I noticed my boat has three areas, ~2' X 2' each on the underwater portion of the hull that have ~20 very small blisters per area. I sanded throught the gel coat and took a pen knife and opened up a few. Each one I tested was dry. I then sanded them off and noticed that each pimple has a very tiny crack in the fiberglass that can be picked out to reveal a blue material underneath. I suspect that the blue is from the materials used during manufacturing. For repairing, my original intention was to follow the guidelines provided by Interlux. This could involve lots of work and cost which would be OK if it's appropriate. Don Casey, "This Old Boat" author, suggests that you should open up each blister, clean it out, wash with a brush solvent, fill in with gel coat (including chopped fiberglass if the blister are large or deep)smooth out and your done. He specifically does not recommend the use of an epoxy. Another opinion I found was in Yachtsurvey.com which was a real eye opener. Yachtsurvey.com thoroughly trashed most "solutions" to blisters provided by owners, boat yards, and product companies. After considering all of the material, including many discussions on this web site, I am inclined to break open overy little blister, fill with gel coat, sand off, and then gel coat each of the three areas. I believe this approach will bring the bottom back to the "original" condition and does not have the risk of introducing any problems suggested by Yachtsurvey.com. Any recommendations would be appreciated.