Wiktionary
chainplate
n. (context nautical English) A plate on the side of a sailing ship to which the shrouds are attached.
Wikipedia
Chainplate
A chainplate is a metal plate used to fasten a shroud or stay to the hull of a sailboat. One end of the chainplate is normally fastened to a turnbuckle which is connected to the shroud or stay, whereas the remainder of the chainplate normally has multiple holes that are bolted to the hull. This distributes the load across the hull, making it possible for a somewhat lighter hull to support the load of the shrouds and stays.
Usage examples of "chainplate".
The sails jibed, then crashed back onto starboard tack with a bang that rattled the chainplates.