From a circular plate, rotating around a vertical axis, a circular array of vertical blades 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 the azimuth thruster, the 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. Azimuth thrusters have both advantages and disadvantages when compared to cycloidal drives. The azimuth thruster 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. Instead of a Kort nozzle, VSPs are often fitted with a "thrust plate" or "propeller guard" which acts as a nozzle at low speed, protects the VSP against grounding and provides another blocking location during drydocking. A low acoustic signature favours the device's use in minesweepers by minimising cavitation as the rotor does not need to rotate as fast for a given thrust. The underwater sound signature of the MV North Sea Giantdynamic positioning vessel was measured by the International Centre for Island technology whilst installing a foundation monopile for the Voith tidal energy device in the Falls of Warness, Orkney. VSPs are offered with an input power range of 160 kW to 3900 kW
History
The Voith Schneider propeller was originally a design for a hydro-electricturbine. Its Austrian inventor, Ernst Schneider, had a chance meeting on a train with an employee of Voith's subsidiary St. Pölten works; this led to the turbine being investigated by Voith's engineers, who discovered that although it was no more efficient than other water turbines, Schneider's design worked well as a pump by reversing the flow through the device. By changing the orientation of the vertical blades, it could be made to function as a combined propeller and rudder. In 1928 a prototype was installed in a 60-hp motor launch named Torqueo and trials were carried out on Lake Constance. A number of German minesweepers were fitted with VSPs; the first of these was the R8, built in 1929 by Lürssen. By 1931 VSPs were being fitted in new vessels on Lake Constance run by the German State Railways. 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. Some 80 ships had been installed with VSPs by the end of the 1930s, including the uncompleted 1938 German aircraft carrierGraf Zeppelin, and the Japanese submarine cable laying shipToyo-maru. The three vessels currently used by the Woolwich Ferry feature Voith-Schneider propulsion systems. They were built in 1963 by the Caledon Shipbuilding & Engineering Company of Dundee and feature one VSP in the bow and a second in the stern for remarkable maneuverability. The Tay Ferries Scotscraig and Abercraig which were built by the Caledon in the 1950s also used VSPs The US Navy built twelve VSP-equipped Osprey-class coastal minehunters in the 1990s. These vessels have been decommissioned and are being sold to foreign navies. The French Navy operates sixteen tugboats of the RPC12 type, that can provide a 12-tonne bollard pull thanks to two Voith Schneider Propellers. The same device, mounted on a horizontal rather than a vertical axis, has been used to provide lift and propulsion on a few experimental aeroplanes, known as "cyclogyros". None of them were very successful.
