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Breaking Strength of support webbing/rope/cord

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  • geoflyfisher <geoflyfisher@yahoo.com>
    Ed Speer got me thinking about how strong the supports of a hammock need to be to support myself. I started thinking vectors and trig. This is the result. If
    Message 1 of 11 , Feb 25, 2003
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      Ed Speer got me thinking about how strong the supports of a hammock
      need to be to support myself. I started thinking vectors and trig.
      This is the result. If my analysis is wrong, please point out the
      error, otherwise you will begin to understand why the webbing needs
      to be stronger than anticipated.

      For these purposes, I will assume I weigh 200 pounds.. Actually I
      weigh a little less than that, well most days, without any clothing
      on...

      If I hung my weight from two straps hanging directly above me, each
      strap would have 100 pounds of weight to support. However, if I am
      hanging from the trees in a hammock, the supports are not vertical.
      They pull at an angle. The weight that must be supported (the pull
      of gravity) in the downward direction is still 100 pounds for each of
      the straps, but that 100 pounds is the vertical vector of the pull
      actually pointed from the tree to the support point on the hammock.

      One way to calculate the pull is to use trig. The sine of an angle
      is the length of the opposite (vertical) side divided by the
      hypotanose of a triangle, where the angle is the angle from
      horizontal to the cord going up to the tree.

      If the angle is 45 degrees, (bannana hammock) then the sine of 45
      degrees is .707 If that fraction is inverted one gets 1.41, and the
      result is that each cord/webbing is supporting a pull of 141 pounds
      in order to support my 200 pounds.

      If the angle is 15 degrees (a lot more reasonable for a camping
      hammock) then the sine of 15 degrees is .259, its inverse is 3.86,
      and the cord must support a pull of 386 pounds.

      If the angle is 10 degrees (pretty tight for a hammock) the sine of
      10 degrees is .174, the inverse is 5.76 and each webbing strap needs
      to pull with 576 pounds to hold up my 200 pounds.

      AND THAT IS without any swinging, moving, bouncing, or the like...

      So, like Ed says, make sure the webbing will hold up 600 pounds. If
      you want a pretty good test and can not get a straight answer about
      the strength, string up the hammock tighter than you would normally
      tie it up and give it a good sit. If it does not break, it will
      likely hold you forever at a more modest support angle.

      Oh, by the way, the hammock is also stressed with the same pulls, so
      don't go breaking the thing just to test the straps.

      Oh, and don't get hurt trying this at home... put something soft
      under the hammock, like a bunch of snow.

      Rick
    • colonelcorn76 <colonelcorn76@yahoo.com>
      ... the ... pounds ... So, another way to look at it is to tie your hammock to smaller trees? The bendy kind of trees would reduce the weight the straps need
      Message 2 of 11 , Feb 25, 2003
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        --- In hammockcamping@yahoogroups.com, "geoflyfisher
        <geoflyfisher@y...>" <geoflyfisher@y...> wrote:
        > If the angle is 45 degrees, (bannana hammock) then the sine of 45
        > degrees is .707 If that fraction is inverted one gets 1.41, and
        the
        > result is that each cord/webbing is supporting a pull of 141
        pounds
        > in order to support my 200 pounds.
        >

        So, another way to look at it is to tie your hammock to smaller
        trees? The bendy kind of trees would reduce the weight the straps
        need to support.

        ;-)
      • subypower
        i would disagree with the thought of the weight effect vrs angle of pull those numbers would work if the straps where made of something ridged like steel and
        Message 3 of 11 , Sep 15, 2003
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          i would disagree with the thought of the weight effect vrs angle of
          pull those numbers would work if the straps where made of something
          ridged like steel and fixed at a parallel angle to gravity and you
          where pulling perpendicular to gravity. But the strap is being pulled
          straight and thats how it takes the load it does not matter if it is
          down or side ways it carrys the same weight. there is no such thing a
          torsional strength in a very flexible object.

