The counter rotating props are not for reduced slippage, though that may be a side benefit.
They are to reduce steering torque.
Big motors cause a LOT of steering torque. When a boat is up on plane, or getting up on plane, the bottom of the propeller is getting a lot better bite than the top of the prop. The top is grabbing air, as it is right at the surface, and even above the surface when the boat comes up on plane.
Having to deal with all that torque has 2 negative effects, one is on the steering. Most have power steering which takes the load off the drivers arms, but it takes engine power to run the hydraulic pump.
The other is having to run with the engine at a slight steering correction angle (because of the torque) is terribly inefficient. If you notice, listening to the engine going straight, then enter a gentle curve, you will hear the engine slow slightly. That is not good for efficiency! The counter rotating props help eliminate that, but then it's another set of gears to turn, which takes a bit of power, so it somewhat of a trade off.
But the reduced slippage has to be compensated for by reducing the pitch, diameter, or gear reduction. The goal is to keep the engine at the top of the torque curve/HP under full throttle.
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Today's Featured Article - The Rescue of a Fordson F - by Anthony West. Introduction I live in the UK and have for many years restored Fordson tractors (in the main model N's). I have also restored and shown model F's, E 27N's, Field Marshall Series 2, David Brown Cropmasters and the old rey Fergeson T 20. At one time I had seven restored examples which were shown and used in ploughing matches. As most restorers, I have a number of war stories I can relate on a range of topics that may help other like minded and interested people. Perhaps my first p
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