Hello, would like some advice please

My boat has allot of (what I think is) gellcoat flaking off around the
underside of the hull and on the keels. The flaking is exposing the
GRP underneath, and the flakes are about 3 - 4mm thick I would say -
as far as I know this is the gellcoat. The flaking is not in any sort
of pattern, it is not centered around any stress points etc, it is
more random looking, just looks like old paint flaking off from age
really. The boat is about 40 years old. There is no sign of any
blisters (I know this doesn't mean there is no hydrolysis). I
obviously want to seal it back up to prevent any more moisture getting
into the hull.

So, my question is, what is the best way to go about this? Should I
use a belt sander to strip the flaking gellcoat away, and apply a new
coat? Anything better than a belt sander? I'm not looking to dry the
hull out and fully restore it, I just want to stop more moisture
getting in when I use it this season.

Any advice, opinions, etc welcome