 These thrusters have been developed alongside propellers and have some advantages over propellers due to their construction with a tunnel that reduces losses thrown out the sides as with a propeller and is contained in only the direction intended for use.Positioning thrusters come in 2 main form factors, those being bow thrusters situated on the forward end of the boat and stern thrusters set in the aft of the boat.Their purpose, as the name suggests is to maneuver or position the boat to a greater degree than the propulsion device can ultimately accomplish.