This specification supplies the general characteristics and requirements, and interface details of propeller-type, fixed-tunnel thruster units that are permanently installed in marine vessels or structures. Thrusters manufactured in accordance with this specification shall be identified by the following types and grades: Type I—fixed pitch; and Type II—controllable pitch; Grade 1—intermittent duty for docking and navigation; and Grade 2—continuous duty for stationkeeping or dynamic positioning. The thrusters shall meet the design, manufacturing, dimensional, and workmanship requirements specified herein.