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Catalystic Productions
Boulder climber
Arcata, CA
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Topic Author's Original Post - Dec 17, 2009 - 03:06am PT
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For the first time in the known history of slackline, a catastrophic highline failure has occurred. Had it not been for the backup implemented into the system someone most likely would have died. Luckily only a minor injury occurred.
Please take the time to read this article on slackline.com and learn from this mistake.
This is a prime example of why you ALWAYS use a back up and why you always place your back up on a separate anchor. Every highlines requires different rigging measures and always use your common sense and best judgment when rigging!
-Shaun
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enjoimx
Big Wall climber
SLO Cal
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Dec 17, 2009 - 03:26am PT
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Your always doing things "First" Andy!!!
Good thing nobody got hurt, and SCARY
Rope backups are super important. I remember my first highline was a single piece of webbing, 70 foot line. The webbing was actually messed up and was bottlenecking for a couple inches. We backed it up day 2, thank God.
Rob
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Mungeclimber
Trad climber
sorry, just posting out loud.
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Dec 17, 2009 - 03:43am PT
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"constant element of guessing, and trusting"
really? why guessing? I don't slack, so not sure I follow this idea.
calculated yes, but not guessing
good to learn
like in soloing, be ready to walk away from the set up in the first place allows good choices, eh?
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Catalystic Productions
Boulder climber
Arcata, CA
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Topic Author's Reply - Dec 17, 2009 - 04:31am PT
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What he means is that you don't always know how much force your applying to your anchors and line. When you're using bolts it's not that big of a deal but when using trad gear and natural protection such a slinging boulders it does matter. When you're trad climbing it's easy to say "oh yeah this cam or nut is bomber" but that same cam or nut might be the weakest point in a highline anchor. So there is a constant element of guessing and trusting when using natural pro in highline rigs.
-Shaun
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Scared Silly
Trad climber
UT
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Dec 17, 2009 - 09:04am PT
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Actually, it does not matter whether your anchors are trad gear or bolts. Both will and have failed. People falsely thinks bolts are automatically bomber. Well they might be and they might not be. All depends on the rock and the knucklehead who put them in. IMHO the vast majority of people rigging use PIROMA techniques.
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pFranzen
Boulder climber
Portland, OR
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Dec 17, 2009 - 12:31pm PT
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really? why guessing? I don't slack, so not sure I follow this idea. When you see 3 people yarding in on a slackline with a 3:1 pulley ratio to get it tight there is likely a fair amount of old-fashioned assumptions going on. I'm sure there are plenty of people out there who have done the math and can tell you off the top of their heads how much force is being put on an anchor for a given line, but I would say that most of the time a slackline is installed it's just 2 "bomber" anchors and a lot of tension.
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WBraun
climber
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Dec 17, 2009 - 12:47pm PT
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Without any photos or diagrams of the actual setup there's not much to go on for understanding this completely.
Even if you have a backup and the slack line goes slack the slacker walking the thing can pop off.
Then the slacker trying to grab the line with slack in it can cause a shock bounce and the slacker loose grip falling to the ground (if they are soloing).
You got anything we can see on your failure?
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Clint Cummins
Trad climber
SF Bay area, CA
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Dec 17, 2009 - 01:15pm PT
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The block/boulder sliding failure sounds a lot like when Todd Skinner and Paul Piana almost died on top of the Salathe' Wall. Their boulder slid also when they were hauling a lot of weight. It cut parts of their anchor and shredded ropes, but somehow they survived.
It sounds like the testing of the highline was inadequate.
Shouldn't there be a test where a guy goes out onto the line and jumps up and down on it? (He should have a belay rope that goes to a separate anchor).
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neebee
Social climber
calif/texas
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Dec 17, 2009 - 02:28pm PT
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hey there say, all.... bump for all this info to get seen now...
keep learning all....
god bless...
edit: oooopssss, just remembered, clint: please EMAIL me, got a question...
thanks so very much! :)
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Catalystic Productions
Boulder climber
Arcata, CA
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Topic Author's Reply - Dec 17, 2009 - 02:31pm PT
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I wasn't there so I can't really answer too many of your questions but what I can say is that highline rigs are not like janky lowline rigs with a couple of carabiners and some webbing. You need first hand experience to rig highlines safely and in this event we can see that experience didn't exactly pay off.
