The following is from a work-in-progress called "Moby Dick: a Book Report" in which I read each chapter of Herman Melville's classic novel Moby Dick, and write about what I read.
The title of this chapter is a reference to the part of a harpoon boat where the harpoons are stored. Generally, harpoon boats are out-fitted with at least two harpoons (or irons). Should the first harpoon fail to reach its mark, there is a backup. Given the fact that the Pequod has four harpoon boats, you can imagine the chaotic intercrossing of harpoons and rope that happens during a typical whale chase.