Your hull looks very similar to my hull after it was sandblasted. Here's the deal with my experience. The photographs with red bottom paint are the way my bottom looked in 2004 when we bought the boat. We moved the boat to a freshwater lake and never did anything with the bottom for 11 years because the marina was not equipped to either remove or apply bottom paint. So we lived with a shabby looking bottom, enjoyed sailing, never had any problem with performance and never knew anything about any problems for 11 years.
The we moved our boat to a salt water marina and I wanted to do something to make the bottom nice and smooth, and I figured that anti-fouling would be important. We have our boat at a Marina that has an excellent reputation and they typically use Interlux products, so I was happy with whatever they recommend. We sand-blasted in the fall after removing the boat from the water. The photographs show the results. It looked pretty much the same as yours. Thousands of small divots just breaking through the gel coat were observed. All of the holes are no more than 1/8" to 1/4" in diameter and also very shallow. I saw the hull soon after sandblasting and there was no fluid leaking out. The hull was bone dry as far as I could tell. There weren't any larger sized blisters with oozing fluid weeping from the fiberglass underneath the gel coat as has been described for actual "blisters".
We left it that way until the spring when I authorized the yard to apply thickened epoxy to fair the entire hull. Next, we had 3 barrier coats applied and an ablative bottom paint applied. If I remember correctly, the entire process from sandblasting to bottom paint was about $3,900 for my 27' boat. I think the step to repair the bottom was the most expensive at about $1,800.
With all of the time and travel involved, I was not going to do this work, particularly because the process requires full time involvement. I was perfectly happy to trust this work to the marina, since I wasn't going to devote a week for a DIY job. I can't tell you or show you how this worked out, since the boat was placed in the water before I could arrive to see the result and she is still in the water. I'm a little anxious to see the results in a few weeks.
Just a word about old boats. If you are going to be worried about every imperfection, then you will have to stay away from old boats. They come with all kinds of warts and scars. If you are going to purchase an old boat, be prepared to settle for all kinds of conditions, and also spend money to fix or upgrade as you desire. In the end, most of the folks in here will tell you to run, don't walk, away from all sorts of problem, like blisters, soft decks, moldy sails, troubled engines, otherwise you are wasting your money. Well, that may be true, but if I was worried about wasting money, I would never have been sailing for the past 12 years and enjoying every minute of it, on a boat that is probably worthless because it had a troubled bottom, soft decks, various water leaks and plumbing issues, and I can go on and on. I continue to throw money out the window because that is what you do when you want to own an old boat. If being economical is important to you, then be prepared for a lot of DIY. If you want to offload some of the work that can better be performed by an outside party, then be prepared to do some research and still take some chances with the money you spend. That's my story and I'm sticking to it!
