some people believe that climbing SRT with a pencil zigzag and singing tree rope wrench will cause extreme wear to the zig-zag links swivel poor body and that this wear will lead to unpredictable zigzag failure in this video will address that concern in detail but first a little history of the zig zag the zig zag patent was granted in December 2011 product launch was in the fall of 2012 and the zig zag was first available for sale in early 2013 in August 2013 it was recalled to be following a climbing accident the beefier 2014 version was released ten months later and is still being sold today at the time of this video we have seen pictures of the 2019 zig zag plus but it's not for sale yet more on that in a bit so first let's take a close look at the wear I've put on this 2014 design zigzag and compare it to a brand new zig zag I've been climbing SRT on this zigzag with an aluminum zag wrench tether and rope wrench for close to a year now a conservative estimate is that this zigzag has seen 300 hours of tree time the swivel post and ball shows some superficial wear to the anodized surface but there is no play in the swivel or the rivets the link and Springs all work as intended and it doesn't slip on 11 millimeter or eleven point seven millimeter rope the channel where the Rope contacts the aluminum and resin parts of the zigzag shows minor surface wear kuchel states that if using the zigzag in an SRT setup you should pay particular attention to the hard plastic bumper in this area a small divot a fraction of a millimeter deep can be seen here on my zigzag capsule recently unveiled a zigzag plus rated for SRT when combined with their rope wrench like friction device called the chicane the zigzag Plus is remarkably similar to the previous version of the zigzag and the chicane is functionally identical to the rope wrench I see the lack of originality in pencil zigzag plus as an unspoken endorsement of how I and many other climbers have been using the zigzag for years without any known incidents in fact according to a Petzl rep I spoke with the chicane will be sold separately and can be used with the 2014 design of the zigzag still some people especially American climbers familiar with the an cz 133 standard point out that the 2014 design zigzag is rated by Petzl to just 15 kilonewtons since it was tested in a DRT setup some people conclude that the links of a zigzag are rated to just 7.5 kilonewtons Petzl has never posted brake test results of the 2014 zigzag the only state that the zigzag resists to a static force more than 15 kilonewtons but what if the actual breaking strength is much more than 15 kilonewtons and if it is would that reassure the SAG wrench skeptics incidentally the 15 kilonewton wording is used because that's a requirement of the en 358 European standard it's a misconception that the American and cz 133 standard requires all climbing ropes and all hardware to have a minimum breaking strength of 24 kilonewtons all that is stated in the an cz 133 is that ropes have to withstand 24 kilonewtons of force and carabiners have to a stand 22 kilonewtons of force there is no section that addresses mechanical ascender such as the zigzag let's get to the brake tests Kevin Bingham kindly donated a used rope wrench and Richard Mumford generously offered his hydraulic stress test machine for these experiments thanks to both of you the zigzag is the same one you saw pictures of a moment ago and the zag wrench tether is made by me in North Carolina the first test shows the zig zag in a typical SRT setup with a rope wrench and the zag wrench tether the Rope is unused Yale Blue Moon eleven point seven millimeter rope with a breaking strength of 6,500 pounds or twenty-nine kilonewtons blue moon is fairly static rope with a stretch of less than 2% at the working load limit so here's when it first went up and I think that was probably the max of 1237 pounds and then here you can see where it maxed out and then it started to slip and it just consistently started to slip look at this that's a real consistent snip right there so the zigzag and rope wrench slipped consistently on Bluemoon at least once a force of 1,250 pounds or 5.5 kilonewtons is reached what if we removed the tether and the rope wrench then we'll the links grab more tightly causing the zigzag to fail you look like it putting my child 5 to 600 pounds interestingly the zig zag and pure srt setup slipped at almost exactly half the force 600 pounds or 2.7 kilonewtons compared to when the rope wrench is present this is in line with the rope wrench product information which states that the Rope wrench is a load-bearing device that may bear more than 50% of the climbers weight during the climb in other words the rope wrench and zag wrench tether double the force that the zigzag can hold before slipping so now we know that the zigzag slips at 1250 pounds or 5.5 kilonewtons on blue moon but what about another rope next we repeated the first test on Marlow Vega eleven point seven millimeter rope with a breaking strength of eight thousand two hundred eighty pounds or thirty-seven kilonewtons Vega boasts an elongation of only one point two percent at working load [Music] [Music] settle down down the zigzag holds a bit more force with Vega before it slips probably due to differences in sheath texture between Vega and blue moon the actual number is 1,350 pounds or six kilonewtons with converging observations that the zigzag slips on eleven point seven millimeter rope at about 1300 pounds we guessed that the zigzag in the approved DRT setup would also slip close to the same amount or slightly more due to the friction around the redirection point [Music] so there