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Mighty Hiker
climber
Vancouver, B.C.
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Dec 17, 2009 - 09:00pm PT
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Humans have been walking wires and lines of all kinds for well over a century, perhaps longer. Modern slacklining is simply a sub-species, with its own culture and elaborations.
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WBraun
climber
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Dec 17, 2009 - 09:12pm PT
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Moof
Slacklining goes all the way back in camp 4 to 1971 as I remember.
Pat Ament and his friend (forgot his name) I think it was, introduced it to the Valley.
Everyone got way into it .......
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apogee
climber
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Dec 17, 2009 - 09:13pm PT
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The majority of the lines I have seen rigged were done by relative newbs to climbing, who clearly had little or no understanding of the tremendous forces generated in (even the simplest) slackline. What is surprising to me is that more 'catastrophic' failures haven't been reported.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 17, 2009 - 09:20pm PT
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The difference is that those people aren't rigging the highlines. Few people venture into that realm for a number of reason, cost being one of the biggest issue. Like a climbing rack it takes time to piece together all of the gear needed. It took me 3 years to piece together enough gear to rig safe highlines entirely on my own. Not to mention you want to try highlining before you consider venturing down that path. The majority of the people who are rigging highlines learned the techniques and processes first hand from those who came before them. Think of it almost as an apprenticeship. That's the main contributing factor to the 0 highline related deaths.
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WBraun
climber
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Dec 17, 2009 - 11:20pm PT
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In the above anchor why not just extend the 11mm rope and tie it around the tree itself in a High strength tie off configuration eliminating both a biner and webbing?
High strength tie off example below.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 18, 2009 - 03:22am PT
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Absolutely nothing because it's a hard bark tree with carpet around it? I live in Arcata, don't get me started on tree protection...
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Paul Martzen
Trad climber
Fresno
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Dec 18, 2009 - 03:46am PT
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Trigonometry never really sank in until I started blowing anchors for my slack chain around '77. I think I was using a 5/16 or 3/8 inch steel S hook and bending it to failure just by standing on the chain. I was 175 pounds and the hook could probably hold a few thousand pounds. How was I bending it? Pulled out the trig book and finally understood what I was supposed to be learning.
Hey Catalystic, Fet's calculations are correct, but he is referring to a different angle than you. Fet is referring to the angle of the tightrope itself where the walker is standing on it. If the line is pulled perfectly straight it would be 180 degrees, and it would take infinite force to support him. When the walker stands on it, the line is bent downwards at that point. The angle at that point is what Fet is talking about and that angle along with the weight of the walker and the weight of the line, is what determines the stress on your anchors.
Looking at your calculations you have angles of 30 degrees and 75 degrees and such, so you must be referring to the different angles of multiple anchors supporting one side of the tightrope. Keep those angles less than 45 degrees and they are not very important.
The angle that is important is the angle of the tight rope itself. By definition, if the rope is tight and horizontal, it is approaching 180 degrees, or a straight line.
I find it easier to comprehend if I look at the angle of the tightline from the vertical at one side. If the line was perfectly straight across, that angle will be 90 degrees and the force on the anchor will be infinite. If the line is hanging straight down, the angle will be 0 degrees and the force will be equal to 1/2 the weight of the person plus 1/2 the weight of the line. The other halves are supported by the other side of the line.
The formula I use is:
Force on one side = 1/2 the weight of the line and person x cosecant(angle of the tight line from the vertical)
Say you have a 180 pound walker and 20 pounds of line with a 10 degree droop at the anchor. That gives F = 1/2 x 200 x cosecant(80 degrees)
I get about 576 pounds of force on each side of the tightline.
If you only have 5 degrees of droop then the force increases to 1147 pounds of force on each side.
If you only have 2.5 degrees of droop on each side, it is the same as Fet's V angle of 175 degrees where the walker is on the line. Force on each side increases to 2293 pounds.
If you could decrease the droop to only 1 degree, then the force increases to 5730 pounds on each side.
These are just static forces also. When you walk or bounce on the line you have dynamic forces which have a very big effect. Of course the stretch in the line should absorb some of these increased forces.
Clearly though, you are dealing with very high forces on the line and on the anchors, that is why you are using such beefy anchors.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 18, 2009 - 04:03am PT
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I understand what he's saying, but those formulas are way to general and regardless, you don't get a 175 angle in your anchor or on the line. It bends much more then that. There is a spring constant that must be associated but unfortunately it unknown due to the lack of research and funding.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 18, 2009 - 04:44am PT
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WBraun I've actually used the method you speak of. However I prefer a separate anchor which keeps the backup from rubbing on a tree or rock or whatever. Also remember that the anchors are 11mm threaded through 1" webbing which is going to be stronger then any rope alone. And one last thing to consider is that overall your backup will be taking less of a load then your primary anchors since in the case of catastrophic failure all tension is lost, and if your backup is rigged right, it's not catching any of the force from that tension. As I stated previously, I prefer my backup to be a totally separate rope so that none of the tension force is absorbed with a fall.
