks & systems
-
A stainless steel band tightened by a screw to hold a hose on a fitting. Hoses on through-hulls and seacocks below or near the waterline should be double-clamped with two clamps.
Connecticut's boating program suggests 100 percent stainless clamps (one a magnet won't stick to is probably all stainless); replace rusty clamps.
- Hull Hull & deck
-
The main body of the boat: the outer shell and the structure inside it below the main deck, which together keep the water out and give the boat its strength.
ecfr.gov · higherlogicdownload.s3.amazonaws.com · oregon.gov
- Hull Identification Number (HIN) Crew, roles & paperwork
-
A boat's unique 12-character serial number: maker's code (3 characters), serial number (5), month and year of manufacture or certification (2) and model year (2). The primary HIN is on the starboard side of the transom near the top; a duplicate is hidden inside.
Removing or altering a HIN is prohibited. State agencies may verify it by tracing, photos or inspection before registering a boat.
- Hull speed (Critical speed) Hull & deck
-
The practical top speed of a displacement hull, set by its waterline length: about 1.34 times the square root of the waterline length in feet, in knots. A 36-foot waterline gives about 8 knots.
Pushing a displacement boat past hull speed takes much more power and fuel for very little gain.
- Hurricane force wind warning Weather & sea
-
An NWS warning of sustained winds or frequent gusts of 64 knots (74 mph) or more that are not directly tied to a tropical cyclone. A hurricane itself brings a hurricane warning instead.
- Hypothermia Safety & emergencies
-
A dangerous drop in the body's core temperature from exposure to cold water, air or wind. How fast it sets in depends mostly on water temperature, and to a lesser extent on body size, clothing and behavior.
To slow heat loss, keep your life jacket on, get as much of your body out of the water as you can (onto a capsized hull if possible), and use the HELP posture or a group huddle.
Sources disagree on shortest time to exhaustion or unconsciousness in cold water — left out rather than guessed. Check your local authority.
uscgboating.org · icdept.cgaux.org · nauticalcharts.noaa.gov
I
- Immersion suit (Survival suit) Safety & emergencies
-
An insulated, buoyant suit covering the whole body that delays hypothermia in cold water. The Coast Guard suggests one for each person on boats operating offshore in cold waters.
- Impeller (Raw-water pump impeller, Water pump impeller) Engines & machinery
-
The flexible rubber rotor in the raw-water pump; its blades wipe against a cam inside the housing to move water. The water it pumps is its only lubricant, so running it dry destroys it quickly.
Westerbeke says carry a spare impeller and cover gasket, and if blades break off, find them (often in the heat exchanger). On a jet drive, "impeller" means the pump that propels the boat.
- In sight of one another Rules of the road
-
Two vessels are in sight of one another only when one can be seen by eye from the other. The crossing, meeting and overtaking rules (11 to 18) apply only then; a target seen only on radar in fog falls under Rule 19.
- Inboard engine (Inboard, Direct drive, V-drive) Engines & machinery
-
An engine mounted inside the hull that turns a propeller shaft running out through the bottom. In a direct drive the shaft runs straight aft; in a V-drive it first runs forward into a gearbox, then back aft, so the engine can sit farther aft.
Gasoline inboards must have a backfire flame arrestor and engine-space ventilation under federal rules.
discoverboating.com · higherlogicdownload.s3.amazonaws.com · ionianmarinesurveys.com · uscgboating.org
- Inflatable life jacket (Inflatable PFD) Safety & emergencies
-
A compact life jacket that fills from a gas cylinder, in many models automatically when it hits the water. It only counts toward the carriage requirement if the cylinder is full and all status indicators are green; many are approved only when worn.
The Coast Guard says inflatables are adult sizes only and not appropriate for weak or non-swimmers; service them per the maker's instructions.
- Information and regulatory markers (Regulatory markers, State waterway markers) Navigation & charts
-
White markers or buoys with orange shapes, kept by the states: a diamond warns of danger (rock, shoal), a crossed diamond marks an area boats must keep out of, a circle marks controlled areas (no wake, speed limit) and a square gives information.
- Inland Rules (Inland Navigation Rules) Rules of the road
-
The US version of the Navigation Rules used on harbors, bays, rivers and the Great Lakes, shoreward of the demarcation lines. They match the International Rules in most places but differ in some whistle signals, lights and river right-of-way.
One practical difference: on inland waters, one- and two-blast whistle signals state what you intend to do and expect an answer; under the International Rules they announce a turn you are making.
- Intracoastal Waterway (ICW, Intracoastal) Navigation & charts
-
An inland waterway for small craft and small commercial vessels along the Atlantic and Gulf coasts, in several separate segments. Its aids carry yellow symbols: a yellow triangle means keep the aid on your starboard side, a yellow square on your port side.
- Inverter Electrical & electronics
-
A device that turns 12-volt (or 24- or 32-volt) DC from the batteries into 120-volt AC to run household-type appliances.
- Isolated danger mark Navigation & charts
-
A black mark with one or more broad red bands and two black balls on top, placed on or next to a small danger that has navigable water all around it. If lit, it shows a white light flashing in groups of two.
The Coast Guard Auxiliary advises not approaching these marks closely without special caution.
J
- Jackline (Jack line) Safety & emergencies
-
A strong line or strap run along the deck from bow to stern that a crew member's safety harness tether clips onto, so they can move about the deck without being swept overboard.
- Jib (Genoa, Headsail) Sails & rigging
-
A triangular sail set in front of the mast, usually on the forestay. A genoa is a large jib that overlaps the mast; "headsail" covers any sail set forward of the mast.
discoverboating.com · ionianmarinesurveys.com · icdept.cgaux.org
- Jibe (Gybe, Accidental jibe, Preventer) Sails & rigging
-
Turning the stern through the wind so the boom swings across to the other side. An uncontrolled jibe can swing the boom and mainsheet across with deadly force; a preventer line is rigged to guard against it.
K
- Keel Hull & deck
-
The backbone running fore and aft along the bottom centerline of the hull. On sailboats the keel also reaches well below the hull to resist sideways drift (leeway).
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com · icdept.cgaux.org
- Ketch (Mizzen, Mizzen mast) Sails & rigging
-
A two-masted sailboat with a tall main mast and a shorter mizzen mast aft, the mizzen standing forward of the rudder post. Yawls also have a mizzen.
- Knot (kt, kn) Navigation & charts
-
A unit of speed: one nautical mile per hour, or about 1.15 statute miles per hour. Boat speed, wind speed and current speed are all given in knots on the water.
L
- Lateral marks (Lateral aids, Channel markers) Navigation & charts
-
Buoys and beacons that mark the sides of a channel. Returning from sea, green marks with odd numbers are on your port side and red marks with even numbers on your starboard side, with numbers rising as you go in.
Channel marks do not always sit exactly on the channel edge; some are inside or outside it, and the Light List often gives the offsets.
uscgboating.org · navcen.uscg.gov · dco.uscg.mil · nauticalcharts.noaa.gov
- Latitude (Lat) Navigation & charts
-
How far north or south of the equator a place is, measured in degrees and minutes.
- Lazarette (Laz) Hull & deck
-
A storage compartment in the stern of the boat.
- Lead-acid battery (Flooded battery, Wet-cell battery, AGM battery, Gel battery, Gel cell) Electrical & electronics
-
A battery of lead plates in sulfuric acid, made in three main types. Flooded (wet-cell) types need their water level checked and topped up and give off gas when charging; AGM and gel types are sealed, with the acid held in glass mat or gel, so they resist spills and leaks.
Charging lead-acid batteries gives off hydrogen, which is explosive; keep sparks and flame away.
- Lee shore Directions & positions
-
A shore that the wind is blowing toward, as seen from your boat. If you lose power or drag anchor near one, the wind pushes you toward it.
- Leeward (Lee side, Lee, Downwind) Directions & positions
-
Toward the direction the wind is blowing to; the sheltered, downwind side. The opposite is windward.
- Leeway Docking & boat handling
-
Sideways drift of a boat to leeward caused by the wind (and, loosely, by current), so its track differs from its heading. Sailboat keels help resist it.
dco.uscg.mil · higherlogicdownload.s3.amazonaws.com · icdept.cgaux.org
- Length overall (LOA) Hull & deck
-
The boat's length from the foremost to the aftermost point of the hull, measured in a straight line. The Navigation Rules use length overall for all their size limits (12 m, 20 m and so on).
higherlogicdownload.s3.amazonaws.com · navcen.uscg.gov · discoverboating.com
- Life raft (Liferaft) Safety & emergencies
-
An inflatable survival craft stowed in a canister or valise, big enough for everyone aboard, with an emergency equipment pack. The Coast Guard suggests one for boats going offshore or far from rescue, serviced as the maker specifies.
- Lifelines (Railings, Guardrails) Hull & deck
-
The wires or rails around the edge of the deck, supported by stanchions, that help keep people from falling overboard.
- Light characteristic (Characteristic) Navigation & charts
-
The color and rhythm that identify a lighted aid, written on the chart as, for example, "Fl G 4s" (a green flash every 4 seconds) or "Iso R 6s". Rhythms include fixed, flashing, quick flashing, occulting (on longer than off), isophase (equal on and off) and Morse code.
