you have to clear in at the closest U.S. port which would be Cruz Bay. You will then need to check in again in Culebra. If your boat has a U.S. customs sticker you can phone into Culebra, or you have to present yourself in person to Culebra customs. On the return you can sail directly to BVI and check in. I would spend the night in Christmas Cove, which is about 20 miles from Culebra and check in the next morning in BVI. Try to dine at Susies in Culebra, very good