I also am interested in the Leylon Sneed and how you transfer to and from the dingy. Is it only for the fit and strong or can us weak and not to fit make it? (without too much humiliation, lol).
There is a ladder on the side of the boat that you have to climb down to the dinghie, and back up. There's handles on the boat all the way to the dinghie, and using those you don't have to be a Gold's Gym body builder to get in on and off the boat. Unless you have severe mobility issues you should be able to get on and off the boat without much difficulty.
btw.. when we did the tour, they told us the afternoon version was quite heavily booked, so it seems the idea of going on the morning trip to Trunk Bay, leaving the afternoon for St. Thomas is a good idea.