you can obtain a oupv (6-pack) up too 100 ton, then a master, the master gives you the ability to operate a coast gaurd inspected vessel, which is a vessel that you can carry multi passengers, more than 6. But the tonnage is up to your personal experience. Once you submit your seatime the coast gaurd will evaluate it and tell you how much tonnage you qualify for. Once you reach, i think 500 tons you can upgrade one more time, and that is a master license unlimited tonnage