As far as I know, no cruiseship has a "nude" deck. If you try to go completely nude on a cruiseship, you can expect to be put off the ship at the next port.
The topless decks are now being converted in to miniature golfing areas. There was topless decks on Carnival but a pervert ruined that for everyone.
Also, most of the Caribbean islands DO NOT allow for nude sunbathing unless it is on a private resort like Sandals or the like. There is one island (St. Maarten) that has nude public beaches but that is about it as far as I know.
Beware, many of these islands take this prohibition very seriously and you could end up in the hoosegow for showing off your bod.
(cruzin' solo by design)
Freedom ('09), Imagination ('08), Victory ('08), Destiny ('08), RCCL Navigator ('08), RCCL Majesty ('08), Glory ('07), Liberty ('07), Fantasy ('07), Destiny ('06), NCL PofAm ('05), Fascination ('04), Victory ('04), Fascination ('04), RCCL Voyager ('03), Fantasy ('99)