Nylock Danger

Nylock nuts, or aircraft nuts, have a Nylon insert in them so they don't loosen. They are useful but not infallible.

A friend of mine was sailing to Bermuda when, after five days on the starboard tack, his windward upper shroud came adrift. He made it to Bermuda but he had to carry shortened sail.

The hounds - upper terminus - of his shrouds were at stainless steel tangs, as is typical. The tangs on both sides of the mast (port and starboard shrouds) were secured with a single big bolt passing through the mast, good and strong. But the bolt was secured with an Nylock nut and in due course the nut was able to work loose.

Better the bolt had been drilled with a 3/64 (1.5 mm) hole, so a cotter pin could have backed up the Nylock.