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?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com