flex coupling question

Designs for inboard or outboard power

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Jimbob
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flex coupling question

Post by Jimbob » Thu Sep 20, 2018 9:15 am

Has anyone had any experience with a flex coupling. It goes between the transmission and the prop shaft coupling. They say it eliminates vibration, protects the gears, and works like a u-joint if your alignment is slightly off. Good idea? or a waste of money?
Pic below:

Thanks,
Jim
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Jim Neeley
Building a Barrelback in Sacramento, CA
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neel thompson
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Re: flex coupling question

Post by neel thompson » Thu Sep 20, 2018 9:23 am

Jim,, I have one on my Gentry and I know Roberta has one on her Torpedo. I don't have any vibration, but I have never run the boat without the flexible coupling. So I don't know if I would have the same results without it. I guess it's a good thing to have.

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Bill Edmundson
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Re: flex coupling question

Post by Bill Edmundson » Thu Sep 20, 2018 9:34 am

I don't have one on the Tahoe. Seems to run fine. I thought about it a long time. I do think it is probably a good thing.

Bill
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kens
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Re: flex coupling question

Post by kens » Thu Sep 20, 2018 4:34 pm

neel thompson wrote:Jim,, I have one on my Gentry and I know Roberta has one on her Torpedo. I don't have any vibration, but I have never run the boat without the flexible coupling. So I don't know if I would have the same results without it. I guess it's a good thing to have.
I got one too.....and also never run without it.
I suppose somebody has to run up on the rocks to find out if it really works.!!!!!
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

Brad Tucker
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Re: flex coupling question

Post by Brad Tucker » Thu Sep 20, 2018 6:12 pm

I run one, as well

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sscobra
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Re: flex coupling question

Post by sscobra » Thu Sep 20, 2018 9:42 pm

I put one on my Monaco...no vibration. Skip
Built the Glen-L Monaco, 2016.

PeterG
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Re: flex coupling question

Post by PeterG » Thu Sep 20, 2018 9:44 pm

It couldn't hurt to use one. It will push your prop further aft, so watch clearances back there. In fact a flex coupling might helpful too, especially if you run a down angle transmission. You get your shaft/transmission coupling flanges aligned just right with the boat sitting in the water. Then you run it across the lake where you get a little hull flexing (happens to all boats) and a little torque twist of the engine on it's motor mounts, that's bound to affect alignment. On straight shaft boats with inline transmissions, it's not much of an issue as the shaft is supported by the strut and the transmission, and torque twist is all on the same axis of the shaft through the transmission and engine. The transmission flange stays centered on the axis of shaft and engine rotation; and the shaft log/shaft seal have the flexible tube to prevent shaft binding even if the hull flexes. But with a down angle transmission, the engine torque twist is not on the same axis as the prop shaft. The transmission flange swings a bit to the side, off of the shaft's axis, dragging the prop shaft with it and pulling the coupling flanges out of parallel. This is when the flex coupling helps by allowing this motion to occur without binding the shaft or stressing the coupling flanges. I would not run any down angle transmission in a boat without it.
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Jimbob
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Re: flex coupling question

Post by Jimbob » Mon Sep 24, 2018 9:45 am

Thanks everyone for your responses!
Jim
Jim Neeley
Building a Barrelback in Sacramento, CA
viewtopic.php?f=15&t=28089#p172969

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