Patent ID: 6899576

Claim:
The combination comprising: (a) a watercraft having a hull; (b) a watercraft drive including at least one drive shaft; (c) front and rear propellers, respectively mounted on said at least one drive shaft in coaxial longitudinally displaced relationship; (d) each of said propellers having at least two blades; (e) said front and rear propellers having equal diameters and being driven at like rotational velocities; (f) control means disposed between said front and rear propellers, for increasing the energy of a jet of water exiting the front propeller as said jet is transmitted to the rear propeller; (g) said control means acting on the water jet leaving the front propeller with both circular and axial flow components to reach the rear propeller substantially with axial flow components only; (h) said control means comprising, (i) a hollow shaft having an upper end connected to said hull and a lower end, (ii) a gondola-shaped underwater housing mounted on the lower end of said hollow shaft and containing said watercraft drive with said at least one drive shaft extending from opposite ends of said underwater housing, and (iii) a plurality of guide blades connected to at least one of said hollow shaft and gondola-shaped underwater housing; (i) an energy source mounted in said hull for transmitting energy through said hollow shaft to said watercraft drive for rotating said front and rear propellers; (j) the central portion of said rear propeller up to a diameter equal to the diameter of a water jet arriving at the rear propeller, which water jet, due to the action of the front propeller, has a contracted cross section, is designed to optimize the jet energy exiting the front propeller; and (k) said rear propeller further having an annular area extending from said central portion to the outer circumference of the rear propeller, which is designed with the same design as that characterizing the front propeller, said annular area of the rear propeller interacting with surrounding ambient water.