Anti-siphon valve: Device that admits air to break a water column and prevent unwanted siphoning.
Back pressure: Resistance to exhaust flow. Excessive back pressure can reduce power and raise temperature.
BSFC: Brake-specific fuel consumption, usually mass of fuel used per unit of power and time.
Calorifier: Marine hot-water tank heated by engine coolant, electricity or both.
Common rail: Electronically controlled injection system using a shared high-pressure fuel rail.
Compression ignition: Ignition of injected fuel by air heated through compression.
Cutless bearing: Water-lubricated rubber-lined bearing supporting a propeller shaft.
Duty rating: Manufacturer definition of allowable output and operating pattern.
ECU: Electronic control unit managing injection and other functions.
Heat exchanger: Transfers heat between closed coolant and raw water without mixing them.
Intercooler or aftercooler: Cools compressed intake air after the turbocharger.
Lift pump: Supplies low-pressure fuel from tank and filters towards the injection system.
Mixing elbow: Point where cooling water is injected into the exhaust downstream of the engine.
NMEA 2000: Marine data network that may carry engine measurements and alarms.
Primary filter: Vessel-mounted first-stage fuel filter, often with a water separator.
Raw water: Seawater or lake water drawn through the vessel for cooling.
Reduction ratio: Relationship between engine speed and gearbox output speed.
Saildrive: Geared drive leg passing through a yacht hull to a horizontal propeller shaft.
Secondary filter: Fine fuel filter commonly mounted on the engine.
Stern gland: Assembly sealing around a propeller shaft where it passes through the hull.
Waterlock: Wet-exhaust chamber that collects cooling water and reduces noise while the engine runs.