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Old 31-08-2012, 03:28   #1
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Folding Versus Feathering Props

I know this subject has been up before, but it is a number of years ago.

I have a 40 foot Jeanneau Sun Fast, 55HP Yanmar with a 3 blade folding prop. I like the performance when under sail (folds completely). The prop works well when motoring forward.

Reverse is, well to say it mildly, virtually non-existent. The only way to get it moving in reverse is to play with the throttle,, neutral/gas/neutral/gas and also use the bow thruster to stay in line and finally she will begin to move. She also does not have any real speed in reverse.

I should also mention that she has a hell of a prop walk to port. If I want I can make her turn a 360 going to port without her ever beginning to move backwards.

Needless to sy - this is not ideal. The previous owner has told me that the boat has always behaved that way (the boat is from 2006 and I just bought her this spring).

So - what are my options? Dive down and see if the prop is unfolding correctly in reverse (it should do so since it unfolds correctly when going forward).

Replace the folder with a feather prop.

If I replace - will I see any performance deterioration when I'm under sail? What about prop walk with the feather prop?

Any recommendations?

And no - I don't know the prop manufacturer
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Old 31-08-2012, 03:45   #2
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Re: Folding versus feathering props

I would start by reading this:

http://www.flexofold.com/upload_dir/...onthly_low.pdf

If you have the snorkeling equipment it would be worth checking that the blades move freely and doesn't have lots of nasties growing over it.

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Old 31-08-2012, 04:00   #3
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I just replaced my feathering prop with a three blade folding prop. I did it because I was catching a lot of lobster warps with the feathering prop and diving frequently.

The folding prop works much better in forward and a little less well in reverse than the feathering. I suggest checking fouling because that does seem to have a greater effect on the folding prop. Also check if it is a two blade or three blade. That may have a significant affect in reverse but I'm of totally sure.

My feathering was a MaxiProp. My folding is a Flexofold.
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Old 31-08-2012, 05:34   #4
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Re: Folding versus feathering props

I should note that the previous owner says it has always been that way. I have seen (and unfolded) the prop when the boat was out of the water for a survey. The prop unfolded (moved by hand) easily and there were no little nasties in the teeth etc.

Pete, thank you for the link - I've now read it and it gives some insights. I guess I would still like to hear if anyone else has had this problem with a 3 blade foldable
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Old 31-08-2012, 06:39   #5
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Re: Folding versus feathering props

In my experience, a feathering prop is the only way to go. The difference in drag is negligible (unless you are a racer in search of that last 1/10 knot) and the performance is almost as good as a fixed prop when motoring. Additionally, I look at it as a safety issue; the close quarters maneuvering abilities of a folder just sucks!
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Old 31-08-2012, 07:02   #6
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Re: Folding versus feathering props

Quote:
Originally Posted by carstenb View Post
And no - I don't know the prop manufacturer
Don't suppose you have the original prop do you? only it might be worth measuring the diameter and comparing it to the feathering prop and then check the clearance between the hull and the prop. I am wondering if someone chucked a larger diameter prop on without checking the clearance, hence the huge prop walk.

Also can you identify the prop from the article, might be worth chatting to the manufacturers. Southampton Boat Show in a fortnight, they will all be there. Hop on a plane, the airport is only a short journey to the boatshow.

Pete
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Old 31-08-2012, 07:05   #7
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Re: Folding versus feathering props

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Originally Posted by carstenb View Post
I guess I would still like to hear if anyone else has had this problem with a 3 blade foldable

I have a Flex-O-Fold 3 blade prop and my boat is about the same size as yours, my boat backs up with no problems.
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Old 31-08-2012, 10:29   #8
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Re: Folding versus feathering props

What RPM are you useing in reverse? In my foggy memory I recall being told that to make a folder work in reverse you have to use much higher RPM to get the blades to extend all of the way. A folder in forward has the blades pushing and they extend out to the stops ,but in reverse the blades are pulling backwards which is how they fold. My understanding of it was that it took the higher than normal RPMs to have centrifugal force make the blades go out. Your lack of thrust and lots of prop walk may be from the blades only extending part way and just making a stirred up ball of water,rather than thrust. I dont think any folder will give you the reverse thrust that a fixed pitch prop will, but it should be better than 360 degree prop walk.___Good Luck_____Grant.
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Old 31-08-2012, 16:31   #9
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What brand feather prop does everyone prefer?
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Old 31-08-2012, 17:17   #10
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Re: Folding Versus Feathering Props

This has been discussed before at length, but please be aware that feathering props are inherently LESS efficient than either fixed or folding props of good design. This is due to the blades of feathering props being flat (ie not having any twist) so that they will work in both forward and reverse. This is true for ALL feathering props.

The result of the efficiency loss is it takes more horsepower (and hence more fuel) to generate a given amount of thrust.

Personal data: changed from a Martec Elliptic two blade folder to an Autostream three blade feathering prop. While the feathering prop generated lots more thrust in reverse, our overall fuel consumption rose by about 25% due the the flat blades. We were not happy with this, and so chose a Flexofold 3 blade for our new boat. This prop performs well in both directions, albeit without the static thrust in reverse of a feathering prop.

Cheers,

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Old 31-08-2012, 17:36   #11
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Re: Folding Versus Feathering Props

Feathering includes variable pitch, or no?
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Old 31-08-2012, 17:47   #12
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Re: Folding Versus Feathering Props

Just answered my own question, and found a solution...and it goes in the design folder:

Bruntons Autoprop
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Old 31-08-2012, 18:44   #13
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Nice post and explanation from Jim

Thank you !

Carlisle Spirit
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Old 31-08-2012, 19:30   #14
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Re: Folding Versus Feathering Props

Like others here I had a Flex o fold on my 36 Sun Odyssey and had no complaints in close quarters, open sea, or racing. I would echo Jim, Don, and Rick's comments.
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Old 31-08-2012, 20:04   #15
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Re: Folding Versus Feathering Props

I installed a Gori 3-blade folding prop in August of 2009 and now have about 1,400 hours on it. It has exceeded my expectations. It folds to create virtually zero drag and the shaft doesn't even turn a little bit when we're under sail.

What makes the Gori unique, though, is that it's designed so the pitch increases significantly in reverse. This makes maneuvering in close quarters much easier. However, you can put the blades in the reverse position and shift into forward. Gori calls this 'overdrive' and it's the closest I've ever seen to a two-speed prop.

Fair winds and calm seas.
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