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The supercavitating propeller is a variant of a

propeller A propeller (often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working flu ...

for propulsion in water, where

supercavitation Supercavitation is the phenomenon of a cavitation bubble reducing skin friction drag on a submerged object and enabling high speeds. Applications include torpedoes and propellers, but in theory, the technique could be extended to an entire un ...

is actively employed to gain increased speed by reducing friction. They are being used for military purposes and for high performance racing boats as well as model racing boats. This article distinguishes a supercavitating propeller from a subcavitating propeller running under supercavitating conditions. In general, subcavitating propellers become less efficient when they are running under supercavitating conditions. The supercavitating propeller operates submerged with the entire diameter of the blade below the water line. Its blades are wedge-shaped to force cavitation at the leading edge and to avoid water

skin friction Skin friction drag or viscous drag is a type of aerodynamic or hydrodynamic drag, which is resistant force exerted on an object moving in a fluid. Skin friction drag is caused by the viscosity of fluids and is developed from laminar drag to turb ...

along the whole forward face. As the cavity collapses well behind the blade, the supercavitating propeller avoids the

spall Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ba ...

ing damage due to cavitation that is a problem with conventional propellers. An alternative to the supercavitating propeller is the

surface piercing Surface piercings are Body piercing, piercings that are found on flat parts of the body, giving a double-pierced look that sits flat against the skin. A surface bar follows the plane of skin, while a standard piercing is pierced through the plane. ...

, or ''ventilated'' propeller. These propellers are designed to intentionally leave the water and entrain atmospheric air to fill the void, which means that the resulting gas layer on the forward face of the propeller blade consists of air instead of water vapour. Less energy is thus used, and the surface-piercing propeller generally enjoys lower drag than the supercavitating principle. The surface-piercing propeller also has wedge-shaped blades, and propellers may be designed that can operate in both supercavitating and surface-piercing mode. Supercavitating propellers were developed to usefulness for very fast military vessels by

Vosper & Company Vosper & Company, often referred to simply as Vospers, was a British shipbuilding company based in Portsmouth, England. History The Company was established in 1871 by Herbert Edward Vosper, concentrating on ship repair and refitting work. By ...

. The pioneer of this technology and other high speed offshore boating technologies was

Albert Hickman Albert Edgar Hickman (August 2, 1875 – February 9, 1943) was the seventeenth Prime Minister of Dominion of Newfoundland, Newfoundland. Biography Albert Hickman was born in Grand Bank on August 2, 1875. He married Mary Louise Laurie on Decem ...

(1877–1957), early in the 20th century. His ''Sea Sled'' designs used a surface piercing propeller.

References

''Damned by Faint Praise''
article in ''Wooden Boat'' about Albert Hickman

Propellers Shipbuilding

See also

References