          now there is some thing called bounce and the sretchiness of the
          hammock and straps can very quickly cause a greater load than gravity
          alone, take for instance you said you weigh about 200 lbs but if you
          bounce from a height of 1 foot you would put the force of 200 lbs and
          from 2 foot you put 400 lbs, from 3 feet it would be 800 lbs of
          force, it is not a linear ratio of height to force it is closer to
          squaring the force for doubling the distance. which is why in
          firearms a light bullet at a 10 % increase in speed puts out 20 %
          more energy than a heavier bullet at the slower speed

          scott thacher
          white knight
        • Dave Womble
          Scott, Ricks analysis is correct. I know that it may not be intuitively obvious, but the rope angle does generate a horizontal force that is trying to pull
          Message 4 of 11 , Sep 15, 2003
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            Scott,

            Ricks analysis is correct. I know that it may not be intuitively
            obvious, but the rope angle does generate a horizontal force that is
            trying to pull the hammock supports together and that horizontal
            force is a function of the horizontal angle of the hammock straps.
            The vertical force, the occupants weight, is constant. However, the
            hammock straps experience the vector resultant of the horizontal
            force and the vertical force, just as Rick described. What it
            amounts to for us is that the horizontal strap angle represents
            a 'force multiplier' that is sumarized for Rick's 200 lb load as
            follows:

            200 lbs at a 30.00 degree horizontal angle.
            300 lbs at a 19.47 degree horizontal angle.
            400 lbs at a 14.48 degree horizontal angle.
            500 lbs at a 11.54 degree horizontal angle.
            600 lbs at a 9.59 degree horizontal angle.
            700 lbs at a 8.21 degree horizontal angle.
            800 lbs at a 7.18 degree horizontal angle.
            900 lbs at a 6.38 degree horizontal angle.
            1000 lbs at a 5.74 degree horizontal angle.

            As you can see, a tight pitch is pretty stressful. SAG IS GOOD! You
            will sleep more comfortable and safer with sag. I try to set up my
            homemade Speer hammock's consistantly for a 30 degree angle.

            If you like, I can describe a not to complicated experiment so you
            can see first hand how this works. It is pretty eye-opening and will
            give you a first hand appreciation as to how this works. Let me know
            if you are interested in a little physics experiment.

            Youngblood

            --- In hammockcamping@yahoogroups.com, "subypower" <a9144me@a...>
            wrote:
            > i would disagree with the thought of the weight effect vrs angle of
            > pull those numbers would work if the straps where made of something
            > ridged like steel and fixed at a parallel angle to gravity and you
            > where pulling perpendicular to gravity. But the strap is being
            pulled
            > straight and thats how it takes the load it does not matter if it
            is
            > down or side ways it carrys the same weight. there is no such thing
            a
            > torsional strength in a very flexible object.
            >
            > now there is some thing called bounce and the sretchiness of the
            > hammock and straps can very quickly cause a greater load than
            gravity
            > alone, take for instance you said you weigh about 200 lbs but if
            you
            > bounce from a height of 1 foot you would put the force of 200 lbs
            and
            > from 2 foot you put 400 lbs, from 3 feet it would be 800 lbs of
            > force, it is not a linear ratio of height to force it is closer to
            > squaring the force for doubling the distance. which is why in
            > firearms a light bullet at a 10 % increase in speed puts out 20 %
            > more energy than a heavier bullet at the slower speed
            >
            > scott thacher
            > white knight
          • Risk
            Blush... Hey, I don t even need to defend myself any more! How cool! Risk
            Message 5 of 11 , Sep 16, 2003
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              Blush...

              Hey, I don't even need to defend myself any more! How cool!

