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aarong
Aug 28, 2002, 2:35 PM
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I am curious about the strength of slacklines under "normal" conditions, as in the forces applied to the webbing and gear when they are being walked, and under "fall" conditions. Fall conditions would apply to slacklines stretched above high places (i.e. between trees, spires, boulders, etc.) in which the line itself is used as part of the safety system to arrest a fall. I know there is not much dynamic strength in webbing, in essence, a slackline should be fairly static if it is stretched tight, and the force of a fall on a stretched piece of webbing could be extremely high. Has anyone got any info./ideas on this?
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bouldertoad
Aug 28, 2002, 5:11 PM
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I would have to sya that a slackline does not offe to much in the way of arresting a fall should it occur and it is used as a safety device. Although the line does bounce wuite a bit which may or may nbot help in the dynamkic aspects of the safety line. So I guess I did not help to much. sorry
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joebuzz
Aug 28, 2002, 6:34 PM
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First, let me say I'm no Dean Potter, but I am an avid "slackliner". I started a few years ago and my all around balance has greatly improved.
Now, my slackline is set up between a couple of trees(only about 10 or 12ft apart), three ft. high and streched tight. Start by walking on the line with a couple of skipoles for balance. In no time at all you'll be standing without them and walking soon thereafter.
Back to the original question: I have no idea, but then I'm not worried about falling off The Lost Arrow Spire. I'm sure the stresses are fairly high, but as a 6' 200 lb.er I've actually bounced on the line with all my might and the same line is still up after six yrs. My three yr. old daughter, Kadianne, is even getting up on the line now with my help of course.
Hope this was helpful. Stick with it and watch not only your climbing, but skiing, surfing, skating, even running through a crowed restaurant(I'm a waiter) vastly improve.
Buzz
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aarong
Aug 29, 2002, 2:59 AM
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That's cool my younger brother is really into slacklining...but he also rides a unicycle, and juggles, so...maybe he should have joined the circus. Anyway....
I heard Dean Potter broke a rib once when he fell on a slackline (from high up obviously) and was caught my a rope tied around his waist and hooked to the slackline. But it's these kinds of "forces" that I'm wondering about. Any physics or math majors/professionals out there who can answer my question? How much does it take to break a slackline system?
Also, as I understand it, for long slackline walks, such as Lost Arrow Spire, the webbing can be doubled-up and bar tacked to increase the strength. I'm sure this helps increase the strength.
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krustyklimber
Aug 29, 2002, 3:28 AM
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O.K. here we go,
The forces on a slackline are similar to the forces put on anchors set at a little less than 180 degrees... in other words the anchors will be subjected to nearly 200% of your weight at each end of the slackline.
There is your answer on forces under walking pressures, as far as falling forces, even if you were to fall onto your side while slacklining (I imagine how Dean hurt himself) the farthest you would fall is about 2 feet. From what my engineer friend tells me you gain about one times your body weight in force for every foot you fall...
so the anchors would (if you fell directly on the line equally, without tipping off to one side or the other) be subjected to around 400% of your weight at each end.
On long lines they are generally doubled lines (one big long piece of webbing folded in half and sewn or taped together) and a saftey line consisting of a climbing rope is either run overhead of the slackline (in the case of trees) or underneath (in the case of the Salathé). You then clip a big daddy locking 'biner around all three... the two lines and the rope.
I hope this helps,
Jeff
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clmbnski
Aug 29, 2002, 3:40 AM
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I saw a slackline up in telluride and decided to check it out and maybe try and walk it if it looked safe. Anyway I got up there and found that whoever set it up did a good job. the line was made up of six layers of 1 inch webbing and both sides were backed up with slack dynamic rope going to alternate anchors. I highly doubt six layers of webbing would break so I think the anchor on either side is the weak point in any slackline setup. That is why the backup was a grat idea. also by having the backup loose, if the first anchor failed the backup would be under a lot less stress due to the reduced angle of the vectors (know what I am talking about?) I know it would be shock loaded but hey it was a beefy tree.
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aarong
Aug 29, 2002, 7:16 PM
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Registered: Jun 24, 2002
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Ok. Both of those are good replies. Thanks for the insight.
Sounds like there are plenty of ways to add safety backups into the system (i.e. reinforced webbing, overhead lines, dynamic backups (the equivalent of screamers) at anchor points. Doesn't sound quite so life-threatening now.
Still...I think I'll stick to trying the ones 3-4 feet off the ground.
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