URGENT WARNING
about
GROGs in highline rigs
Hey beautiful highline monkeys, I'm Stephan from raed. In this video I'd like to talk about the dangers of using so called GROG splices as connectors for segmented highlines.
WHAT ARE HGHLINE CONNECTORS?
In modern highlines the lines don't consist of one piece of slackline webbing anymore. To improve the safety of a highline it nowadays consists of multiple segments that are attached to each other. The attachment points, usually sewn loop ends of the webbing pieces, are connected with "connectors". These connectors bear the full load of the line and need to function under all critical circumstances. If they fail, the whole line fails and the highliner falls to the ground.
WHAT IS A GROG?
A GROG is a ring, spliced of 12 braid Dyneema rope. They are made by first creating a brummel splice, followed by 2 buries for the tails. In the end it connects 2 or 4 sewn loops of highline webbing. Usually GROGs are doubbled up for redundancy - in this case main and backup are both connected with these doubled rings.
FIRST ONLINE RUMORS
Some months ago we heard the first rumors about strange things occuring involving GROGs. The riggers of a multiple km highline discovered that the grogs they used to connect their segments could easily be unspliced without undoing the brummels. The same could be seen for the grogs in a freestyle perma rig. This made us highly curious: How can something that's spliced in a supposedly secure brummel lock be disassembled in a way that has no locking mechanism at all anymore?
RING LOADING BRUMMEL LOCK SPLICES
A brummel in an end loop is straight loaded in the longer strand, the shorter strand is buried. Each side of the loop carries 50% of the load that the longer strand carries. Since the load in the long strand is higher than the force of one loop strand, the long strand can never become inverted by these forces.
Ring loading a GROG is different though. In this configuration the brummel is not straight loaded but ring loaded. In this demonstration you can see what happens to a brummel lock when it's ring loaded: It inverts and the locking mechanism collapses, even under very low loads that can be applied by hands. In a GROG none of the tails is under tension - both of them are simply buried without any load keeping them in place. This allows this inversion to also happen under load. We tested some GROGs for their Fmax strength in our ZWICK ROELL tensile test machine. This high precision machine allows us to destroy anything at up to 50 kN of force. In case of testing a GROG for Fmax the whole GROG construction inverts and then fails at about 30 kN.
THE EFFECTS OF CYCLIC LOADING
When installed in a highline, all connectors are loaded cyclic. Be it bounces, leash falls or wind loads, all these types of movement create load patterns that increase and decrease the load in the line in a cyclic way. So we asked ourselves: Could the strange unsplicing found in the lines mentioned above have anything to do with the cyclic loads these connectors have experienced before? Luckily we just invested in a brand new high precision ZWICK ROELL tensile test machine that's capable of performing cyclic load tests. So we're in the highly privileged position to find out.
In our first test we used a double GROG, connecting 2 pieces of Dyneemite pro, we cycled the loads based on the measurements that have been published about several multi-km highlines: A Fmax of 18 kN and a Fmin of 2 kN to simulate the worst case amplitude of a high wind scenario. As you can see, the whole construction inverted after only 2000 cycles to a state where the brummel is not locking anymore. The strength of these grogs now only depends on the buried tails and they start slipping fast with each single cycle. After only 4.000 cycles the first grog completely collapsed. After that test we wanted to know: Is this repeatable in freestyle loads? So we made another test, this time cycling the loads at the max freestyle forces of big guys: 2 to 7 kN, to also simulate the worst case for this configuration. As you can see, the effect of inverting the splice happens a bit later due to the lower loads, but it still happens within a few hours. Only a few thousand cycles later this splice also completely collapsed.
HOW MANY OF THESE CASES ARE THERE?
When talking about our initial findings to a friend, he told me, they also found a strange looking GROG in one of their lines some weeks ago. Here you can see what he filmed while being on that line. As you can see the tail of one grog is out of its bury, leaving a tail loop ouside. What's interesting here is that this whole connector was not under load anymore when he checked it - the full load was only carried by the second GROG. It's important to point out that unloaded bury splices can easily undo themselves from vibrations and shaking due to the fact that the chinese fingertrap does not keep the tail trapped anymore - this only works if the whole construction is under tension. We don't exactly know if this tail walked out due to cyclic loading or if it was rigged this way initially. But it's safe to say that such a home made spliced construction leaves plenty of room for human error. Once this flawd connection was discovered, the whole line was derigged and the connection replaced.
