- Red, right, returning
- The memory aid for the lateral buoy system: when returning from open water toward a harbor, keep red markers on your right (starboard) and green markers on your left (port). Marker numbers increase as you return from the sea.
- Bow
- The front of a boat. When you face the bow, the left side is port and the right side is starboard.
- Stern
- The rear of a boat. 'Aft' is toward the stern; 'forward' is toward the bow.
- Port
- The left side of a boat when facing the bow (front). Its navigation light is red. Memory aid: 'port' and 'left' both have four letters.
- Starboard
- The right side of a boat when facing the bow (front). Its navigation light is green.
- Hull
- The body of a boat that sits in the water. Its shape determines how the boat handles, rides, and carries weight.
- Displacement hull
- A hull that pushes water aside and moves through it at slower, steady speeds rather than rising on top. Efficient and stable but slow.
- Planing hull
- A hull shaped to generate lift at speed so the boat rises and skims across the surface, reducing drag. Used by most fast recreational powerboats.
- Deep-V hull
- A hull that cuts through chop and rough water comfortably on larger lakes and coastal water, at the cost of stability at rest.
- Flat-bottom hull
- A very stable hull in calm water (like a jon boat), but it rides rough and pounds in chop.
- Pontoon (multi-hull) boat
- A boat that rides on two or more metal tubes rather than a single hull. A very stable platform, but slower to turn.
- Capacity plate
- A plate near the helm or transom listing a boat's maximum number of people, maximum total weight, and maximum recommended horsepower. Exceeding any limit makes the boat unstable.
- Why overloading is dangerous
- It raises the center of gravity and lowers freeboard, so the boat takes on water and capsizes far more easily in waves or turns.
- Hull identification number (HIN)
- The unique 12-character code molded into a boat's transom that identifies it, like a vehicle's VIN. Tampering with it is illegal.
- Maximum horsepower rating
- The largest engine a boat is built to handle, shown on the capacity plate. An oversized engine can make the boat unstable and hard to control.
- Freeboard
- The distance from the waterline to the lowest point where water could come aboard. Overloading reduces freeboard and increases swamping risk.
- Round-bottom hull
- A hull that moves smoothly through the water but is known to roll more than other hull shapes.
- Personal watercraft (PWC)
- A small jet-powered craft (like a Jet Ski) steered by directing engine thrust. Riders must wear a life jacket and use the engine cut-off lanyard.
- Helm
- The steering station of a boat, where the wheel or tiller and controls are located. The capacity plate is often mounted near it.
- Transom
- The flat, vertical surface at the stern of a boat where an outboard motor mounts and where the HIN is found.
- PFD (personal flotation device)
- A Coast Guard-approved life jacket. Every boat must carry one wearable PFD per person; boats 16 feet and longer must also carry a throwable (Type IV).
- Type I PFD
- An offshore life jacket with the highest buoyancy that turns most unconscious wearers face-up. Best for rough, open, or remote water where rescue may be slow.
- Type II PFD
- A near-shore buoyant vest, less bulky than a Type I, that turns some unconscious wearers face-up. For calm inland and near-shore water with quick rescue likely.
- Type III PFD
- A flotation aid for conscious wearers in calm water (skiing, fishing). Comfortable, but will not reliably turn you face-up.
- Type IV PFD
- A throwable device (cushion or ring buoy) meant to be thrown to a person in the water, not worn. Required on boats 16 feet and longer.
- Type V PFD
- A special-use device (inflatable, work vest, hybrid). It only counts toward the requirement if worn and used exactly as labeled.
- Serviceable PFD
- A life jacket that legally counts: Coast Guard-approved, the right size, in good condition, and readily accessible — not in its packaging or buried under gear.
- Marine fire extinguisher (Class B)
- The extinguisher type required on most powerboats, rated for flammable-liquid fires (fuel and oil). It only counts if charged — a gauge in the red means recharge or replace.
- Sound-producing device
- An efficient whistle, horn, or bell every boat must carry to warn other vessels and signal intended maneuvers.
- Visual distress signal (VDS)
- Coast Guard-approved gear to signal an emergency: flares (day or night), an orange distress flag (day only), or an electric distress light (night only).
- Navigation lights
- Required from sunset to sunrise and in low visibility: a red sidelight to port, a green sidelight to starboard, and a white all-around or stern light.
- Backfire flame arrestor
- A device required on inboard gasoline engines that stops a carburetor backfire from igniting fuel vapor in the engine compartment.
- Engine cut-off switch (kill switch)
- A lanyard or wireless device that stops the engine if the operator is thrown from the helm, preventing a runaway boat. Required to be used on many vessels.
- Throwable device rule
- Boats 16 feet and longer must carry at least one Type IV throwable (cushion or ring buoy) in addition to a wearable PFD for each person aboard.
- Orange distress flag
- A daytime-only visual distress signal — an orange flag with a black square and circle. It cannot be used at night.
- Electric distress light
- A night-only visual distress signal that automatically flashes the SOS pattern. It cannot be used as a daytime signal.
