Explain better? Location? Strake? It looks like it's already had an attempt at "fixing" with some sort of bondo. It appears to be an air void, but sand/grind all of the paint and loose fiberglass away, then post some more pics. Once we can better see what's going on, a fix can better be offered.
Edit: Oh... is this something you are comfortable taking on yourself (grinding/epoxy filling/etc)? Just wondering, before we go into too much detail. Otherwise, it's probably (assuming the damge isn't more than anticipated) about a two hour job at a decent marina or fiberglass shop.
There are a few ways to attack this: The fast, cheap way or the pro way. The cheap way is to remove the loose stuff, fill with marinetex, shape, sand and then bottom paint.
You have to decide which route to take. Good fiberglass technicians are expensive but will do it right.
I'd grind it out and see how it looks. You can probably address with some base glass and matting, then touch up with Marinetex and sand down. It's a 30+ year hull. Likely worse than that going on somewhere else.
Interesting suggestion. The glass is what I would recommend (actually mat and glass cloth). The Marinetex will probably be a lot easier to shape the chine than resin and filler. I think the key is to use Marinetex for cosmetic shaping and the resin and glass for the structural base.
Sanded down then filled with 3M Marine Premium Filler in the spot and shaped it to match and fill the shape of hull. Then sanded that, plan on adding another layer of marine filler to strengthen the spot. Any advice? Have a cold spell coming through town for a week or so, so I won't be able to work on it with below freezing temps. Any advice is Greatly Appreciated!
It looks like you didn't sand enough. That spot where the void was/is needs to be completely sanded/ground away till you get to solid glass. Trying to just fill into the hole won't be successful in the long run - it's still a weak spot. What you have at this point is kinda what the repair was before - a "band aid" - and that's why it didn't last.
If you did sand/grind it completely away, I just can't tell from the picture. But from what I can see, it appears that you need to go at it again to make it a permanent repair.