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 - Tuning-Up Your Tractor: Plugs & Compression Testing - by Curtis Von Fange. The engine seems to run rough. In the exhaust you can hear an occasion 'poofing' sound like somethings not firing on all cylinders. Under loaded conditions the tractor seems to lack power and it belches black smoke out of the exhaust. For some reason it just doesn't want to start up without cranking and cranking the starter. All these conditions can be signals that your unit is in need of a tune up. Ok, so what is involved in a tune up? You say, swap plugs and file the points....now tha
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