"Glenn Ashmore" wrote in message
news:2P5Bc.1470$Pa4.98@lakeread04...
Has anyone ever had any experience with or heard of a Nyloc nylon lined
nut backing off a bolt?

Not in my experience.

Here is the situation: I import a very good anchor called a Spade from
Tunisia.

"Very Good" is a matter of opinion. Mine performed poorly in
grass over sand to the point where I had to revert to a CQR. In
other conditions my Bruce performed just as well.

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.

Mine didn't have a 1/2" bolt. Whatever it was was metric and may have
been around 3/8" or a little bigger.

About 1" of bolt extends beyond the nut.

Not on mine. It exended perhaps 1/4" beyong the end of 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.

Well it is until one tries to dissassemble the anchor for storage as is
advertised. When I did, the bolt galled and I had to grind the bolt
off. Trying to replace the bolt was not easy as it is a metric sized
bolt and not easily found. I slightly drilled out the hole and replaced
it with larger bolt with a nylock nut after using some anti-sieze
to prevent the former problem. Held without problem all the way to the
Bahamas and back.

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?

Sounds unlikely to me. If the nylon retainer failed the nut would probably
have seized anyway.

--
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