A cruise ship seems to be a self-contained world once it is at sea. It occurred to me that if one could ensure that anyone on board s free from the virus, or immune, then occupants could associate freely without risk. This would reduce some of the burden from society, and provide some income for the operators. They wouldn't even need to leave port to be effective. Of course they would need to have medical facilities on board, and any supplies or visitors would need to be checked thoroughly.