The safest journey to this fort is to sail in from the west for a straightforward assault with Mortar fire and broadsides. There is usually a few gunboats in the area, but these should be no problem for the Jackdaw at this point and you can concentrate fire on the fort itself. Once the defenses are gone you can finish off the surrounding boats so you can dock.
Once you are on the ground, enter the fort via the left wall of the main gate and then jump across to the roofing and find the part of the wall that will let you climb up. When you reach the upper level use the crates to reach the beams coming out of the walls to air assassinate the first Captain. From there make your way down and behind the final Captain and defeat him as well. Now climb back up the fort and enter the war room to kill the fort's Commander.
After the fort is cleared you can get the Treasure x2, Animus Fragment x2, and start the Naval Contract, Eye for an Eye.
