An inboard motor is a marine propulsion system for . As opposed to an outboard motor, where an engine is mounted outside the hull of the craft, an inboard motor is an engine enclosed within the hull of the boat, usually connected to a propulsion propeller by a driveshaft.
Marine diesel engines used in international shipping are the largest, most powerful engines ever produced.
History
The first marine craft to utilize inboard motors were steam engines going back to 1805 and the
Clermont and the
Charlotte Dundas. Harbour tugs, and small steam launches had
inboard steam engines. In the 1880s the
naphtha engine made its appearance and a few boat engines appeared. Such engines had low power and high fuel consumption.
The gasoline (petrol) engine pioneer
Gottlieb Daimler and Maybach built a four-cycle boat engine and tested it in 1887 on the Neckar River. Sintz in America built several commercially available engines from 1893.
Sizes
Inboard motors may be of several types, suitable for the size of craft they are fitted to. Boats can use one cylinder to v12 engines, depending if they are used for racing or trolling.
Small craft
For pleasure craft, such as sailboats and speedboats, diesel,
gasoline and electric
engines are used. Many inboard motors are derivatives of automobile engines, known as marine automobile engines. The advent of the
stern drive propulsion leg improved design so that auto engines could easily power boats.
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 engine,
gas turbine, or even fossil-fuel or nuclear-generated steam. Some early models used coal for steam-driven ships.
The largest engines in the world are marine diesel engines used to power supertankers and . The Wärtsilä RT-flex96C produces , weighs , stands tall, is long, and has a maximum of 109 rpm.
Cooling
Some inboard motors are freshwater cooled, while others have a raw
water cooling system where water from the
lake,
river or
sea is pumped by the engine to cool it.
However, as seawater is corrosive, and can damage engine blocks and cylinder heads, some seagoing craft have engines which are indirectly cooled via heat exchanger in a keel cooler. Other engines, notably small single and twin cylinder diesels specifically designed for marine use, use raw seawater for cooling and zinc sacrificial are employed to protect the internal metal castings.
