Well I took my Hunter 25 out of the water two weekends ago.
Turns out I had about 100 blisters. I ground them out, and put a few layers of glass cloth in the ground out area. I then filled with epoxy and filler. However, after drying the filler shrunk a bit and still left an approximately 1/8 inch depression. My father showed up with some automotive Bondo filler, and filled the depressions before I could say "that's not marine grade!". Well, it's there now, under my new bottom paint. Is it gonna fall out? I am confident that the epoxy underneath will hold, but I am worried I will have sloughs of my bottom paint just fall off with the bondo under it...
The other, related issue I had was with the rudder. After grinding what appeared to be a blister, the wet part just kept getting deeper. I finally got down to the steel:
It appears that water go into the rudder itself, and was trapped between the steel and the laminate of the rudder. I got as much water as possible out with the grinder, let it dry overnight, hit it with a heat gun, and glassed/filled it in with many layers of glass and a healthy amount of filler too in all the crevices. The rudder is solid, but there is a thin layer of rust between the steel and the laminate. The laminate doesn't seem securely attached to the steel, but somehow there is no play at all in the rudder... Is this a long term problem? Did I "fix" it? I didn't cut out all of the wet/rusty stuff, probably less than half, because any more and I would have had to build a new rudder. Anyone else had this problem?