I have the same problem on my J/24. I just grind out the blisters and fill with West Epoxy. Then sand the repairs smooth and paint over them. Unfortunately, each year I have a new set of blisters to repair because I have no barrier coat, but the repair job is easy and inexpensive. It only takes a few hours each spring. I think this is easier than removing the whole bottom and barrier coating. Beware - unless you thoroughly dry out the hull before barrier coating, you'll just get blisters under your barrier coat!
