Hull Breach

Hull Breach is a side quest in the Fallout 4 add-on Far Harbor.

Part 1
Go to the Mariner; her office is to the immediate left upon entering Far Harbor. She asks the Sole Survivor to find her a special set of tools to help improve the capabilities of the hull. The tools can be found in Eagle's Cove Tannery which is occupied by feral ghouls. Recover the tools and return to her. Exiting the tannery through either the front or back door will lead to the player character meeting a man named Machete Mike, who claims the tools are a rare set of Pelman's. He offers 2000 caps for them (2750 after a Speech check), wherein one accepts the offer, but fails the quest; or, refuses the offer without any further conflict.

Mike may be killed after refusing his offer, netting the around 3000 caps, but will restrict advancement in the questline. However, if one tries to pickpocket Machete Mike, he will turn hostile and attack; at this point, one can kill him in self-defense and loot the caps from his body or simply run away without being penalized (inconsistent), and the quest can be continued. However, even killing Mike in this way may still result in the player character being barred from starting the second and third portions of this quest. Return the tools to the Mariner to receive the caps and experience. The next time Far Harbor is visited, large spiked barriers will be found on the outside of the Hull.

Part 2
During, or after completing, Rite of Passage, the Mariner will offer a second opportunity to improve the Hull even more. Conversing with her reveals that she desires completion as soon as possible due to the doctor diagnosing her with an incurable illness.

She sends the player character to the MS Azalea, to clear it of the occupying trappers. After killing the leader, Bilge, the Sole Survivor must return to Far Harbor to accept the caps and the Mariner's respect. The next time Far Harbor is visited, two large sections of the Azalea's hull will have been attached to sections of the Hull.

Part 3
During The Changing Tide, the Mariner needs one more task completing, in order to finalize the Hull's defenses, primarily against the corrosive acid of mirelurk queens. She sends the Sole Survivor to collect three mirelurk carapaces to coat the Hull with, making it acid-resistant. Collecting the carapaces takes the Sole Survivor back to the Mariner, who thanks them and rewards them with the Defender's Harpoon Gun. The next time Far Harbor is visited, three overhangs built out of the carapaces will be added along the walkway above the Hull.

Bugs
If you enter Eagle's Cove Tannery through the basement door, Machete Mike may not appear.