- Pyrotechnic flare
- A handheld or aerial visual distress signal usable day or night. Flares have an expiration date and should be aimed downwind, away from people and the boat.
- Float plan
- A written description of your boat, everyone aboard, your route and destination, and expected return time — left with a responsible person ashore, not on the boat, so searchers can find you.
- Pre-departure check
- The routine before each trip: confirm safety gear is aboard and accessible, fuel is adequate, the bilge is dry, the drain plug is in, lights and battery work, and passengers know where gear is.
- Carbon monoxide (CO)
- A colorless, odorless, poisonous gas from engines and generators. It collects in cabins and around the swim platform; early symptoms (headache, dizziness, nausea) mimic seasickness.
- Station wagon (back-drafting) effect
- When a boat moving forward or idling draws its own exhaust back into the cockpit or cabin, raising carbon monoxide to dangerous levels.
- Run the blower (~4 minutes)
- Before starting an enclosed gasoline engine, run the exhaust blower about four minutes and sniff for fumes to clear explosive fuel vapor from the bilge.
- Fueling safety
- Dock and shut off engines, close hatches, keep the nozzle touching the fill pipe (to prevent static sparks), don't overfill, and ventilate before restarting. Fill portable tanks on the dock.
- Boat registration
- Most states require the owner of a motorized boat to register it before operating on public waters and to keep the certificate of registration aboard.
- Bow numbers display
- Registration numbers must be on both sides of the bow in plain block letters at least 3 inches tall, in a color contrasting with the hull, read left to right, with validation decals as the state directs.
- Small craft advisory
- A marine warning that wind and sea conditions are hazardous to small boats. Recreational boaters should stay off the water when one is posted.
- Reading a storm on the water
- Darkening clouds, a sudden temperature drop, rising wind, and choppy water signal an approaching storm. Head for the nearest safe harbor early.
- Why fill portable tanks on the dock
- Filling a portable gas tank on the dock (not in the boat) lets spilled fuel and vapor disperse in the open air instead of collecting in the bilge where it could explode.
- CO detector
- A device installed in enclosed cabins that sounds an alarm when carbon monoxide reaches dangerous levels, warning occupants before symptoms appear.
- Float plan — change of plans
- If your plans change partway through a trip, contact your float-plan holder so they don't launch an unnecessary search.
- Drain plug
- A removable plug that seals the bilge or transom. Confirm it is installed during the pre-departure check, or the boat will take on water once launched.
- Navigation rules
- The 'rules of the road' for boats (COLREGS and U.S. Inland Rules) governing how vessels meet, cross, and overtake to prevent collisions, including which vessel must give way.
- Give-way vessel
- The vessel required to take early, obvious action to keep clear. In a crossing, the boat that has the other on its starboard (right) side is the give-way vessel.
- Stand-on vessel
- The vessel that holds its course and speed while the give-way vessel maneuvers to avoid it — though it must still act to avoid a collision if the other boat doesn't.
- Meeting head-on
- When two power boats approach head-on, neither has the right of way. Both turn to starboard (right) and pass port-to-port (left side to left side).
- Crossing situation
- When two boats' paths cross, the boat on the right is the stand-on vessel. The boat that sees the other on its starboard side must give way.
- Overtaking
- When passing another boat, the boat being passed is the stand-on vessel; the overtaking boat is the give-way vessel and must keep clear until well past.
- Nun buoy
- A red, cone-topped lateral buoy with an even number. Keep it on your right (starboard) when returning from open water.
- Can buoy
- A green, flat-topped lateral buoy with an odd number. Keep it on your left (port) when returning from open water.
- Safe-water marker
- A red-and-white vertically striped buoy indicating open, navigable water all around — often a channel entrance or mid-channel. Pass it on either side.
- Preferred-channel (junction) marker
- A buoy with red and green horizontal bands. The color of the topmost band tells you which side to keep it on for the preferred channel.
- Soundings
- The depth numbers scattered across the water areas of a nautical chart, given in the unit named in the chart's title block (feet or fathoms).
- Nautical chart
- A map of a waterway showing depths, hazards, channels, and aids to navigation. Read it before a trip on unfamiliar water to avoid running aground.
- Regulatory marker — circle
- A white marker with an orange circle marks a controlled area, such as a no-wake or speed-restricted zone.
- Regulatory marker — diamond
- A white marker with an orange diamond warns of danger, such as rocks, a dam, or other hazards.
- Regulatory marker — diamond with a cross
- A white marker with an orange diamond enclosing a cross marks a keep-out area where boats are prohibited, like a swimming area.
- Daymark
- A fixed navigation sign mounted on a piling: a green square daymark marks the port side, a red triangle daymark marks the starboard side (when returning).
- Power gives way to sail
- A power-driven vessel generally must keep clear of (give way to) a sailing vessel and human-powered craft like canoes and kayaks.
- No absolute right of way
- There is no absolute right of way on the water — even the stand-on vessel must take action to avoid a collision if the give-way vessel fails to act.
- Safe speed
- Going slowly enough to stop or turn in time to avoid a hazard, given visibility, traffic, and your boat's maneuverability. A boat has no brakes, so distance and momentum matter.
