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.