Sizes

Inboard motors may be of several types, suitable for the size of craft they are fitted to.

Small craft

For pleasure craft, such as sailboats and speedboats, both diesel and gasoline engines are used. Many inboard motors are derivatives of automobile engines, known as marine automobile engines.

Large 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.

Cooling

Some inboard motors are freshwater cooled, using a traditional radiator, while others have a raw water cooling system where water from the lake, river or sea is pumped by the engine to cool it. As salt water is corrosive, and would damage the engine, seagoing craft are indirectly cooled via a heat exchanger.