Voith-Schneider propeller (VSP)

The Voith-Schneider propeller is a cycloidal, vertical-axis propulsor: a rotating disk flush with the hull bottom carries several vertical blades whose pitch is cyclically varied each revolution by a kinematic linkage, so the resultant thrust can be set to any magnitude and direction in the horizontal plane without a rudder. Moving the linkage’s steering center changes the blade-pitch schedule and steers the thrust vector instantly, giving the precise low-speed station-keeping that tugs and ferries need. Efficiency is lower than a screw at transit speed because the blades work a full cycle of incidence, but omnidirectional control and fast thrust reversal are the trade. It is a cycloidal drive, distinct from an azimuth thruster that rotates a fixed screw.