Here is some more information from International. Note that, if you do not remove all other anti-fouling paint, you'll need to use a primer. PrimeKote, if I recall correctly. VC-17 isn't compatible with other anti-fouling paints.
Usually the easiest way to determine if you have a compatibility issue is to take some of the solvent for the paint you wish to apply new and try that solvent on the old coating. If you can rub off paint with the solvent, you're going to have a problem with the new paint. Either strip or prime, with stripping being the most desirable if the most arduous.