If I bend it, will it hold?

[erlaursen]

I am building a Pooduck skiff which has a concave facet on the transom where the garboard plank attaches. The facet is about 14 inches in length and the concave curve is about 5/16 inches deep. This means I must bend the garboard plank, which is 3/8 inch plywood, to fit the curve. I will then use wood screws and epoxy to attach the plank to the end grain of the transom. The transom is ¾ plywood. I have to put a lot of pressure on the plank to make it bend. Will the plank hold under such pressure? Should I cut grooves in the plank to make it bend easier? Any ideas?

[AstoriaDave]

That is not a super aggressive curve in three-eights ply. I would not groove the plywood. However, screws into endgrain plywood run parallel to the plies are weak. If you can't clamp it while the resin sets up, consider angling the screws so they cross as many glue lines as possible, per the method illustrated here, in this case for a ring nail: http://bartenderboats.com/images/samplejoint.JPG

It is worth making a little drill guide to get the angle just right, and to alternate the angles left right for placements.

[Mrleft8]

Do not cut grooves. Leave your garboard long (3-4+" ought to be enough) so that you don't mash out the inner laminations when you drive your screw in. Trim off the excess only after the epoxy has fully cured.

[aitwood]

There are curved plywood panels that are readily available for just such applications. Check out www.aitwood.com and look under the millwork components and then quarter circles. With a good sealer epoxy these would make the job quick and have a good stable piece with integrity. We also stock a full line of marine grade plywood, AquaTekm (marine mertanti) SuperMarine, (100% Okoume), Finland Birch (exterior 4 x 8 100% birch.

That is not a super aggressive curve in three-eights ply. I would not groove the plywood. However, screws into endgrain plywood run parallel to the plies are weak. If you can't clamp it while the resin sets up, consider angling the screws so they cross as many glue lines as possible, per the method illustrated here, in this case for a ring nail: http://bartenderboats.com/images/samplejoint.JPG

It is worth making a little drill guide to get the angle just right, and to alternate the angles left right for placements.

[Dave Gray]

I built a Poo Duck. I recall wondering about the same curve. It ended up not being a problem as the plywood pulled in with slight pressure when using screws and epoxy.

[bigrob]

I am finishing up my Pooduck now. I too wondered about the plywood making the bend at the transom, but had no problem with 9mm sapele. I do think I used a pipe clamp to take the tension off while tightening the screws - and kept the clamp in place until the epoxy cured overnight.

[Dave Gray]

I found this an invaluable resource:
http://www.woodenboatstore.com/How-to-Build-Shellback-Dinghy/productinfo/325-040/

It answered a lot of questions I had (and answers to questions I hadn't thought about asking). The Shellback is a smaller version of the Poo Duck.

[AJZimm]

I faced a similar situation (different boat) with more concavity to contend with. I happened to have some 3 mm ply left from a previous boat and used it to fashion the end piece of the plank at the transom. You can see here how I laminated 3 pieces together in place to get the concave curve (3/8" = 9 mm).

http://i368.photobucket.com/albums/oo123/AJZimmerman/Hornpipe/planking/IMGP3888.jpg

I then took the laminated plank end piece and cut the scarf at the other end and the gains at the transom and glued it on

http://i368.photobucket.com/albums/oo123/AJZimmerman/Hornpipe/planking/IMGP3893.jpg

[James McMullen]

Don't create a problem where none exists--several hundreds of Pooducks and her smaller sister Shellback have been built. The curve in the garboard at the transom works just fine. Build to the plans.

You do not need to kerf or groove the planking. The screws are really there just to hold it until the epoxy cures. No worries, Amigo. It's been done many, many times before.

[erlaursen]

Thank you all for the advice. I have the clamps and now thanks to you I have the courage.
Erik

[BearHillBoater]

Hi,

I don't frequent the forums that much, and I came across your posting today looking at something else. I built Pooduck about a decade ago and I also faced the dreaded compound bend. The solution I came up with worked really well, hopefully you can try it also.
I followed the "how to" guide for the Shellback, which recommended leaving the plank long, running well past the transom and trimming later. I had about 6 inches of garboard plank past the transom.
I can't post a picture, hopefully my description is clear enough.
I clamped a 2x2 board across the end of the plank beyond the transom, one clamp on each side. Then I inserted a wooden spacer like a shim in the center of the plank between the plywood plank and the 2x2. I could get any curvature I needed by increasing the shim thickness, and was able to perfectly match the transom curvature, with the whole arrangement outside the transom.
I had trouble with the angle of the screws, as has been noted, but epoxy and sawdust covers all errors on the learning curve.
I can't recall how I buttered up the plank with the epoxy and the bending jig. I probably set it up and predrilled the screws, removed the plank and then applied the epoxy, then refit the plank and the bending jig, then drove the screws home. I left the jig in place until until the epoxy had cured.

Pooduck is great boat, enjoy it.
Paul