              Risk

              --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
              wrote:
              > Scott,
              >
              > Ricks analysis is correct. I know that it may not be intuitively
              > obvious, but the rope angle does generate a horizontal force that is
              > trying to pull the hammock supports together and that horizontal
              > force is a function of the horizontal angle of the hammock straps.
              > The vertical force, the occupants weight, is constant. However, the
              > hammock straps experience the vector resultant of the horizontal
              > force and the vertical force, just as Rick described. What it
              > amounts to for us is that the horizontal strap angle represents
              > a 'force multiplier' that is sumarized for Rick's 200 lb load as
              > follows:
              >
              > 200 lbs at a 30.00 degree horizontal angle.
              > 300 lbs at a 19.47 degree horizontal angle.
              > 400 lbs at a 14.48 degree horizontal angle.
              > 500 lbs at a 11.54 degree horizontal angle.
              > 600 lbs at a 9.59 degree horizontal angle.
              > 700 lbs at a 8.21 degree horizontal angle.
              > 800 lbs at a 7.18 degree horizontal angle.
              > 900 lbs at a 6.38 degree horizontal angle.
              > 1000 lbs at a 5.74 degree horizontal angle.
              >
              > As you can see, a tight pitch is pretty stressful. SAG IS GOOD! You
              > will sleep more comfortable and safer with sag. I try to set up my
              > homemade Speer hammock's consistantly for a 30 degree angle.
              >
              > If you like, I can describe a not to complicated experiment so you
              > can see first hand how this works. It is pretty eye-opening and will
              > give you a first hand appreciation as to how this works. Let me know
              > if you are interested in a little physics experiment.
              >
              > Youngblood
              >
              > --- In hammockcamping@yahoogroups.com, "subypower" <a9144me@a...>
              > wrote:
              > > i would disagree with the thought of the weight effect vrs angle of
              > > pull those numbers would work if the straps where made of something
              > > ridged like steel and fixed at a parallel angle to gravity and you
              > > where pulling perpendicular to gravity. But the strap is being
              > pulled
              > > straight and thats how it takes the load it does not matter if it
              > is
              > > down or side ways it carrys the same weight. there is no such thing
              > a
              > > torsional strength in a very flexible object.
              > >
              > > now there is some thing called bounce and the sretchiness of the
              > > hammock and straps can very quickly cause a greater load than
              > gravity
              > > alone, take for instance you said you weigh about 200 lbs but if
              > you
              > > bounce from a height of 1 foot you would put the force of 200 lbs
              > and
              > > from 2 foot you put 400 lbs, from 3 feet it would be 800 lbs of
              > > force, it is not a linear ratio of height to force it is closer to
              > > squaring the force for doubling the distance. which is why in
              > > firearms a light bullet at a 10 % increase in speed puts out 20 %
              > > more energy than a heavier bullet at the slower speed
              > >
              > > scott thacher
              > > white knight
            • Thomas Peltier
              This type of information is good. When everyone talks about sag and how much sag having a degree of sag takes all the ambiguity out of it. Now I know what
              Message 6 of 11 , Sep 16, 2003
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                This type of information is good.  When everyone talks about sag and how much sag having a degree of sag takes all the ambiguity out of it.  Now I know what sag you are talking about.  In my case I have to tighten things up, I tend to get to much sag.  As I think about it the 30 degree mark seems to be about were the hammock works best for me.  More sag than that and I start having trouble.  I don’t think I’ve ever been tighter than that; at least not by much.

                 


                From: Dave Womble [mailto:dpwomble@...]
                Sent: Monday, September 15, 2003 7:23 PM
                To: hammockcamping@yahoogroups.com

                 

                Scott,

                Ricks analysis is correct.  I know that it may not be intuitively
                obvious, but the rope angle does generate a horizontal force that is
                trying to pull the hammock supports together and that horizontal
                force is a function of the horizontal angle of the hammock straps. 
                The vertical force, the occupants weight, is constant.  However, the
                hammock straps experience the vector resultant of the horizontal
                force and the vertical force, just as Rick described.  What it
                amounts to for us is that the horizontal strap angle represents
                a 'force multiplier' that is sumarized for Rick's 200 lb load as
                follows:

                200 lbs at a 30.00 degree horizontal angle.
                300 lbs at a 19.47 degree horizontal angle.
                400 lbs at a 14.48 degree horizontal angle.
                500 lbs at a 11.54 degree horizontal angle.
                600 lbs at a 9.59 degree horizontal angle.
                700 lbs at a 8.21 degree horizontal angle.
                800 lbs at a 7.18 degree horizontal angle.
                900 lbs at a 6.38 degree horizontal angle.
                1000 lbs at a 5.74 degree horizontal angle.

