International waters don't mean a thing when you're on a cruise ship. If you leave port from the USA, the laws of the USA apply the whole time you're on the ship. I went on a Carnival cruise about 5 years ago, best thing I've ever done, and me and my brother bought some shit in Curacao and brought it on the ship with us. Stuffed it in my boxers if I remember correctly. Just a metal detector, but some ports do have k-9s sniffing about. We had a smoking room and just puffed it in our room amid a cloud of cigarette smoke and up on the top deck late at night which was next to vacant.