I nominate "The Death Ship" by B. Traven—the same guy who wrote "The Treasure of the Sierra Madre." It's a highly political novel, in the style of "The Jungle" or "The Grapes of Wrath" except the people being exploited by their bosses are sailors. The hero, a sailor, figures out in mid-voyage that the ship owners are planning to scuttle the ship for the insurance money.