Usually a boat hull is painted with a barrier coat of epoxy followed
by another coat of anti fouling paint.
The epoxy paint is to prevent blistering, but if you are trailering
your boat like I do then you don't need any paint on the bottom.
My boat is in the water for a week at a time max, and I clean the hull
pretty often with some simple green and/or a pressure washer so it
stays nice and white.
John C.