Webbing slippage and tie-offs in highline rigging

Guest Post by Ben Donnelly

Recently, Shane Hickman posted some photos [PHOTOS 1 & 2] from the Poudre Canyon Highline which sparked an important discussion about: tail tie offs and weblock slippage; the need for pretension in shorter highlines; and general safety concerns when it comes to highline festivals. The Facebook post can be found here. There is some really good information in that post, but the thread gets a bit convoluted. I will try to distill the important information here:

hickman1-webbing-slippage

hickman2-webbing-slippage

The following represents a combination of my opinions and the best of my knowledge. I do not believe it is an end all be all. On the contrary, I hope it sparks useful discussion and I hope that the community will critique, confirm, negate and build on what I write.

WEBBING SLIPPAGE AND TAIL TIE OFF:

Shane Hickman took these photos [PHOTOS 1 & 2] of the 120’ t18 rig at the Breath Poudre Canyon Highline Festival last weekend. They show twists being pulled into the weblocks after repeated whippers.

As can be seen by the photos [PHOTOS 2 & 4] originally posted by Reggea Daddle, this phenomenon can and eventually will cause catastrophic mane line failure.

raegge1-webbing-slippage

 

raegge2-webbing-slippage

For what it’s worth, I know of 4 rigs at the same festival that eventually ended up with twists in the weblocks or load transferred to the tail tie off rather than the weblocks in the masterpoint. I personally fixed two of them.

We know from the article linked below that webbing slippage in weblocks occurs continuously and progressively with every load cycle (whip or catch) on a highline. (This occurs on 1.5 and double wraps, too.) This means that every time the slacker falls, tail is pulled through the weblocks. We also know that the slippage is worse in looser lines. And, of course, this points to the fact that all lines will end up loose after enough falls. (Though, as Faith Dickey pints out, tight lines tend to hold their tension.) I would argue (i have no evidence except what I’ve observed), that shorter lines loose their tension faster because of higher peak loads and the ratio of slippage amount to the line’s length. This becomes especially problematic when short lines become loose and dangerous. More on that later.

All of the above information leads me to believe that THE PRIMARY GOAL OF TAIL TIE OFF SHOULD BE TO MITIGATE THE RISK OF A WEBBING TWIST GETTING PULLED INTO THE WEBLOCK. Towards this end, I believe that a well dressed MMO is the best tail tie off solution. After you tie your MMO, it’s classy to “close the system” and tie off your excess tail. I believe that this particular redundancy is more about craftsmanship and aesthetic than practicality. Does anyone else have a better tie off method??

HOW TO TIE AN MMO:

http://www.balancecommunity.com/…/how-to-mitigate-webbing-…/

Finally, this all highlights the reality that there is no such thing as “set it and forget it” for highlines. Even the most bomber rig is vulnerable to problems. Tail can pull through; MMOs can loose their dress; padding can become abraded; rodents can chew anchors (no joke); and the list goes on. HIGHLINES AND THEIR ANCHORS MUST BE CONSTANTLY MONITORED AND ADJUSTED.

STUDY SHOWING WEBBING SLIPPAGE IN WEBLCOKS:

https://www.google.com/…/webbing-slippage-in-low-tens…/amp/…

As a final thought on this: we’ve taken to the habit of wrapping our weblocks with padding. Though there are a few good reasons for this, it’s a little disconcerting that it effectively hides the most dynamic/changing and high risk part of our rigs!

THE DANGERS OF SHORT LINES:

Another important topic brought up by yesterday’s discussion was the fallacy that looser lines are safer.

We know that when lines are really long, they can safely be rigged at hand tension or lower. This is because long lines have a lot of webbing to absorb the force and spread it over time. On the flip side, if a short line is rigged at low tension, a whip will cause dangerously high peak loads to the slacker, the leash and potentially the anchors. This is because all webbing is low stretch at low tension. (To understand this statement, look at a stretch curve. [PHOTO 5] All webbing is essentially 0% stretch at 0kn of force!) Accordingly, on short lines, we must add pretension to the webbing. This pretension allows us to “access” the higher stretch properties of the webbing thus spreading the force of a leash fall over time.

I don’t think we have any hard fast rules but generally, lines less than 100’ long need pretension. Of course, these lines may need to be adjusted and tightened after a number of falls.

t18-stretch-table

 

STUDY DISCUSSING FORCES ON SHORT LINES:

http://slacklab.de/en/highline-1/forces-in-highlines…

It’s worth mentioning here that shorter lines must be rigged with higher stretch webbing.

This all is particularly important at festivals. I believe that all of the short lines at the Poudre Canyon Fest were rigged with pretensioned high stretch webbing. Good! However, whip after whip and improper tail tie off caused these lines to loose their tension and become potentially dangerous. For example, when I was about to walk the 40’ line (the highest one), I approached a group of beginners taking BRUTAL whips on a line that had become less than hand tensioned. No one there, at that time, knew that the tails, not the wedlocks were loaded and that the line had become unsafe in more ways than one.

MY FINAL THOUGHT:

It is becoming more and more common that folks will hop on a highline without even checking the rig. Some may not even have the skills to do so. It seems that beginners come to a festival under the potentially false assumption that all lines are rigged safely.

I believe that festivals should have monitors that continually walk around to check anchors and make the appropriate adjustments. Beginner lines require closer monitoring and generally require more frequent tensioning.

At this point it seems that trusting slackers to examine a rig and make their own informed decision about its risks is becoming a thing of the past. 🙁 As a community, I still think we should keep these people safe!

If someone wants to rewrite this in a better format, especially after some discussion, that’d be great!!!!

Love, Ben

And remember: rigging is art!!!

Related resources:

Webbing Slippage in Low Tension Highlines – Slackline Tübingen
Slack Science, Knowledge Center – Balance Community
Slacklab.de, Germany (English & German)
Slack Tübingen, Germany (English)
Katlein, Germany (German)

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