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Old 08-06-2007
j.g.evans j.g.evans is offline
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Unhappy Feathering and folding props

I have a 3GM30F Yanmar on a C+C36. I was using a folding 17"x10" Martec that is a good match to the engine. MIT tests show it is very effiicient in forward. A fixed pitch prop can have max efficiency at one speed. It is nice in that it doesn't have to be locked to stop auto rotation. Just put it in gear to stop the rotation and then into neutral.
I switched to a 16.3" 3B Autoprop to get smoother operation and more reverse thrust. The MIT tests showed this auto pitching prop got more efficiency at any speed. This prop was not a good match to the engine, i.e. 6 K @ 2100 rpm rather than 6K @ 2500 rpm for the Martec. It was not smoother. It auto rotated unless I put the engine in reverse. Then it jams there with the water pressure and the engine had to be started in reverse. It did provide good reverse. The final blow was a blade fell off and it will cost almost $2K to repair.
A feathering prop will not be as efficient. It should not auto rotate. Getting the pitch right is VERY DIFFICULT. Feathering props usually have adjustable pitch in both forward and reverse. I recommend 17" 2B or 16"3B for your engine if it is a 3GM Yanmar.
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