Probably 3/4 of the bottom has blisters. The boat is about 10 year old, but I don't think the previous owner kept it in the water. When I got it last year the hull looked perfect. There don't seem to be any soft spots. I suspect it is thin Gelcoat and a good cold winter that did it in.
I decided to sand down the top part of the keel and put on Interprotect as a temporary measure. As for the bottom, it will have to wait until winter. I am looking at having the entire bottom done with Interprotect and then Performance Epoxy. The keel will come out and get redone at the same time. This is going to be expensive...