"I've found some fairly affordable houses/apartments with available docks. "
IN NEW YORK?!
Either your definition of affordable is somewhat higher than mine, or you are seeing ads for illegal basements apartments in flood zones on the "canals" on the south shore of Long Island. I'd be curious to know what you've found (I'm not in that market) but caveat emptor, bigtime. And check out the nautical charts of the area, while you're at it.