- No-wake zone
- An area where boats must travel at idle or headway speed — the slowest speed that still maintains steerage — so they produce little or no wake.
- BUI (boating under the influence)
- Operating a boat impaired by alcohol or drugs. It is illegal in every state at a blood alcohol concentration of 0.08 percent, the same limit as for driving.
- Boater's fatigue
- The way sun, wind, noise, vibration, and motion intensify alcohol's effects on the water, so a boater becomes dangerously impaired faster than someone on land.
- Reckless operation
- Dangerous boat handling — weaving through traffic, bow-riding, jumping wakes near others, or excessive speed near boats and swimmers. It is illegal everywhere.
- Man-overboard first action
- Reduce speed and assign someone to point at and keep eyes on the person at all times — losing sight of them is the greatest danger. Then throw flotation and turn back.
- Shut off the engine before recovery
- When bringing a person aboard after a man-overboard, stop the engine before they reach the side so the propeller can't injure them.
- Capsizing — stay with the boat
- If a boat capsizes or swamps but keeps floating, stay with it, climb onto or hold the hull, and signal for help. A floating boat is far easier to spot than a swimmer.
- Cold-water shock
- The body's reaction to sudden cold-water immersion: in the first minute, an involuntary gasp reflex and rapid breathing that can cause drowning — the deadliest phase, before hypothermia.
- Hypothermia
- A dangerous drop in core body temperature from prolonged cold-water exposure. Signs include shivering, confusion, and weakness; rewarm the person gently and seek help.
- Mayday
- The spoken signal for a grave, life-threatening emergency. Say it three times on VHF Channel 16, then give your boat's name, position, the emergency, and number aboard.
- Pan-Pan
- The spoken radio signal for an urgent but not immediately life-threatening situation, such as a disabled but safe vessel. Less urgent than Mayday.
- VHF Channel 16
- The international distress, safety, and calling frequency monitored by the Coast Guard. Make distress (Mayday) calls here.
- EPIRB / PLB
- An emergency beacon that, when activated, automatically transmits a distress signal and your position. An EPIRB registers to a vessel; a PLB is wearable and registers to a person.
- Anchoring scope
- The length of anchor line let out, recommended at about 7 to 10 times the water depth. Set the anchor off the bow — never the stern, which can swamp the boat.
- Running aground
- When a boat's hull contacts the bottom. Check the bilge and hull for damage and leaks before trying to free it, and don't gun the engine, which can worsen damage.
- Engine compartment fire
- If a fire breaks out, shut off the engine and fuel, get people into PFDs, position the boat so wind carries flames away, and aim the extinguisher at the base of the fire.
- Diver-down flag
- A red flag with a white diagonal stripe meaning a scuba diver is in the water nearby. Slow to idle and stay well clear — generally at least 100 feet.
- Alfa (diver-down) flag
- A blue-and-white swallowtail pennant signaling a vessel has a diver down and is restricted in its ability to maneuver. Give it a wide berth.
- Water-skiing observer
- When towing a skier, you need an observer aboard, separate from the operator, to watch the person being towed and relay signals so the driver can focus on steering.
- Illegal discharge of oil
- Federal law forbids discharging oil or fuel that causes a sheen on the water. Any such spill is prohibited and may have to be reported to the National Response Center.
- Aquatic invasive species
- Non-native plants and animals like zebra mussels and hydrilla that hitchhike on boats and damage ecosystems. Stop their spread by cleaning, draining, and drying your boat.
- Clean, drain, dry
- The method to prevent spreading invasive species: clean off all plants and debris, drain all water from the boat and gear, and let everything dry before launching elsewhere.
- Marine sanitation device (MSD)
- Required equipment on boats with an installed toilet to treat or hold sewage. Discharging untreated sewage into inland and many coastal waters is illegal.
- Garbage discharge rule
- Federal law prohibits dumping plastic anywhere and restricts other garbage by distance from shore. Stow trash aboard and dispose of it ashore.
- Idle speed away from the dock
- Keep a slow, controlled idle-type speed until well clear of docks and other boats, to minimize wake and keep full maneuvering control in congested areas.
- Fenders
- Cushions hung along a boat's side to protect the hull from rubbing or banging against a dock or another boat when coming alongside.
- Why not fend off by hand
- Never use hands or feet to push a boat off a dock — a heavy boat can crush them. Use fenders and lines, and reposition with the engine instead.
- Lightning on open water
- If caught in a storm, head for safe harbor early; if you can't, lower antennas, stay low and centered, and keep away from metal — life jackets on everyone.
- Towing a disabled vessel
- Use a strong line and the longest scope practical, keep speed low, and have everyone wear PFDs. Watch for sudden tension that could snap the line.
- Steering failure
- If steering fails at speed, reduce throttle immediately and use the engine cut-off switch if needed, then signal other boats and try to anchor or get a tow.
- Severe seasickness
- Beyond comfort, a severely seasick person can become dehydrated and weak; keep them hydrated, in fresh air watching the horizon, and head for calmer water.