Note: One of the chests contains a plan – Flower Sails .
Swim south from the diving bell and enter the shipwreck on the sea floor. Avoid the urchins and jellyfish within and grab the chest. Follow the wreck until the end and swim out the far side. Just across from the exit you’ll see yet another wreck. Swim over and use the air barrel to your right and then enter the hull of the wreck to find a second chest.
From the chest, turn to the right to find a small ship corridor. Enter this and swim over the first beam covered with urchins to find a chest. Change your view to find the ramp nearby (it’s on the roof!) and swim up to the upper level of the hull. As you get up, immediately look behind you to find another chest. From here, follow the path out through the door back outside, this time on the deck of the ship.
Move outside and look in the open hatch just before the fallen mast to find an Animus Fragment. Return outside and use the air barrel nearby. After using this, swim across the gap to the next section of the ship. Find the air barrel here and ignore it for the moment. Instead look in the right-hand corner of the room for a chest. Now go and use that air barrel.
From the barrel swim upwards and then down into the next section of the deck to the north. Swim to the right and as you approach the hole in the hull, look in the hallway to the right to find another chest. Grab this and swim out of the hull. Swim past the air barrel immediately outside and enter the small shipwreck to the east. Near the far end, you’ll find an Animus Fragment hiding behind a support pillar.
Exit the far end of the smaller wreck, turn right and swim back the way you came to use the air barrel we ignored just moments ago. After refilling your air, follow the shipwreck to the north and once you reach the large rocky passages, hug the left-hand wall for a short distance until you see another wreck lying up against the wall. Look in here for the final chest. Now swim over to the east and interact with the diving bell to return to the Jackdaw.