Inboard motor
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An inboard motor is a marine propulsion system for boats. As opposed to an outboard motor where an engine is mounted outside of the hull of the craft, an inboard motor is an engine enclosed within the hull of the boat, usually connected to a propulsion screw by a driveshaft.
Inboard motors may be of several types, suitable for the size of craft they are fitted to. For pleasure craft, such as sailboats and speedboats, both diesel and petrol engines are used, though diesels are often preferred, as they are more efficient and pose less of a fire or explosion hazard in the air-tight environment of a boat's hull. In addition, diesels produce only small amounts of carbon monoxide gas, which can also collect in fatal amounts in and near the stern of marine craft.
For larger craft, including ships (where outboard propulsion would in any case not be suitable) the propulsion system may include many types, such as diesel, gas turbine, or even fossil-fuel or nuclear generated steam.