1974 20' sceptre transom replacement and i/o to outboard bracket conversion

[flyingfrizzle]

Originally Posted by Big fish

Is vinyl ester much better than poly resin? I'm probably going with epoxy for core to outer skin and wondering how much better ve is to poly. Cost is somewhat an issue but piece of mind is most important. I don't want to have any doubts or regrets.

The elements of boat strength by David Gerr has a chapter on this. (A great book to own)
Ortho - polyester will elongated about 2% before cracking the tensile strength is 9,400 psi

iso-polyester is about the same but is more resistant to chemical attack

Vinylester will elongate 5% before cracking, the tensile strength is 11,800 psi

Epoxy will elongation is usually more than 5% and a tensile strength of 12,500

Ve and epoxy is water resistant when poly is not. If you use a high strength glass like 1700 biaxel or 1708 you need the strength of the ve or epoxy. The polyester resin will fail well before the fibers will and you will loose the potential strength of the lament due to it is not strong enough to get the full potential strength out of the cloth. There are many poly made boats that are plenty strong but with the ve or epoxy you will get a much stronger, waterproof and durable product. I would use the ve on any situations that requires high strength.