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Old 04-08-2016, 11:42 PM   #21
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Originally Posted by markpierce View Post
With twin props turning in the same direction, I'd expect the rudders would need to offset the prop walk when going forward. My single-engine boat requires a three-degree rudder angle to compensate for the forward walk. So, twins turning in opposite directions should be more efficient than turning in the same direction.
Mark good point and I've thought that for years. One of the reasons twins are tend to be more efficient than singles but of course there are other variables that have been argued about extensively in the past. Counter rotating twins are a very good setup.
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Old 04-08-2016, 11:49 PM   #22
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...One of the reasons twins are tend to be more efficient than singles but of course there are other variables that have been argued about extensively in the past...
But most all twin-engine boats are wastefully overpowered and expensive if one wishes to move at an efficient one-knot-below hull speed.
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Old 04-09-2016, 06:28 AM   #23
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One extra advantage to an opposite rotation on the props might be the ability to stern walk in either direction.

Single screw does best when the prop will drag the stern alongside in reverse.

Twin screw , two choices for the action.
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Old 04-09-2016, 08:22 AM   #24
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Cappy, the gears in question are Velvet Drive 72s, not reversible. The boat is a heavy full displacement hull, identical to the Krogen 42 but bigger at 46 feet on the waterline and 14 foot beam at the water. Props are fairly close together and 30 inch diameter, sitting on either side of a good sized keel. She was never a "good" handling boat in tight situations because of this configuration. But, the props are tucked up into the stern more than a flat bottom twin screw would be so when aground they are still protected somewhat. I really like the VD gears, they are one of the most efficient designs available and with just 50 hp available per engine gear loss is a factor.
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