Has anyone ever had any experience with or heard of a Nyloc nylon lined nut backing off a bolt?
Here is the situation: I import a very good anchor called a Spade from Tunisia. They come in two pieces a shank and a fluke which mate together in a tapered socket that locks the shank in position when any load is placed on it. When there is no load the two pieces are held together with a 1/2" stainless bolt and stainless Nyloc nut tightened snug to the sides of the socket. About 1" of bolt extends beyond the nut. The nut is not torqued down because the shank must be loose enough to slip forward into the taper to lock. All the load on the bolt is in shear. There is no force in tension or torque. Overall it is a very solid arangement.
Now the problem. A New Zealand sailor is claiming that his anchor (which thankfully I did not sell) failed because the nut backed completely off the bolt which allowed the bolt to fall out. There is very little vibration and no torque on the bolt. The nut was in good condition, new when installed and had never been removed. Is there any way that a Nyloc nut in good condition could possibly make more than 20 turns on a loose bolt on its own?