You knew it had to exist. Ravelry for cruisers. Or Facebook for cruisers; anyway some kind of net work for those who like to spend time in those floating resorts AKA Cruise Ships.
In fact, Cruise Critic (dot COM) is much more like Ravelry than Facebook. News and reviews, message boards, roll calls for the various ships and sailings. Of course, it is supported by adds…. (you were expecting?)
The membership is heavily US/CA/UK with a sprinkling of other languages. There are members (free registration) on their first cruise along with a few who have been with the site since its origins back in the beginnings of bulletin boards and seem to live on ships. At least I think that might be the case when your cruise days number over 10k.
I have had the site recommended to me numerous times over the last several years and noted a meet-up on the Grandeur cruise last fall. I registered in March in order to read reviews on that less than sterling Costa Classica ship.
Like other social bulletin boards, threads seem to be the responsibility of whomever starts them – or in the case of a roll-call – whomever wants to organize something. RCI and Celebrity seem to be quite supportive; even having a registration form on their site for participation in Meet and Mingles. Minimum members to get a location set aside (and on the schedule) seems to be ~25. In the case of this cruise – the initial sign up list for the Sail Away Party was 56 and the M&M at 32.
It was a good time – sunshine, fun people and feeling like you know a few others on the ship.