Sources disagree on flash rate that counts as quick flashing — left out rather than guessed. Check your local authority.
dco.uscg.mil · pdept.cgaux.org · uscgboating.org · navcen.uscg.gov
- Light List Navigation & charts
-
The Coast Guard publication, updated weekly on the Navigation Center website, describing the aids in a region: light characteristics and visibility, light structures, buoys, sound signals and electronic aids.
- Line (Rope) Lines & knots
-
Rope in use aboard a boat. On boats, ropes are usually called lines, and each gets a name from its job: dock line, sheet, halyard, anchor line.
- Line of position (LOP) Navigation & charts
-
A line on the chart that your boat is somewhere on, drawn from a single observation such as a compass bearing to a charted lighthouse. Two or more lines crossing give a fix.
- List Docking & boat handling
-
A steady lean to one side caused by uneven weight in the boat. Unlike heel, it doesn't go away when the wind drops or the turn ends.
- Local Notice to Mariners (LNM) Navigation & charts
-
A notice published by each Coast Guard District listing changes to aids to navigation, channel depths, new charts, bridge work, marine events and other safety information for local waters.
- Longitude (Long, Lon) Navigation & charts
-
How far east or west of the prime meridian at Greenwich, England a place is, measured in degrees and minutes.
- Lookout (Look-out) Rules of the road
-
Rule 5 requires every vessel to keep a proper lookout at all times, by sight, by hearing and by every other available means such as radar, so it can fully judge the situation and any risk of collision. It applies to small boats and single-handers too.
The Coast Guard says that on all but the smallest boats the lookout should ideally be someone other than the helmsman, placed where they can best see and hear.
- Low water (Low tide, LW) Weather & sea
-
The lowest level reached by a falling tide. Wind, pressure and river flow can make it lower or higher than predicted.
- Luff (Luffing) Sails & rigging
-
The front edge of a sail. As a verb, a sail luffs when it flaps along that edge, as happens when the boat turns too close to the wind or the sail is let out too far.
- Lunch hook Anchoring & mooring
-
A small, light anchor for brief stops in calm weather, such as lunch or a swim, carried in addition to a larger working anchor.
M
- Macerator (Macerator pump) Plumbing, tanks & systems
-
An electric pump that grinds up waste as it pumps, used to empty a holding tank overboard where that is legal, or built into some electric toilets. It does not treat sewage and is not a Type I or II MSD.
Its motor, seal or impeller can burn up if it runs dry.
- Magnetic north Navigation & charts
-
The direction a compass needle points under the earth's magnetic field alone. It differs from true north by the local variation and slowly shifts over the years.
- Mainsail (Main) Sails & rigging
-
The sail set behind the mast along the boom; normally the largest regular sail aboard.
- Make fast (Belay, Secure) Lines & knots
-
To tie off or secure a line so it will hold, usually to a cleat, bitt or post. "Cast off" is the opposite: to untie and release.
- Making way Rules of the road
-
Moving through the water under power or sail. A vessel can be underway without making way, for example stopped and drifting, and the fog signals differ: one prolonged blast when making way, two when stopped.
- Man overboard (MOB, Crew overboard, Person overboard) Safety & emergencies
-
The shout that someone has fallen off the boat, and the emergency of getting them back. Shout it with the side ("Man overboard, port side!") so everyone knows where to look.
The Williamson turn is one maneuver used to bring a powered vessel back along its own track to the person.
- Maneuvering signals (Whistle signals) Rules of the road
-
Rule 34 whistle signals between power-driven vessels in sight of each other: one short blast for a turn to starboard (inland: "I intend to leave you on my port side"), two short for port, and three short for "operating astern propulsion".
Inland, a passing agreement made by VHF radio can replace the whistle signals; if no agreement is reached, sound them.
- Manufacturer's Statement of Origin (MSO, Manufacturer's Certificate of Origin, MCO) Crew, roles & paperwork
-
The builder's document that comes with a new boat, listing its HIN and engine serial numbers and recording its transfer to the dealer. You need it to register or document a new boat.
- Marine head (Head, Marine toilet) Plumbing, tanks & systems
-
A boat's toilet, and the compartment it is in. Heads are manual (pumped by hand), electric (often grinding waste) or vacuum types, and usually flush with seawater drawn through a seacock.
Many heads sit below the waterline, so intake and discharge lines need siphon breaks and the seacocks should be closed when the head isn't in use.
discoverboating.com · ionianmarinesurveys.com · portal.ct.gov · usna.edu
- Marine sanitation device (MSD, Type I MSD, Type II MSD, Type III MSD) Plumbing, tanks & systems
-
The federally required equipment that treats or holds toilet waste on any boat with an installed toilet. Types I and II are flow-through treatment devices; Type III is a holding tank. Boats 65 feet and under may use any type; longer boats need Type II or III.
- Marine survey (Survey, Condition and valuation survey, C&V survey, Pre-purchase survey, Prepurchase survey) Maintenance & haul-out
-
A professional inspection of a boat by a marine surveyor. The condition and valuation (C&V) survey used when buying covers the hull, structure and systems, includes a haul-out to see the bottom, and puts a value on the boat; lenders and insurers usually require one.
The surveyor works for you, the buyer. BoatUS suggests making the sale contingent on a satisfactory survey and sea trial, and hiring separate engine and rigging surveys where needed.
- Marine surveyor (Surveyor, SAMS, NAMS) Crew, roles & paperwork
-
An independent professional who inspects a boat and reports on its condition and value, usually for a buyer, lender or insurer. The two main professional associations are SAMS (Society of Accredited Marine Surveyors) and NAMS (National Association of Marine Surveyors).
The surveyor works for you, not the seller, broker or lender: you choose and pay them and the report is yours. Some insurers only accept members of one association or the other.
- Marine wire (Tinned wire) Electrical & electronics
-
Stranded, tin-plated copper wire suited to boats; never solid wire. Size it by American Wire Gauge (AWG) for the current and the round-trip length so voltage drop stays small, and finish ends with proper crimp terminals.
BoatUS Foundation recommends the most flexible (Type 3) wire, a voltage drop of no more than 3 percent, and wire strippers made for AWG rather than the smaller SAE gauge.
- Mast (Spar, Mast step, Deck-stepped mast, Keel-stepped mast) Sails & rigging
-
The vertical pole (spar) that carries the sails. Its foot sits in a mast step, either on deck (deck-stepped, usually easier to raise and lower) or down through the cabin onto the keel (keel-stepped).
discoverboating.com · icdept.cgaux.org · ionianmarinesurveys.com · usna.edu
- Masthead light Rules of the road
-
A white light on the centerline showing forward over 225 degrees, from dead ahead to 22.5 degrees abaft the beam on each side. Power-driven vessels underway show one; vessels 50 m and longer add a second, higher one aft.
A power-driven boat under 12 m may show an all-round white light plus sidelights instead (Rule 23(d)).
- Mayday (Distress call) Safety & emergencies
-
The spoken radio distress signal, repeated three times, meaning grave and immediate danger to life or the boat; it has priority over all other calls. Call on VHF channel 16 with the boat's name, position, nature of distress, number aboard and help needed.
A DSC-equipped VHF with an MMSI and GPS connection can send a distress alert with your position by holding the red button for about 5 seconds.
- Mean Lower Low Water (MLLW) Navigation & charts
-
A tidal datum: the average height of the lower of each day's two low tides, taken over NOAA's 19-year National Tidal Datum Epoch. It is the chart datum for US tidal waters, and tide-table heights are measured from it too.
A minus tide in the tide tables means the water will drop below MLLW, giving less depth than the chart shows.
tidesandcurrents.noaa.gov · oceanservice.noaa.gov · tidesandcurrents.noaa.gov
- MMSI (Maritime Mobile Service Identity) Electrical & electronics
-
A nine-digit number that identifies a boat's DSC radio and AIS. U.S. numbers start with 338 or 366 to 369. Boats that need a station license get one from the FCC; recreational boats in U.S. waters can get one from BoatUS or America's Boating Club.
- Moisture meter (Percussion sounding, Hammer sounding, Sounding the hull) Maintenance & haul-out
-
An instrument a surveyor passes over fiberglass to detect water in the laminate or core, used together with tapping the hull with a small hammer: sound laminate rings sharply, while a dull thud suggests a void, delamination or wet core.
- Mooring (Mooring ball, Mooring buoy) Anchoring & mooring
-
A permanent anchor or screw on the bottom, with chain up to a floating buoy that boats tie to. Mooring buoys are white with a blue horizontal band and are the only buoys you may legally tie up to.
Use only a mooring you are permitted to use; public ones are usually rented from the harbormaster, who can tell you the size limit.
boatus.org · higherlogicdownload.s3.amazonaws.com · boatus.com · navcen.uscg.gov
- Mooring pennant (Pennant, Mooring line) Anchoring & mooring
-
The short, strong line from the mooring buoy that you bring aboard and make fast to your bow cleat or post. Watch for chafe where it crosses the boat.
- Mousing (Moused shackle, Seizing) Anchoring & mooring
-
Wrapping a shackle pin (or hook opening) with wire or small line so it cannot unscrew or come open. The Coast Guard handbook advises seizing anchor shackle pins, noting that many anchors have been lost through poorly attached rodes.