                As you can see, a tight pitch is pretty stressful.  SAG IS GOOD!  You
                will sleep more comfortable and safer with sag.  I try to set up my
                homemade Speer hammock's consistantly for a 30 degree angle.

                If you like, I can describe a not to complicated experiment so you
                can see first hand how this works.  It is pretty eye-opening and will
                give you a first hand appreciation as to how this works.  Let me know
                if you are interested in a little physics experiment.

                Youngblood

                --- In hammockcamping@yahoogroups.com, "subypower" <a9144me@a...>
                wrote:
                > i would disagree with the thought of the weight effect vrs angle of
                > pull those numbers would work if the straps where made of something
                > ridged like steel and fixed at a parallel angle to gravity and you
                > where pulling perpendicular to gravity. But the strap is being
                pulled
                > straight and thats how it takes the load it does not matter if it
                is
                > down or side ways it carrys the same weight. there is no such thing
                a
                > torsional strength in a very flexible object.
                >
                > now there is some thing called bounce and the sretchiness of the
                > hammock and straps can very quickly cause a greater load than
                gravity
                > alone, take for instance you said you weigh about 200 lbs but if
                you
                > bounce from a height of 1 foot you would put the force of 200 lbs
                and
                > from 2 foot you put 400 lbs, from 3 feet it would be 800 lbs of
                > force, it is not a linear ratio of height to force it is closer to
                > squaring the force for doubling the distance.  which is why in
                > firearms a light bullet at a 10 % increase in speed puts out 20 %
                > more energy than a heavier bullet at the slower speed
                >
                > scott thacher
                > white knight



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                hammockcamping-unsubscribe@yahoogroups.com



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              • subypower
                well i guess i get to defend myself now... but i did an experiment to prove either way so here it goes: took my mayan hammock, strung it up with a scale on one
                Message 7 of 11 , Sep 16, 2003
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                  well i guess i get to defend myself now... but i did an experiment to
                  prove either way so here it goes:

                  took my mayan hammock, strung it up with a scale on one end

                  put 30 lbs ( loaded pack )in the hammock, and change angle of hammock
                  record numbers

                  well here it is ( all angles aprox. ):

                  30 17 lbs
                  45 22 lbs
                  15 37 lbs

                  well I was wrong and bow to everyones master hood

                  but it is not as bad as the math says it is... never doubled the
                  original weight on each end but did increase past the weight

                  so in retrospect a 200 lb person would put about 250 lbs per side at
                  15 or so degrees and the standard rating i have heard is 4 times
                  working load should be the min breaking point, so you want 1000 lb
                  straps ( 4 times is also the DOT rating for pressure vessels )

                  so i go now bowing out the door

                  scott
                • Thomas Peltier
                  I weigh about 155 and I use 550 lb test. That is plenty for my comfort. _____ From: subypower [mailto:a9144me@aol.com] Sent: Tuesday, September 16, 2003 3:49
                  Message 8 of 11 , Sep 16, 2003
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                    I weigh about 155 and I use 550 lb test.  That is plenty for my comfort. 

                     

                     


                    From: subypower [mailto:a9144me@...]
                    Sent: Tuesday, September 16, 2003 3:49 PM
                    To: hammockcamping@yahoogroups.com

                     

                    well i guess i get to defend myself now... but i did an experiment to
                    prove either way so here it goes:

                    took my mayan hammock, strung it up with a scale on one end

                    put 30 lbs ( loaded pack )in the hammock, and change angle of hammock
                    record numbers

                    well here it is ( all angles aprox. ):

