My informations is, the boat and owner never separate on Ambergris. The boat, motor and etc. is so expensive, therefore the boat would not be trusted out of the owner's control, due to that being his total livelyhood. The coral heads are just below the top surface of the water. Guide and his boat is not that expensive, so rent both, and enjoy the trip, by leaving the driving to them.
Just kidding, but who would rent a boat to a person with your name..."thebeachdrunk".