Marine propulsion system supported by a strut

A marine propulsion system, supported by a strut, comprising:

• an inner propeller shaft supporting a first propeller adjacent a trailing end thereof, and the inner propeller shaft having an interface, at a leading end thereof, to facilitate connection with a drive shaft for receiving torque therefrom and supplying a first portion of the torque to the first propeller;
• an outer propeller shaft supporting a second propeller, adjacent a trailing end thereof, and the outer propeller shaft surrounding the inner propeller shaft;
• the strut having a strut through bore for accommodating and surrounding the inner and the outer propeller shafts, and the strut having a flat end face configured to abut an outwardly facing bottom surface of a hull of a vessel;
• and
• a planetary gear assembly for receiving a second portion of the torque from the drive shaft and supplying the second portion of torque to the outer propeller shaft so that the second propeller rotates in an opposite rotational direction than the first propeller;
• wherein at least a portion of the planetary gear assembly is accommodated vertically above the flat end face of the strut for reducing hydrodynamic drag generated by the strut as the marine propulsion system travels through water;
• an aft sun gear is formed integrally with the inner propeller shaft for driving the second propeller;
• a forward sun gear is securely fastened to a housing assembly so as to prevent rotation of the forward sun gear during operation of the marine propulsion system;
• the forward sun gear and the aft sun gear comprise components of a rotatable planetary gear assembly, the planetary gear assembly further comprises a forward planetary hub and an aft planetary hub and each of the forward and aft planetary hubs has an identical number of pinion through bores formed therein, and a first end of a respective planetary pinion shaft is supported by the forward planetary hub while a second respective end of each planetary pinion shaft is supported by the aft planetary hub;
• and
• wherein each the planetary pinion shaft supports an integrally formed double planetary gear, the integral double planetary gear comprises a slightly smaller diameter forward planetary gear, which engages with the forward sun gear and a slightly larger diameter aft planetary gear which engages with the aft sun gear.

A method of using a marine propulsion system to power a vessel, the method comprising:

• supporting the marine propulsion system on the vessel by a strut;
• supporting a first propeller adjacent a trailing end of an inner propeller shaft;
• providing an interface at a leading end of the inner propeller shaft to facilitate connection with a drive shaft for receiving torque therefrom and supplying a first portion of the torque to the first propeller;
• supporting a second propeller adjacent a trailing of an outer propeller shaft, and the outer propeller shaft surrounding the inner propeller shaft;
• providing the strut with a flat end face that abuts an outwardly facing bottom surface of a hull of the vessel, and providing the strut with a strut through bore for accommodating and surrounding the inner and the outer propeller shafts;
• and
• providing a planetary gear assembly for receiving a second portion of the torque from the drive shaft and supplying the second portion of torque to the outer propeller shaft so that the second propeller rotates in an opposite rotational direction to the first propeller;
• and
• accommodating at least a portion of the planetary gear assembly vertically above the flat end face of the strut so as to reduce hydrodynamic drag, generated by the strut, as the marine propulsion system travels through water.