Boat. Depends on how fast your boat is. If you take the harbor cruise that is available it is about half hour each way with about an hour on the island
You can only get there by using one of the authorized tour boats. Approximately a 30 minute ride each way.
Because it is a Federally protected National Historical Monument, i don't think it is available for private boats to dock, need to call before you try, cost $22 to ride ferry out to island and worth every penny, excellent tour
Spend the money for the NPS boat tour. It's about 2 hours in total length, to, on, and back from the Fort. I was hesitant before hand but happy I did afterwards. Bonus, look for dolphins playing in the wake of the boat and in the water around the fort. So fun to watch. It was like two cruises in one!
Thanks! Your answer is awaiting moderation.