Majid that's a sick looking rig you got there, but there's quite a few problems with it in the terms of highlining. But since you're not highlining in the sense that I'm talking about, it's solid for sure.
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wildone
climber
GHOST TOWN
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Dec 18, 2009 - 05:34am PT
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This is awesome! Werner is getting rigging lessons!
Gotta love the taco!
Teach us more Cat Pro!
Just a thought.
It is very easy to get an angle of 175 degrees, especially on a mega tensioned not-so-dynamic highline. The angle of deflection can be minimal.
The force-vector analysis makes me want to puke.
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healyje
Trad climber
Portland, Oregon
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Dec 18, 2009 - 07:19am PT
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Cat, I've been walking tightwires and pulleyed-tight 11mm since '75 and am trying to understand your use of the 11mm in the picture on the first page. Is that 11mm threaded through the principle walking line? If so, wouldn't it change the geometry, dynamics, and feel of the 1" such that it you loose the 'normal' feel of walking webbing?
When Adam got us all going on this back in SoIll it was on our climbing ropes at first and then webbing when some wanted more horizontal dynamics. I stayed with cranked down 11mm all these years because I don't care for the 'float' and prefer the faster, cleaner, and crisper bounce of the 11mm. Drug mine out for the first time in a couple of years at the first Susifest which was interesting (given I'd just been sporadically walking chains around town). Have been setting it up and spending more time with it of late which has gotten me into checking out some of the various highline anchors pics that are available. To be honest, I'm somewhat amazed at some of the rigs I've seen, with respect to being what appears either under- or over-built not too many inbetween. Some have been pretty scary and I'm surprised, but glad, this is the first instance of a serious line failure. I'm equally glad to hear your friend wasn't killed.
Probably was about time for a collective wake-up call.
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Captain...or Skully
Social climber
Top of the 5.2-5.12 Boulder
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Dec 18, 2009 - 08:22am PT
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I wonder who decided they were"slack" lines.
Seem like really tight lines to me.
Carry on.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 18, 2009 - 01:56pm PT
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The 11mm threaded through 1" is the anchor as was already explained... It doesn't not go through the slackline, it goes around the tree...
The term slackline is self explanatory. A slack, line. As long as you're walking on webbing, it's going to bounce, wobble, and sway, thus making it a slackline. It's all about what your preference is.
This thread really wasn't meant to discuss rigging practices. If you want to learn more go to slackline.com.
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Paul Martzen
Trad climber
Fresno
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Dec 18, 2009 - 02:11pm PT
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This is very interesting Shaun.
How much droop in the line do you generally get? Should be simple enough to measure the angle of the line from the vertical or horizontal where the line first leaves the anchor.
I am also curious about how your back up line is connected to the tensioned line. In some of the pictures it looks like a back up rope is taped underneath the tensioned webbing. You stated that you have rope running through 1" webbing, but you were referring to the anchor slings only, I think?
Gonna have to look at more pictures and websites about highlining and tight rope walking, to get a better understanding of common rigging techniques.
Got thinking about the boulder that moved also. Seems to me that the size of the boulder is important, but you only have to overcome sliding friction to move it, and that could vary a lot depending on the surface it is resting on and the manner of contact. It could be resting on a bunch of little gravelly ball bearings and shift at pretty low force. If it was resting smooth water polish or glacier polish it might move relatively easily also.
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the Fet
climber
Tu-Tok-A-Nu-La
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Dec 18, 2009 - 02:30pm PT
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Thanks Paul, yes that's what I was referring to the V angle of the slackline itself and the resulting forces on the complete anchor on each side.
What is the average V angle on a highline? (oops Paul just asked this above) The spring constant of webbing must be known, have you checked with the manufacturers? The spring constant of webbing is probably not going to be nice and linear though especially since it's been pre-stretched. Find this out and you'll be getting there in the calculations. But of course real world testing is where it's at to see what's truly going on.
My understanding is slackline started on chains and such that were "slack" and eveolved to tight webbing. That's why it's called slackline (as opposed to tight rope).
Rigging questions are going to come up in a thread about an inproperly rigged highline. Most people here aren't going to sign up on another forum to give their input unless they are really into slackline.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 18, 2009 - 03:06pm PT
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It turns out that the boulder which moved was the size a large human torso. When the line was rigged, it was believe that the boulder was part of the overall block and not separate. Unfortunately this was not the case. The line was not rigged improperly by any means, it was just a misjudgment about the rock itself. Because proper safety measures were taken (back up on a separate anchor) no one died.
In the photos I posted the back up rope is hand tensioned, and place on a separate anchor. It is then taped to the slackline. The main line is anchored to the tree using separate anchors consisting of 11mm threaded through 1" webbing. To help visualize it... Think of a single rope tied around a tree to a power point. That's what the first picture I posted shows, with additional back up anchors in place. My direct quote is:
"11mm static threaded through 1" tubular webbing is the primary anchor. figure 8's are used to attach to the shackle."
So I guess I don't understand where everyone's confusion is coming from.
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