The ship represents the hospital. The characters on board only have counterpoints in the hospital, not in the outside world; this is why Mackenzie, Max, Shelby, and Caden’s parents do not appear there. The ship holds the crow’s nest, the bar where Caden receives his medications, the White Plastic Kitchen, the cannon (MRI machine), and the monstrous creatures that are the delusions created by his condition and medications. 

The Marianas Trench is the deepest spot on earth; Challenger Deep is the deepest spot of the Trench, the ship’s final destination. In Caden’s delusions, it holds the promise of treasure but also of certain death. The bottom of the trench represents the lowest point Caden encounters in his journey. When he ascends after the encounter with the Parrot and the gold coin, he truly begins to reverse the trajectory of his mental health. 

The Abyssal Serpent, which represents Caden’s schizophrenia, is a monster that stalks both the ship and Caden. The Captain calls it a formidable adversary and says that it will never stop hunting Caden. At the end of the novel, Caden makes it clear that he knows he has not vanquished the Serpent.