The idea is: Two propellers, two duct- rudders.
In theory that would enable to move the stern to one side but not moving the ship forward or aft
when one propeller runs forward and one backward, cancelling out the forward / backward motion
but adding the sideward motion by the tilt of the rudders (one to the left, the other to the right right).
And it realy works:
To balance the strong force of that control method, a big paddle wheel bow thruster is installed:
Bow thruster action
Combined action: