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  #1  
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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Old 07-08-2013
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Re: 3 blade prop or two blade folder

I am all about maximizing sailing performance, so I use a Gori 2 blade folding prop. I used to have a Martec, which was terrible because the blades flopped around independently, so if one blade got a bit fouled you had balance issues. The Gori is geared so the blades open and close together. The Gori was also a big improvement in reverse, but still not great. When I buy my next boat, which will be bigger and more expensive, I will definitely spend the money on a feathering prop, which is the best of both worlds.

I don't know what you would need a shaft brake for. A good folding prop folds any time the boat is moving forward and the shaft isn't turning. (assuming it isn't fouled of course!) It is a fixed prop that is prone to "windmilling" when the tranny is in neutral.

As for performance gains, a fixed prop can easily cost you up to a knot of boatspeed under sail. PHRF treats a folding prop as a significant performance upgrade. All you have to do is take a fixed prop into the water with you, hold it under water and swish it back and forth and you will see how much drag you are dealing with! Couple that with the turbulence you create over your rudder and it is a big performance hit!
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Old 07-08-2013
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Re: 3 blade prop or two blade folder

The performance hit is way worst than the credit one gets too!

I would go with a 3 blade folder if it were me. i ahve a 2 blade max prop, wish it was a 3 at times, But I go thru and battle a few currents here in the salish sea, so a 3 blade does deliver a bit more bite than a 2 blade......I would not want a fixed 3 blade on ANY sailboat! a 2 blade is bad enough!

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

I had a Gori two blade folder and it was a very good prop even in reverse.
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Old 07-08-2013
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Re: 3 blade prop or two blade folder

Went from 2 blade fixed to 3 blade maxi feathering prop. Huge improvement for docking , backing , stopping.
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Old 07-08-2013
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Re: 3 blade prop or two blade folder

I tested a bunch of props years ago, very scientific, we wore white shirts. We found the Max three blade to be the best prop but not by a lot. It was also the most expensive prop we tested.
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Old 07-08-2013
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Re: 3 blade prop or two blade folder

I am still amazed at the reverse performance of a folder on the Cal which went from pretty much worthless with the fixed 12 X 8 to tugboat like reverse performance with the 12 x 7 folder


And it always FOLDS with the gears



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

unless racing 3 blades are better than 2. I find boats stop much faster in reverse with 3 blades . And it's always good to have that extra bite when a lee shore comes a callin.
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Old 07-08-2013
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Re: 3 blade prop or two blade folder

IMO it's all about the absolutely worst situation you could ever be in.
Are you willing to risk your boat to an inferior prop? Folding props without gearing could leave you with no prop in an emergency, if it doesn't open. A geared prop will always open, even if terribly fouled, which is a nice feature. I also prefer a feathering prop to a folding one.
Two blade fixed props are fine if you have a shaft brake and can line up the prop vertically when sailing, a real pain.
Our 3 blade MaxProp has been fine, low drag and no noise from spinning while sailing. However they do require occasional greasing and service after a lot of use.
We are also sailing the West Indies and I doubt we've used the engine 15 hours over the last year, so it's wonderful not to have all that drag.We carry a 2 blade fixed prop for emergencies; they are easier than a 3 to stow.
One item I really recommend is a cutter; a real lifesaver for sure, especially with all the traps down here. Without a cutter I wouldn't run any of the the lees after dark under power. There are numerous cutters of many designs, but I'd go with the Spurs Cutter; great company support and a well rated cutter.
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Old 07-08-2013
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Re: 3 blade prop or two blade folder

I have had Martec folders on my current and previous boats. I find them to work well. Fold reliably, good efficiency in forward, and surprising good reverse power. Support from Martec is excellent. They do a great of reconditioning their props for a reasonable price when needed.
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