OK here is my 2 cents worth:
I've made repairs like this before and an outside patch will work for a while as evident with the last fix. But to make a strong fix cut a hole in the inside of the hull as an access port so you can get in and fix the area from the inside. Then fix it from the outside. The last step will be to fix your access hole. Here is a link to the type of repair I'm talking about:
http://themanshed.net/archived-projects/g-cat-catamaran/?g2_page=2
Few other things I’ve learned from experience use epoxy not a poly resin it just holds better and don’t use Bondo or plastic filler it will swell and absorb water. Do not use any fillers where your cross beam touches the fiber glass. The lay-up under the cross beam should be long pieces – no seams. Remember Mat has no strength. I use a woven biaxial or triaxial. Budweiser or Rum usually helps with the fiberglass itch if taken early enough.