Try wet sanding with very coarse wet/dry paper, kinda looks like emery cloth. There are also foam sanding blocks that may work. Use plenty of water to keep the dust down.

Some bottom paints are very soft and will sand easily. If the boat is small enough this may not be the nightmare it appears to be.

If the layers are separating, there is probably an adhesion problem and a paint scraper may take away large chunks.

Give it a try before breaking out the heavy equipment.