Larry:
I was looking at the TAP Plastics website (www.tapplastics.com) just after reading your post and happened to see this quote under their "Marine Grade Epoxy" section.

"Currently the majority of watercraft are made with polyester resins, which are excellent for initial construction; for repairs, however, they lack the tenacious adhesive properties of Marine Grade Epoxy. This epoxy is a stronger adhesive and forms a superior bond to polyester and many other materials. Polyester will shrink during cure, creating stress at the point of repair. Marine Grade has no significant shrinkage problem during cure."

Hope this helps.

Regards,
Marcel