The title may seem like a duh title—hello, Nailer and his crew are actual ship breakers—but at second glance, it's more complex. In the most literal sense, Nailer and his crew break apart oil tankers and freighters for parts. They are the lowest of the low in society, just scraping by. But there's a lot less ship breaking and a lot more soul searching in the book than we might predict.
So why Ship Breaker, singular? We think the title refers to Nailer, but we have to consider all the ships that are broken in the novel: The tankers Nailer works on, Nita's clipper ship that wrecks on the island, the Pole Star at the end of the novel. It's possible that the title Ship Breaker is less of a job description and more of a description of who Nailer is—he is a breaker of ships whether they are meant to be stripped for parts or they are stranded on underwater skyscrapers. And this gives him a lot more agency than he thinks he has.