- Mushroom anchor Anchoring & mooring
-
A round, bowl-shaped anchor named for its mushroom shape. Large ones weighing up to several thousand pounds are widely used to hold permanent moorings.
N
- Narrow channel (Fairway) Rules of the road
-
Rule 9: in a narrow channel or fairway keep as near its starboard edge as is safe. Boats under 20 m and sailing vessels must not impede a vessel that can only navigate inside the channel, and no one should cross in a way that does. Avoid anchoring in one.
What counts as "narrow" depends on the vessels involved; the Coast Guard advises erring on the side of following Rule 9.
- National Vessel Documentation Center (NVDC) Crew, roles & paperwork
-
The Coast Guard office in Falling Waters, West Virginia that documents vessels, renews certificates, records mortgages, liens and bills of sale, and issues abstracts of title and deletion letters, including through its online eStorefront.
The NVDC warns that private companies offering to handle documentation for a fee are not part of the Coast Guard.
- Nautical chart (Chart) Navigation & charts
-
A map made for navigation on the water. It shows water depths, the shape of the shore, hazards, the bottom type, aids to navigation, landmarks and port facilities. In US waters NOAA makes them, in print and electronic form.
The Coast Guard stresses keeping charts current: a GPS tells you where you are, not what is around or under the boat.
uscgboating.org · oceanservice.noaa.gov · nauticalcharts.noaa.gov
- Nautical mile (NM, Sea mile) Navigation & charts
-
The unit of distance used on the water: about the length of one minute of latitude, fixed internationally at 1,852 meters (about 6,076 feet, or roughly 1.15 statute miles).
Because a minute of latitude is about a nautical mile, you can measure distance on a chart against its latitude scale.
dco.uscg.mil · weather.gov · discoverboating.com · ionianmarinesurveys.com · higherlogicdownload.s3.amazonaws.com
- Neap tide (Neap tides) Weather & sea
-
Tides with a smaller-than-average range, twice a month when the moon is at first and last quarter: lower highs and higher lows.
- Net tonnage (Five net tons, Net tons) Crew, roles & paperwork
-
A measure of a vessel's enclosed volume, not its weight: the gross measured volume minus certain spaces, worked out by formula. A recreational boat must measure at least 5 net tons to be eligible for Coast Guard documentation.
- NMEA 2000 (N2K, NMEA 0183) Electrical & electronics
-
The standard network that lets marine electronics such as GPS, plotters, autopilots and instruments share data on a single network, with many devices both talking and listening. Its older predecessor, NMEA 0183, is a simple serial link where one device talks to several listeners.
- No-discharge zone (NDZ, No Discharge Zone) Plumbing, tanks & systems
-
A body of water where discharging any boat sewage, treated or untreated, is prohibited. States apply to the EPA to designate them. Inside one, toilet discharge valves must be secured closed.
Accepted methods include padlocking or wire-tying the overboard valve closed, removing its handle, or locking the head door.
- No-wake zone (Idle speed zone, Slow no wake) Docking & boat handling
-
An area, marked by a white regulatory marker with an orange circle or by signs, where boats must go slowly enough to make no significant wake. The markers are maintained by the states.
- NOAA Weather Radio (NWR, WX channels) Weather & sea
-
Round-the-clock NWS broadcasts on seven VHF frequencies (162.40 to 162.55 MHz), with marine forecasts along the coasts and Great Lakes. Boaters can receive them on the weather channels of a VHF radio.
During severe weather NWS interrupts the routine broadcast with warnings.
- Not under command (NUC, Vessel not under command) Rules of the road
-
A vessel that, through some exceptional circumstance such as a steering failure, cannot maneuver as the Rules require and so cannot keep out of the way. It shows two all-round red lights in a vertical line, or two black balls by day.
These are not distress signals (Rule 27(h)); a vessel that needs help uses the distress signals of Annex IV.
- Nun buoy (Nun) Navigation & charts
-
An unlighted buoy with a cone-shaped top. In the US system nuns are red with even numbers and mark the starboard (right) side of a channel when returning from sea.
- Nylon line (Nylon) Lines & knots
-
Synthetic line that is strong and very stretchy, so it absorbs shock loads. That makes it the choice for anchor rodes, snubbers and dock lines, where some give is wanted.
Its stretch also stores energy: if a loaded nylon line or its fitting parts, it can snap back violently. Stand clear of lines under heavy strain.
O
- Official number (Documentation number, O.N.) Crew, roles & paperwork
-
The number the Coast Guard assigns a documented vessel. It must be permanently marked inside the hull on a structural part, in block numerals at least 3 inches high preceded by "NO.", so that removing or changing it would be obvious.
- Oil analysis (Oil sample, Oil sampling) Maintenance & haul-out
-
Sending a small sample of engine (or transmission) oil to a lab that measures metals, water and other contaminants, which can point to internal wear or leaks. It is especially useful on older engines.
Results usually need a mechanic to interpret them.
- Oil discharge placard (Oil pollution placard, Discharge of Oil Prohibited placard) Crew, roles & paperwork
-
A placard at least 5 by 8 inches, required on boats 26 feet and longer with a machinery space, posted in the engine space or at the bilge pump control, stating that discharging oil or oily waste into US waters is prohibited.
Pumping an oily bilge overboard is illegal; any discharge that leaves a sheen or discoloration counts. Spills should be reported to the National Response Center.
- On the bow (Broad on the bow) Directions & positions
-
About 45 degrees off the bow on either side: relative bearing 045 on the starboard bow, 315 on the port bow. "Broad on the bow" means exactly 45 degrees.
- On the quarter (Broad on the quarter) Directions & positions
-
About 45 degrees off the stern on either side: relative bearing 135 on the starboard quarter, 225 on the port quarter. The "quarters" are the after parts of the boat's sides.
- Osmotic blistering (Blisters, Osmosis, Hull blisters, Boat pox) Maintenance & haul-out
-
Blisters in a fiberglass hull below the waterline, formed when water passes through the gelcoat and reacts with chemicals in the laminate, building pressure that pushes the gelcoat into domes.
An occasional blister is not serious and can be ground out, dried and filled with epoxy; a bottom covered in them ("boat pox") means a saturated hull needing specialist repair. BoatUS Foundation notes dry storage in winter reduces blistering.
- Outboard motor (Outboard, Lower unit, Kicker) Engines & machinery
-
A self-contained engine mounted on the transom, combining the engine (powerhead), driveshaft and propeller in one unit that pivots to steer and tilts to trim. The underwater gear housing is the lower unit; a small spare outboard is a kicker.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Overtaking (Overtaking situation) Rules of the road
-
Coming up on another vessel from more than 22.5 degrees abaft her beam, where at night you would see only her sternlight. The overtaking vessel must keep clear until finally past and clear, whatever kind of vessels are involved (Rule 13).
If in doubt whether you are overtaking, the Rules say assume you are.
P
- Pan-pan (Urgency call) Safety & emergencies
-
The spoken radio urgency signal, said three times, for an urgent message about the safety of a person or boat when there is not yet an immediate threat to life.
It has priority over safety calls but not over a Mayday; a pan-pan situation can grow into a Mayday.
- Passengers for hire (Paying passengers, Charter) Crew, roles & paperwork
-
People carried in return for payment. Once a boat carries passengers for hire it is a commercial operation and needs a licensed operator, and more than six passengers require a Coast Guard-inspected vessel.
- Performance level (Level 50, Level 70, Level 100, Level 150, Level 275) Safety & emergencies
-
The newer life jacket rating: the number is the minimum buoyancy in newtons. Level 50 and 70 are for use near shore with help close by; Level 100 for sheltered water; Level 150 turns an unconscious wearer face up for general use; Level 275 is for offshore in extreme conditions.
A higher level means more flotation and better turning, suited to longer waits for rescue; the Coast Guard notes the best life jacket is the one you will actually wear.
- Personal flotation device (PFD, Life jacket, Lifejacket, Wearable PFD) Safety & emergencies
-
The Coast Guard's term for life jackets and buoyancy aids. Every recreational boat must carry a Coast Guard-approved wearable PFD of the right size for each person aboard, readily accessible, and in good and serviceable condition.
Children under 13 must wear one while the boat is underway unless below deck or in an enclosed cabin (federal rule; some states differ). Drowning is the leading cause of boating deaths.
- PFD type (Type I PFD, Type II PFD, Type III PFD, Type V PFD) Safety & emergencies
-
The older way of rating life jackets, still on many labels: Type I turns most unconscious wearers face up and has the most buoyancy; Type II turns some; Type III supports a conscious person upright; Type V is approved only for specific uses stated on the label; Type IV is a throwable.
Federal regulations now speak of "wearable" and "throwable" PFDs, and newer jackets carry performance levels instead of types. The Coast Guard guide lists both so you can compare labels.
- Pickup buoy (Pickup float, Whip) Anchoring & mooring
-
The small float on the end of a mooring pennant (sometimes with a stiff whip) that you grab with a boat hook to bring the pennant aboard.
Approach a mooring from downwind (or down-current), slowly, and stop the boat as the pickup comes alongside the bow.
- Pitchpole Docking & boat handling
-
Capsizing end over end, when a large wave lifts the stern and the bow buries into the sea ahead.
