To find this unique quest, head to the east end of Greater Boston. You'll know you're on the right path when you've reached Bunker Hill. Your destination, a retrofitted ship, will be east of the monument. The robot crew of this vessel needs your help and expertise to make the ship air and seaworthy. Start by speaking with Mr. Handy at the base of the ship.
To access the USS Constitution, navigate your way up and around the building that the ship is resting on. Work your way up the ship's three-level hull to reach the upper deck. Once there, speak with Ironsides, the ship's captain. Of the various objectives he'll assign you, the first one you should knock out should be test firing the cannons nearby.
Head below deck and speak with Bosun. There are three sets of power cables that need repairing or replacing. This bit of work is hardly challenging. You can grab replacement cables from a box nearby, or you can salvage the broken cables if you have +3 Intelligence (which you'll most likely have if you've taken your time getting to this part of the map). Whatever you decide, report to Bosun after you've fixed the cables.
Your next objective will be to replace the power relay coil. If you have +5 Intelligence, you can repair the coil without buying new parts. If you need new parts, most salvage shops should be able to provide a relay coil (or at least the parts for one). If you're looking for a shop nearby, check the settlement at Bunker Hill. After you've fixed the power relay coil, report the good news to Bosun.
Head back up to the deck for a conversation with the Navigator. He's in need of a new guidance chip, which you can obtain from a small Scavenger outpost nearby. Jump off the ship (assuming you're fortified enough to survive the landing) and head to the quest waypoint.
Now that you have the Scavengers' attention, their leader, Mandy, will attempt to coerce you into betraying the robots. You can decline the offer, genuinely accept the offer, or make the Scavengers think you're siding with them. If you side with them, they'll gladly let you take the the guidance chip. If not, you can try to steal it from them, or you can just outright kill them and then steal the chip. Head back to the deck of the USS Constitution, install the guidance chip, and speak with the Navigator.
You're now tasked with picking up a radio transmitter. The quest waypoint will be marked at a random location. You can either head there or repair the transmitter yourself, if your Intelligence is at least +9. However you decide to fix it, talk to the Navigator and then Ironsides for the next objective.
The final part they need is a set of FLL3 Turbopump Bearings. You'll find this at a randomly marked location, most likely a factory filled with hostiles. When you've returned to the USS Constitution, you'll have a choice to make.
SIDING WITH THE SCAVENGERS
First, you can follow through with your betrayal and side with the Scavengers. If you do so, meet with Mandy and give her the Turbopump Bearings. She'll promptly give it back to you, altered so that it can sabotage the ship. Head up to the USS Constitution and install the modified bearings in the captain's quarters.
Head to the ruined four-story building immediately south of the ship. Flip the circuit breaker at the top floor and watch the robots fail to get the ship moving. Join the Scavengers as you deal with the robots scattered throughout the area. Defeat Ironsides to complete the objective. Then speak with Mandy to complete the quest — though be ready for a surprise.
SIDING WITH THE ROBOTS
If you decide to side with the robots, be sure to avoid Mandy and the Scavengers when you come back from finding the bearings. Head straight to the USS Constitution and install the bearings in the captain's quarters. Speak to Ironsides on deck. A final assault from the Scavengers will commence. Feel free to take them on however you wish, but note that the quest will fail if you accidentally attack any robots helping out in the fight.
Head to the ruined four-story building immediately south of the ship. Flip the circuit breaker at the top floor and watch the USS Constitution depart. This scene will conclude the quest.