What I can say about the rigging used in this case is, the backup that saved the guy was the line he was walking on. It was a double threaded line with 2 pieces of 9/16" on the inside. On both ends the longer piece of 9/16" came out of the line and was linelockered and attached to separate anchors. This is a system Andy came up with over the past year and has been using pretty regularly. I personally do not use this system and would rather have a nice separate climbing rope attached to my line so that if something like this were to happen to me, the back up would not be shock loaded by the tension that was in the line. Anyways, I'll try and get Andy to post up some more details.
-Shaun
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the Fet
climber
Tu-Tok-A-Nu-La
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Dec 17, 2009 - 05:29pm PT
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Is it a catastrophic failure if the backup does what it's designed to do?
Does anyone know what the approximate forces are put on a slackline anchor?
A V-angle of 175 degrees puts 1146% of the downward force on each anchor. Plus add the pre-tension. That's some scary force.
180 lb slacker * 1146% = 2062 lbs on each anchor. Biners are good for about 5000 lbs properly setup (1350 to 1800 lbs open gate or cross loaded). 1" webbing is about 5000 lbs too(no knots) What force will a bouncing slacker generate? If its 2 Gs, that's 4125 lbs on each anchor.
Webbing will stretch a few percent limiting forces, but you take most of that out when you tension it.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 17, 2009 - 05:39pm PT
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It's considered catastrophic when the line or anchor fails. As stated this has never happened before.
The majority of highliners use steel carabiners, the ones I use and Andy use are 65kn Omega Pacific's. Slackers developed a method of removing all knots from the webbing by making linelockers (see picture where line is attached to pulley) which allows for webbing to break at it's MBS. Spansets are generally used because they're burly as all hell and pretty resistant to abrasion. A lot of people use shackles in powerpoints where triloading is occuring.
If you're interested in learning rigging techniques check out slackline.comand visit the forums.
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the Fet
climber
Tu-Tok-A-Nu-La
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Dec 17, 2009 - 07:05pm PT
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Thanks Shaun.
I haven't highlined, too many other activities and responsibilities taking up my time to get into it. But I do setup regular lines. And I may hook up with someone on a Rostrum or other highline at some point so it's good to see what a correctly setup system looks like.
It's easy to imagine a burly setup like that generating enough force to move a boulder.
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Mighty Hiker
climber
Vancouver, B.C.
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Dec 17, 2009 - 07:11pm PT
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I'm not a slacker, but wonder if anyone has done an analysis of the engineering and physics of slacklines? Just working from force triangles, it looks like a slackline could generate enormous forces, forces much greater than we usually encounter in climbing.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 17, 2009 - 07:52pm PT
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Actually there are quite a few folks in the slackline realm who have backgrounds in engineering and physics. I've personally done some force calculations on anchors. You can find my work on this page and a pretty decent discussion.
The stuff I was doing was more or less proving that by changing the angle or your anchor, changes the force upon your anchor and if you increase the angle you increase the force. A lot of folks have done tests with a dynamometer but are hesitant to share their results which is boogus in my opinion. Having real world numbers would actually allow slackers with engineering and physics background to figure out some true forces rather then just theoretical forces.
Calculations Page 1
Calculations Page 2
Calculations Page 3
Edit:
As far as what Fet said, that's a huge speculations and I've never heard of or seen someone create an angle greater then 90 in a slackline rig. So those numbers your posted a irrelevant for the most part, but it does point out the obvious, your anchors need to be bomb.com.
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GhoulweJ
Trad climber
Sacramento, CA
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Dec 17, 2009 - 08:36pm PT
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Let me know if your in Yosemite some time and want to borrow a dynamometer.
Happy to help.
Jay Renneberg
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Moof
Big Wall climber
A cube at my soul sucking job in Oregon
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Dec 17, 2009 - 08:49pm PT
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Free solo a slack line? Strange concept to me, as slacklining is inherently closer to aid climbing than free soloing.
Most of the "slack" lines I've witnessed were anything but slack. The stoners setting them up were anything but safety conscious, let alone capable of figuring out the forces (I saw one with about a 7:1 rigging and 3 dudes yarding on it, scary tight).
It will be a good day when this dud of a fad dies out.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 17, 2009 - 08:57pm PT
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Hate to break it too you Moof but slackline is approaching the 40 year mark pretty soon, so unfortunately for you it's not going away. Sounds to me that if you saw someone rigging 7:1 then they probably weren't the dumbass stoners you're making them out to be because rigging 7:1 is pretty complicated. Nice try though I applaud your effort to demoralize a sport you obviously know nothing about. Maybe you can go flame a topic which isn't related to life and death since you obviously don't have anything constructive to say. I also have no idea how you can connect slacklining to aid climbing... Free soloing means you don't have a leash which means if you fall and don't catch the line you die.
