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

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  • Dave Womble
    ... 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
    Message 1 of 9 , Jan 31, 2006
      --- 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
    • 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 2 of 9 , Jan 31, 2006
        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 3 of 9 , Jan 31, 2006
          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 4 of 9 , Jan 31, 2006
            --- 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 5 of 9 , Jan 31, 2006
              --- 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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