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A propeller imparts momentum to a fluid which causes a force to act on the ship. [1] The ideal efficiency of any propulsor is that of an actuator disc in an ideal fluid. This is called the Froude efficiency and is a natural limit which cannot be exceeded by any device, no matter how good it is.
For a displacement vessel, that is the usual type of ship, three main types of resistance are considered: that due to wave-making, that due to the pressure of the moving water on the form, often not calculated or measured separately, and that due to friction of moving water on the wetted surface of the hull. These can be split up into more ...
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 ...
Contra-rotating propellers have benefits when providing thrust in marine applications. 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 ...
A supercavitating propeller uses supercavitation to reduce water skin friction and increase propeller speed. The design is used in military applications, high-performance racing boats, and model racing boats. It operates fully submerged with wedge-shaped blades to force cavitation on the entire forward face, starting at the leading edge.
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 ...
A view of the end of the thruster unit from Yamato I, at the Ship Science Museum in Tokyo. MHD has no moving parts, which means that a good design might be silent, reliable, and efficient. Additionally, the MHD design eliminates many of the wear and friction pieces of the drivetrain with a directly driven propeller by an engine. Problems with ...
The first such ship to use the Voith Schneider propeller was the excursion boat Kempten. Two German 1935-type M class minesweepers M-1 and M-2 were fitted with VSPs. The first British ship to use Voith Schneider propellers was the double-ended Isle of Wight ferry MV Lymington , launched in 1938.