We did a Trunk Bay Excursion from the Carnival Destiny in 2001, didn't snorkle, just the ferry and bus to the beach and back. The other posters are right, most of the time was getting there and back. We had about 1&1/2 hrs on the beach, not really enough time to enjoy that beautiful beach and island. You can go on your own from the Red Hook ferry and taking cabs, haven't tried that yet, though. PapaBill is right about Sapphire Beach on St. Thomas. It is really nice and not a very long taxi ride, you would have more beach time.