If you slackline or highline you MUST read this!


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Trad climber
Portland, Oregon
Dec 18, 2009 - 03:34pm PT
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.

Social climber
Flatland, Ca
Dec 18, 2009 - 03:44pm PT
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...
Catalystic Productions

Trad climber
Arcata, CA
Topic Author's Reply - Dec 18, 2009 - 04:30pm PT
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 :-)

Social climber
san joser
Dec 18, 2009 - 04:44pm PT
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.

Trad climber
Sacramento, CA
Dec 18, 2009 - 04:46pm PT
Call me sometime when ur in Sacto and you can borrow the Dyno.... U promise to return it right????

916 316 5015
Paul Martzen

Trad climber
Dec 18, 2009 - 05:01pm PT
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

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.

Mountain climber
Bay Area , California
Dec 18, 2009 - 07:11pm PT
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.
Paul Martzen

Trad climber
Dec 18, 2009 - 08:18pm PT
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.

Catalystic Productions

Trad climber
Arcata, CA
Topic Author's Reply - Dec 19, 2009 - 03:00am PT

Trad climber
Portland, Oregon
Dec 19, 2009 - 03:35am PT
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.
Catalystic Productions

Trad climber
Arcata, CA
Topic Author's Reply - Dec 19, 2009 - 03:03pm PT
I'll make sure to post a trip report after winter break :-)

Social climber
So Cal
Dec 19, 2009 - 04:31pm PT
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!
Catalystic Productions

Trad climber
Arcata, CA
Topic Author's Reply - Dec 20, 2009 - 02:55pm PT

Who knows?
Dec 21, 2009 - 09:17am PT
good thread!


Trad climber
Bend, OR
Jan 4, 2010 - 01:38pm PT
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

south lake tahoe
Jan 4, 2010 - 05:14pm PT
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).


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.
Chris McNamara

SuperTopo staff member
Aug 18, 2011 - 11:20am PT
Wow, I can't believe I missed this thread the first time around. Great stuff. I will add it as a reference to the best slackline review we just released.
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