I had a virgin bottom, I did some looking and asking, knowing my boat will sit in water for 6 months a year-
I started with a 80gt DA sander, knocked shine off, wipped down with thinner/cleaner. (Products at West Marine)Applied (INTLUX) Pro-Teck 2001 or something, it was a gray barrier gaurd- supossed to act shingle like effect on a house, to keep water from working into gelcoat. Then 2 coats of blue anti-fouling. The boat went 2 years without any blue chipping off at all, this year I gave it a quick freshing up to take the fadded look away.
This method worked great, but took twice the time- but is/was worth it to me. I believe pease of mind was mentioned in a previous post. I will do this exactlly the same nest time-100%.
Barrier gaurd was $115 and anti about $50 qt. The Blue goes along way, 1 qt did my 24" boat.