On the several cruises/crossings I've been on, I've seen scores of celebrities, from actors/actresses to authors to politicians. From my experiences, it's rather remarkable how other passengers leave them alone when they're "off duty" - many will give lectures and presentations, and have a time set aside for autographs, but beyond that, I've never seen anyone bother them on the "confinement" of a passenger ship.
david selby...david selby...his wife and an assistant were sitting alone at a table selling david's books.