Abstract: The invention comprises a steerable propeller unit for use in place of a steerable rudder and fixed propeller on watercraft employing inboard straight line propulsion systems. A coupler is fitted to the rear of the drive shaft projecting from the craft in place of a propeller. The coupler is affixed to a splined shaft which, in turn, is connected to a universal drive joint. A pivotable rudder shaft interconnects with the steering mechanism for the craft, and carries at its lower end a strut bearing. A short shaft connected to the universal joint extends through the strut bearing, and the propeller is affixed to the shaft behind the strut bearing. The propeller may thus be swung through an arc to either side of the center line of the craft by the steering mechanism. Top, bottom and side rudder plates may optionally be affixed to the strut bearing assembly.