Re: Gelcoat help needed...
I'm in the middle of the same type repiar. Just a few days ago I started a thread asking for the same help.
http://forums.iboats.com/showthread.php?t=444078
I was afraid the cracks were structural and possibly leaking water. What I found was that the cracks ended at the first layer of laminate.
Take a look at the thread above. There is a lot of suggested reading and you can see my before and ongoing progress photos. I think you'll find that thread to be a help.
One thing you might want to consider is not grinding out a path down to the laminate as wide as mine. If yours isn't cracked any worser than mine turned out to be that would be a lot of work for nothing. So how do you know how deep it is you ask? Well you have to slowly grind down to until you don't see the crack any more.... taking very little material as you go. Maybe you could grind out some test spots to see how deep the crack runs.
Knowing what I know now I would have done that first and used my Dremel to cut a gouge through the gel into the laminate. That would have made my repair a lot simpler. If the crack was deep... well I would have had to grind it out deeper and wider anyway.
PS... I can tell you.... I'm no gel coat expert, but if you want the true "experts" to reply to this thread you need to post some photos.