CAN THE RISK BE MITIGATED?
The problem with this failure scenario is obvious: It can happen anytime under load, even over night when the wind loads work the line. This means, that you could potentially enter the line the next morning when your GROGs already inverted and you can only check them by walking out to them to check them up close. Or worse: It could even happen while you bounce on the line, since every single bounce is one load cycle adding to the potential inversion of the splice. So we don't believe that there is a viable strategy to mitigate this risk. That's why we publish these findings to issue an urgent warning of GROG splices in highlines.
LEGAL IMPLICATIONS OF HOME MADE CONNECTORS
GROGs are home made connectors. They are manufactured by yourself from a simple piece of rope. They are not manufactured under controlled, repeatable conditions. They are not tested, they are not proof loaded, they have no guaranteed strength. They are not certified after any standard. You are the manufacturer, so you are fully responsible for whatever happens with them. This means: You're fully liable for using them - If anything goes wrong, your insurance will most likely not cover the cost of an accident.
ARE SOFT SHACKLES AN ALTERNATIVE?
The ISA safety standard for highline connectors states: "The locking mechanism shall ensure, that there is no single action that releases or opens the device nor can the connector be accidentally opened in normal use" which means every connector must have a double locking mechanism - this criterium is not fulfilled by soft shackles as they can easily open up just by shakings when being not under load, please watch m,y video from 2019 for more details, link in the comments ( https://www.youtube.com/watch?v=pDOFUMcp5pk ). In addition there's not a single soft shackle in the market world wide that's certified for the use at height. That simple fact already tells a lot: While we have dozens of manufacturers certifying carabiners and quicklinks, not a single manufacturer or notified body on the planet is willing to take actual liability for a soft shackle used at height.
WHAT ALTERNATIVE TO GROGs DO YOU RECOMMEND?
Right now the only viable alternative that can be recommended without jeapordizing a highline rigger' are quicklinks ( https://raed-sports.com/collections/connectors ). To connect highline segments with quicklinks we offer the DuraLaVida connection system ( https://raed-sports.com/collections/sewing-service ). This system brings full redundancy to your line, is easy to install, simple to check and contains certified connectors. When attached correctly it stacks extremely small and allows even smaller leash rings to pass easily across the connection.
We brought the DLV system to the market in 2020 following an idea of the New Zealand highliner Fernando. It has proven to work extremely well since then, so well that nowadays even other manufacturers like SlackHouse and BalanceCommunity offer them. We're happy to see this idea spreading and truly hope that even more manufacturers join the club of DuraLaVida manufacturers.
WHAT ABOUT QUICKLINKS ACCIDENTALLY OPENING?
We know about several cases where quicklinks failed on slackliners by accidentally opening. In one case we've even seen a big highline rig being compromised by a quicklink failing over night in a storm (https://www.youtube.com/watch?v=q--gERjUEuw). In none of the known cases the quicklinks were closed with a wrench and taped shut. For our next test we wanted to know: What exactly does it take to accidentally open a quicklink? How many load cycles does this take? So we again went to our ZWICK ROELL tensile test machine and started another cyclic load test, this time replacing the GROG with a quicklink that was only hand tightened. We had this test running for many, many hours in big line loads as well as in freestyle loads, without being able to observe any movement in the quicklink. Our conclusion: It's not cyclic loading that opens them up. But if it's not the load cycles, what else makes them fail? We went on testing for vibrations. In the next test we took a simple electric tooth brush and had it get in contact with the quicklink - et voila: The mechanism opened up, it nearly looked like magic being at works.
OUR RECOMMENDATION FOR QUICKLINKS
Quicklinks need to be tightened according to the manufacturer's user manual to be safely closed. Peguet, the manufacturer of the French "Maillon Rapide" instructs a wrench torque of 2.5 Nm for 7mm quicklinks, 3 Nm for 8mm quicklinks and 7 Nm for 10mm quicklinks. In addition we recommend to add some wraps of a sticky tape around the quicklink to prevent them from accidental opening caused by vibrations.