Propellers: folding X feathering - SailNet Community
 
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post #1 of 7 Old 07-09-2008 Thread Starter
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Propellers: folding X feathering

My vessel displaces 8600 lb, LWL is 23' 4", has a Volvo 13 hp engine (MD7), a sail drive (S110) and a two blade bronze folding propeller (14x8). The combination moves the vessel at approx 4.25Kn at 2200 rpm (max 2600 rpm). The prop works fine in forward motion but requires a lot of initial throttle for the blades to open in reverse, and generates a strong walk to SB. While not ideal, I'm used to this deficiency.

The prop is wobbling on the shaft and I'll be replacing it in the fall.

I believe there are feathering props available for saildrives and I wonder if technically it is an improvement over the folding prop? if you take the cost difference in consideration, which is better "value"?

Is there any way I can find out if a different pitch will improve final speed? If I can better the system, this is the time.

All other things being equal, what is the advantage of a three blade over a two blade prop?

While I'm at it, any suggestion for local suppliers in western Canada (BC)?


I'd appreciate any feedback, and thank you in advance.

SV Strudel, Niagara 31
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post #2 of 7 Old 07-09-2008
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A feathering prop will cost 2-3 times a folder. Feathering props are more efficient than a folder so you will get some more drive and speed, whether the "some" is worth it to you is a personal call. Typically serious racers stick with folders, owners of higher-end boats buy feathering props. Our MaxProp has the benefit of having equal thrust in reverse as forward and not much prop walk...but at a cost.

Prop sizing seems as much art as science, you need to find someone like H & H Propeller :: CUSTOM PROPS :: DRIVELINES :: STAINLESS FABRICATION :: ISO COMPLIANT ::to work with, pay them full price for a prop that will work for you, in return for their expertise. My understanding is that prop drive is a function of blade area, you only need to go to another blade when the necessary blade area results in the 2 (or 3) blade being too large to fit comfortably in the space permitted. Others may coment that 3 is somehow mysteriously better, but that is not what the prop people say.

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post #3 of 7 Old 07-09-2008 Thread Starter
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Thanks SF. Your comment is very helpfull and much appreciated.

SV Strudel, Niagara 31
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post #4 of 7 Old 07-09-2008
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Talk to Norm at.... West by North Enterprises He's got a wide range of prop styles, and costs, locally here in BC.

BTW I'd expect your boat to perform quite a bit better than 4.25 knots at cruising speed... he can help you with that too, I expect.

Also-- saw you at Smugglers July 1 weekend... we were part of that big raftup!

Ron

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post #5 of 7 Old 07-09-2008
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I have a feathering prop on my own boat, an old Morgan 36T, and it works fine.

Island Breeze, 56' and 26 tons, has one of those British Auto-Props. Three blades, etc. It works great going forward, so-so in reverse. The big problem is that if the boat sits still for two or three weeks during the summer, the worms jam up the bearings and the blades of the prop can't move. Sometimes you can break the blades free by going from fwd to rvs, but usually, it takes a trip into the water to bust things loose again.

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post #6 of 7 Old 07-10-2008
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Pick a manufacturer you like and then contact them directly. In my experience they are very helpful in taking the details of your vessl, engine, clearance etc and recomending a prop size.

I have a folding Gori prop which is OK in forward and just so-so in reverse but my main requirement is racing so I am happy with that.
The folding props are pretty bad in reverse but then I don't back up a lot.

Gary
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post #7 of 7 Old 07-10-2008
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I have a feathering prop, the Martec Autostream. It performs well both in forward and reverse. With our old fixed, 3-blade prop, we found ourselves unable to sail in less than 8 kts. Now our threshhold is 5 kts. In western LI Sound, that makes a big difference during the dog days. The pitch is easily adjustable, separately for forward and reverse, and can be done in the water. We're very satisfied. We've got it dialed in pretty well, I think.

IRMV
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