Counterrotating dual-propeller boat drive

In combination with a watercraft drive unit having a generally horizontal and annular drive support fixed on the craft and a drive shaft projecting from the rear end of the support and rotatable about a drive axis, the drive support forming a rearwardly directed exhaust port, a propeller assembly comprising:

• a hub fixed on the shaft adjacent the support and having a front hub portion immediately behind the rear support end and a rear portion spaced therefrom;
• a rear propeller fixed to the rear portion of the hub;
• a planet carrier defining a plurality of planet axes parallel to and spaced equiangularly about the drive axis;
• means for securing the carrier to the support for fixing of the planet axes relative to the support and drive axis;
• a sun gear fixed on the front portion of the hub within the planet axes and axially between the rear hub portion and the rear support end;
• respective planet gears meshing with the sun gear and rotatable on the carrier about the planet axes axially between the rear hub portion and the rear support end, the planet carrier, planet gears, and rear propeller forming at least one axially throughgoing passage aligned with the port, whereby the vented exhaust can pass axially through the drive;
• and
• a front propeller surrounding the planet gears, lying between the rear propeller and the rear support end, and formed internally as a ring gear meshing with the planet gears, whereby rotation of the drive shaft in one direction rotates the rear propeller and sun gear in the same direction and rotates the planet gears and front propeller in the opposite direction.

In combination with a watercraft drive unit having a generally horizontal and annular drive support fixed on the craft and a drive shaft projecting from the rear end of the support and rotatable about a drive axis, a propeller assembly comprising:

• a hub fixed on the shaft adjacent the support and having a front hub portion immediately behind the rear support end and a rear portion spaced therefrom;
• a rear propeller fixed to the rear portion of the hub;
• a planet carrier defining a plurality of planet axes parallel to and spaced equiangularly about the drive axis;
• means including a rigid support tube snugly and coaxially surrounding the drive support for securing the carrier to the support for fixing of the planet axes relative to the support and drive axis;
• a sun gear fixed on the front portion of the hub within the planet axes and axially between the rear hub portion and the rear support end;
• respective planet gears meshing with the sun gear and rotatable on the carrier about the planet axes axially between the rear hub and the rear support end;
• and
• a front propeller surrounding the planet gears, lying between the rear propeller and the rear support end, and formed internally as a ring gear meshing with the planet gears, whereby rotation of the drive shaft in one direction rotates the rear propeller and sun gear in the same direction and rotates the planet gears and front propeller in the opposite direction.