PURPOSE: To make the oscillation of a steering seat and a cabin smaller than the oscillation of a hull so as to improve the riding comfortableness by accommodating a float having the low position of center of gravity where a steering seat, a cabin and an engine are united in a body in the inside of a notch formed on the rear portion of a hull facing the outside water in such a manner as to freely oscillate.

CONSTITUTION: A notch 2 is formed on the rear portion of a hull 1 in such a manner as to face the outside water, and a float 3 is accommodated in the inside of the notch 2 in such a manner as to freely oscillate. The front surface of the float 3 is formed semi-spherically, a balance weight 4 is charged on the bottom portion of the float 3 and an engine 5 is disposed thereon. A propeller 6 projected from the float 3 backward is connected directly to the engine 5. An upward extending shaft 7 is provided on the float 3, and a steering seat 8 is formed integral with the upper end of the shaft 7. A steering and trim cylinder 9 is interposed between the lower surface of the steering seat 8 and the tail portion of the hull 1, and driven to elongate and contract, interlocking with the steering operation from the steering seat. Thus, more stable posture against rolling and pitching of the hull can be retained in the cabin and the steering seat.