Between the devil and the deep blue sea

A popular nautical explanation claims that "the devil" was sailors' nickname for a particular seam in a wooden ship's hull, an awkward one near the waterline that was especially difficult and dangerous to caulk while at sea, leaving a sailor working on it trapped between that seam and the ocean itself. It's a vivid, plausible-sounding story, but there's no solid documentary evidence that shipbuilders or sailors actually used "the devil" as a technical term for any specific seam. The phrase may simply be a general figurative pairing of two dreaded things, without a literal nautical object behind it at all.