Nautical terms
16 of 469 terms in Plumbing, tanks & systems. Show all
B
- 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.
G
- Gray water (Graywater, Drain water) Plumbing, tanks & systems
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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.
H
- Holding tank (Type III MSD tank, Waste tank) Plumbing, tanks & systems
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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
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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.
M
- Macerator (Macerator pump) Plumbing, tanks & systems
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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.
- Marine head (Head, Marine toilet) Plumbing, tanks & systems
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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
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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.
N
- No-discharge zone (NDZ, No Discharge Zone) Plumbing, tanks & systems
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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.
P
- Pressure water system (Freshwater system, Freshwater pump, Accumulator tank) Plumbing, tanks & systems
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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.
- Pump-out (Pumpout, Pumpout station, Deck pumpout fitting) Plumbing, tanks & systems
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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.
S
- Sea strainer (Raw-water strainer, Strainer) Plumbing, tanks & systems
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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.
- Seacock (Sea cock) Plumbing, tanks & systems
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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
- Siphon break (Vented loop, Anti-siphon valve, Anti-siphon loop) Plumbing, tanks & systems
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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.
T
- Through-hull (Thru-hull, Through-hull fitting) Plumbing, tanks & systems
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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.
W
- Water heater (Hot water heater) Plumbing, tanks & systems
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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.
Y
- Y-valve (Diverter valve, Y valve) Plumbing, tanks & systems
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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.
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.