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Old 07-08-2013
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3 blade prop or two blade folder

OK Thinking of buying a prop. My 44ft cruising boat a lightish 70s IOR hull with a cruising interior, 3/4 keel and skeg hung rudder has a Perkins 154 with a hydraulic gearbox driving an 18 x 17 three blade fixed prop. I am overpropped by many peoples standards 6 knts at 1600 rpm with WO rpm being 2000. The prop is showing signs of dezincification with pink blotches and some nibbling on the edges. .

I am lucky enough to be out in the Caribbean where the trades blow so rarely use the engine other than a few minutes at either end of the day. I plan my passages at 6 knts and mostly do better. Beam reaching between the islands at 7.5 to 8.5 knts is the norm on a good day.

I have no interest in racing.

I can get a good used similar 3 blader for about 400 to 500 US delivered down here in Grenada.

I have been recomended to use the Brunton Autoprop which seems to be about $4000 US however the benefit of better drive under power is not required as I sail most of the time.

So maybe a simple folder would suit?

A Gori 3 blade folder is also about $4000 US

A Gori 2 blade folder is about 1500 US

A Martec is even less at about $1000 but as it is not geared will it vibrate more esp when fouled with barnacles. BIG problem down here.

So should I go for a 2 blade folder. I can live with the poor performance in revese which I only use to set the anchor. Will I need a shaft brake?

I saw this


Quote:
I think that there is a solution to your problem. When shutting down the engine whilst sailing, briefly put it in reverse at idle speed. This spins the prop backwards. Then shut down the engine. The motion of the boat will try to spin the prop forwards. During the time when the rotation is stopped, the blades will fold, and then there is nothing to spin your shaft as you sail along. Will this work?
What sort of speed gain will I get with a 2 blade folder? Will it be mostly as lower windspeeds?
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