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Wake-equalising Duct
A wake-equalising duct is a ship hull appendage mounted in the inflow region of a screw propeller intended to realign and adjust the velocity of the wake (physics), wake at the inflow to the propeller disc. Wake velocity may be straightened out, given contra-rotational swirl, accelerated, or a combination of these effects, all of which can improve propeller efficiency, giving either higher thrust or reducing power requirement for the same thrust. Structure The wake-equalising duct is a static flow modifier attached to the Hull (watercraft), hull upstream of the propeller within the Wake (physics), wake. It may be made of a single circular section duct directly ahead of the propeller, with fixed internal and/or external fins to impart rotational changes to the wake flow, or as two semicircular ducts mounted further forwards, one on each side of the hull, aligned to provide the desired flow modification. The duct(s) may be eccentrically mounted to include mainly the thickest part of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Screw Propeller
A propeller (colloquially 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 fluid such as water or air. Propellers are used to pump fluid through a pipe or duct, or to create thrust to propel a boat through water or an aircraft through air. The blades are specially shaped so that their rotational motion through the fluid causes a pressure difference between the two surfaces of the blade by Bernoulli's principle which exerts force on the fluid. Most marine propellers are screw propellers with helical blades rotating on a propeller shaft with an approximately horizontal axis. History Early developments The principle employed in using a screw propeller is derived from sculling. In sculling, a single blade is moved through an arc, from side to side taking care to keep presenting the blade to the water at t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
