There is a small marina on the south end of Valpariso, which is the next town south of Vina del Mar. It is south of the shipping terminal if I remember correctly. The local south bound buses go right by it I think. I can't say that I remember any charter boats. Vina del Mar is a big weekend spot for the folks from Santiago, more of a summer spot for local tourists (than Valpo) so you may find some boats there, don't know.