wrote:

What are the relative merits of polyester resin vs epoxy resin?

Trying to compare polyester and woven roving to epoxy and knitted
glass is like trying to compare oranges and apples.

Both are "fiberglass" laminates, but the similarity ends there.

About the best you get is 35%glass/65%resin using woven roving, mat,
and polyester.

OTOH, it is quite common to get a 50%glass/50%resin using knitted
glass and epoxy. This laminate does not require any mat.

Bottom line....................

Polyester/roving produces a rather brittle, heavy laminate.

Epoxy/knitted glass produces a more ductile, lighter weight laminate.

Pound for pound, polyester and woven roving cost less per pound, but
you use more pounds, so the cost differences tend to disappear.

Epoxy, knitted glass and a 1/2" Airex foam core would produce a very
light weight, bullet proof, dinghy or kayak.

Just remember three things.

1)You will buy a commercial dinghy for less money than you will spend
to build one.

2)You build one because you want to do it.

3)Once you use epoxy and knitted glass, you will never consider
polyester again.

Lew