I've never been in STT and the BVIs. I wonder if 45 minutes are enough time to leave the plane in STT and get a ferry in Charlotte Amalie to Road Town. I don't have any checked baggage, so I can head directly from the plane to the taxi stand. How much time do you usually need from the airfield to the ferry dock? I rather spend time on a beach in the BVIs than waiting another 2.5 hours for the next ferry.
