I'll also add to Stonny's info, that if possible try and time going around Half Tide Rocks for after the ferry goes around it.
We took our catamaran up there a while ago and were coming in with an incoming tide when the ferry appeared going out. You are beam on to some of the current when approaching the turn and there's not enough width for the ferry and my cat there. It's a bit unnerving pointing the bows towards the shallows to account for the tide pushing you into the ferry's path!
Luckily we just pulled up the centreboards and made a run for the shallows to get out of the way...