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Old 11-05-2012, 11:11 AM   #1
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Counter rotation

For the folks with twin engines, how many have counter-rotation? And is this done by the engines or the transmissions? My Perkins 4-236s and Velvet drives both go the same direction. I am leaning toward the idea that counter rotation is a better set up, but can it be done with the transmission instead of the the engine? The archives aren't much help here. Comments?

"Keep putting off till tomorrow, and you'll end up with a lot of empty yesterdays" Prof. Harold Hill
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Old 11-05-2012, 12:45 PM   #2
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Most twins counter rotate. Most are done with the transmission although the Perkins 6-354 and the DDs can be done at the engine. Cummins, Lehmans and Yanmars cannot.

Some Velvet Drive transmissions can be set up to counter rotate, but I recall that some internals must be changed. If you change rotation, you will have to get a new prop.

I don't see enough benefit (no torque steer in forward, backs straight with both engines at same rpm) to make it worthwhile.


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Old 11-05-2012, 12:58 PM   #3
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Most twins today are counter- rotating. While there are some counter- rotating engines out there most boats do it with gears.

The obvious advantage to counter-rotating props is that you have no prop walk when you don't want it and a lot of propwalk when you do.
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Old 11-05-2012, 02:15 PM   #4
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I have the same setup and I would not find this of any value to me. Coming from a single this is still night and day to back into my slip.
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Old 11-05-2012, 02:21 PM   #5
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One of my Velvet drive Trans has a reversing gear added. It also changes the reduction slightly, from 1.9 to about 2.0.
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