i agree with darwin91, we were just on the 3/23 cruise, and we did the 5 star trunk bay excursion. it is about a 45 minute ride on a replica of an oyster boat to get to the bay. the crew is very friendly and helpful. very reasonably priced snacks and drinks are available (i bought a granola bar for .50!) a free punch is available after spending time at trunk bay. i have only snorkeled once before in the keys, and i enjoyed my time at this area. i saw a lot of fish and coral, and was surrounded by a large school of some 6"-8" bright blue fish. what a site! maybe i was just lucky. dang, i knew i should of bought that underwater disposable camera...
you can enter the water by jumping off the back of the boat (which i did, since it was fastest, about a four foot drop), climb down a ladder into the water, or take a dinghy to the beach, and swim from there.
it was our lst cruise, so we did this excursion since it covered all the details. we didnt feel herded like cattle, although it was frustrating to have only a little over an hour and a half at the area. if we were to go again, we would take the ferry from red hook and go to hawknest and enjoy being able to have more time on site. but overall we felt this excursion was worth it, and enjoyed it a great deal. the beach and water were beautiful, just what you think of as the carribean being like. 45 minutes sounds like a long time, but a decent and laid-back narration is provided by the crew as they discuss pirate history, the condos, nice homes, island history, etc. it is a well-run trip, just wish you had more time at trunk bay, but the trade-off is all the details are taken care of versus not as much time on site.