- Pivot point Docking & boat handling
-
The point around which the boat turns. On most boats it is a little forward of amidships at rest, moves forward as the boat gains headway (about one-third of the length back from the bow at normal speed) and aft when backing.
Because the stern swings around the pivot point, check that the stern will clear the dock before you turn away from it.
- Planing hull Hull & deck
-
A hull shaped so that, with enough power, it lifts and skims on the surface ("gets on plane"). Once on plane a small increase in power gives a large increase in speed.
The Coast Guard handbook advises bringing power on and off gradually when going on or off plane; a sudden drop off plane stops the boat abruptly.
- PLB (Personal Locator Beacon) Safety & emergencies
-
A pocket-sized 406 MHz distress beacon carried by a person, activated by hand only. Like an EPIRB it alerts rescuers by satellite, and many include GPS; its battery runs at least 24 hours once on.
Register it with NOAA like an EPIRB.
- Plow anchor (CQR, Delta anchor, Plough anchor) Anchoring & mooring
-
An anchor shaped like a farm plow, with a fixed or hinged shank, that turns over and buries itself when pulled. A common choice for cruising boats; it holds in many bottoms and resets fairly easily when the boat swings.
- Points of sail (Close-hauled, Beam reach, Broad reach, Reach, Running, Beating) Sails & rigging
-
The boat's angle to the wind: close-hauled (as close to the wind as the boat will sail), reaching (wind across the boat, with the beam reach at about 90 degrees) and running (sailing downwind, with the wind from astern).
- Polyester line (Dacron line, Polyester, Dacron) Lines & knots
-
Synthetic line (Dacron is a common trade name) that stretches much less than nylon. Practical Sailor found a longer length can still work as an anchor snubber.
Sources disagree on strength of polyester compared with nylon — left out rather than guessed. Check your local authority.
- Polypropylene line (Polypro) Lines & knots
-
Light synthetic line that floats, but it is weaker than nylon of the same size, chafes easily and weakens quickly in sunlight.
The Coast Guard handbook says it can lose up to 40 percent of its strength in three months of sun exposure, so keep it covered and replace it often.
- Porpoising Docking & boat handling
-
A planing boat's bow rising and falling in a steady rhythm at speed. Adjusting trim tabs or drive trim usually corrects it.
- Port (Port side) Directions & positions
-
The left-hand side of the boat when you face the bow. It stays the port side no matter which way anyone aboard is facing, which is why crews use it instead of "left".
A common memory aid: "port" and "left" both have four letters. The port sidelight is red.
- Port tack Directions & positions
-
A sailboat is on port tack when the wind comes over its port side, so the mainsail is out on the starboard side.
Under Rule 12, when two sailboats on opposite tacks risk collision, the one on port tack keeps out of the way.
- Power-driven vessel Rules of the road
-
Any vessel moved by machinery. A sailboat with its engine in gear is a power-driven vessel under the Rules, even with its sails up.
When motor-sailing by day, Rule 25(e) calls for a cone, point down, hoisted forward; on inland waters a boat under 12 m may skip it.
- Preferred channel mark (Junction buoy, Junction mark) Navigation & charts
-
A red-and-green banded mark, lettered rather than numbered, where a channel splits. The top band shows the preferred channel: green on top means treat it as a green (port-side) mark; red on top, as a red one.
- Preferred ship mortgage (Preferred mortgage) Crew, roles & paperwork
-
A boat loan recorded against a documented vessel with the Coast Guard. The availability of this kind of mortgage is a main reason lenders ask for larger boats to be documented.
- Pressure water system (Freshwater system, Freshwater pump, Accumulator tank) Plumbing, tanks & systems
-
The boat's household-style water supply: a DC pump draws from the freshwater tank and switches on and off to keep the lines pressurized, often with an accumulator tank so it doesn't run every time a tap opens.
BoatUS Foundation says boats have sunk from burst dockside water hoses or water-heater fittings; turn off the dock water when you leave and use a pressure reducer and reinforced hose.
- Prolonged blast Rules of the road
-
A whistle or horn blast lasting four to six seconds (Rule 32). One prolonged blast is sounded when nearing a blind bend in a channel and, on inland waters, when a power-driven vessel leaves a dock or berth.
- Prop walk (Propeller side force, Side force) Docking & boat handling
-
The sideways push of a turning propeller on the stern. With a right-handed propeller (clockwise seen from astern), the stern tends to move to starboard in forward gear and to port in reverse. A left-handed propeller does the opposite.
The Coast Guard handbook's back-and-fill turn relies on it. Know which way your stern walks before backing into a slip.
- Propeller (Prop, Screw, Right-handed propeller, Left-handed propeller) Engines & machinery
-
The bladed hub that turns in the water to push the boat. Propellers are described by pitch and by hand: a right-handed prop turns clockwise in forward gear when seen from astern, a left-handed one counterclockwise.
BoatUS Foundation advises inspecting props at haul-out for dings, pitting and distortion, which cause vibration and cost speed and fuel economy.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · boatus.org
- Propeller pitch (Pitch) Engines & machinery
-
The distance a propeller would move forward in one full turn if it did not slip in the water. A real prop advances somewhat less; that loss is called slip. "Pitching" is also the rise and fall of the bow and stern in waves.
- Propeller shaft (Shaft, Prop shaft, Stern tube, Shaft log) Engines & machinery
-
The metal bar that carries power from the transmission, out through the hull, to the propeller. It leaves the boat through a tube (the stern tube or shaft log) sealed by a stuffing box or dripless seal, and is supported outside by a strut.
higherlogicdownload.s3.amazonaws.com · ionianmarinesurveys.com · shaftseal.com
- Pulpit (Bow pulpit, Stern pulpit) Hull & deck
-
A rail structure at the bow, and on many sailboats a matching one at the stern, at the ends of the lifelines.
- Pump-out (Pumpout, Pumpout station, Deck pumpout fitting) Plumbing, tanks & systems
-
Emptying a holding tank by suction at a shore pumpout station, through a deck fitting connected to the tank.
The federal standard deck fitting is 1-1/2 inch pipe thread; most stations have adapters.
R
- Radar Electrical & electronics
-
An electronic system that uses radio waves to detect other boats, land and buoys and show their positions, useful at night and in poor visibility. The Navigation Rules require proper use of radar if it is fitted.
Recreational radar needs no FCC license. Overlaying radar on the chart requires a heading sensor.
discoverboating.com · navcen.uscg.gov · uscgboating.org · nmea.org
- Range (Range lights, Leading lights) Navigation & charts
-
Two marks or lights at different heights and distances, with the rear one higher. When you see them lined up one above the other you are on the charted line, usually the center of a channel.
- Range of tide (Tidal range) Weather & sea
-
The difference in height between a high water and the next low water. It varies from place to place and through the month, being largest at spring tides and smallest at neap tides.
- Raw-water cooling (Raw water, Seawater cooling, Raw-water pump) Engines & machinery
-
The circuit that draws outside water in through a seacock and strainer, pumps it with an impeller pump through the heat exchanger, and then sprays it into the exhaust to cool the gases on their way overboard.
BoatUS Foundation notes a 300-hp engine moves about 30 gallons of cooling water a minute, so a failed hose or fitting can flood the bilge quickly.
- Recommissioning (Spring commissioning, Fitting out, Commissioning) Maintenance & haul-out
-
Getting a boat ready to use after lay-up: reversing the winterizing steps (reinstalling the impeller, removing plugs and rags, refilling systems), then checking zincs, props, hoses, seacocks, steering, batteries and safety gear before launch.
- Red right returning (Three R rule, 3-R rule) Navigation & charts
-
The memory aid for US lateral marks: when returning from seaward, or heading upstream, keep the red marks on your right (starboard) side.
- Reef (Reefing, Reef points) Sails & rigging
-
To make a sail smaller so the boat is not overpowered in strong wind, by lowering part of the mainsail and tying or pulling it down to the boom, or partly rolling up a furling sail.
- Registration numbers (Bow numbers, State numbers) Crew, roles & paperwork
-
The state-issued number painted or attached on both sides of the forward half of the hull, in plain vertical block letters at least 3 inches high, contrasting with the hull color, with the state validation decal placed as your state requires.
- Relative bearing Directions & positions
-
The direction of an object measured from your boat's heading, usually clockwise from 000 degrees at the bow through 360. An object at 090 relative is directly off the starboard side.
- Restricted in ability to maneuver (RAM, Vessel restricted in her ability to maneuver) Rules of the road
-
A vessel whose work, such as dredging, surveying, diving, laying cable, servicing a buoy or certain towing, keeps it from getting out of the way. It shows red-white-red all-round lights in a vertical line, or ball-diamond-ball shapes by day.
- Restricted Radiotelephone Operator Permit (RP, Operator permit) Crew, roles & paperwork
-
An FCC permit for the person operating a marine radio, needed when you travel to or talk with foreign ports. It requires no exam and is valid for life.
- Restricted visibility Rules of the road
-
Any condition in which fog, mist, falling snow, heavy rain, sandstorms or something similar limits how far you can see. Rule 19 (conduct in restricted visibility) and the fog signals of Rule 35 then apply.