Ghoulwej I'll actually be in Sacramento this Sunday for the next week and half. If you have a dyno that can be used I would love to rig with you. My engineering buddy and I are both from Sac and we were planning on spending a good amount of time over break working some calculations so that we could maybe post up a solid slackline physics paper. Shoot me an email at catalysticproductions@gmail.com.
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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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healyje
Trad climber
Portland, Oregon
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Dec 18, 2009 - 03:34pm PT
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Ah, your second explanation was better in combination with the pics. When a person looks at the pic with the first explanation the immediate impression is the 11mm is threaded through the length of the slackline with tape at some sort of entry point despite what the eye actually sees. The eye is not drawn to the 1" around the tree. But I've got it now that you redirect to the tree 1" which I now see the threading. The confusion was the 11mm threading/taped on the walking line. Personally I'd do the opposite, walk 11mm - but then I've always been bit out of 'step' with the times.
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Jingy
Social climber
Flatland, Ca
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Dec 18, 2009 - 03:44pm PT
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Catalyst writes - So there is a constant element of guessing and trusting when using natural pro in highline rigs.
This and the fact that I no longer have any balance whatsoever would be the main reason I will never take on Highlining as a art/hobby/activity....
too much guessing!
Good post, good information to relay, and both those dudes were very lucky...
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 18, 2009 - 04:30pm PT
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Why? You do it when you climb all the time. Should you stop climbing because you could potentially kill yourself my not placing an anchor properly? We're not using blind faith when we do this stuff. We always plan for the worst and hope for the best. That is why our rigs are super redundant with back up lines on separate anchors then the main line. That means that when your main line goes, all of your tension force is lost and your backup anchor is taking way less of a load then your original anchor. In fact the only load it's taking is the force of your fall. That is exactly why no one was killed.
You're looking at the negative and not looking at the positive. The negative is that for the first time in a 30 year history of highline, an anchor gave out and the backup was actually used. The positive is that the redundancy in highline rigging and assuming for the worst saved someone. The backup did EXACTLY what it was suppose to do which is why we rig them. I can't think of a time that I've seen someone trad climbing and set two anchors, one for the main load and one for a backup...
My point is just because something appears to be dangerous and ridiculous doesn't mean it is. Sh#t look at big wall climbers! That stuff is insane! People die doing it all the time yet it is excepted as climbing culture.
Even if your balance isn't that great, if you start low lining it will help your footwork and climbing technique immensely. After all highline is just a branch from the original practice of low-line slacklining as a cross training to climbing :-)
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cragnshag
Social climber
san joser
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Dec 18, 2009 - 04:44pm PT
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As stated above, why not just hook up a load cell to the system, and ask your biggest buddy to bounce up 'n down on it whilst you record the load.
Banquo has some stuff in his garage that would work and access to more at the university. Bribe him with beer, booze, and cigars.
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GhoulweJ
Trad climber
Sacramento, CA
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Dec 18, 2009 - 04:46pm PT
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Call me sometime when ur in Sacto and you can borrow the Dyno.... U promise to return it right????
916 316 5015
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Paul Martzen
Trad climber
Fresno
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Dec 18, 2009 - 05:01pm PT
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Here are links to a couple of entries with dynometer data. http://forum.slackline.com/archive/modules.php?name=Forums&file=viewtopic&t=1437&highlight=
and this one in French
http://3.bp.blogspot.com/_0Tmb2RtZi9I/SOGngh6JeGI/AAAAAAAAAcw/PLTXlXZSXPI/s1600-h/testing+parmelan+2008+fran%C3%A7ais.jpg
I am surprised that the forces from falling are as low as they show. Especially when you look at various videos and see how tight and how horizontal the lines are. In the first link they tensioned the line to 1400 lbs. They don't say what the tension is when they stand on the line. But when they drop a few feet onto their leash, the forces only go up to around 2000 lbs. When the line was tensioned to only 1150 lbs the force generated by falling was usually less than 2000 lbs.
Very interesting.
