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  1. #1
    Senior Member DemostiX's Avatar
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    Stronger stopper knots for soft shackles?

    What is the basis for Stu's estimate of lower strength of the soft shackle with a stevedore knot as the stopper? Just conservatism?

    Attractive and symmetric as the diamond knot is, I can see how it might be better for retained strength, but still not great.

    Suggestions or experiments of of a stopper knot that retains more of the strength of the line?

    I'm trying easy-to-make zeppelin / Rosendahl bends with doubled initial loops and two more passes of the ends through those loops.* That bulks up the knot, and to the point, enlarges all the bending radiuses, which should strain the cord less and retain more strength. But I have no way to test the result.

    *You always see illustrations with the two standing ends going in opposite directions. For the stopper use, the ropes in the illustration would be on the same side

  2. #2
    Redoleary's Avatar
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    Do you have a pic of the ends going in the same direction? I can't seem to envision how doubling the knot would redirect the ends?

    I have wondered about using a monkey fist for the stopper knot but never got around to trying it. When using 7/64 or 1/8 even if it were derated by 60% I'm sure it would still never let you down.
    Good luck,
    RED

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  3. #3
    Senior Member DemostiX's Avatar
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    Red:
    What this knot becomes, structurally, with the standing ends always being pulled in the same direction from the shackle, is something like a monkey's fist. It is a coil (ie several loops) of cord wrapped and bound by two coils of cord made from ends.

    Only issue for me: Is this the strongest possible stopper knot, distributing stresses as broadly as possible.

  4. #4
    Redoleary's Avatar
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    How about a Turks head stopper knot as in #545 in ABOK. It makes a fine looking large knot and the bend radius is at least less than 180 for the working and standing parts of the knot. IDK but I imagine the reduction is strength from knotting must have something to do with the angle the line has to take to form the knot??
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    SmokeBait's Avatar
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    Quote Originally Posted by DemostiX View Post
    What is the basis for Stu's estimate of lower strength of the soft shackle with a stevedore knot as the stopper? Just conservatism?
    I'm always on the conservative side when it comes to weight bearing applications. Better safe than sorry. Our testing of both knots was done by lifting large loads with the soft shackles and watching the knot for elongation and distress. The diamond knot on a 7/64" Amsteel soft shackle easily held up to a 2700 pound load multiple times with no sign of distress. Thus I deemed it appropriate for weight bearing applications. Is there a stronger knot? Maybe. Is it needed? I don't think so for this purpose. The diamond knot is easy to tie and has proved itself with regards to strength.

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    Stu: if you don't mind me asking, what was the result of testing 7/64th amsteel with the light duty knot?

  7. #7
    SmokeBait's Avatar
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    Quote Originally Posted by rcracin24 View Post
    Stu: if you don't mind me asking, what was the result of testing 7/64th amsteel with the light duty knot?
    The light duty knot tested with the same 2700 pound load held just fine. But the knot compressed quite a bit causing a reduction in the outer diameter. Thus we labeled it for light duty use such as connecting hammock ridge lines, etc. Many folks have hung on them without incident but we would prefer folks use the standard duty soft shackle with the diamond knot for that.

  8. #8
    Senior Member DemostiX's Avatar
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    If the breaking strength of soft shackles from 7/64" Amsteel Blue with their stopper knots were 2700 lb, then they could be lighter and less expensively made of lighter material, say from Zing-It. The straps and lines the shackles connect break at half that.

    But, those results were not replicated in more recent informal testing done by New England Ropes. Whatever one HF member may think think of NERopes, there's no reason to doubt their testing by professional and Cordage Institute protocols. (See the table in http://l-36.com/soft_shackle_testing_3.php )

    The diamond knot, beautiful as it may be in its symmetry and design, is not just the weak part of the shackle, but not much to brag on for retained strength.

    To the point I am suggesting, finding a stronger stopper by increasing the radius of turns within it, look at http://l-36.com/soft_shackle_8.php, and notice exactly that feature in the strangle knots included in the double shackle.
    Last edited by DemostiX; 09-05-2012 at 18:42. Reason: cord component

  9. #9
    SmokeBait's Avatar
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    Quote Originally Posted by DemostiX View Post
    If the breaking strength of soft shackles from 7/64" Amsteel Blue with their stopper knots were 2700 lb, then they could be lighter and less expensively made of lighter material, say from Zing-It. The straps and lines the shackles connect break at half that.
    The soft shackles DID NOT break at 2700 pounds. They held just fine. That was the available load we had to test with. You are more than welcome to try smaller lines and/or different stopper knots. We have an insurance underwriter to deal with and will stay with what we both feel is adequate.

  10. #10
    Redoleary's Avatar
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    Quote Originally Posted by DemostiX View Post
    But, those results were not replicated in more recent informal testing done by New England Ropes. Whatever one HF member may think think of NERopes, there's no reason to doubt their testing by professional and Cordage Institute protocols. (See the table in http://l-36.com/soft_shackle_testing_3.php )
    They also weren't testing amsteel.
    Good luck,
    RED

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