[voodoo]

Previous owner kept my boat in the water, muddy crappy water. It lives on a trailer now, seeing water for maybe a few hours at a time.
He painted the bottom black. Many times it seems over the growth. It's ugly.
It has blisters, lots, under the ugly bottom paint and cracks in the gel cote above the water line.
Last fall I jacked it up off the trailer, and a body guy buddy of mine had his trailer mounted compressor ready to go to blast it.
I was going to get him to blast and re-gel the bottom but I had a problem getting new gel cote, so she went back on the trailer and into storage.
My buddy does nice work, I've seen it on cars and have other friends, in the automotive industry with nothing to gain, tell me he is excellent at what he does.
I've read that blasting it can open up problems with air in the glass.
I have the time, tools and money to blast and gel cote, but could live with the ugliness if the cons outweigh the pros.
Any tips or advice?

My good news for the day is my truck mechanic buddy has a 30 year marine mechanic working for him.
I was worried the drive hadn't been off in 17 years.
Pulled my drive and it does appear the previous owner, who seemed legit, did indeed have it dealer serviced every year as he claimed when I bought it.
Wear parts looked like new, greased parts were in as new condition.

[DCB_MINDED]

Here is a rather extensive write up that I found online. I read a little bit of it, but not the entire thing. Seems like you can sand blast part of the way, then use a DA to finish it off.... Either way, it's going to be quite the chore, and once you start..... Theres no going back!

http://www.westsystem.com/ss/assets/...Prevention.pdf

[Hudson River Steve]

I have heard of using Soda blasting (baking soda) as a safer alternative to sand as a media...supposed to more gentle on the gel coat.

[DFZ272]

Learn this from fooling with sailboats, bottom growth, a pain to fix, but if u do it it must be done right. It sounds like the previous owner applied anti fouling paint. Soda blast it or sand it with an orbital, sand blasting probably not a great idea, then inspect the blisters. West marine has some good information on blister types and repairs. If the blisters are soft or contain water, or have cracks that penetrate the gel coat, the repair will be a little more indepth and expensive if you have to pay somebody to do it. It involves sanding off the blisters and damaged areas of gel coat, filling the blisters with epoxy and filler, fairing them off, then applying an epoxy paint barrier coat to seal the bottom. The only problem is you will have to coat that with another anti fouling paint(not all of it is ugly and there are may different types and colors. BUT underlying layers of glass must be completely dry before fixing the blisters or they will come back after repairs are made. Now if you always keep it on a trailer and the blisters are strictly cosmetic, soda blast it and have fun, but keep an eye on it for the problem getting worse.
Good Luck
Dan