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

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  • Rick
    Breaking strength, as promoted by the maker is usually much less than the real breaking strength. I can tell you by experience that the little ropes I tried
    Message 1 of 9 , Jan 31, 2006
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      Breaking strength, as promoted by the maker is usually much less than
      the real breaking strength. I can tell you by experience that the
      little ropes I tried seemed very very strong in this application. They
      are undoubtedly much stronger than the polypropylene lines I have also
      used.

      Before considering use of lines like this for climbing or hanging from
      40 feet up in a tree, I'd have grave concerns. However, the risks of
      falling a foot or two (probably slowly) in a hammock application is not
      something that gives me bad dreams. I sometimes think it is easier to
      just test a cord or piece of webbing by attaching it to a hammock rather
      than getting my slide rule out.

      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 continue to use polypropylene or Polyester line or webbing for that
      reason.

      Risk

      LHM wrote:
      > Difference between rated working load and breaking strength is
      > usually a factor of at least five or six -- and particularly so for
      > non-stretch rope or cord. Given a breaking strength of 950 lbs, the
      > working load could be as little as about 150 lbs, and the main
      > support rope for a hammock is likely to see a load of several times
      > the weight of the inhabitant (perhaps as much as that weight
      > multiplied by the tangent of the angle between support rope and
      > vertical-down?). I don't know much about hammocks, but I know a lot
      > about cordage in other applications, and I wouldn't be inclined to
      > bet my safety on a nearly-horizontal hammock rope unless it had a
      > *working strength* of several times my weight. If it were nylon, of
      > course, I'd know I had a problem when the stretch exceeded about ten
      > percent ... but if it's dacron, you don't necessarily know until it fails.
      >
      > If I'm wrong, please tell me why ...
      >
    • 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 2 of 9 , Jan 31, 2006
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        --- 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 3 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 4 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 5 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 6 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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