My daughter and I acquired a 1970's 16 and one of the hulls has serious soft spots from the rear trapeze post almost to the bow. It is my understanding that there is a sandwich of fiberglass, foam and fiberglass including gelcoat that is about 3/4" thick. Rather than using the process of drilling numerous holes and injecting epoxy, howabout drilling a series of 1/2" holes about four inchs on center all over the soft area. Then take a drill with a piece of coat hanger in the dril and bent at 90 degrees for about 2 1/2 inches and "beat out the foam between the fiberglass using compressed air to blow out the pieces. Then, instead of using epoxy, use low expansion foam sold at home supply centers for insulation to fill the void. Unlike heaver fiberglass epoxy, the foam adds very little weight and, like epoxy, is very sticky. With enough holes drilled the foam excess could escape instead of distorting the top deck and still be strong and solid. After filling, simply feather out the holes and lay up fiberglass cloth and fair out each to the deck before refinishing.

Also, foam can be melted with Acetone. Instead of trying to remove the foam could Acetone be poured in the holes in moderation to remove the foam? Of course if there isn't a water tight fiberglass connection between the lower layer of the top of the hull and the flotation blocks, severe damage to the flotation could happen.

Any thoughts?