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 Bow thruster tunnel and propeller on smaller craft
Thrusters can be placed in tunnels right through the ship that are open to both the port and starboard sides. One or more propellers in the tunnels can be reversed to draw water from either the port or starboard side. If the ship is going slow enough (about 4 knots) for the propeller to suck a large amount of water through the tunnel, it will force that part of the ship to one side or the other. To steer to port, you would suck water in from the port side of the bow thruster and the starboard side of the stern thruster. If the ship is still in the water, she can be made to pirouette in place.
To slide sideways into the dock, the bow and stern thrusters would be sucking water from the same side of the ship. Without thrusters, tug boats are almost a necessity.
The faster that the ship is moving through the water, the less effective the thruster is at sucking in water. If the thrusters are used at high speed, they may well self destruct.
 Twin bow thruster tunnel covers
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