Before epoxy came along with it's excessive marketing (they all buy the
same stuff, add a few things to make it "special", and spend a lot of
money trying to convince buyers that their product is marginally better),
polyester was being sucessfuly used to repair poylester boats for decades.
The first book I read on fibreglass boat repair said a polyester repair is
stronger than the original. Epoxy may be stronger than polyester (both the
bond and the resin itself) but you don't need it. For more strength you
can use additional layers of polyester. Use epoxy to build a boat which is
as strong as a polyester boat but weighs less overall.

Gelcoat is there to provide protection from the sun. Both polyester and
epoxy will break down if exposed to sunlight for long periods of time and
then neither is very strong. You have to cover exposed epoxy with
something to protect it from the sun. Gelcoat also provides extra
resistence to water penetration because over time polyester can soak up
water. Epoxy is waterproof and will not soak up water unless it's stressed
and develops lots of tiny cracks. Putting a more waterproof epoxy
patch on a hull made with polyester will not do anything to keep the hull from
absorbing moisture it it's going to. Keep the boat's gelcoat in good shape
instead.


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