The Sheraton Key Largo has rental Hobies on the beach, but they are not free to use when you rent a room there. You can also stay elsewhere and rent their boats. The rental operation at the Sheraton is Caribbean Water Sports, and their number is 305-852-4707.
The Key Lime Sailing Club has some little beachfront cottages, and your rental includes free use of a boat -- I think they are Catalina 25's. Their rates are very reasonable considering the boat is included. Their web site is
www.keylimesailingclub.comThose are the only two places I know of in Key Largo.