Propulsion device for boats

Claim 1

A propulsion device for boats comprising: a. a housing having a front wall through which said housing is mounted upon the outside of a transom of a boat, right and left side walls fixed to said bottom wall, a bottom fixed to said front and side walls and having a bottom wall formed semicircular in cross-section at the rear end portion of said bottom, and right and left extension walls extending substantially vertically from the bottom so as to connect said bottom with the lower ends of the corresponding side walls, said bottom and extension walls defining a cavity having an inverted U-shaped cross-section and a progressively increasing depth toward the rear end thereof; b. a propeller shaft penetrating said bottom and said front wall and having the rear end portion thereof disposed substantially on the center of the semi-circular rear portion of said bottom wall; c. a propeller fixed to said rear end portion of said propeller shaft so as to be disposed in the rear end portion of said cavity; d. said side walls and corresponding extension walls each having a partition wall to define a pair of exhaust conduits; and e. an exhaust tube disposed in said housing and having one end connected with the exhaust manifold of an engine of the boat for driving said propeller shaft and the other end connected with said exhaust conduits.