I hate to disagree with Ann (HI ANN

) But, we have done both the 5 Star Snorkel you mentioned and St John on our own. We MUCH prefered going on our own. The excustion took a LONG time to get to Trunk Bay (about 45 min) and we only stayed there about 1 1/2 hours, then another 45 min ride back. So you spend as much time going to and from as you do at St John. When we went on our own we were there in about 1 hour, and stayed until about 2pm. (I think we took the 9:00am ferry to St John and the 2:00pm ferry back) We spent about 3+ hours at the beach at Trunk Bay and had a fantastic day! Nothing against the excursion, the crew was nice and the ride to and from pleasent, but for us it was about spending time swimming, snorkeling and relaxing on the beach, not a boat ride. Plus it worked out to be a few bucks cheaper, even with renting beach chairs, to do this on our own.
The other ST John Trunk Bay excursion with
DCL uses a much faster boat. They will pass the Leylond Sneed when you are about
halfway to Trunk Bay. I think the "Leylond Steed" is the name of the boat. If I remember correctly it was the name of the owners mother.
No mater what you deside, you will have a great time at Trunk Bay. It is a beautiful place!