Loose-fitting long-sleeved shirts and long pants made from tightly woven fabric offer the best protection. A wet T-shirt offers you much less UV protection than does a dry one, but if you're in the water a T-shirt will help. Just be sure to use sunblock with high SPF, too.
Carnival Liberty - 2/2007
Carnival Destiny - 4/2004
RCCL Monarch of the Seas - 7/2001
NCL Sunward II - 1982