I just read Maryland's Clean Marina Program. As I suspected, it recommends using a set of Best Management Practices for hull cleaning. So if your marina is banning in-water hull cleaning outright, they are doing it of their own accord and likely going profit from the increased haulouts for hull cleaning. Which, BTW, are a $225.00 minimum at the OP's marina/boatyard. Probably a bit more than he is used to paying a diver for the same service.