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A Mark 46 Mod 5A torpedo is inspected aboard a destroyer in April 2005. 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 higher the angular momentum, the greater the resisting force of the gyro to external torque (in this case more ability to cancel boat roll). A gyroscope has three axes: a spin axis, an input axis, and an output axis. The spin axis is the axis about which the flywheel is spinning and is vertical for a boat gyro.
The flow field behind the aft propeller of a contra-rotating set has very little "swirl", and this reduction in energy loss is seen as an increased efficiency of the aft propeller. An azimuthing propeller is a propeller that turns around the vertical axis. The individual airfoil-shaped blades turn as the propeller moves so that they are always ...
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.
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 ...
The process of determining the PHRF for an individual boat begins with the regional PHRF rating, then adjustments are made for the individual attributes of the boat such as: modifications to the rig, the size of the largest foresail (jib or genoa), the size of the spinnakers, type of keel (full, fin, wing etc.), the number of blades on the propeller, and the style of the propeller (fixed ...
Using Newton's laws of motion, one may usefully think of a propeller's forward thrust as being a reaction proportionate to the mass of fluid sent backward per time and the speed the propeller adds to that mass, and in practice there is more loss associated with producing a fast jet than with creating a heavier, slower jet.
The weight of the hull is similarly calculated for that length, and the weight of equipment and systems. Cargo weight is then added in to that section depending on the loading conditions being checked. The total still water bending moment is then calculated by integrating the difference between buoyancy and total weight along the length of the ...
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