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Re: [Hammock Camping] Hammock Rope Diameter for Spectra Cord

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  • Dave Womble
    Opps, noticed and error... When the ropes stretch because of the tension applied to them, they reduce the rope angle and relieve the tension that is causing
    Message 1 of 9 , Jan 31, 2006
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      Opps, noticed and error...

      "When the ropes stretch because of the tension applied to them, they
      reduce the rope angle and relieve the tension that is causing the
      stretch to a tension that they can support and the ropes don't break
      when by design they probably should have failed? Us hammock hangers
      got lucky on this one."

      I said it backwards, 'reduce' should be 'increase'... like this:

      "When the ropes stretch because of the tension applied to them, they
      INCREASE the rope angle and relieve the tension that is causing the
      stretch to a tension that they can support and the ropes don't break
      when by design they probably should have failed? Us hammock hangers
      got lucky on this one."


      --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
      wrote:
      >
      > --- In hammockcamping@yahoogroups.com, Rick <ra1@i...> wrote:
      > >
      > > Breaking strength, as promoted by the maker is usually much less
      than
      > > the real breaking strength.
      >
      > We've talked about this from time to time on this web site. Rick
      makes
      > a good point that the manufacturer's specs might be conservative.
      It
      > makes sense with high quality manufacturers and as long as they
      don't
      > get in a 'strength war' that will likely remain the case... for
      high
      > quality manufacturers.
      >
      > There is another factor that I think also comes into play.
      > Unfortunately I don't have expert knowledge on how it all works so
      I
      > can't explain it very well, but I'll try anyway. The tension on
      the
      > hammock suspension lines are understood and are a function of the
      > weight in the hammock and the angle of the hammock suspension lines
      > relative to the horizon. This chart shows how this angle affects
      the
      > tension of the hammock suspension lines:
      http://tinyurl.com/7onfm .
      > What this chart is saying is that at a 30 degree rope angle the
      tension
      > on both hammock suspension lines is equal to the weight in the
      hammock,
      > at 15 degrees it is twice the weight in the hammock, at 10 degrees
      it
      > is three times the weight, at 6 degrees it is five times the
      weight,
      > etc. It dramatically shows that where you get in trouble fast is
      at
      > small rope angles. But this is where is gets interesting-- at
      these
      > small angles there isn't much difference in the rope lengths. For
      > instance if I calculate the rope lengths for a hammock with a 10
      foot
      > length and 15 feet between the supports, I get rope lengths of 2.54
      > feet at 6 degrees, 2.62 feet at 10 degrees and 2.76 feet at 15
      > degrees. Now pay attention because this is like a magic trick!
      The
      > percentage difference in rope lengths when you use the 2.54 feet at
      6
      > degrees as a reference is: 3.1 percent at 10 degrees and 8.61
      percent
      > at 15 degrees... and the hammock body itself is also made of nylon
      > (which is stretchy) which will also help. When the ropes stretch
      > because of the tension applied to them, they reduce the rope angle
      and
      > relieve the tension that is causing the stretch to a tension that
      they
      > can support and the ropes don't break when by design they probably
      > should have failed? Us hammock hangers got lucky on this one.
      >
      > This does make it hard to hang a hammock because of the stretch
      when it
      > is occupied but this is not near the problem for the folks that
      start
      > off hanging their hammocks with more rope angle-- you are not
      stressing
      > the ropes as bad so they don't stretch as much and because of the
      > geometry of the larger angles the rope angle is not as sensitive to
      > changes in the rope lengths.
      >
      > Now, about those mountain top lots I have for sell in south
      Florida...
      >
      > Youngblood
      >
    • Bill in Houston
      Good point. The higher a rope s elongation at breaking tension is, the more room for error you have. But, too much elongation is a hassle. Bill in Houston
      Message 2 of 9 , Jan 31, 2006
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        Good point. The higher a rope's elongation at breaking tension is,
        the more room for error you have. But, too much elongation is a
        hassle.

        Bill in Houston

        --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
        wrote:
        > We've talked about this from time to time on this web site. Rick
        makes
        > a good point that the manufacturer's specs might be conservative.
        It
        > makes sense with high quality manufacturers and as long as they
        don't
        > get in a 'strength war' that will likely remain the case... for
        high
        > quality manufacturers.
        >
        > There is another factor that I think also comes into play.
        > Unfortunately I don't have expert knowledge on how it all works so
        I
        > can't explain it very well, but I'll try anyway. The tension on
        the
        > hammock suspension lines are understood and are a function of the
        > weight in the hammock and the angle of the hammock suspension lines
        > relative to the horizon.
      • J.D. Hoessle
        ... Yes, I think you demonstrated that in Hot Springs with my HH. Thanks again for that lesson! ... I ll take one. Where should I mail the check? Happy
        Message 3 of 9 , Jan 31, 2006
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          --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
          wrote:
          > but this is not near the problem for the folks that start
          > off hanging their hammocks with more rope angle-- you are not
          > stressing the ropes as bad so they don't stretch as much and because
          > of the geometry of the larger angles the rope angle is not as
          > sensitive to changes in the rope lengths.

          Yes, I think you demonstrated that in Hot Springs with my HH. Thanks
          again for that lesson!

          > Now, about those mountain top lots I have for sell in south Florida...

          I'll take one. Where should I mail the check?

          Happy Trails,

          J.D.
        • jonas4321
          ... line abraids the nylon of the hammock itself. The line does not flatten out ... I have not had the spectra cord I bought (made by New England Rope) have
          Message 4 of 9 , Jan 31, 2006
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            --- In hammockcamping@yahoogroups.com, Rick <ra1@i...> wrote:
            >
            > To tell you the truth, I did not like the little spectra lines on my
            > hammock any more than I like them on the Hennessey Hammocks. The
            > braided exterior of mine tends to get little puffy pulls, and the
            line abraids the nylon of the hammock itself. The line does not
            flatten out
            > on a tree, so tree huggers become absolutely necessary to protect the
            > tree. It is all a lot of trouble.

            I have not had the spectra cord I bought (made by New England Rope)
            have any of the puffy pulls, but I don't have them anywhere near
            velcro or other such stuff, maybe that makes a difference?

            I did not like the way they worked against the fabric of my hammock,
            either. The small diameter gave me concerns that I would "slice" the
            fabric in the double sheet bend configuration. That's why I went to
            the hammock hugger strap on the hammock ends (pictures soon).

            I agree that the use of these ropes makes tree huggers necessary, but
            I am at the stage where I appreciate tree huggers, I have not reached
            a level of frequency of use or of weight concerns that others may
            have. In fact, I am using a carabiner on the strap to tie to- it makes
            the Hennessy knot very quick and easy to tie (but weight-conscious
            folks would not like the 'biner weights).

            Finally, I do LOVE the lack of stretch that these ropes provide. When
            I hang my hammock, there's no longer a need to adjust- it stays where
            I tied it and keeps its "sag" the same all night. That is the biggest
            benefit in my opinion.

            Jonas

            ps- I don't relish the thought of dropping a few feet to the ground,
            thanks for putting that "visual" into my head, Rick <grin>!!!
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