Drift Boat Inner Sheer Issue.

Canoes, Kayaks, Pedal power

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Roger9
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Drift Boat Inner Sheer Issue.

Postby Roger9 » Mon Oct 21, 2013 4:41 pm

I am currently building a Inner Sheer for the 16' Drifter. I have scarfed the 19' sheers 3 times now and the joint has failed every time. I am using a marine epoxy to glue the joint and am attempting the joint again using high strength wood glue. Before I attempt to stretch the piece to the form tomorrow I am wondering if there is anything to help prevent the joint from failing. I know that steaming would be ideal, but I am trying to avoid building that. Thanks any help is appreciated.

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thudpucker
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Re: Drift Boat Inner Sheer Issue.

Postby thudpucker » Mon Oct 21, 2013 7:44 pm

I don't mean to Monkey Up somebody's good plans.
But... :D Maybe you'd get more of the boat done if you used a Butt Joint with a Back board at the Butt.

Also, how are you doing your Glassing? I'd guess that's the real problem.

Roger9
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Re: Drift Boat Inner Sheer Issue.

Postby Roger9 » Mon Oct 21, 2013 8:11 pm

What do you mean by glassing? I have been epoxying the joint and clamping to a bench. I have no previous experience with load bearing scarf joints so if I am missing something, please let me know. I would rather not butt joint just for aesthetics. Any suggestions?

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Lowka53
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Re: Drift Boat Inner Sheer Issue.

Postby Lowka53 » Tue Oct 22, 2013 1:25 am

Roger9 wrote:What do you mean by glassing? I have been epoxying the joint and clamping to a bench. I have no previous experience with load bearing scarf joints so if I am missing something, please let me know. I would rather not butt joint just for aesthetics. Any suggestions?
how much of a angle you using with your scarf joints
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Roger9
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Re: Drift Boat Inner Sheer Issue.

Postby Roger9 » Tue Oct 22, 2013 7:57 am

I read about a ratio in which the scarf must be 3 times the length of the width of the piece to be joined. As a result of this i have made my joint about 5 inches long.

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Lowka53
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Re: Drift Boat Inner Sheer Issue.

Postby Lowka53 » Tue Oct 22, 2013 9:18 am

Roger9 wrote:I read about a ratio in which the scarf must be 3 times the length of the width of the piece to be joined. As a result of this i have made my joint about 5 inches long.
is it about a 12% angle if it is it should be good but it is better to have a lower angle. the longer the scarf the better and less chance of it breaking at the joint also you might be starving the joint if you are adding to much pressure ( over tightening the clamps) to it when you epoxy it together also use thicken epoxy
Don't be afraid to attempt anything. You might surprise your self in the attempt.
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gdcarpenter
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Re: Drift Boat Inner Sheer Issue.

Postby gdcarpenter » Tue Oct 22, 2013 11:14 am

A good glued joint should be stronger than the wood itself. Glue starvation from over tightening clamp could do it. I'm a bit of an heretic here but for that joint I would use Titebond III, a waterproof wood glue, good for close/tight fitting surfaces.
This is my first, last and only boat build.

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galamb
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Re: Drift Boat Inner Sheer Issue.

Postby galamb » Tue Oct 22, 2013 1:13 pm

what type of wood are you using? - white oak sometimes has bonding issues.

Also, are you wetting out the joint first with un-thickened epoxy, letting it "soak in" for a couple minutes then using a thickened mixture for your glue (bulked up with silica, microfibers etc)?

How "smooth" is your surfaces that you are bonding - if they are very smooth/hard there may not be enough for the epoxy to "bite into"..

That's the first three things that come to mind.

I scarfed my chine and ended up snapping it when bending/twisting into the bow (actually it's more like it exploded), but that was the wood itself, the scarf joint was fine..
Graham

Yes, Plywood is "real" wood :)

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slug
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Re: Drift Boat Inner Sheer Issue.

Postby slug » Thu Oct 24, 2013 10:52 am

I stand to be corrected here, but I think the standard ratio for scarf joints is 1 in 8.
If you're using a quality name brand epoxy ( Not a hardware store type in two tubes ) the wood will fail before the glue joint. Never had a problem with joints seperating using either MAS of West System. I'm sure Glen-L's product is equal to these. I try to avoid placing the scarf in a severe bend area on the sheer, prefering to place them near the stern.

Doug

Roger9
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Re: Drift Boat Inner Sheer Issue.

Postby Roger9 » Mon Oct 28, 2013 1:03 pm

Thanks everybody! I successfully completed the joint and stretched it to the form. By increasing the length of the joint and decreasing the amount of pressure of the clamps which were starving the joint, I was able to complete a strong and successful joint. I cut the angle at 12 degrees as Lowka53 had suggested.

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Lowka53
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Re: Drift Boat Inner Sheer Issue.

Postby Lowka53 » Mon Oct 28, 2013 6:08 pm

Roger9 wrote:Thanks everybody! I successfully completed the joint and stretched it to the form. By increasing the length of the joint and decreasing the amount of pressure of the clamps which were starving the joint, I was able to complete a strong and successful joint. I cut the angle at 12 degrees as Lowka53 had suggested.

I am glad it worked out for now upward and forward some pictures would be nice also :wink: 8)
Don't be afraid to attempt anything. You might surprise your self in the attempt.
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Bon Voyage-"Wild Flower" 40' house boat being built
14' Mr John-being built
32' Supper Huck-in design

Rod H

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thudpucker
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Re: Drift Boat Inner Sheer Issue.

Postby thudpucker » Mon Oct 28, 2013 9:24 pm

Please Post a Photo.
I don't know what an inner shear is. :wink:

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Stuart
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Re: Drift Boat Inner Sheer Issue.

Postby Stuart » Tue Oct 29, 2013 1:58 pm

I recognize I am a bit late on this but the scarf length was for sure to short. However, that being said, with stressed joints the builder really needs to let the glue harden for perhaps a week before putting any stress on it.

Stuart

Roger9
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Re: Drift Boat Inner Sheer Issue.

Postby Roger9 » Wed Nov 13, 2013 3:48 pm

Inner Sheer is similar to a chine but only on the top... Pictures are of the completed frame with sheers attached with a close up of the successful scarf. Im now preparing the plywood to be attached sometime when I can get a day off!
Attachments
PA220483.JPG
PA220486.JPG
PA220488.JPG

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jprice
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Re: Drift Boat Inner Sheer Issue.

Postby jprice » Wed Nov 13, 2013 5:11 pm

Good job on the scarf.
Just curious though, are those MDF frames?


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