Gay/LGBTQ cruising (the kind on the high seas, haha) has been booming in recent years, with mainstream brands courting this market segment on regular cruises as well as increasing numbers of ship charters by gay travel companies, the main players including Atlantis Events, Brand G Vacations, Olivia (aimed at lesbians), OUTbound, R Family, RSVP (the pioneer in this sector), and VACAYA-
Most of the passengers are overwhelmingly male, and the onboard focus is partying (an Atlantis cruise party is shown here), including costume parties and drag shows. Drugs aren´t allowed, by the way, but unfortunately they do get inevitably smuggled aboard.
A couple of interesting articles here. This one´s a recent survey of this market sector and the choices it offers:
And this one´s a look from Out Traveler about the phenomenon in general: