1) If you want profit, you need to rent a fleet, not a single boat. Way too much hazards on a single customer. Court are not free, and indelicate renter may be insolvent.
2) You must not own boats. Owning the boat means that if the boat is not rented, you will still have to assume financial costs. The best is to ask other owners if they are willing to rent their boats thru your company. Owner will get partly paid only if the boat is rented, but the amount paid will never recover financial costs.