T Series hydraulic tunnel thrusters are compact and easy to fit units that can be supplied complete with steel, aluminium or composite tunnels, pre-drilled ready for installation. The thruster hub units are protected by twin shaft seals on each propeller shaft, and a single shaft seal on the vertical input shaft. The tunnel thruster uses high torque spiral bevel gears and twin con-tra-rotating propellers to develop a high thrust to tunnel diameter ratio.