If i am remembering correctly, cause it has been awhile, it was called the St. Christopher Shipwreck Sail and Snorkel to Buck Island. This was on a catamaran that held about twenty to thirty people, and there were three crew members. You didn't go all the way to the island.
There was a shipwreck to look at. The water was about thirty five feet deep, but clear as a bell. The snorkeling was pretty good.
maybe I should go look at Dave's site, and see if he still has that as one of the disney excursions, or if maybe they don't have that one anymore and this one that you booked has taken it's place.