Yep, they're osmotic blisters. After having fixed a couple thousand of them on a monohull once, I can tell you the best way to fix them is with a gallon of gas and a match.

Do you moor this boat or dry sail it? If you moor it, you're not only going to have to fix them, you'll have to prevent them from from recurring in the future.

Either way, you're looking at a substantial amount of work.