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Antifouling paint is one kind of bottom paint, the most common kind. If it is adhering well, you can usualyl paint over it but there are some paints that are incompatible and if you do not know what the old paint was, you might want to strip it to be sure the new paint will adhere properly.
The problem with stripping the old paint is that it is regulated as HazMat and if you sand or scrape it, whatever you remove must be treated as HazMat, contained and disposed of in a HazMat landfill. Sand it off on open ground, and the EPA may later order that ground scraped and shipped off as Hazmat--at a much larger cost and fine, ignoring the pollution/health issues.
The exterior portion of the hull above the waterline is called the "topsides" and you would use a topside "coating" on it. Coatings include paints and more spohisticated compounds like urethane paints, some of which are toxic to work with. Some can be rolled and tipped, some must be sprayed. Generally you would try to just clean what is there, because the original material is gelcoat (a fiberglass resin material) and that's more durable than coatings. Your local auto body shop supplier carries 3M's line of cleaners, polishes, and compounds for fiberglass gelcoat, they are the same for cars and boats.
Normally you paint the bottom, then after it dries, move the boat so it rests on new spots and paint the ones you missed.