Tunnel Thruster is a system with the purpose of manoeuvring the bow or the stern of a vessel sideways and to allow agile movements in even the most restricted areas.

The propeller that generates the thrust is powered by an electric motor, hydraulic motor or diesel engine via a right angle gearbox. The driving parts are assembled as a system by means of a tunnel structure which can be located in the bow or stern part of the ship's hull.

The counter rotating propeller tunnel thruster make the size of gearbox and lower box significantly smaller, and the lower gearbox tends to streamline,reducing the flow resistance and noise.

The counter rotating propellers greatly reduces the bearing load and improves the safety and reliability of the thruster operation.

Possibility for flexible installation to reduce vibration.
link:https://www.thrusterleader.net/counter-rotataing-propeller-tunnel-thruster/