Re: what type of paint for painting over bottom paint?
It depends on the type of bottom paint you have. If it's ablative you should only apply more of the same paint, or remove it completely.
Here's a short description of bottom paints:
Types of Anti-Fouling Paint
There are two main types of antifouling paint: Ablative and hard-finish antifouling paint. Ablative paint is suitable for sailboats and slower powerboats, while hard-finish paint is better for racing sailboats and faster powerboats.
Ablative Antifouling Paint:
Ablative paint is a soft bottom paint that is designed to wear away as your boat is used. As the water moving over the boat's surface wears away the paint, fresh layers of biocide are continuously exposed, so that the anti-fouling characteristic is constantly refreshed as long as some of the paint remains on the boat's hull. Ablative antifouling paints can be applied over other antifouling paints, so that you don't need to remove the previous paint before applying a fresh coat. It can be useful to apply 2 or 3 coats when applying an ablative antifouling paint. Ablative paints work well in marine environments with high levels of marine growth.
The drawback to ablative paints is that, because it's such a soft paint, you will remove some of the paint whenever you scrub down the hull. Also, ablative paints will wear away faster from trailer rollers and bunks and in high-friction areas such as the rudder.
Hard Finish Antifouling Paint:
These paints are not designed to wear off the way ablative paints do. If you frequently use your boat for high-speed motoring, or if you give the boat's bottom a good scrubbing after each use, a hard paint is probably your better choice. The hard antifouling paints start leaching out biocides on contact with the water, in a sort of timed-release fashion.
After a period of time, most often 6 months to a year, the paint has leached out all of its biocides, and a new coat of paint will be needed.
Hard antifouling paint builds up and needs to be removed before a fresh coat is applied.
