## Breaking Strength of support webbing/rope/cord

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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
Message 1 of 11 , Feb 25, 2003
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
• ... 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
--- 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.

;-)
• 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
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
• 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
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
• Blush... Hey, I don t even need to defend myself any more! How cool! Risk
Message 5 of 11 , Sep 16, 2003
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
• 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

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

• 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
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
• 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

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

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