If you are docking at Crown Bay -- ask the taxi if you could make the Charlotte Amalie ferry to STJ - they are less frequent from town and if you are not able to just proceed to Red Hook --- --- --- - from Havensite get a taxi to Red Hook - ferries leave every hour there. O the way home you might want to take the ferry from STJ to Charlotte Amalie - again that is a less frequent route - but you would be closer to Crown Bay if your ship is there or you may just want to shop in town no matter where the ship is.

the taxi + ferry cost is about the same no matter what combo you use.

As an aside - there is no 'S involved - it's just Saint John. Otherwise the folks in Newfoundland and Antigua get upset.