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A ducted propeller, also known as a Kort nozzle, is a marine propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. It was developed first by Luigi Stipa (1931) and later by Ludwig Kort (1934). The Kort nozzle is ...
An advanced type of propeller used on the American Los Angeles-class submarine as well as the German Type 212 submarine is called a skewback propeller. As in the scimitar blades used on some aircraft, the blade tips of a skewback propeller are swept back against the direction of rotation. In addition, the blades are tilted rearward along the ...
Other vessels may have twin, triple or quadruple screws. Power is transmitted from the engine to the screw by way of a propeller shaft, which may be connected to a gearbox. The propeller then moves the vessel by creating thrust. When the propeller rotates the pressure in front of the propeller is lower than the pressure behind the propeller.
Contra-rotating propellers are used on torpedoes due to the natural torque compensation and are also used in some motor boats. The cost of boring out the outer shafts and problems of mounting the inner shaft bearings are not worth pursuing in case of normal ships .
Replica of a propeller from the USS Monitor. Since the introduction of the marine propeller in the early 19th century, cavitation during operation has been a limiting factor in the efficiency of ships. Cavitation in marine propellers develops when the propeller operates at a high speed and reduces the efficiency of the propeller.
[clarification needed] The choice between using thrusters or traditional propellers to propel marine vessels is a compromise between versatility and efficiency. Propellers are designed to work in-line with a propulsion plant and produce one-directional thrust while thrusters are more customizable and have a more versatile application.
In marine propulsion, a variable-pitch propeller is a type of propeller with blades that can be rotated around their long axis to change the blade pitch. Reversible propellers—those where the pitch can be set to negative values—can also create reverse thrust for braking or going backwards without the need to change the direction of shaft revolution.
Diameter of the propeller. The propeller advance ratio or coefficient is a dimensionless number used in aeronautics and marine hydrodynamics to describe the relationship between the speed at which a vehicle (like an airplane or a boat) is moving forward and the speed at which its propeller is turning.
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