Kim and Lorraine, Ok, from what I researched, the 2 best sail/snorkel excursions that Carnival offers are:
Captain Nautica Ultimate Sail and Snorkel
Christmas Cove Sail and Snorkel
I found info about both on Google. The first is 3 1/2 hours, the second one is 4 hours. BOTH got very good reviews by those who actually went on these exursions.
Rob