Scott...
I use CSC on my boat too. As Ross suggested, I use whatever is left over from the year before to prime any bare spots created when the storage yard pressure washes the hull each fall at haul-out. I roll on a fresh coat each Spring. Before I do I "cut-in" with a brush all the leading edges, the hull/keel, shaft log, and keel areas as well as around all thru-hulls. One good idea is to apply a different color (red under blue for instance) as the first coat on the hull so you can see when a fresh coat of paint is needed. Two seasons is about as long as a well applied coating (at least two layers) of CSC will last in our area.