One is, as Larry suggested, to bore many small holes either in the inside or outside of the area and heat the area to dry it out THOROUGHLY...or at least damn good. If it's the hull, the only real option IMHO is to drill inside.

Another option is remove a section of the inside/outside of the hull, replace the core, 12 to 1 bevel grind the surrounding area, reglass carefully. In this case I would NOT put core back in but build up the area with fiberglass so this will never happen again. Don't get me started on cored hulls and lazy builders or prior owners...mostly lazy builders.

If you choose to remove a section of the hull, use a router with an 1/8" or such straight bit set to the thickness of the inside skin adequately to route out your area. Be sure all core is out and what is left is dry. By beveling the inside skin/core back to a 12 to 1 ratio (I repeat myself" and filling it up with carefully place in 'glass circles to match the hole, you can effect a very good repair. I prefer to use the largest circle put in place and wet out (or vice versa) first, followed by slightly small pieces to full. There are two schools of thought on this and that is one. The other is to use smaller pieces first. For me that is counterintuitive as you start with the smallest area of contact and I prefer the larger.

Another option you might consider is to scrape deeper. I have used 1/8" thick by 1" aluminum with a slight hook ground into the "digging" side. It can be a foot long or 18" long...but you have to replace the core with 'glass carefully by poking wet out 'glass into the void with your stick or whatever for full contact all around until it is full. I have not done this on a hull but have on a deck. It can be done.

Thems my thoughts, best of luck in whatever you do.