A boat can be more easily maneuvered by the use of a bow thruster which consists of a water pump and a valve arrangement for diverting the water into either of two pipelines that open at the opposite sides of the boat near the bow. It would be desirable if the thrust obtainable from a water pump placed on board a vessel could be used to help maneuver the boat, or if required, to propel the boat forwardly, as when the propeller has been broken or where the propeller could cause injury to persons or articles in the water.