Marine propulsion system supported by a strut

A marine propulsion system comprising:

• a strut having a strut through bore extending therethrough;
• 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 as well as for transferring thrust, generated by the first propeller, along the inner propeller shaft back to the drive shaft;
• an outer propeller shaft supporting a second propeller adjacent a trailing end thereof, and the outer propeller shaft surrounding a portion of the inner propeller shaft;
• the inner and the outer propeller shafts both extending completely through the strut through bore;
• a differential gear set being accommodated within the strut and surrounding both the outer and inner propeller shafts, the differential gear set comprising a differential input shaft, a differential output shaft and first and second idle gears, and the differential input shaft being drivingly connected to the inner propeller shaft in order to receive a second portion of the torque supplied thereto and the differential gear set reversing the second portion of the torque so that the differential output shaft drives the outer propeller shaft so as to rotate the second propeller in an opposite rotational direction than the first propeller;
• and
• a leading end of the outer propeller shaft being connected to a leading end of the inner propeller shaft to facilitate, during operation, both rotation of the outer propeller shaft with respect to the inner propeller shaft as well as transfer of thrust, generated by the second propeller, to the inner propeller shaft and back to the drive shaft.

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

• providing a strut having a strut through bore extending therethrough;
• supporting a first propeller adjacent a trailing end of an inner propeller shaft, and forming an interface, adjacent a leading end of the inner propeller shaft, to facilitate connection with a drive shaft and receive torque therefrom, and the inner propeller shaft supplying a first portion of the torque to the first propeller as well as transferring thrust, generated by the first propeller, along the inner propeller shaft back to the drive shaft;
• supporting a second propeller adjacent a trailing end of an outer propeller shaft, and surrounding the inner propeller shaft with the outer propeller shaft;
• extending both the inner and the outer propeller shafts completely through the strut through bore;
• accommodating a differential gear set within the strut and surrounding the outer propeller shaft with the differential gear set, the differential gear set comprising a differential input shaft, a differential output shaft and a pair idler gears;
• drivingly connecting the differential input shaft to the inner propeller shaft in order to receive a second portion of the torque supplied thereto and drivingly connecting the differential output shaft to the outer propeller shaft with the differential gear set causing the second propeller to rotate in an opposite rotational direction than the first propeller;
• and
• connecting a leading end of the outer propeller shaft to a leading end of the inner propeller shaft to facilitate, during operation, both rotation of the outer propeller shaft with respect to the inner propeller shaft as well as transfer of thrust, generated by the second propeller, to the inner propeller shaft and back to the drive shaft.