- When the iron fittings (such as nails and the like) in a wooden vessel become loose due to corrosion from the saltwater and the acids in the surrounding wood. Subsequently, the wood becomes rotted due to the rust.
Probably earlier than the 17th century. Likely originally a slang term used by sailors and shipyard workers.
Unless treated, iron rapidly oxides when exposed to saltwater. Even today, rust is a part of life at sea with ships. In the days when wooden ships with iron nails and fittings were common, corrosion of the iron fittings and rotting of the wood was inevitable. If left unchecked, the ship could literally fall apart at the seams.
Of course, this isn’t limited to wooden ships since any object or structure with iron fittings is subject to the same chemical process. Rust.
King, D., Hattendorf, J.B, & Estes, J.W. (1997). A Sea of Words: A Lexicon and Companion for Patrick O’Brian’s Seafaring Tales (2nd Ed.). Owl Books.
Rogers, J.G. (1985). Origins of Sea Terms. Mystic Seaport.