Peeling with the carbide cutters, then drying (either tenting with dehumidifier and heat, or hot vacuuming) are the proper ways to attack the problem. Never sandblast the bottom of a boat. It leaves sand particles embeded in the laminate and these become a nidus for more blistering in the future. Soda blasting is OK, just for paint removal, but I have heard of poor technique in soda blasting causing damage to the laminate. The peel is controled in depth, and may just take gel coat, or gel coat and a layer of mat.
If the boat is badly damaged, it may require relamination of a layer of 6 oz cloth, as well as epoxy. (Epoxy is more resistant to water permeation than vinlyester is, so is prefered. Also secondary bonding with epoxy is better, than with vinylester resin) But drying the boat out is most important.
We were looking at a 34 footer yesterday which had a defective layer of mat under the gel coat on the bottom, and discussing if it was better to just fix the blisters, with epoxy, or do the peel/dry. The estimate was $20,000 or about $600 a foot when the bottom was peeled, dryed for several months and then a new layer of cloth laminated. The boat had the blisters repaired and was launched the next day!
The cause of osmosis/blistering is complex, but basically there is a semipermiable membrane--the gel coat, and there are some poorly catalyzed areas, poorly cured resin, defect in the laminate, particles in the laminate etc-and water gets under the gel coat. Osmotic pressure increases the amount of blistering. You can grind down the blisters with a 6" air grinder (If you are young and strong, you probably can use a 1 1/2 hp electric grinder, but it will be a lot of work. I would grind the entire bottom, get the gel coat off, open any blisters, then grind out the blisters with a die grinder with a 1/2 circle carbide router bit, until you are to dry solid laminate. Then relaminate the areas which you had to grind out, with concentric circles of fiberglass cloth and epoxy (I use West System). Never use polyester for filler, never use Bondo. After you have filled the defects, fair the surface with high density filler mixed in epoxy, and after faired, then you put on at least 4 coats of epoxy. It is quite possiable that you will get a number of years out of the boat. You can just go ahead and use it--at some place the fuel tank will have to be replaced. Exhaust risers probably have to be re-done if they have not been replaced in the last 3 to 4 years.
I am sorry to hear of your father's passing. That makes it a more emotional experience and maybe clouds your judgement. But your statement above seems to be objective.
I have a good friend who bought one of these exact same boats, for $10,000, fixed it up (cost about $5,000) and sold it a year later for $12,000. They are nice boats, and ride very nicely.