- Reverse polarity Electrical & electronics
-
A wiring fault in which the hot and neutral wires of an AC circuit are swapped, which can be very dangerous. Most boat AC panels have an indicator light that warns of it.
- Rigging survey (Rig inspection, Dye test) Maintenance & haul-out
-
An inspection of a sailboat's mast, boom, spreaders, stays, shrouds, turnbuckles and accessible chainplates by a professional rigger who goes aloft, looking mainly for rust and crevice corrosion that can hide cracks. A dye test can reveal cracks too fine to see.
General surveys usually stay at deck level. BoatUS suggests a rigging survey for a rig over about 10 years old, one showing wear, or one headed offshore.
- Right of way (Right-of-way) Rules of the road
-
A common phrase the Rules mostly avoid: they give vessels duties to keep clear or to stand on, not privileges. The main exception is Inland Rule 9, which gives right-of-way to a downbound power-driven vessel with a following current in narrow channels on the Great Lakes and Western Rivers.
- Risk of collision Rules of the road
-
Rule 7: use every available means to judge whether you might collide, and if in doubt assume you might. If an approaching vessel's compass bearing does not change noticeably, risk of collision is deemed to exist.
The bearing can still change while risk remains, especially near a large ship, a tow, or a vessel at close range.
- Rode (Anchor rode, Anchor line) Anchoring & mooring
-
The line, chain or combination of both that connects the anchor to the boat. Nylon three-strand is the usual choice for rope rodes because it stretches to absorb shock; a length of chain at the anchor end lowers the angle of pull and resists chafe.
Markers along the rode show how much is out, which helps you set the right scope.
higherlogicdownload.s3.amazonaws.com · maxwellmarine.com · boatus.org
- Roller furling (Furler, Furling, In-mast furling) Sails & rigging
-
A system that stores and reduces a sail by rolling it up, usually a headsail wound around the forestay. In-mast and in-boom versions roll the mainsail inside the mast or boom.
- Rolling hitch Lines & knots
-
A hitch that grips another line or a spar and holds against a pull along it, used to attach one line to another that is under strain, or to attach a snubber to an anchor chain.
- Round turn (Turn) Lines & knots
-
Passing a line completely around a post, rail or ring. A single turn goes partway around; a round turn encircles the object fully, as in the knot called a round turn and two half hitches.
- Rubrail (Rub rail, Rubbing strake) Hull & deck
-
A protective strip, often rubber, running around the hull where the deck meets the sides, to take bumps against docks and pilings.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Rudder Hull & deck
-
The movable vertical blade at the stern, turned by the wheel or tiller, that steers the boat by deflecting water flowing past it.
- Running rigging Sails & rigging
-
The lines and hardware that raise, lower and trim the sails, such as halyards, sheets, reefing lines and the boom vang, along with the blocks and winches they run through.
S
- Sacrificial anode (Zinc, Zincs, Anode, Zinc anode, Pencil zinc) Electrical & electronics
-
A piece of less noble metal, most often zinc, fastened to underwater metal or inside an engine's cooling system so it corrodes instead of the propeller, shaft, outdrive or heat exchanger.
BoatUS Foundation says replace zincs that are badly eroded, and zincs gone after one season point to a bonding or electrical problem. Westerbeke checks the engine zinc monthly.
bluesea.com · discoverboating.com · boatus.org · westerbeke.com · boatus.com
- Safe speed Rules of the road
-
Rule 6: always travel at a speed that lets you act effectively to avoid a collision and stop within a suitable distance. Visibility, traffic, your boat's stopping and turning ability, wind, sea, current, nearby hazards and depth all count.
The Rules set no number for safe speed or passing distance; it depends on the conditions at the time.
- Safe water mark (Fairway buoy, Mid-channel buoy) Navigation & charts
-
A mark with red and white vertical stripes showing navigable water all around it, used for fairways, mid-channels and sea approaches. It is never numbered, and if lit it shows a white light in Morse code "A" (short-long).
- Sailing vessel Rules of the road
-
Any vessel under sail, provided that any engine it has is not being used to drive it. Start the engine and put it in gear, and the boat counts as a power-driven vessel.
- Scope (Anchor scope) Anchoring & mooring
-
The ratio of rode let out to the height from the bottom up to the bow roller or chock (water depth plus bow height, not depth alone). Enough scope keeps the pull on the anchor near horizontal so it digs in rather than lifting out.
Guidance from the Coast Guard and BoatUS: 5:1 as a minimum in good conditions, 7:1 where you have room or for overnight. Example: 10 ft of water plus 4 ft of bow height at 7:1 is 98 ft of rode. Add more as wind rises.
uscgboating.org · boatus.com · boatus.org · higherlogicdownload.s3.amazonaws.com
- Scupper (Scuppers) Hull & deck
-
A drain opening in the deck, toe rail or bulwark that lets water on deck run overboard. Self-bailing cockpits drain through scuppers.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Sea breeze (Land breeze) Weather & sea
-
A breeze blowing from the sea onto land, usually by day when the land is warmer than the water. At night it may be replaced by a land breeze blowing offshore.
- Sea strainer (Raw-water strainer, Strainer) Plumbing, tanks & systems
-
A filter with a removable bowl, fitted between an intake seacock and the pump, that catches weed and debris before water reaches the engine's raw-water pump or other equipment.
BoatUS Foundation notes ice can bend a strainer that wasn't drained or filled with antifreeze for winter, and strainers are among the fittings behind dockside sinkings.
- Sea trial (Trial run) Maintenance & haul-out
-
Running a boat under way before purchase so the engines and running gear can be checked under load. Buyers usually make the sale contingent on a satisfactory survey and sea trial.
BoatUS Magazine distinguishes the short "trial run" on survey day, when the surveyor runs the engines to full capacity checking for smoke, overheating and leaks, from a full sea trial in rough water. Ideally the engines are started cold.
- Seacock (Sea cock) Plumbing, tanks & systems
-
A valve mounted directly on a below-waterline through-hull that can shut off the flow of seawater. Its lever handle shows at a glance whether it is open or closed; it is closed when the handle is turned parallel to the hull.
BoatUS Foundation and Connecticut's Clean Vessel Act program both advise against gate valves, which corrode and don't show whether they are shut. Close seacocks when away from the boat for long, and inspect and lubricate them at haul-out.
discoverboating.com · ionianmarinesurveys.com · boatus.org · portal.ct.gov
- Securite (Securité, Safety call) Safety & emergencies
-
The spoken radio safety signal, said three times, before an important safety message for other mariners. It ranks below Mayday and Pan-pan but ahead of routine calls.
- Semi-displacement hull (Semi-planing hull) Hull & deck
-
A hull between displacement and planing types, often with soft chines or a rounded bottom, that partly lifts at higher speed but never fully planes.
- Set (Set of current) Weather & sea
-
The direction toward which a current is flowing (the opposite of how wind direction is given). In navigation, "set and drift" describe how a current is pushing your boat.
- Setting the anchor (Setting the hook) Anchoring & mooring
-
Getting the anchor dug in: lower it (don't throw it) while the boat drifts or backs slowly, pay out rode, snub it to let the anchor bite, then back gently to confirm it holds before settling in.
Approach the spot heading into wind or current. Taking two bearings or a natural range right after anchoring lets you check later whether you are dragging.
- Shackle (Anchor shackle) Anchoring & mooring
-
A U-shaped metal fitting closed with a screw pin, used to join chain, anchor, swivel and thimble. On anchor gear the pin should be moused (wired) so it cannot work loose.
- Shaft coupling (Coupling, Flexible coupling) Engines & machinery
-
The bolted pair of flanges that joins the transmission's output to the propeller shaft. A flexible coupling adds a cushioning piece that eases strain on the gearbox from engine movement and hull flexing.
Westerbeke advises unbolting the coupling halves when a larger boat is hauled, launched or stored in a cradle, because hull flexing can bend the shaft.
- Shank Anchoring & mooring
-
The long main bar of an anchor, to which the rode is attached at one end and the flukes at the other.
- Sheer (Sheer line) Hull & deck
-
The curve of the deck edge from bow to stern seen from the side. A strong sheer raises the bow, adding buoyancy forward.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Sheet (Mainsheet, Jib sheet) Sails & rigging
-
A line that controls the angle of a sail to the wind, attached at the sail's lower aft corner (the clew). Pulling it in is "trimming"; letting it out is "easing".
Despite the name, a sheet is a line, not a sail.
- Sheet bend (Becket bend) Lines & knots
-
A bend for joining two lines, or a line to an eye splice, that comes apart easily even after loading. The single version joins lines of about the same size; the doubled version suits lines of unequal size.
- Ship station license (FCC ship radio license, Station license) Crew, roles & paperwork
-
The FCC license for the radios aboard a vessel. Recreational boats operating only in US waters do not need one for a VHF, radar or EPIRB, but you do if you travel to a foreign port such as Canada, Mexico or the Bahamas.
Going to a foreign port also requires the operator to hold a Restricted Radiotelephone Operator Permit, a lifetime FCC permit with no test.
- Shore power (Shore power cord, Shore cord) Electrical & electronics
-
AC electricity from the dock's utility supply, brought aboard through a shore power cord to run the boat's AC outlets and equipment while it is tied up.
