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  1. #21
    Knotty's Avatar
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    Quote Originally Posted by Albert Skye View Post
    Using them as pictured (with a very small radius bend) also cuts the strength efficiency of the rope (by the way, the numbers are likely worse for HM cord). I like soft shackles but I wouldn't use them in that application.

    I believe this pic is being used for hammock suspension and it will work fine for this application. Testing showed that these loop biners made from 7/64" Amsteel failed at around 2800#!

    From the other thread:
    Quote Originally Posted by Schneiderlein View Post
    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.
    Knotty
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  2. #22
    Senior Member Albert Skye's Avatar
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    Quote Originally Posted by Knotty View Post
    Testing showed that these loop biners made from 7/64" Amsteel failed at around 2800#!
    I'd be surprised if he tested the shackles over such a small radius. Anyway, I imagine the single strand running round the shackle would fail before the shackle (assuming the webbing is not the weak link).

    To be sure, I'm not suggesting that the arrangement is going to fail for you. My point is simply that strength efficiency is reduced (and more efficient arrangements are possible).

    I don't mean to pick on you. I continue posting about these things because they're relevant and many might benefit from the information.

  3. #23
    Quote Originally Posted by Festus Hagen View Post
    Actually, it's knotted in exactly the way I'm thinking I just figured it would be harder to get the stopper knot to hold in Amsteel (never having tried this, myself, so I prolly should have shut up)
    In that case, you're way ahead of the game. The first time I saw it, I had no clue what the heck a diamond hitch was. When Schneiderlein tested these using 7/64" amsteel, the diamond knot collapsed at 2800 lbs regardless of the configuration of the loop. He intentionally made them so that one leg was shorter than the other which means the force was all on one piece of amsteel, not both.

    Quote Originally Posted by Knotty View Post
    I believe this pic is being used for hammock suspension and it will work fine for this application. Testing showed that these loop biners made from 7/64" Amsteel failed at around 2800#!
    The failure at 2800 lbs was the knot collapsing which doesn't directly relate to what Albert was saying. There's a post later in that thread where Schneiderlein explains that he used 3/4" steel pins during the test. That should derate the amsteel to about 82% (1300 lbs). The knot collapsed at 2800 lbs and he described "damage" to the amsteel so 7/64 amsteel derated to 1300 lbs was able to survive with some damage even though it didn't fail. If you run that same piece of amsteel over another piece of amsteel, it's derated to 50% or 800 lbs. We don't know for sure what the failure mode will be in that configuration. We also don't know what difference a dynamic load would make.

    Since the nacrabiner thread is huge, we need to be careful how we summarize the info, but after saying all of that, I'm still hanging my 250 lb butt from whoppie slings and nacrabiners made of 7/64 amsteel because I don't think it'll ever matter.

  4. #24
    Senior Member Albert Skye's Avatar
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    Quote Originally Posted by Boris Losdindawoods View Post
    That should derate the amsteel to about [...]
    The plot I posted is for wire rope.

    I requested similar D:d data from several manufacturers of HMPE (Dyneema/Spectra) cordage but all reported that they had not done those tests. One engineer did however suggest that HMPE is likely to be less efficient in D:d strength than wire rope.

    In any case, an eye is twice as strong because it has two legs (i.e., a reduction of up to 50% for two lines is no weaker than a single line).

  5. #25
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