Michael Daly wrote:

Butt joins on fiberglass and butt joins on plywood are not the same thing. The
difference in strength between the base material and the adhesive is
significant. Plywood is thick and weak, fiberglass is thin and strong. Lapping
a tape over one side of a plywood joint is not going to have the same effect as
doing the same with fiberglass.

Wood is as strong, pound for pound, as steel. Fibreglass versions of
plywood boats weigh more. Plywood is as strong as fibreglass used on
the same boat design. I don't get your point here.


As I've already pointed out - if single taped butt joints in kayak seams were
sufficiently strong, we wouldn't see so many failures and so many paddlers
condemn the manufacturing technique. If the joint was sufficiently strong, it
wouldn't be so sensitive to labour and quality of construction as you have claimed.

I assume you mean single-sided taped butt joins. (I don't know if it's
proper to call them "scarfs".) Single layer slingle-sided taped butt
joins would problably be okay but if I were doing it I'd use
single-sided double-layer joins, 4" glass over 2" glass. It adds so
little in wieght, cost, and effort.

A lot of experiments have been done in single- and double-sided taped
butt joins in plywood with different adhesives and fibres. People have
built with polyester, epoxy, and polyurethane resins, and glass and
polyester fibre, to my knowledge, with satisfactory results. On the
19-year-old fibreglass kayak in question I'd stick with polyester
(epoxy for those who want to spend more money) and glass fibre.


Mike