Wm Watt wrote:

A lot of experiments have been done in single- and double-sided taped
butt joins in plywood with different adhesives and fibres.

And other people have done the same with different results. However, we are
talking about fiberglass boats here, not plywood. When you load a butt joint in
tension, the asymmetric, single-sided joint will fail with a significant flexure
in the joint. If it is symmetric, double sided, it will be in pure tension.
The difference in strength is considerable. The difference in fatigue
performance is considerable.

Single-sided seams along a sheer line will _buckle_ if the hull is subjected to
serious load - I've seen this happen. It buckles because the joint is not
symmetric. Under those conditions, the single sided joint can split - I've seen
this happen too.

Why do you assume that _your_ experiments count for more than the experience
that many others have had with single-taped joints? Good kayaks use a lapped
and double-taped seam. That is much stronger than a butted joint and much, much
stronger than a single sided seam.

Mike