Hi guys, thanks for the replies.

So what I need to do is sand off the gelcoat (and whatever other
layers are there), as I can definitely see the fiberglass where flakes
have come away.

Do I just need to prepare the bare (fiberglass) surface, and apply a
new gelcoat? Or do I need layers of other stuff also? Lets say I have
a large area of hull/keel that I have sanded back to the fiberglass.
What are the steps I should take? Phantman mentioned bottom paint, and
Bruce mentioned epoxy. Would it be epoxy, then gelcoat, then bottom
paint?

Thanks for the help!