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Re: [Hammock Camping] Re: webbing strength

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  • Rick
    Tim, The way I hang a hammock with webbing, even though I use a knot, there is little loss of strength at the tree. This is because there is very little
    Message 1 of 4 , Oct 31, 2005
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      Tim,

      The way I hang a hammock with webbing, even though I use a knot, there
      is little loss of strength at the tree. This is because there is very
      little stress on the knot. Most of the stress is taken up by the wraps
      of webbing around the tree, and only a small portion is taken up by the
      keeper knot at the end. The same is true of a hennessey knot.

      http://www.imrisk.com/hammock/improvedknot.htm

      Your point is well taken especially regarding the loop I make back at
      the hammock. This is the reson that I form that loop by sewing. It can
      be sewn, like Ed Speer shows in his book, by sewing the loop around the
      hammock. However, what I have begun to do is to sew a loop in the end
      of the strap and then bring the end of the strap through the loop to
      make a slip knot that goes around the hammock. With this set-up it is
      easy to remove the strap to wash the hammock. Add a whipped end to the
      hammock, and now I can quickly and easily remove the gathering at the
      end of the hammock to dry it quickly after washing.

      I read what Youngblood wrote about differential stress and agree with
      that too. This is the reason that climbing knots using webbing are made
      carefully without bunching the webbing.

      Risk
      ________________
      Rick Allnutt MD
      Author of "A Wildly Successful 200-Mile Hike"
      http://www.wayahpress.com
      personal hiking website: http://www.imrisk.com

      > --- In hammockcamping@yahoogroups.com, "tim garner" <slowhike@y...>
      > wrote:
      > >
      > > some of you have talked about the strength of webbing (& rope too i
      > > belive) being compromised w/ knots. so i`m wondering if webbing being
      > > forced to bunch up tightly together will cause a weak place too?
      >
      >


      [Non-text portions of this message have been removed]
    • dlfrost_1
      ... not ... outter ... unison, or ... would ... designed ... strength ... Your description of unequal loading inside/outside is correct. But there is an
      Message 2 of 4 , Oct 31, 2005
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        --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
        wrote:
        > I always thought that rope strength was degraded with tight bends
        > (which knots do) that required the individual fibers to stretch at
        > significantly different rates. When that happens, the stress is
        not
        > shared equally by all the fibers that make up the rope, with the
        outter
        > fibers at the bend taking on more of the stress and causing them to
        > fail first and at a lower stress than a rope without bends... it is
        > like all the fibers that make up the rope are not working in
        unison, or
        > parallel anymore. So applying that philosophy with webbing it
        would
        > depend on how it is being reshaped. It seems like webbing is
        designed
        > to handle tight bends along its flat part but not so much along its
        > edge. But if you are just gathering webbing and rolling it into a
        > tubular position, I wouldn't think you would be degrading its
        strength
        > much, it at all.

        Your description of unequal loading inside/outside is correct. But
        there is an additional factor: The inner-radius segment of the line
        acts as a static bulk about which the outer segment is stretched in a
        levering action which amplifies the loading much further. If it
        weren't for this levering action rope would have a working load
        rating that's 33% of its maximum (as webbing does) rather than the 10-
        20% used currently. (You can also see why nylon is so superior for
        rope: The memory-stretch allows it to accommodate both the radius
        the levering problems much better than other fibers.)

        When rumpled, webbing only has the partial-loading problem to contend
        with, and so retains much of its strength. For example, a water knot
        loop in webbing retains about 75% of the webbing's total strength.
        When loops are properly sewn into webbing (i.e. X-box and oversewn)
        that figure is over 90%. (I also suggest that loops be 3 inches long
        after sewing so that any rumpling at the tie-off is smoothed out by
        the time it reaches the stitching.)

        Webbing's only weakness is wear. Because all of the fibers are
        exposed, it wears out faster than core-and-sheath ropes. On the
        other hand, you can easily see the wear, so inspection and
        replacement are not problematic.

        Doug Frost
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