ABYC-certified technicians check shore power connections, and ABYC standards now call for an ELCI on the shore power system of new boats.
- Short blast Rules of the road
-
A blast of about one second on the whistle or horn (Rule 32).
- Shroud (Shrouds, Upper shroud, Lower shroud) Sails & rigging
-
Standing rigging that runs from the mast down to each side of the boat and keeps the mast from falling sideways. Upper shrouds pass over spreaders to the masthead; lowers attach lower on the mast.
- Sidelights Rules of the road
-
A green light on the starboard side and a red light on the port side, each shining from dead ahead to 22.5 degrees abaft the beam (112.5 degrees). On vessels under 20 m they may be combined in one lantern on the centerline.
- Significant wave height (SWH, Seas (forecast)) Weather & sea
-
The average height of the highest one-third of the waves, roughly what an experienced observer would estimate. It is what "seas 3 to 5 ft" means in a marine forecast; individual waves will sometimes be much higher.
NWS gives an example: with a significant wave height of 10 ft, about 1 wave in 1,000 is 19 ft or more.
- Siphon break (Vented loop, Anti-siphon valve, Anti-siphon loop) Plumbing, tanks & systems
-
A loop of hose raised well above the waterline with a small air valve at the top, which stops seawater from siphoning back into a toilet, bilge pump line or engine when they sit near or below the waterline.
Westerbeke says the loop for its engines' raw-water line must be at least 20 inches above the waterline at every angle of heel, and the valve needs periodic cleaning; neglecting it can let seawater into the engine.
- Skeg Hull & deck
-
A fin or extension of the keel aft, ahead of or under the rudder and propeller, that helps the boat track straight and in some boats supports the rudder's lower bearing.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · ionianmarinesurveys.com
- Skipper (Captain, Master, Operator, Person in charge) Crew, roles & paperwork
-
The person in command of the boat and responsible for its safe operation, whether or not they hold a license. On a recreational boat that is usually the owner or whoever is running it.
The law holds the master or person in charge responsible for giving any help that can safely be given to someone in danger at sea, and the Navigation Rules do not excuse the owner, master or crew from the consequences of neglect.
- Slack water (Slack) Weather & sea
-
The time when a tidal current is at or near zero, especially when it reverses direction.
The time of slack water relative to high and low tide varies from place to place.
- Slip (Berth) Docking & boat handling
-
A boat's parking space at a marina, between two piers, floats or finger docks. "Berth" also means a bed aboard.
- Sloop Sails & rigging
-
A sailboat with one mast, set forward of amidships, carrying a mainsail and a single headsail. Compare the cutter, which carries two.
- Small craft advisory (SCA) Weather & sea
-
An NWS advisory for coastal and Great Lakes waters when winds or seas are expected to be hazardous to small boats, or ice is present. The wind and sea thresholds differ by region, and there is no legal definition of a "small craft": any boat those conditions could endanger is one.
NWS regional thresholds include: Southern region (Georgia to Texas) sustained winds 20 to 33 knots or seas 7 ft or more; Western (Washington to California) 21 to 33 knots or waves over 10 ft; Central (Minnesota to Ohio) 22 to 33 knots or waves over 4 ft. Check your local NWS office.
- Small craft should exercise caution (SCEC) Weather & sea
-
A precautionary statement in NWS marine forecasts alerting mariners with small, weather-sensitive boats to conditions that are building but below advisory level.
- Snap-back (Snapback) Lines & knots
-
The violent recoil of a stretched line, or a torn-out fitting, when something parts under load. Nylon's stretch makes it especially dangerous, so never stand in line with a heavily loaded line.
- Snubber (Snubbing line, Anchor snubber) Anchoring & mooring
-
A length of stretchy nylon line attached to an all-chain rode with a chain hook or hitch and led to a bow cleat, so it absorbs sudden jerks and takes the load off the windlass.
Practical Sailor found nylon (or a longer polyester line) works best and recommends chafe guards and a spare; snubbers can fail without warning, so the chain should also be secured with a chain lock or stopper.
- Sole (Cabin sole, Cockpit sole) Hull & deck
-
The floor of a cabin or cockpit. The cockpit sole is the floor you stand on in the cockpit.
- Sound-producing device (Horn, Whistle, Ship's bell) Safety & emergencies
-
Vessels 12 m (39.4 ft) and longer must carry a whistle (horn), and those 20 m (65.6 ft) and longer also a bell. Smaller boats must have some other means of making an efficient sound signal.
- Sounding (Depth sounding) Navigation & charts
-
A measured or charted depth of water. The small numbers scattered over the water on a chart are soundings, in feet, fathoms or meters (check the chart title) below chart datum.
dco.uscg.mil · oceanservice.noaa.gov · nauticalcharts.noaa.gov
- Special marine warning (SMW) Weather & sea
-
An NWS warning for short-lived hazards on the water, usually lasting up to 2 hours: thunderstorm winds or gusts of 34 knots or more, hail 3/4 inch or larger, or waterspouts. It is often issued for a squall line or strong front.
- Special mark (Yellow buoy) Navigation & charts
-
A solid yellow buoy or beacon that marks a special area or feature rather than a channel side, such as an anchorage, a cable or pipeline area, a military exercise zone or an ocean data buoy. If lit, it shows a yellow light. Many are private aids.
- Speed over ground (SOG) Navigation & charts
-
Your actual speed over the bottom, which is what GPS shows. With a current against you it is less than your speed through the water; with a fair current it is more.
- Spreader (Spreaders) Sails & rigging
-
A short strut sticking out from each side of the mast that holds the shrouds away from it, giving them a better angle to support the mast. Rigs are called single- or double-spreader by how many sets they have.
- Spring line (Spring, Forward spring, Aft spring) Docking & boat handling
-
A dock line that runs at a shallow angle along the boat, from a cleat near the bow or stern to a point on the dock well aft or forward. Springs stop the boat surging fore and aft, and the boat can be powered against one to swing the bow or stern in or out.
higherlogicdownload.s3.amazonaws.com · boatus.org · ionianmarinesurveys.com
- Spring tide (Spring tides) Weather & sea
-
Tides with a larger-than-average range, twice a month around new and full moon: higher highs and lower lows. The name has nothing to do with the season.
- Springing off (Springing, Spring off) Docking & boat handling
-
Using a spring line and the engine to move the boat against the line. With a line from a forward cleat to the dock aft, idling ahead with the wheel turned away from the dock walks the boat in sideways; with a line from a stern cleat to the dock forward, backing swings the bow out.
BoatUS Foundation describes using springs this way to get into or out of tight spots when wind is pinning you to the dock.
- Squall Weather & sea
-
A sudden strong wind that builds and dies away fairly quickly, often with rain, thunder and lightning. A squall line is a band of thunderstorms moving together.
- Squat Docking & boat handling
-
The stern sinking lower in the water when a boat accelerates hard, because water rushing under the hull reduces the lift under the stern.
higherlogicdownload.s3.amazonaws.com · ionianmarinesurveys.com
- Stanchion Hull & deck
-
An upright post, usually metal, along the deck edge that holds the lifelines or railing.
BoatUS lists re-bedding leaking stanchions and cleats to protect a cored deck from rot among common survey recommendations.
higherlogicdownload.s3.amazonaws.com · ionianmarinesurveys.com · boatus.com
- Stand-on vessel (Privileged vessel) Rules of the road
-
The vessel that must hold its course and speed while the other keeps clear (Rule 17). If the give-way vessel is plainly not acting, it may maneuver to avoid collision, and it must act if collision can no longer be avoided by the other alone.
In a crossing situation a stand-on power-driven vessel that does act should, if it can, avoid turning to port for a vessel on its own port side (Rule 17(c)).
- Standing part Lines & knots
-
The long, unused or made-fast part of a line, as opposed to the end you are working with when tying a knot.
- Standing rigging Sails & rigging
-
The fixed wires or rods (stays and shrouds) that hold the mast up and in place. Once tuned, it is not adjusted while sailing.
BoatUS lists a rig more than about 10 years old, frayed stays, cracked swage fittings, weeping chainplates and bottomed-out turnbuckles as signs a rigging survey is needed.
usna.edu · discoverboating.com · ionianmarinesurveys.com · boatus.com
- Starboard (Starboard side) Directions & positions
-
The right-hand side of the boat when you face the bow, whichever way you happen to be standing. The word comes from the old "steering board" that early ships carried on that side.
The starboard sidelight is green.
- Starboard tack Directions & positions
-
A sailboat is on starboard tack when the wind comes over its starboard side, so the mainsail is out on the port side.
When sailboats on the same tack meet, the Rules make the windward boat keep clear of the leeward one (Rule 12).
- State registration (Certificate of Number, CON, Registration) Crew, roles & paperwork
-
State numbering of a boat. Boats with propulsion machinery must be registered in the state of principal use (unless documented, and some states register those too), and the Certificate of Number must be aboard whenever the boat is used.
If you move the boat to a new state of principal use, the old certificate stays valid for 60 days.
- State title (Boat title, Title) Crew, roles & paperwork
-
A state certificate of ownership for a boat, required in most states for boats that are not federally documented. Trailers often need their own titles and registration.
