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[phatdaddy]

i would avoid sanding to remove paint. soda blasting, chemical stripping, pressure washing, etc. would be a better alternative in the long run.

blisters are usually caused by exposing the hull to long term exposure to water. weak spots of polyester resin absorb water and it "pools" under the laminant.

if the previous owner has sanded through the gelcoat, then yes, your going to have to put a coat of something on it to protect the polyester resin.