thats a hard one, because if its a full cruise, then u have to find a place where people dont go often near rails to water. you cant do it inside, there are smoke detectors, even in the rooms, unless the boat u are going on has smokin rooms, but the 1 i went on didnt, some do, then just do it in your bathroom, make sure u put towel under door that leads outside so no one will smell it!