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Old 01-03-2008, 10:03   #1
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Folding / Feathering Props

I've been reading old posts which mention a review done by MIT on feathering & folding props, but the links to it no longer work & I can't find it on the MIT site. Can anyone help me find it or paste me a copy? I'm buying a new prop for my 40' Najad and need some help deciding between a Brunton Autoprop and the J Prop.
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Old 01-03-2008, 14:19   #2
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I found a link to it in one of the other threads here that worked... Try Max-prop versus Foldable
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Old 01-03-2008, 14:45   #3
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I would be wary of making such a choice based on the MIT paper - the paper was produced around 15 years ago and is quite possible that the tested props have undergone design changes since then.
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Old 02-03-2008, 01:09   #4
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Old 02-03-2008, 01:56   #5
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The paper is on my website which moved since the last time this subject came up.

Click Here for the link
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Old 02-03-2008, 02:48   #6
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Feathering/Folding Props

Thanks Guys - very helpful. Bearing in mind the warning about the age of this report, is there anything more up-to-date, e.g. that might include the J Prop?
I've reads tons of posts about the Autoprop & am none the wiser as to whether it really does help as claimed when motor-sailing. I gues I'm most interested in performance either sailing or motor-sailing rather than just motoring.
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Old 02-03-2008, 08:54   #7
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I'm not as concerned by the age of the report as I am by the fact that the props were held perfectly in line with the current flow. Most of us don't have saildrives and so our props are held at a 10-25 degree angle to the flow. It's in this orientation that I suspect you'd see some advantage of the foldable over the feathering.

Another reason I chose foldable is because I like the idea of the blades being tucked away and unable to snag any crab pots. Oh yeah, also because they're a lot cheaper than feathering/pitching!
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Old 02-03-2008, 09:40   #8
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Take a look at Flex-O-Fold, www.flexofold.com. After doing my research and talking to a lot of people, I’ve just ordered one to replace an old feathering Martec that just doesn’t work for my boat. Flex-O-Fold is very low drag while sailing; and with good motoring performance. Mechanically, it’s very simple, making it easier to maintain. I agree with a folding prop being less of line catcher.
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Old 02-03-2008, 09:44   #9
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I have had an Autoprop on our 34' pilothouse for about 12 years or so. We went from a 3 blade fixed and gained about 1/2 to 3/4 of a knot sailing in light (10K) winds, it was very noticable. We gained a solid 1K motoring at the same RPM and were able to reduce cruising RPM while maintaining our old speed which decreased engine noise. Absolutely no trouble with it. There is a learning curve when manuevering in tight areas, you have less thrust initially so you have to learn to use a lot of throttle from a stop or when reversing initially. Doesn't take long to pick up. It eliminated prop walk in reverse.

Wish I could afford one for the new boat- $4000!!!

John
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Old 02-03-2008, 09:49   #10
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DINWood,

I don't see where the drag data in the report really helps you choose between one folding/feathering prop and another. Drag for any of these is so low that the difference will only matter to very serious speed demon sailors. My apoligies if my assumption you are not one is incorrrect...

I think you might be better off making your choice based on performance and handling characteristics.

For example, there is no question that the comments Hubec makes in support of folding props are accurate, if those characteristics are the most important, there you go. But you do pay a penalty in motoring performance with a folding prop, especially in reverse. If close quarter manuvering or engine power efficency is important, then folding props aren't for you, and a traditional feathering or autoprop might be the right choice.

The drag difference between the slickest folding prop and the clunkiest feathering prop is going to be measured in hundreds of yards over a day's sailing, not miles. For some people that is important, for the rest of us, we look at other characteristics and might end up with other choices that are also "correct".

For what it's worth, I use a three blade Max-Prop, and am very happy with it. The drag difference between that and the old two blade fixed prop is very noticable especially in light winds, and the engine performance is better as well. Win/Win. The support from the US distributer has been fantastic.
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Old 02-03-2008, 11:53   #11
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Quote:
Originally Posted by GreatKetch View Post
For what it's worth, I use a three blade Max-Prop, and am very happy with it. The drag difference between that and the old two blade fixed prop is very noticable especially in light winds, and the engine performance is better as well. Win/Win. The support from the US distributer has been fantastic.
Not to mention the support from the diver who installed it.
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Old 02-03-2008, 11:57   #12
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Not to mention the support from the diver who installed it.
Yep, Matt's good too!
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Old 02-03-2008, 13:00   #13
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"TAKE A LOOK AT FLEX-O-FOLD"
Totem great choice Flex-o-fold, after much research and discussion I purchased one last year and am very pleased 1...can sail in less wind.
2...sails faster
3...points slightly higher (bonus) than with fixed prop
4...motors better/less rpms,no problem in reverse/stop
5...no maint. or maint issuses
Very robust build, they advertise they are standard equipement on some very nice
boats Swan, Najad, others ...
I did go larger in diam. 1" and changed pitch some from prev prop, boat is only 10,000
lbs. and has sail drive.
Don't want to sound like a ad here ...wished all my purchases worked out this well!
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Old 02-03-2008, 18:21   #14
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Hugosalt,

I've got a 2 blade Gori which I'm thinking of replacing. It works fine, but the vibration I get during motoring is really depressing. The shaft is straight, the motor mounts and alignment are fine.

Maybe I'm all wet, but I suspect it's because of the straight edges on the blades causing pressure pulses on the hull.

Flexofold is on my list as is the Varifold, as both of them have rounded blade design.

What is your experience with the Flexofold regarding vibration, and what did you replace?


Steve B.
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Old 02-03-2008, 19:49   #15
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Steve,
My set up may not be the best to judge as far as vibrations go because I have a saildrive unit and there are 2 big heavy rubber seals that dampen vibration and noise.
Motor and prop, (old and new), have always been very smooth and low noise level.
Having said that... my old prop was a very square 2 bladed fixed Volvo 14x9 with clearence of 2" between prop and hull. The new Flex o fold is 15x11...this gives me only of only 1 1/2" between prop and hull. I was very concerned (about vibs) before purchase because this is less than recommended distance, but no vibrations at all.
Your not all wet because there was no way I wanted to put a larger square prop of any kind that close to the hull just for that reason.(Or maybe were both all wet!!!)
Do you know how far your prop is from hull and is the hull flat at that point? If it is to close it could be source of vibrations. I think conventional wisdom says prop should be at least 10% of prop diameter distance away from bottom. BUT I AM NOT SURE...
check if your prop might be to close.
Hope this helps,
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