[Fr. Frank]

I spent many years managing marinas in the south. I echo that the previous paint is probably peeling/flaking off because of poor prep. The other reason it can flake of if it was an ablative paint that spent a lot of time in the air before being initially immersed - like months.

Regardless of the cause of the problem, the old paint has to be removed to get new paint to adhere properly, AND it needs a good barrier coat if you're going to keep the boat in the water using an ablative paint like Interlux Micron or Petit Horizons. If you're going to use a hard bottom paint like Interlux Ultra or Petit Trinidad, simply removing the old paint and sanding the bare bottom with 80-120 grit sandpaper will provide you with excellent adhesion and durability.

If you intend to keep the boat on a trailer, you need a hard bottom paint that uses biocide leaching for antifouling, as well as being resistant to wearing away from launching and reloading onto the trailer.