Re: [Hammock Camping] Re: webbing strength
The way I hang a hammock with webbing, even though I use a knot, there
is little loss of strength at the tree. This is because there is very
little stress on the knot. Most of the stress is taken up by the wraps
of webbing around the tree, and only a small portion is taken up by the
keeper knot at the end. The same is true of a hennessey knot.
Your point is well taken especially regarding the loop I make back at
the hammock. This is the reson that I form that loop by sewing. It can
be sewn, like Ed Speer shows in his book, by sewing the loop around the
hammock. However, what I have begun to do is to sew a loop in the end
of the strap and then bring the end of the strap through the loop to
make a slip knot that goes around the hammock. With this set-up it is
easy to remove the strap to wash the hammock. Add a whipped end to the
hammock, and now I can quickly and easily remove the gathering at the
end of the hammock to dry it quickly after washing.
I read what Youngblood wrote about differential stress and agree with
that too. This is the reason that climbing knots using webbing are made
carefully without bunching the webbing.
Rick Allnutt MD
Author of "A Wildly Successful 200-Mile Hike"
personal hiking website: http://www.imrisk.com
> --- In firstname.lastname@example.org, "tim garner" <slowhike@y...>[Non-text portions of this message have been removed]
> > some of you have talked about the strength of webbing (& rope too i
> > belive) being compromised w/ knots. so i`m wondering if webbing being
> > forced to bunch up tightly together will cause a weak place too?
- --- In email@example.com, "Dave Womble" <dpwomble@y...>
> I always thought that rope strength was degraded with tight bendsnot
> (which knots do) that required the individual fibers to stretch at
> significantly different rates. When that happens, the stress is
> shared equally by all the fibers that make up the rope, with theoutter
> fibers at the bend taking on more of the stress and causing them tounison, or
> fail first and at a lower stress than a rope without bends... it is
> like all the fibers that make up the rope are not working in
> parallel anymore. So applying that philosophy with webbing itwould
> depend on how it is being reshaped. It seems like webbing isdesigned
> to handle tight bends along its flat part but not so much along itsstrength
> edge. But if you are just gathering webbing and rolling it into a
> tubular position, I wouldn't think you would be degrading its
> much, it at all.Your description of unequal loading inside/outside is correct. But
there is an additional factor: The inner-radius segment of the line
acts as a static bulk about which the outer segment is stretched in a
levering action which amplifies the loading much further. If it
weren't for this levering action rope would have a working load
rating that's 33% of its maximum (as webbing does) rather than the 10-
20% used currently. (You can also see why nylon is so superior for
rope: The memory-stretch allows it to accommodate both the radius
the levering problems much better than other fibers.)
When rumpled, webbing only has the partial-loading problem to contend
with, and so retains much of its strength. For example, a water knot
loop in webbing retains about 75% of the webbing's total strength.
When loops are properly sewn into webbing (i.e. X-box and oversewn)
that figure is over 90%. (I also suggest that loops be 3 inches long
after sewing so that any rumpling at the tie-off is smoothed out by
the time it reaches the stitching.)
Webbing's only weakness is wear. Because all of the fibers are
exposed, it wears out faster than core-and-sheath ropes. On the
other hand, you can easily see the wear, so inspection and
replacement are not problematic.