I have been grinding off all of the bottom paint and gel coat on my boat MaJic Carpet. I have maybe 35+% of this project done, but today I got to the area under the exhaust and found some of the worst and the largest blisters I have seen so far. All in the area that I know to be "wet".

So did the moisture coming from the exhaust hole getting the core wet cause or exacerbate these blisters, or did these blisters contribute to the problem. The port side in the same area does not have near the number or severity of blisters.

The wet core caused the blisters. I had the exact same problem on Rhapsody.

ps: I used the old laminate on the outer skin when I recored and had problems with the blisters returning. If I were to do that all over again, I would have replaced the outer skin there, or as a minimum ground about half the thickness of the laminate and glassed in a couple of layers to make sure there was a good outer skin that would not blister.

I have noticed that the positioning of the exhaust port is way down just above the waterline where on Judicious it is about 18" above the waterline with no issue's of wet core in the transom guess it was one of the things Westerly did differently when they built the boat.

When I do this repair it will not be optional as to replacing the outer skin, it is almost gone now in this area. I thought it was interesting that this area is by far the worst for blistering that I have seen so far. Still have a long ways to go though with this lovely grinding project.

While I will do the skin repair in this area with epoxy and plan to epoxy fill all the many other blisters, I am leaning now toward recovering the entire bottom with either 4 or 6 oz. cloth and using vinyl ester resin (because I have a long and expensive laundry list of other repairs I also need to address). I'm having a hard time thinking that just addressing the blisters that I find will solve this problem even with a barrier coat. This old poly ester resin is just too problematic to be left alone. After taking this step I would then do the barrier coat as the final protection for the glass.

Once I fix these blisters and wet core problems I really do not want to have to revisit any of these hull issues again.

I would think that they did more than raise the height of the exhaust passage. Somehow doing a better job of sealing the port and managing the inevitable expansion, contraction and vibration that would tend to make the seal fail seems likely.

what the early builds didn't do was isolate the core where the exhaust went through the hull with epoxy, so water would leak in and spread. Just remember to cut your exhaust hole a bit larger than necessary and use thickened epoxy to isolate the core when you're ready to put it back together