I've created a 55 second YouTube Short guide showing how to get the Get Off My Ship! achievement by killing the Leviathan Remnant.
The Leviathan Remnant is the boss in Chapter 8: Search and Rescue. The strategy for this fight is to use the ADS cannons to attack the boss's yellow weak points. This fight takes place outside the ship so you'll have to watch your air the whole time, but there are O2 stations near each cannon.
This boss fight has 3 phases and will attack you in between phases. Between 1 & 2 there's a sweeping attack with a tentacle. Go high to dodge this. Between 2 & 3 the boss deploys mines that you can shoot to destroy if needed.
- Phase 1: Dodge the tentacles when they try to hit you and shoot the yellow target on the boss.
- Phase 2: Dodge the yellow pods the Leviathan shoots at you and shoot the yellow target on the boss.
- Phase 3: You'll now be dodging the tentacles and pods and avoiding any mines near you. Again, shoot the yellow target. About halfway through the last target a tentacle will destroy your cannon. Start catching the pods and throwing them to do damage until the fight is through.
https://youtube.com/shorts/oHiV03pHXtQ?feature=share