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Old 03-02-2020, 09:28   #1
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Folding prop won't work, need feathering

I'm really bummed that my new Flex-O-Fold props will not work. Terrapin has a skeg rudder and the props overlap the skeg when folded. I did measure and consulted with FOF but we still got it wrong. The good news is that FOF will refund my purchase price and pay for return shipping. I can't speak highly enough about the FOF customer service.


I believe this means that any folding prop will have this same issue, so I am now looking at feathering props. I've read the YM review of props and many threads here. Wow, they are expensive! To help me decide, I'd like to hear from feathering prop owners who have them on smallish cats with a similar power train. Terrapin is 32' and has two inboard Yanmar 2gm20F with shaft drive. I know Beliezesailor has Kiwi props and seems to like them. Anyone else?
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Old 03-02-2020, 09:48   #2
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Re: Folding prop won't work, need feathering

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Originally Posted by Jerry Woodward View Post
I'm really bummed that my new Flex-O-Fold props will not work. Terrapin has a skeg rudder and the props overlap the skeg when folded. I did measure and consulted with FOF but we still got it wrong. The good news is that FOF will refund my purchase price and pay for return shipping. I can't speak highly enough about the FOF customer service.


I believe this means that any folding prop will have this same issue, so I am now looking at feathering props. I've read the YM review of props and many threads here. Wow, they are expensive! To help me decide, I'd like to hear from feathering prop owners who have them on smallish cats with a similar power train. Terrapin is 32' and has two inboard Yanmar 2gm20F with shaft drive. I know Beliezesailor has Kiwi props and seems to like them. Anyone else?
You have too much shaft between strut and prop
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Old 03-02-2020, 10:36   #3
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Re: Folding prop won't work, need feathering

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You have too much shaft between strut and prop

How much is too much? It measures about 2" between the strut and the prop hub. We discussed cutting the shaft, and it might then barely fit, but I am reluctant to do this only to find that it is still touching.
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Old 03-02-2020, 10:55   #4
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Re: Folding prop won't work, need feathering

Replace the strut and cut 3.0-3.5” instead of just 2”?
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Old 03-02-2020, 11:09   #5
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Re: Folding prop won't work, need feathering

The general boat guys rule of thumb is one shaft diameter between prop and strut

You might ask a prop pro for minimum distance

Remember... if you shorten the shaft the tips of the prop blades become closer to the hull when rotating

This has consequences

Also remember that the prop applies thrust to the shaft and pushes the engine forward on its mounts

Zero distance prop strut would be a bad idea
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Old 03-02-2020, 11:23   #6
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Re: Folding prop won't work, need feathering

I agree that you have a bit to much shaft aft of the strut but it's a LOT of work to rectify. For your HP motor the Kiwiprop will be fine. It's very light weight, relatively speaking, so the longish shaft will not likely whip. The Kiwi is also very well balanced so that's a plus too. It's a very good prop it's just much more inefficient than the FOF. Check the weight of any featherer you may want to look at since weight may be an issue with the excess shaft length.
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Old 03-02-2020, 13:07   #7
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Re: Folding prop won't work, need feathering

Quote:
Originally Posted by slug View Post
The general boat guys rule of thumb is one shaft diameter between prop and strut

You might ask a prop pro for minimum distance

Remember... if you shorten the shaft the tips of the prop blades become closer to the hull when rotating

This has consequences

Also remember that the prop applies thrust to the shaft and pushes the engine forward on its mounts

Zero distance prop strut would be a bad idea

My current clearance is 2", so only 1" longer than the "1 shaft diameter rule". This doesn't seem to me like a big deal. But even if I cut the shaft to a 1" clearance, that wouldn't help. I would have to shorten it to less than a half inch between strut and prop hub, and I don't want to do that.. No, I'm not going to relocate the strut.
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Old 04-02-2020, 09:51   #8
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Re: Folding prop won't work, need feathering

First accurately measure the strut, prop, rudder clearance and distance between the end of the shaft and the forward part of the rudder and shaft beyond the strut. Check the dimensions with the shaft cut one diameter behind the strut. Now calculate how much further you need to either shorten the strut or shorten the forward prop collar. Next decide how much of that Dimension you want to take from the rear of the strut and the forward part of the prop. Also include the position of the set screws on the shaft bearing and prop for your decision. Drilling and tapping the set screw is not difficult even with a hand drill. Be careful when shortening the strut with the shaft inside. It will be easy to cut with a hacksaw just make sure you don't cuddle into the shaft. The prop should be off when you cut it so there should be no problem. A slight angle will not affect the balance as the distance from the center of the shaft will only be about an inch. Don't forget to think about a zinc if it had one mounted on the shaft.
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Old 04-02-2020, 09:54   #9
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Re: Folding prop won't work, need feathering

Why not opt for a feathering prop eg. MaxProp. Then the shaft won't need to be modified.
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Old 04-02-2020, 09:55   #10
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Re: Folding prop won't work, need feathering

You might consider Maxprop. Not cheap to buy or refurbish, but it works very well on my mono hull. I have the classic from years ago, which is nearly impossible to install/remove in the water. I would suggest checking out the Easy model that can be serviced in the water. The reverse function is way better than fixed or folding props and feathering is simple.
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Old 04-02-2020, 10:04   #11
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Re: Folding prop won't work, need feathering

I love my Flex-O-Fold. I had a similar problem, the blades when folded would have hit the skeg. I considered cutting out a bit of the skeg, but I cut the prop shaft on the inboard end, shaved 1/2" off the "P" strut, took slightly shorter blades from FOF and I am very happy with the results. FOF props got very high ratings in a prop test by Yachting Monthly, I have much less prop walk in reverse and they are supposed to have good "braking" power. As I dock slowly, I don't use the engine to brake often.
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Old 04-02-2020, 10:09   #12
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Re: Folding prop won't work, need feathering

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Originally Posted by Jerry Woodward View Post
My current clearance is 2", so only 1" longer than the "1 shaft diameter rule". This doesn't seem to me like a big deal. But even if I cut the shaft to a 1" clearance, that wouldn't help. I would have to shorten it to less than a half inch between strut and prop hub, and I don't want to do that.. No, I'm not going to relocate the strut.
Hard to see the geometry, distances in pictures

Those duckbill style props have the advantage of staying clean of weed and plastic when sailing because they are folded

Great feature for certain parts of the world

I’ve seen feathered three blade max props grow to the size of a hay bale when sailing thru sargasso weed

I also once picked up a large plastic tarp on a feathered max prop while sailing

It was a Bad day
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Old 04-02-2020, 10:31   #13
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Re: Folding prop won't work, need feathering

I had a similar problem on my Beneteau 331. I went with the Variprop profile. It has a short hub and great forward and reverse.
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Old 04-02-2020, 10:35   #14
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Re: Folding prop won't work, need feathering

Utilize a feathering prop instead of the folding prop. It will fit properly without modification and perform better.
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Old 04-02-2020, 11:26   #15
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Re: Folding prop won't work, need feathering

I need a new folding prop for my 2GM. Might be willing to work out a purchase of your prop. My current prop is a Martec 13x13x7/8" shaft.
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