Wm Watt wrote:
Michael Daly wrote:

If you only reinforce on one side, as Brian pointed out, you'll get a weak
joint. Hull-to-deck seams on some cheaper sea kayaks are only taped on the
inside and are known to have split. No one I know would trust a one-sided seam
for strength.

Hull to deck seams are not only problems on fibreglass kayaks but also
on fibregalss sailboats of all sizes, even very large, very costly
ones. It's not because they are only taped on the inside. It's design
and workmanship.

I have a couple of open plywood sailboats which get quite a bit more
stress than kayaks do. Sails can pull 75% dieways and only 25%
forwards when going upwind. That putsa lot of twisting stress on the
hull and pulls it over in the water, all too often to the point of
capsize if you don't stay alert. The plywood panels on my boats are
butt blocked with adhesives that are 1/20ht as strong as epoxy (urha
formaldahyse and polyurethane). I've n to had any problems with teh
butt joins even when the plywood has been delainating.

I got kicked off the computer at the public library at the end of the
time slot. So to continue ...

The hulls on these two plywood boats are less rigid than the hulls on
the kayaks I've paddled (about 20 models so far). I've done fibreglass
repairs after reading one or two books on the subject. In spite of what
you read from promoters of epoxy, polyester repairs can be made stonger
than the origninal hull. The same repairs with epoxy are many times
stronger than necessary. That's why I do not see any strength problem
in cutting through a kayak hull and joining with interior taped butt
joins. For the other reasons we have mentioned in this discussion
(cockpit, reduced stability and bouyancy) it's not a good idea to take
the extra lengthout of the centre of the hull so this part of the
discussion is moot.