I read an interesting article on the Naval Sea Systems Command web site that shows pictures of the propulsion system used on the US mine hunter ships. The ships use a Vertical Axis Cycloidal Propeller system designed and manufactured by a German based company, Voith Schneider. The Voith Schneider Propeller (VSP) not only eliminates the need for conventional props and rudders, it also eliminates the requirement for bow thrusters. This propulsion system makes the boats quieter than conventional propellor boats.
Read the full article here.