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Old 11-05-2012, 12:11 PM   #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?
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Old 11-05-2012, 01:45 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.

David
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Old 11-05-2012, 01:58 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, 03:15 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, 03:21 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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