The Voith Schneider propeller (VSP), also known as a cycloidal drive is a specialized marine propulsion system. It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries.
From a circular plate, rotating around a vertical axis, a circular array of vertical blades (in the shape of hydrofoils) protrude out of the bottom of the ship. Each blade can rotate itself around a vertical axis. The internal gear changes the angle of attack of the blades in sync with the rotation of the plate, so that each blade can provide thrust in any direction, very similar to the collective pitch control and cyclic in a helicopter.
Unlike a Z-drive (where a conventional propeller is tilted on a vertical rudder axis) changing the direction of thrust with a Voith-Schneider drive merely requires changing the pattern of orientation of the vertical blades. In a marine situation this provides for a drive which can be directed in any direction and thus does away with the need for a rudder. It is highly efficient and provides for an almost instantaneous change of direction. These drives are becoming increasingly common in work boats such as fireboats and tugboats where extreme maneuverability is needed.
Z-drives (and Kort nozzles) have both advantages and disadvantages when compared to cycloidal drives. The Z-drive is less efficient and slower to maneuver, but is likely to be cheaper in the short term. Life cycle costs favor the Voith solution, something reflected in the residual value of a Voith water tractor. A choice is made on the basis of perceived performance requirements. Also the blades of the drive protrude from the bottom of the hull making shallow water operation a problem.
A low acoustic signature favors the device's use in minesweepers.
 Lift forces of the VSP on the water body |
 Path of a blade in the water |
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