No, the claims are not true in so far as the epoxy being *in* the
vinylester resin. What may have some validity is the claim that
vinylester resins are "very close" to epoxy when the end product is an
all fiberglass boat hull.

The chemical makeup of polyester resins (of which vinylester is a
family member) are a concoction of anhydrides, polybasic acids, glycols
and styrene, plus an 'accelarator' of cobalt napthanate. Once a small
percentage (1 - 2 % by weight) of Methyl Ethyl Ketone Peroxide is added
(called the "catalyst"), a chemical reaction occurs as the result of
rapid oxidation.

Epoxy resins are quite different chemically, baed largely on Bisphenol
products and Ethyl Hexyl Glycidyl Ether. Once mixed with a "hardner"
(in a ratio of anywhere between 25 to 100 % by weight) a chemical
reaction occurs due to molucular bonding.

It's ludicrous to supose that these two vastly different chemical
'systems' could be made to work together in one product. If you can
find a manufacturer who claims to have both systems in one product, I'd
love to hear about it!

However... Vinylester resins exhibit many of the properties that are
associated with Epoxies when describing qualities that comprise a sound
fiberglass hull, namely: High chemical and corosion resistance, high
elongation flexibility, and reduced water permiation. Vinylesters are
the 'best' of the polyester resin family, and are (of course) priced
accordingly (albeit considerably less than Epoxy).

Remeber that all polyester resins are *not* very good adhesives, which
is primarily why early attempts to sheath wooden hulls with fiberglass
failed; ultimately the bond between the wood and the resin let loose,
water got to the wood and...

So: If you'll be laying-up a fiberglass hull and can stand the styrene
smell, Vinylester resin would be a sound choice, especially for
traditional e-glass materials.

Mike Worrall
Los Angeles