For me, any rise on the scale is just that. It's not a gain, it's not fat. It's just a temporary upward rise on the scale. It represents water, it represents extra food in the body...but a short cruise isn't even enough time to create fat let alone gain many pounds of it.
Like others have said, it's what I have done or not done AFTER the cruise that changed the results. If I get right back into my normal food habits, it all drops off. If I don't, uh oh.