Operation
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 and cyclic of helicopter flight controls.
Unlike a Z-drive (where a conventional propeller is tilted on a vertical rudder axis) changing the direction of thrust, 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 manoeuvrability 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 manoeuvre, but is likely to be cheaper in the short term. Life cycle costs favour 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 favours the device's use in minesweepers by minimising cavitation (usually produced at the tips of axial propellers) as the rotor does not need to rotate as fast for a given thrust. The underwater sound signature of the MV North Sea Giant (IMO: 9524073, MMSI: 248039000) Dynamic Positioning (DP) vessel was measured by the International Centre for Island technology (ICIT) whilst installing a foundation monopile for the Voith tidal energy device in the Falls of Warness, Orkney (Ref Beharie and Side, 2011).
Read more about this topic: Voith Schneider Propeller
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