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

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• ... 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.

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
• 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.
>
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
>
• 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:
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.
• ... 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.
• ... 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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