What kind of profile is needed for the repair? If similar to surrounding area, I would tend to make this profile out of marine ply (a little smaller to allow you to cover with GRP) and expoxy resin the ply to the existing wood - consider installing epoxied wooden dowels to provide extra support. Then use epoxy resin and woven tape as suggested to complete the repair. Epoxy works better as an adhesive if there is a gap to fill and is damned strong when done properly. It can also be affected by UV - so does need to be coated with something - but this could possibly be just etch primer and boat paint.
Polyester resin is great for initialy molding, but is not an ideal adhesive. Epoxy resin is a much better adhesive. The advice on chopped- strand matt is true and is only suitable for polyester resins.
I'd tend to suggest posting on rec.boats.building or on a forum like
HTH, Mark