Loop Shackles/Connectors aka The Nacrabiner

[Schneiderlein]

I pulled a few loop shackles in an MTS machine to get their failure load. I tested one specimen made from 3mm Lash-It and it failed at about 2,200 lbf. The remaining samples were made from 7/64" Amsteel blue. Failure loads for three samples with diamond knots were consistently around 2,800 lbf. All samples failed at the knot and the spliced loop remained intact. The samples were intentionally made such that they had different sized loops, i.e., the legs of the shackles were made different lengths. The very tight loop showed substantially more damage than the other two, but the knot remained the weak point.

I also tested the "cinch wind" method suggested by lonetracker. While I personally find it less convenient than the spliced loop, the shackle also held to about 2,800 lbf before failure at the knot.

The Ashley stopper knot and the overhand knot failed at between 600 and 700 lbf. The tail was pulled through the knot and the shackles were perfectly intact with no damage after the test, but no longer had the stopper knot in them.

Summary:
- Use a diamond knot for loop shackles made from Amsteel.
- It is not critical to have the legs of the shackle perfectly balanced.
- The loop shackles have a failure load around 175% of the line's rating (190% for the 3mm Lash-It).
- The Ashley stopper knot and the overhand knot are not suitable for this application.

[NCPatrick]

It takes a lot of force to turn the rope inside out. I don't think it is an issue, just close them before putting them away. Even if you manage to turn it inside out, you can turn it right-side out again. I have done this a couple of times when splicing a locked brummel where I could not pass the other end through.

Thanks for that. I appreciate it. One less thing to wonder about...

[Knotty]

Those are some very important findings Schneiderlein.

Can you edit your message and put the notes about the stopper knots in large bold red font so no one misses this?

[Schneiderlein]

Those are some very important findings Schneiderlein.

Can you edit your message and put the notes about the stopper knots in large bold red font so no one misses this?

I made it bold, but red just looks too ugly. If possible (nacra, admins?), it would be nice to add a bold statement to the first post in this thread.

Sooner or later somebody is going to have to post a tutorial on making these things. Any volunteers?

[Schneiderlein]

Here is a picture of the tension test setup. All samples were pulled on 3/4" pins and the knot was off to the side. The picture shows the specimen with the "cinch wind" closure mechanism by lonetracker (yellow 1.75mm Zing-it).

[Shane]

Was the overhand a double or single?(not that it really matters, I'm switching to the lanyard)


S

[Rug]

Thank-you.
This solved a problem I was working on in my head.

I think we should call them: Nacra-loops.

[Frawg]

Even if you manage to turn it inside out, you can turn it right-side out again. I have done this a couple of times when splicing a locked brummel where I could not pass the other end through.

I inadvertently did the same while tying the diamond knot. Easily fixed. I think I'll stow the loop in 'closed' position, i.e., insert knot through the eye then snug up the eye. Can't figure out how to get the equivalent of a 'biner's springy gate.

[Frawg]

Many thanks for the testing report, Schneiderlein -- we're in your debt!

[Just Jeff]

I added a blurb from Schneiderlein's Post 71 to the first post in this thread...should help anyone who starts reading from the beginning.