Before buying, BoatUS advises cross-checking the HIN on the boat against the seller's papers and searching the title and registration with the state.
- Stay (Forestay, Headstay) Sails & rigging
-
Standing rigging that supports the mast fore and aft. The forestay (or headstay) runs from the bow to high on the mast and usually carries the jib or a roller furler.
discoverboating.com · ionianmarinesurveys.com · icdept.cgaux.org · usna.edu
- Steerageway Docking & boat handling
-
The lowest speed at which the boat still answers the helm. Below it, the rudder has too little water flowing past to steer.
- Stern Hull & deck
-
The back end of the boat. Moving toward it is going aft; the back corners are the port and starboard quarters.
- Stern drive (Inboard/outboard, I/O, Outdrive, Outdrive bellows) Engines & machinery
-
An inboard engine connected through the transom to a steerable drive unit outside (the outdrive) that holds the gears and propeller. Like an outboard, it steers by pointing its thrust and can be trimmed up and down.
The rubber bellows (boots) where the drive passes through the transom can crack and sink a boat; BoatUS Foundation advises checking them, especially in the folds, two or three times a year.
higherlogicdownload.s3.amazonaws.com · discoverboating.com · boatus.org
- Stern line Docking & boat handling
-
A dock line led from the stern of the boat to the dock or a piling.
- Sternlight (Stern light) Rules of the road
-
A white light at the stern shining aft over 135 degrees, 67.5 degrees either side of dead astern. If a vessel's sternlight is the only light of hers you can see, you are overtaking her.
- Sternway Docking & boat handling
-
Movement of the boat backward through the water. The opposite is headway.
- Storm surge Weather & sea
-
A rise (or drop) in sea level caused by a storm's strong winds and low pressure, on top of the normal tide. It is most dangerous when it arrives at high water with onshore winds.
- Storm warning Weather & sea
-
An NWS warning of sustained winds or frequent gusts of 48 to 63 knots (55 to 73 mph), forecast or occurring, not directly tied to a tropical cyclone.
- Stray current corrosion (Stray current) Electrical & electronics
-
Corrosion caused when current from a battery or other outside DC source, such as a partial short in the wiring, makes an underwater metal part act as an anode so it wastes away.
- Stringer (Longitudinal) Hull & deck
-
A fore-and-aft structural member inside the hull, running parallel to the keel, that gives the hull strength along its length.
discoverboating.com · ionianmarinesurveys.com · higherlogicdownload.s3.amazonaws.com
- Stuffing box (Packing gland, Stern gland, Shaft packing) Engines & machinery
-
The traditional seal where the propeller shaft leaves the hull: rings of greased flax (or PTFE) packing are squeezed around the shaft by a packing nut on the shaft log. It is meant to drip slightly while the shaft turns, which lubricates the packing; overtightening can score the shaft.
BoatUS claim files rank leaking stuffing boxes as a leading cause of boats sinking at the dock. BoatUS and Practical Sailor articles call a few drips a minute underway, and none at rest, normal.
Sources disagree on share of dockside sinkings caused by stuffing boxes — left out rather than guessed. Check your local authority.
- Sustained wind Weather & sea
-
The wind speed averaged over at least one minute. Warning and advisory thresholds are usually based on sustained wind or frequent gusts.
- Swell Weather & sea
-
Waves that have traveled away from the area where the wind made them. Swell is smoother and more regular than local wind waves, with a longer period, and it can arrive from a distant storm.
- Swim platform (Swim step) Hull & deck
-
A platform across the transom, usually with a ladder, for boarding from the water or a dinghy.
The Coast Guard warns that carbon monoxide can collect around the swim platform while engines or a generator run; keep people off it then.
- Swing radius (Swing area, Swinging room) Anchoring & mooring
-
The circle your boat can sweep around its anchor as wind and current change. Never drop anchor inside another boat's swing area.
Different boats ride to their anchors differently, so the Coast Guard handbook and BoatUS advise leaving plenty of room.
- Swivel (Anchor swivel) Anchoring & mooring
-
A fitting in the ground tackle that lets the boat turn around its anchor without twisting the chain or line.
T
- Tacking (Tack, Come about, Coming about) Sails & rigging
-
Turning the bow through the wind so the wind comes over the other side and the sails cross to the new side. Each leg of a zigzag course to windward is also called a tack.
- Thermostat Engines & machinery
-
A valve that stays closed while the engine is cold so it warms quickly, then opens gradually to send coolant to the heat exchanger and hold a steady running temperature.
Westerbeke suggests carrying a spare thermostat and gasket.
- Thimble Lines & knots
-
A grooved metal or plastic ring set inside an eye splice so the line is protected from chafe and sharp bends where it meets a shackle or chain.
- Three-strand line (Laid line, Twisted line, Plain-laid line) Lines & knots
-
Rope made of three strands twisted together. It is easy to splice, stretchy in nylon, and the usual choice for anchor rodes and many dock lines.
higherlogicdownload.s3.amazonaws.com · boatus.org · practical-sailor.com
- Through-hull (Thru-hull, Through-hull fitting) Plumbing, tanks & systems
-
A fitting that passes through the hull so water can come in or go out, such as an engine or toilet intake, a sink or cockpit drain, or a transducer. Industry standards call for a seacock on any through-hull below the heeled waterline.
BoatUS Foundation warns that ordinary plastic through-hulls turn brittle in sunlight and have cracked and sunk boats; it recommends bronze or Marelon near the waterline, and notes fittings above the waterline don't always stay above it.
- Throwable device (Type IV PFD, Throwable PFD, Throw cushion, Ring buoy) Safety & emergencies
-
A cushion or ring buoy meant to be thrown to someone in the water, not worn. Boats 16 feet and longer (except canoes and kayaks) must carry one, kept immediately available.
- Tidal current (Tidal stream, Current) Weather & sea
-
The horizontal flow of water caused by the tide. The timing of slack water and strongest current does not always line up with high and low tide and varies by place, so use current predictions, not only tide tables.
- Tide Weather & sea
-
The regular rise and fall of the water caused mainly by the pull of the moon and sun. Tide is the up-and-down movement; the sideways flow it causes is the tidal current. Most US coasts see two highs and two lows about every 24 hours 50 minutes.
dco.uscg.mil · oceanservice.noaa.gov · tidesandcurrents.noaa.gov
- Toe rail Hull & deck
-
A low rail or raised strip along the edge of the deck that helps you keep your footing. It often has slots or holes for drainage and for attaching blocks and lines.
- Topsides Hull & deck
-
The sides of the hull between the waterline and the deck. The word is also used for the area on deck, as in "going topside".
discoverboating.com · ionianmarinesurveys.com · higherlogicdownload.s3.amazonaws.com
- Traffic separation scheme (TSS) Rules of the road
-
A charted set of one-way lanes for ships approaching busy ports. Rule 10: cross a lane as close to a right angle as practicable, avoid anchoring in or near one, and if you are under 20 m or under sail do not impede ships following a lane.
- Transmission (Marine gear, Gearbox, Damper plate) Engines & machinery
-
The gearbox behind the engine that shifts between forward, neutral and reverse. A damper plate between engine and gearbox absorbs shock; chattering at idle is a sign it is worn.
Many hydraulic transmissions have a neutral safety switch so the engine will only crank in neutral. Westerbeke's schedule changes the fluid at 25 hours, then about every 300 hours or at winter lay-up.
- Transom Hull & deck
-
The flat or slightly curved surface across the stern of a square-sterned boat. The primary HIN is on the starboard side of it, and outboards and swim platforms mount to it.
The Coast Guard handbook notes a wide transom stern gives following seas a large surface to push on.
higherlogicdownload.s3.amazonaws.com · oregon.gov · discoverboating.com · ecfr.gov
- Trim (Down by the bow, Down by the stern) Docking & boat handling
-
How the boat sits fore and aft in the water: level, bow down or stern down. A change in trim changes the drafts forward and aft. On outboards and stern drives, "trim" also means tilting the drive to adjust the running angle.
- Trim tabs (Tabs) Docking & boat handling
-
Adjustable plates at the bottom of the transom of a planing boat. Lowering them lifts the stern and brings the bow down, used to get on plane, level the ride, correct a list and reduce pounding or porpoising.
The Coast Guard handbook advises adjusting them in short bursts and warns that over-trimming at high speed makes handling unpredictable.
- True north Navigation & charts
-
The direction to the geographic North Pole. Chart meridians run true north-south, and bearings and courses in the Coast Pilot are given in degrees true.
dco.uscg.mil · oceanservice.noaa.gov · nauticalcharts.noaa.gov
- True wind Directions & positions
-
The actual wind speed and direction relative to the earth, as you would feel it standing still at anchor or ashore.
- Turnbuckle (Bottlescrew, Rigging screw) Sails & rigging
-
A threaded fitting at the bottom of a stay or shroud that is turned to tighten or loosen it. Adjusting the turnbuckles to keep the mast straight and centered is called tuning the rig.
A turnbuckle screwed all the way in ("bottomed out") is one of the BoatUS red flags calling for a rigging survey.
usna.edu · ionianmarinesurveys.com · icdept.cgaux.org · boatus.com
- Twin-screw (Twin engines, Splitting throttles, Opposed propulsion) Docking & boat handling
-
A boat with two engines and propellers, usually turning in opposite directions. Running one ahead and the other astern ("splitting the throttles") twists the boat, and many can turn nearly in their own length.
