Nautical terms
24 of 469 terms in Engines & machinery. Show all
B
- 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.
C
- 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
D
- Diesel engine (Diesel) Engines & machinery
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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.
- Dripless shaft seal (Dripless seal, PSS seal, Face seal, Mechanical shaft seal) Engines & machinery
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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
- Engine hours (Hour meter, Hours, Elapsed time meter) Engines & machinery
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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.
- Exhaust elbow (Mixing elbow, Water-injected exhaust elbow, Wet exhaust, Muffler) Engines & machinery
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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.
F
- Freshwater cooling (Closed cooling, Coolant, Antifreeze, Coolant recovery tank) Engines & machinery
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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
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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
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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.
G
- Generator (Genset) Engines & machinery
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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.
- Glow plug (Glow plugs, Preheat) Engines & machinery
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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.
H
- Heat exchanger Engines & machinery
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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.
I
- Impeller (Raw-water pump impeller, Water pump impeller) Engines & machinery
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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.
- Inboard engine (Inboard, Direct drive, V-drive) Engines & machinery
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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
O
- Outboard motor (Outboard, Lower unit, Kicker) Engines & machinery
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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
P
- Propeller (Prop, Screw, Right-handed propeller, Left-handed propeller) Engines & machinery
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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
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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
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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
R
- Raw-water cooling (Raw water, Seawater cooling, Raw-water pump) Engines & machinery
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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.
S
- Shaft coupling (Coupling, Flexible coupling) Engines & machinery
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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.
- Stern drive (Inboard/outboard, I/O, Outdrive, Outdrive bellows) Engines & machinery
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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
- Stuffing box (Packing gland, Stern gland, Shaft packing) Engines & machinery
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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.
T
- Thermostat Engines & machinery
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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.
- Transmission (Marine gear, Gearbox, Damper plate) Engines & machinery
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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.
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.