This fort is easiest if approached from the west side, allowing you to defeat all its defenses in a single pass and then dock on the east side. Although it may seem like a potential threat, Eleuthera has weak firepower and will likely do little to no damage to the Jackdaw.
Once you are on the ground, enter the fort via the wall to the left of the main gate and follow the rampart to the far side. You can then head north up the stairs and climb up the scaffolding on the nearby building to reach the upper level where you'll spot the Captain below on the other side for an easy air assassination.
After the fort is cleared you can get the Treasure x2, Animus Fragment x2, and start the Naval Contract, A Spanish Plague.