Seems to me that tensioning the line to 1400 lbs can get the V angle very close to 180 degrees, maybe within 1/2 or 1 degree, which would be hard to see on a video. But when the angles are that close to horizontal, small changes have very big effects. So if the angle of the line at the anchor was 89.5 degrees at first but then stretches to only 89 degrees the force on the anchor is reduced by 1/2. Meaning it could also support 2 times the weight with the same tension. It looks like to me that 1400 lbs of tension on the line should be able to support 200 lbs of weight (line and walker) with about 4 degrees of sag at either end.
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Majid_S
Mountain climber
Bay Area , California
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Dec 18, 2009 - 07:11pm PT
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Catalystic Productions
so that do you see that may cause a problem ?
Keep in mind that we had limited supply of gear with us but used 1/2 rope to beef up the guideline.
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Paul Martzen
Trad climber
Fresno
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Dec 18, 2009 - 08:18pm PT
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Hey Shaun, awesome videos. It is eye opening to see how much the lines flex and bounce. Seeing that over and over, makes it much easier to understand the relatively low forces and what you are talking about. It is like you are on a super narrow trampoline.
I especially like this Swingset to slackline video.
http://www.youtube.com/watch?v=EYCEOS3p-v4&NR=1&feature=fvwp
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healyje
Trad climber
Portland, Oregon
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Dec 19, 2009 - 03:35am PT
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Over the years I rigged my 11mm with two old Chouinard pulleys. It wasn't til I drug it all out again this summer that I got to looking at the rope which is about 15 years old and pulleys that are about 35 years old. Now that I'm old that sh#t all of a sudden looked mank, so I replaced the rope and got some new, bigger CMI pulleys. It was always a drag setting it up alone, I'd have to crank it down once and walk on it for awhile and then retighten it after about 20 minutes; the new stuff made it all so much easier. Should have done it years ago.
People are doing some great things with it all, though I pity the poor children within eyeshot of the hijinks.
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Catalystic Productions
Trad climber
Arcata, CA
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Topic Author's Reply - Dec 19, 2009 - 03:03pm PT
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I'll make sure to post a trip report after winter break :-)
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TGT
Social climber
So Cal
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Dec 19, 2009 - 04:31pm PT
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I don't slackline, but I've got plenty of first hand experience with the forces involved.
I've pulled thousands of feet of 500 and 750 mcm copper thru conduit.
SOP for removing stuck cable was to max out the tugger capstan at about 6500 lb, and then get everyone out of the way and jump on the pull rope.
Most of the time that would free a 300 + ft length of cable that had been frozzen in place for decades.
Sometimes it broke the rope or the shackle, both rated at 12,000lb.
Paul's math don't lie!
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KevinN
Trad climber
Bend, OR
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Shaun
Maybe you've discovered this already, but you have some unit problems in your calculations. You start with a load of 453 kg (which is about 1000 lbs - is that what you intended?) You calculate your tensions and call it newtons. Really, you are still using kg, so multiply your results by about 10 and you have the tension in Newtons (261 N=~50 lbs). It would be pretty easy to leave the climbers weight and theta as variables, then others could insert their own weight and observed angle in the line and could make a reasonable estimate of the line tension in their setup.
Remember also that all load ratings on equipment are statistical averages, so will hold more, some less. This calculation is pretty simple and will give you at best a reasonable estimate. If I were to calculate anchor loads like this I'd add in a safety factor of at least 3 or 4.
Thanks for the post
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jhog
climber
south lake tahoe
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This is a rigging calculator (http://design.cablepick.com/rigging); used in the entertainment industry to figure out bridal vector forces (a way to hang heavy lighting and sound equipment over stages and audiences). A slackline is essentially a bridal configuration using an extreme obtuse angle, something that is strictly forbidden in entertainment rigging. You can get an idea of the forces an average weight man places on the anchor points wherever he might be in relation the the anchor points (in the middle or close to one end and how the amount of slack effects forces).
http://design.cablepick.com/rigging
I thought it was important to include this link after reading the story of someone who almost died due to an anchor failure. When I talk to people about the forces involved in the slackline setup they often find it hard to believe the amount of weight being placed on the anchors.
The calculator will not exceed an angle of 170* because as the angle approaches 180* (a perfectly taut slackline with no deflection with weight applied to the center) the forces compound exponentially to infinity at the anchors! Such configurations are never considered past 120* in the industrial rigging world.
It may take a minute of playing with the calculator to understand what's going on but just think of the box in the lower right corner as the slackline with someone weighting the middle and apply weights and distances in the main box on the left and upper right. The box in the upper right corner will show the anchor forces but, of course, doesn't factor in the pre-tensioning of a nylon type slackline.
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