Regarding skill checks. The percentages I list worked for me. Higher percentages will give you a greater chance of passing skill checks the first time. A quiet two-note tone will play every time you pass a check. IMPORTANT If you fail a skill check immediately dashboard then quit the game. Reload the game and you’ll be restarted from the last checkpoint. If you’re not fast enough then the option will be gone forever and you’ll be locked out. Since inventory and items do not carry over you'll have to restart the game If you do have to reload be sure to pick up all collectibles that did not save.
After talking to Fitzroy the harbormaster the alleyway past the Stranded Whale bar will open up. Walk to the end and find a large open door on the left. Inside find three hidden items
LEVER - As soon as you walk in on the left-hand side on the floor behind the movable board.
RATCHET DEVICE - On the left-hand wall in a broken crate to the left of the roof support beam.
COGWHEEL - Turn 180% and look to the left of the beam on the other side of the room. Partially hidden between metal plates
From the cogwheel turn right and go up the ladder. Interact with the winch, then mount the ratchet device > cogwheel > lever, then turn the handle SKILL CHECK HERE [STRENGTH SKILL 50%]
Drop down through the grate and turn right at the bottom to wade through the water. A cutscene plays and after you'll get the achievement.