                    30  17 lbs
                    45  22 lbs
                    15  37 lbs

                    well I was wrong and bow to everyones master hood

                    but it is not as bad as the math says it is... never doubled the
                    original weight on each end but did increase past the weight

                    so in retrospect a 200 lb person would put about 250 lbs per side at
                    15 or so degrees and the standard rating i have heard is 4 times
                    working load should be the min breaking point, so you want 1000 lb
                    straps ( 4 times is also the DOT rating for pressure vessels )

                    so i go now bowing out the door

                    scott



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                    hammockcamping-unsubscribe@yahoogroups.com



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                  • Dave Womble
                    Rick, Every now and then we get a freebe. :-) Youngblood
                    Message 9 of 11 , Sep 16, 2003
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                      Rick,

                      Every now and then we get a freebe. :-)

                      Youngblood

                      --- In hammockcamping@yahoogroups.com, "Risk" <geoflyfisher@y...>
                      wrote:
                      > Blush...
                      >
                      > Hey, I don't even need to defend myself any more! How cool!
                      >
                      > Risk
                      >
                    • Dave Womble
                      Scott, That s how we usually learn, we challenge something and see what falls out. As long as we are having fun... and I guess we are or we wouldn t be
                      Message 10 of 11 , Sep 16, 2003
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                        Scott,

                        That's how we usually learn, we challenge something and see what
                        falls out. As long as we are having fun... and I guess we are or we
                        wouldn't be spending or time on these web sites. Now you have to
                        admit, the experiment you did was fun, right?

                        Now about all that bouncing up & down in the hammock...

                        Later,
                        Youngblood

                        --- In hammockcamping@yahoogroups.com, "subypower" <a9144me@a...>
                        wrote:
                        > well i guess i get to defend myself now... but i did an experiment
                        to
                        > prove either way so here it goes:
                        >
                        > took my mayan hammock, strung it up with a scale on one end
                        >
                        > put 30 lbs ( loaded pack )in the hammock, and change angle of
                        hammock
                        > record numbers
                        >
                        > well here it is ( all angles aprox. ):
                        >
                        > 30 17 lbs
                        > 45 22 lbs
                        > 15 37 lbs
                        >
                        > well I was wrong and bow to everyones master hood
                        >
                        > but it is not as bad as the math says it is... never doubled the
                        > original weight on each end but did increase past the weight
                        >
                        > so in retrospect a 200 lb person would put about 250 lbs per side
                        at
                        > 15 or so degrees and the standard rating i have heard is 4 times
                        > working load should be the min breaking point, so you want 1000 lb
                        > straps ( 4 times is also the DOT rating for pressure vessels )
                        >
                        > so i go now bowing out the door
                        >
                        > scott
                      • Ed Speer
                        Wow Scott--actual numbers instead of book quotes! Your testing is interesting to say the least--thanks muncho...Ed ... From: subypower
                        Message 11 of 11 , Sep 16, 2003
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                          Message
                          Wow Scott--actual numbers instead of book quotes!  Your testing is interesting to say the least--thanks muncho...Ed
                           
                          -----Original Message-----
                          From: subypower [mailto:a9144me@...]
                          Sent: Tuesday, September 16, 2003 6:49 PM
                          To: hammockcamping@yahoogroups.com
                          Subject: Hammock Camping Re: Breaking Strength of support webbing/rope/cord

                          well i guess i get to defend myself now... but i did an experiment to
                          prove either way so here it goes:

                          took my mayan hammock, strung it up with a scale on one end

                          put 30 lbs ( loaded pack )in the hammock, and change angle of hammock
                          record numbers

                          well here it is ( all angles aprox. ):

                          30  17 lbs
                          45  22 lbs
                          15  37 lbs

                          well I was wrong and bow to everyones master hood

                          but it is not as bad as the math says it is... never doubled the
                          original weight on each end but did increase past the weight

                          so in retrospect a 200 lb person would put about 250 lbs per side at
                          15 or so degrees and the standard rating i have heard is 4 times
                          working load should be the min breaking point, so you want 1000 lb
                          straps ( 4 times is also the DOT rating for pressure vessels )

                          so i go now bowing out the door

                          scott



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                          hammockcamping-unsubscribe@yahoogroups.com



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