The format of “kids on a cruise ship get in trouble and have romantic issues” is well established at this point. I’ve read one, maybe two, YA books with this sort of conceit, and Once Upon a Cruise exists for the modern middle grade set. Primarily involving a bunch of cruise performers, it explores an interesting and underappreciated aspect of cruise culture for the age group, and the book is fun and light and inoffensive. It’s not designed to be anything more than that, and it succeeds at its intention.
Great for intermediate-age girls who are looking into the sorts of teen romances that are maybe a little too old or content-heavy for them.