Done both the car barge, once, and the ferry many times. Passenger ferry is the way to go. A lot less hassle. Rent a car or even better, call Hibiscus, with Starfish Tours. We've driven around the island with her several times when we have family or visitors on St. Thomas. She'll do a island tour or go where ever you like. Stop at the east end for lunch, Sloop Jones is on the way for some funky shopping or whatever. Then just hop on the next ferry when you want. Great day trip.