Z-drive tug (Z-Peller)

A Z-drive tug is a tug propelled by azimuth thrusters whose pods rotate a full 360 degrees, vectoring thrust in any direction and replacing the rudder. The name comes from the driveshaft, which makes two right-angle turns in the shape of a Z to carry power down to the underwater propeller. Z-Peller is the brand name for the Niigata azimuth thruster widely used in these tugs. An azimuth stern-drive (ASD) tug mounts two such units aft and tows over the bow, giving the precise indirect-towing control that has displaced conventional single- and twin-screw harbor tugs. The competing tractor-tug layout uses bow-mounted Voith Schneider cycloidal propellers instead.