I decided that after 38 years of this girls bottom being painted, and the added benefit of less resistance and better fuel economy, its all coming off and being rebuilt.
Once this far.....the rest is easy...if pros are doing it.
I ground till I found dry laminates.
One spot I ground/peeled off was 6 layers of roving and 6 layers of mat...almost a 1/2 inch deep through 1 inch thick hull for a 6 foot by 5 foot section. The rest of the hull was only bad... but not that bad.
Layered epoxy laminates filling all deep failures back to original thickness, then a 6 oz cloth/epoxied over the whole hull. Interprotect 2000 as required...bottom paint.... and not a blister after 9 years of full time liveaboard in the water.
Good luck .....but it's worth the piece of mind over listening to the "blisters are nothing" crowd.
