Lloyd Sumpter wrote:

I think you have the image sideways, though: the seam is
longitudinal.
Think of a jonboat-like structure, where I'd be bending the bottom up
to
form a bow, and the seam is lenghwise down the keel.

But you're right - there's not a lot of strengh required here, so I
might
just do the lap-joint, and possibly tape one side (to ensure
water-tightness!) How much do you lap (I used an inch on the floor)?

I've destructive tested full lap joints to find the minimum lap length
and with epoxy it always came out to 2.5 times thickness. For a half
lap it might be less, but for 1/4 inch, it would only be 5/8" anyway.
If you make the half lap joint first, let it cure and then make your
bend you would get a smooth bend and you could glass over that. If you
have doubts about the joint taking the bend, you can make a test of the
same material and bend it over the sharpest part of your mold before
cutting into the big sheets.

If the boat will be stored upside down in the sun after it is built,
that seam might get hot and the epoxy could soften from the heat and
move a little, possibly causing problems. To be on the safe side, I'd
want to put a heat lamp on the joint or set it in the sun so it gets a
good high temp cure and has a chance to cool down before doing the
bend. That, at least in theory, will make it more stable.

Al

Oh, for a longitudinal butt you could edge glue the pieces with epoxy and
lift them carefully into place together to get a nice tight seam, then
fibreglass the inside. When I butt two pieces of plywood together with PL
Premuim and a plywood butt block, I first put a little epoxy all along the
edge before pushing the pieces together. It saturates the end grain to
keep water out and gives a better seal, at least that's my assumption.

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