Water-Jet Propeller

a driving mechanism for a ship in which the motive force is created by the expulsion of a water jet.

A water-jet propeller consists of a shaped tube (water conduit) in which the flow of water is accelerated by an impeller (screw propeller or wing pump), by the combustion energy of fuel, or by the pressure of a compressed gas to provide the directional ejection of the jet. The water conduit can be either within or outside of the ship’s hull. The efficiency of a waterjet mechanism, which depends on the shape of the water conduits and on the location and design of the water scoops, is generally lower than for a screw propeller. Its advantages are that it is well protected from mechanical damage and that cavitation can be avoided. Water-jet propellers are usually used on ships sailing in shallow water or to serve as steering devices to improve a ship’s maneuverability.