Propulsion systems

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Propulsion systems
A ship's engineroom
Main article: Marine propulsion

Propulsion systems for ships fall into three categories: human propulsion, sailing, and mechanical propulsion. Human propulsion includes rowing, which was used even on large galleys. Propulsion by sail generally consists of a sail hoisted on an erect mast, supported by stays and spars and controlled by ropes. Sail systems were the dominant form of propulsion until the 19th century. They are now generally used for recreation and competition, although experimental sail systems, such as the turbosails, rotorsails, and wingsails have been used on larger modern vessels for fuel savings.

Mechanical propulsion systems generally consist of a motor or engine turning a propeller, or less frequently, an impeller or wave propulsion fins. Steam engines were first used for this purpose, but have mostly been replaced by two-stroke or four-stroke diesel engines, outboard motors, and gas turbine engines on faster ships. Nuclear reactors producing steam are used to propel warships and icebreakers, and there have been attempts to utilize them to power commercial vessels (see NS Savannah).

There are many variations of propeller systems, including twin, contra-rotating, controllable-pitch, and nozzle-style propellers. Smaller vessels tend to have a single propeller. Large vessels use multiple propellers, supplemented with bow- and stern-thrusters. Power is transmitted from the engine to the propeller by way of a propeller shaft, which may or may not be connected to a gearbox. Some modern vessels use electric motors connected directly to the propeller shaft, usually powered by generators. These electric systems are often more energy efficient than o




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