Another option is getting a private water taxi from STT to Tortola. We did that one way last year and the regular ferry on the way home. Have already decided that even though it was expensive we are definitely going to add it both ways to the budget for our next trip. It was so relaxing compared to our time on the regular ferry! That is unless I can convince my husband to fly to EIS - he's not too excited about taking the tiny plane over there.