Re: what to do about hairline cracks on top gelcoat
It needs to be sanded down to the where the crack starts, it may be in the gel coat, or it could be in the glass, you won't know until you route them out. Then they need to be filled with something very strong, if you are painting you can use epoxy and glass fibers, if you are going to use gel coat, then you need to use something compatible with it. The problem is that to keep the old cracks from returning, or new ones from starting, you need to find out why they started in the begining. It's normally from flexing, so you need to stiffen the structure to stop the cracking, this may move the stress to another location and start cracks in that area.
