it really depends on the waves and where the cruise is going, but it doesn't rock too much. i took a cruise to Alaska a few months ago, and it wasn't too bad, though i did see a few people get sea sick. if it's a problem, they do have pills for it, and if it gets really bad, i think they have an injection or patch for it (i saw it on a few people, but i couldn't tell if it was a patch or injection).