power: For torque: Actual performance When a propeller is added to a ship its performance is altered; there is the mechanical losses in the transmission of power; a general increase in total resistance; and the hull also impedes and renders non-uniform the flow through the propeller. The ratio between a propeller's efficiency attached to a ship () and in open water () is termed relative rotative efficiency. The overall propulsive efficiency (an extension of effective power ()) is developed from the propulsive coefficient (), which is derived from the installed shaft power () modified by the effective power for the hull with appendages (), the propeller's thrust power (), and the relative rotative efficiency. / = hull efficiency = / = propeller efficiency = / = relative rotative efficiency = / = shaft transmission efficiency Producing the following: The terms contained within the brackets are commonly grouped as the quasi-propulsive coefficient (, ). The is produced from small-scale experiments and is modified with a load factor for full size ships. Wake is the interaction between the ship and the water with its own velocity relative to the ship. The wake has three parts: the velocity of the water around the hull; the boundary layer between the water dragged by the hull and the surrounding flow; and the waves created by the movement of the ship. The first two parts will reduce the velocity of water into the propeller, the third will either increase or decrease the velocity depending on whether the waves create a crest or trough at the propeller. See also Propeller Variable-pitch propeller (disambiguation) Propeller (aeronautics) Ground-adjustable propeller Cavitation References Propellers