A couple of other tips.

Don't get the round trip ferry ticket. If for any reason your plans change (or the ferry co's) you'll be stuck with a ticket you can't use.

Make sure you know when the last "reliable" ferry leaves Tortola. We like to take our time leaving - overnight close by, sail back, check out and head for the ferry. Last time Sunsail took all of our departure information but I never heard back from them. During check out they asked when our flight was, it was late afternoon, she immediately said oh, you should have been on the 10 o'clock ferry from RT. Those are some liming ending words! Now even those that deal with the ferries on a daily basis don't know for sure if or when one will go but they do seem to have a sense of some they don't trust will go. So we ended up taxiing to West End for the next ferry to Red Hook, which by the way has to stop at Cruz Bay to clear in because there is no C&I in Red Hook. So despite assurances from the cab drivers and the bartenders that we should have plenty of time to make our flight we ended up at arrivals late, at least there were no lines. Got the standard you have to be here (I think it's 90 minutes) ahead of time, you can't board. It was a game of chicken, my wife rattling off all the reasons it's not our fault and me looking into the eyes of each person behind the desk until someone maintains eye contact and gives in (a practice we have perfected over the years).

I guess what I'm saying is you should pump the charter company for when you need to be back to make it in time for your flight out and play the what if game (what if the ferry leaves 20 minutes late, the taxi van takes 10 minutes to fill up and C&I is really slow). I try hard to get some of that vacation bliss all the way back home but all too often I seem to get myself thrown right back into the rat race before I even leave Tortola!

Sorry to be so long winded everybody...
Have a great trip!