I don't know about NY, but...
the possession of weapons in the home is illegal in the nearby District of Columbia. Whether this local law is constitutional or not is currently being argued at the Supreme Court. At present, defending your home (or boat, or whatever) with a firearm will land you jail. So if you are sailing up the Potomac, and you are packing, you in a heap a trouble, Andy....I also would not assume anything about being able to carry a firearm on any kind of boat while in NY City limits. It, too, has one of the strictest gun control laws in the nation and claiming ignorance would not be a viable defense,IMHO. I would leave the weapon home if I were headed that way, or get written permission from the police or city attorney prior to entering their waters armed....