Enhanced Tractor Tug (ETT)

A very powerful tug boat with cycloidal drive (Voith-Schneider) systems, fire fighting system, and towing winches. The cycloidal drive system consists of revolving vertical blades having a variable pitch that can produce a propelling force in any horizontal direction. An ETT is capable of applying a greater than its maximum propulsion force when it uses its keel to skeg. The Nanuq and Tan’erliq are the two ETT’s used in Prince William Sound.