Backing both engines evenly cancels their side forces, so a twin backs straighter than a single-screw boat.
U
- U.S. Chart No. 1 (Chart No. 1, Chart 1) Navigation & charts
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The official key to the symbols, abbreviations and terms used on US paper and electronic nautical charts, kept jointly by NOAA and the National Geospatial-Intelligence Agency and free online.
- Underway (Under way) Rules of the road
-
In the Rules, a vessel is underway whenever it is not anchored, not made fast to the shore and not aground. A boat drifting with its engine stopped is still underway.
V
- Variation (Magnetic variation, Declination) Navigation & charts
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The angle between true north and magnetic north at a given place, in degrees east or west. It is printed on the chart's compass rose with its yearly change, and it is the same for every boat in that area.
dco.uscg.mil · oceanservice.noaa.gov · nauticalcharts.noaa.gov
- Veer (Veering, Back, Backing) Weather & sea
-
Wind veers when its direction shifts clockwise (for example from south to west) and backs when it shifts counterclockwise, in the Northern Hemisphere.
- Vertical clearance (Bridge clearance) Navigation & charts
-
The charted height of open space under a bridge or overhead cable. In tidal waters it is measured from Mean High Water, so at higher tides there is less room than charted. Some bridges have gauges showing the actual space at the present water level.
Know your boat's air draft and compare it with the clearance and the current water level before approaching.
- Vessel Rules of the road
-
In the Navigation Rules, any watercraft used or able to be used to travel on water, including seaplanes and hovering or wing-in-ground craft. A dinghy, a kayak and a 50-foot trawler are all vessels with duties under the Rules.
- Vessel engaged in fishing Rules of the road
-
A vessel fishing with nets, lines, trawls or other gear that limits its ability to maneuver. A boat trolling lines that do not hamper its maneuvering is not "engaged in fishing" under the Rules.
Power-driven and sailing vessels underway must keep out of the way of a vessel engaged in fishing (Rule 18), but a fishing vessel must not impede traffic in a narrow channel (Rule 9).
- Vessel Safety Check (VSC, Courtesy safety check) Safety & emergencies
-
A free check of your boat's required safety equipment offered by volunteer examiners from the Coast Guard Auxiliary and America's Boating Club (US Power Squadrons), who also explain the rules and answer questions.
- VHF radio (VHF, VHF-FM, Marine radio) Electrical & electronics
-
The main short-range marine radio, working on the very high frequency band. Channel 16 is for distress and calling; channel 9 is the recreational calling channel. Recreational boats on domestic trips generally need no FCC license to use one.
Most recreational boats under 65.6 feet (20 m) are not required to carry a radio, but any radio aboard must be used under FCC rules.
uscgboating.org · dco.uscg.mil · discoverboating.com · fcc.gov
- Visual distress signals (VDS) Safety & emergencies
-
Coast Guard-approved flares, smoke, distress flags or electric lights that boats must carry on coastal waters, the Great Lakes and connected waters more than 2 nautical miles wide. Most boats need signals for both day and night use.
Boats under 16 feet, open sailboats under 26 feet without an engine, manually propelled boats and boats in organized events need only night signals when out between sunset and sunrise.
W
- Wake Docking & boat handling
-
The waves and disturbed water a moving boat leaves behind. The Coast Guard handbook says operators are responsible for their wake.
Whether you are liable for wake damage is a matter of state and federal law; the Rules don't excuse neglect such as unsafe speed, and many states set their own wake rules.
higherlogicdownload.s3.amazonaws.com · navcen.uscg.gov · discoverboating.com
- Water heater (Hot water heater) Plumbing, tanks & systems
-
A tank that heats fresh water for the galley and shower. Some are plumbed into the engine's cooling circuit so engine heat warms the water underway.
Winterize it with the rest of the freshwater system; BoatUS Foundation notes a broken water-heater fitting is one way dockside water sinks boats.
- Waterline (Boot stripe, Boot top, LWL, Length on waterline) Hull & deck
-
The line where the hull meets the water surface, often marked by a painted boot stripe at the designed waterline. Length on the waterline (LWL) is the hull's length measured there.
discoverboating.com · ionianmarinesurveys.com · higherlogicdownload.s3.amazonaws.com
- Waterspout Weather & sea
-
A rotating column of air over water, hanging from a cumulus or thunderstorm cloud and reaching the surface; some are tornadoes over water. NWS issues special marine warnings for them.
- Wave period (Period) Weather & sea
-
The time in seconds between two wave crests passing the same point. Marine forecasts often give it alongside wave height; swell has a longer period than local wind waves.
- Waypoint (WPT) Navigation & charts
-
A position you save in a GPS or chartplotter, such as a harbor entrance, a turn or a destination. Two or more waypoints joined into legs make a route.
The plotter draws straight lines between waypoints and does not know about hazards on them; check the whole route on the chart.
simrad-yachting.com · nauticalcharts.noaa.gov · oceanservice.noaa.gov
- Weather helm Sails & rigging
-
A sailboat's tendency to turn toward the wind, so the helmsman must hold the wheel or tiller to keep it straight. Too much of it usually means the mainsail is trimmed too tight; easing the main or reefing reduces it.
- Weigh anchor (Hauling, Anchors aweigh) Anchoring & mooring
-
To raise the anchor off the bottom and bring it aboard, by hand or with the windlass.
- Western Rivers Rules of the road
-
An Inland Rules term for the Mississippi River and its tributaries, South and Southwest Passes, and parts of the Atchafalaya and Red Rivers. Some special rules apply there, such as right-of-way for power-driven vessels heading downstream with the current.
- Whipping Lines & knots
-
Turns of twine or small line wrapped tightly around the end of a rope to stop it unraveling. Temporary whippings are quick; permanent ones are sewn through the line.
- Whitecap (Whitecaps) Weather & sea
-
A wave crest in open water that breaks and shows white foam because the wind is adding energy faster than the wave can carry it. Scattered whitecaps appear at about Force 3 on the Beaufort scale.
- Williamson turn Safety & emergencies
-
A maneuver that brings a vessel under power back onto its own track in the opposite direction, used to return to a person who fell overboard when you are not sure exactly where they are.
- Winch (Self-tailing winch, Winch handle) Sails & rigging
-
A geared drum turned by a handle, used to pull in heavily loaded lines such as sheets and halyards, with a removable winch handle for extra leverage.
- Wind waves (Sea, Seas, Wind sea) Weather & sea
-
Waves raised by the local wind, still in the area where they are forming. They tend to be steeper, shorter and more irregular than swell.
- Windage (Sail area) Docking & boat handling
-
The surface of the boat above water that the wind pushes on: hull sides, cabin, flybridge, canvas and rigging. A high bow or foredeck lets the wind swing the bow more easily at low speed.
The Coast Guard handbook notes a single-screw boat will generally back into the wind when it has more "sail" area forward of its pivot point.
- Windlass (Anchor windlass, Anchor winch) Anchoring & mooring
-
The winch at the bow, manual or powered, that raises and lowers the anchor rode. It may be horizontal or vertical and usually has a gypsy for chain and a capstan drum for rope.
The maker's normal working load is typically a fraction of its maximum pull; don't use the windlass to hold the boat at anchor, use a chain stopper or snubber.
- Windward (Weather side, Upwind) Directions & positions
-
Toward the direction the wind is blowing from; the side of the boat or object the wind strikes. The opposite is leeward.
For the sailing rules, a sailboat's windward side is the side opposite to where its mainsail is carried (Rule 12(b)).
- Winterizing (Lay-up, Winter lay-up, Decommissioning) Maintenance & haul-out
-
Preparing a boat for a winter or long idle period: changing oil, filling tanks and treating fuel, running antifreeze through the raw-water and freshwater systems, removing the impeller, protecting batteries and closing seacocks.
BoatUS Foundation found California had more freeze-damage claims than any other state, and notes boats stored ashore are more exposed to a sudden freeze than boats in the water.
Y
- Y-valve (Diverter valve, Y valve) Plumbing, tanks & systems
-
A three-way valve in the toilet discharge line that sends waste either to the holding tank or directly overboard (or to a pumpout fitting). Discharging untreated sewage is illegal within 3 nautical miles of shore.
In a No Discharge Zone the valve must be secured closed, for example with a padlock or a non-releasable wire tie, or by removing the handle.
Sources disagree on where an overboard Y-valve must be physically secured — left out rather than guessed. Check your local authority.
- Yacht broker (Boat broker, Broker, CPYB) Crew, roles & paperwork
-
An agent who sells used boats for owners, much like a real estate agent. In a normal sale the broker is paid by and works for the seller; a buyer's broker agreement is needed to have one represent you.
BoatUS notes only Florida and California license brokers. A Certified Professional Yacht Broker (CPYB) has passed an exam and agreed to a code of ethics.
- Yaw (Yawing) Docking & boat handling
-
Swinging from side to side off course, especially when running in a following or quartering sea; also the swinging of a boat back and forth at anchor.
higherlogicdownload.s3.amazonaws.com · ionianmarinesurveys.com · practical-sailor.com
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.