If it were a Saturday or Sunday I would agree with Malcomb. But on a Wednesday you should be fine with the 11:30 ferry. Personally I would take an earlier ferry. Not for fear of getting to the airport on time. More to have a relaxing breakfast/lunch before having to deal with that awful airport. We love the outdoor bar at Emerald Beach and the food is decent. Then a 10 minute walk or a quick cap ride to STT. No stress.