Voith Schneider

The Voith Schneider Propeller is a cycloidal propeller from Voith: a set of vertical blades on a rotating disc under the hull, each blade pitching on its own axis as the disc turns. Changing the blade-pitch pattern vectors thrust to any direction in the horizontal plane instantly, with no rudder, so the unit steers and propels at once and reverses without changing rotation. This gives precise low-speed control and fast thrust reversal, which suits harbor tugs, double-ended ferries, and buoy tenders. The trade-off is mechanical complexity and lower top-speed efficiency than a screw propeller. Voith introduced it in the late 1920s.