dual prop shaft ?

I realize it is a sterndrive, but thanks for pointing out the obvious. Actually, I have one on the back of my boat, so I know quite a lot about these units. I wasn't necessarily responding to you, I was responding to the ealier posts that asked if there were any counter rotating surface drives.

 

I've installed on the same boat the single and the duoprop of Volvo Penta.
At the same displacement and power the gains in speed have been:

single duoprop
---------------------
25.0 > 27.5 knots
30.0 > 32.4 "
35.0 > 37.6 "

In effect 2.5 knots more. Better acceleration too.

RANCHI OTTO

 

ZF Marine's New Project Disruption https://www.boatingmag.com/zf-marines-new-project-disruption/

 

ZF Marine's Contra-Rotating Propeller is a Game Changer https://www.yachtingmagazine.com/zf-marines-contra-rotating-propeller-is-game-changer/

 

Hi,
a counter-rotating drive can be implemented very well with just one propeller shaft. For this you have to integrate a differential gear into the front propeller hub, which means that the gear housing serves as an output for the front propeller and the other gear input serves as a connection for the rear propeller. With a differential gear, the power is distributed to the two propellers depending on the power requirement. The propeller that requires more torque due to pitch, diameter or blade surface rotates more slowly while the other propeller rotates at a higher speed. We have developed this type of gearbox for aerobatic model aircraft and have used it successfully. The aluminum-colored drive can be seen in the picture. The motor is only connected to the differential gear with the motor shaft. The lower propeller is connected to the differential gear housing and is driven in this way, and the upper propeller is connected to the other connecting shaft and is driven in opposite directions at approximately half the engine speed. If the propellers are well coordinated, the propellers rotate at almost exactly half the engine speed. This saves an additional gearbox and allows you to drive larger, more efficient propellers.

Happy Amps Christian