was a team the beacon 1500 and then it looked like it was holding just under a thousand in line with our hypothesis we saw slippage at 1500 pounds or 6.7 kilonewtons the possibility of slippage in your life support system may be a source of concern for some climbers but minimal slippage is actually a good thing and can prevent catastrophic damage to your climbing line and to your body in the event of a bad fall in these tests the force dissipated by the slipping zigzag and rope wrench was roughly 44 kilonewtons over 23 inches since the break strength of Vega rope is 37 kilonewtons the slipping zigzag dissipated a quantity of force that would have more than broken the rope here's another way of thinking about it a fall with enough force to break the Vega rope if the zigzag had locked on could be dissipated by the zigzag slipping about 16 inches and during that process the rope would never feel more than about 1,300 pounds of force well below its breaking strength another commonly cited concern about climbing SRT with a zigzag and rope wrench is the angle of the swivel post when used in dr t vs srt setup some people claim that the post jams against the zigzag housing when it is used with a tether and a rope wrench to address this concern we put tension on each system and took pictures of the angle of the post as you can see in these overlaid pictures there is a slight difference in the angle of the post relative to the zigzag body with the post somewhat closer to the lower rivet in the SRT setup regardless there is still free space between the swivel post and the plastic bumper as shown in this photo it appears that Petzl increased the clearance for the swivel post in the 2019 zigzag plus by slightly shifting the angle of the links the rope channel and the tether connection pole so with four pull tests already on this beleaguered zigzag we wanted to see if there was anything that could break the zigzag itself the easiest way to test that is to prevent the system from slipping by adding a stopper knot below the zigzag we figured that our best chance of breaking the zigzag before breaking the rope would be to use Vega rope with its 8,000 280 or 37 kilonewton breaking strength [Music] [Music] almost 5,000 it's very consistent it was a pretty consistent curve yep 1000 that's where the slide was we're sliding again and then hit the Alpha and butterfly the zigzag was in remarkably good shape after this test despite withstanding a force of 5,000 pounds or 22.2 kilonewton and being shot toward and bouncing off the pulling piston the zigzag had now resisted five full tests and additive forces of more than ten thousand pounds we speculated on which part of the zigzag would end up being the weak link and we didn't have to wait long to find out for the sixth and final test we configured the zigzag in a DRT setup on blue moon rope and started pulling [Music] [Music] there's the rest of the solo right there I'm so broke the housing it didn't even break the stem no that's the other thing people often worry about outside house [Music] thousand six hundred and sixty-two pounds before seeing the Swivl outside of the zig zag I assumed the swivel post bulb and connection point were somehow welded together but on closer inspection it looks to me like the entire swivel assembly is machined from a single piece of aluminum now the last thing to break was the Zagg wrench tether it's made of t 6061 aluminum and each piece is cut with a waterjet cutter at a veteran owned and operated metal shelves at North Carolina [Music] [Music] the zag wrench tether broke at 5500 pounds or 24.4 kilonewtons a stainless steel tending shackle distorted but the actual failure was due to the steel pin pulling through the aluminum side plate the zag wrench tether withstood nearly 1,000 pounds of force more than the zigzag a one-piece stiff metal tether between the zig zag and the rope wrench eliminates any play in the system and allows the rope wrench to engage immediately upon sit back so that it diverts half the climbers weight from the zigzag links and makes descent as smooth as when descending DRT on the zigzag the detailed design file for this Agron's tether is freely available for download at the link in the video description below more than 175 people have accessed the file to make their own tether since I shared it publicly in February 2018 if you want to tether but don't have access to a metal shop the same link has information about how you can buy a ready to use a grinch tether for $74 the zag wrench tether is perfectly fitted to both the 2014 design of the zig zag and the new 2019 zigzag plus at the time I uploaded this video it was easy to find the 2014 design zigzag on sale for as low as 250 dollars I'm told the zig zag Plus will go on sale in spring 2019 for somewhere between 350 and 400 dollars not only is this a Grunch tether a great way to pair your existing row per inch with the 2014 or the 2019 zig zag plus for a super reliable srt system it's also a great way to support Kevin Bingham in his patented rope wrench the second part of this video attempts to answer the question could a force capable of breaking the zigzag ever be created by a climber in a tree the zigzag withstood a poll of 5,000 pounds or 22 kilonewtons but when the Vega rope finally broke on the next pole the swivel pulled out at 4,600 pounds or 20 kilonewtons the equation to determine the force exerted on a climbing line by a falling climber is equal to the weight of the climber plus the square root of the weight squared plus the product of two times the fall factor time's the weight of the climber times a constant that will caulk a known as the rope modulus the modulus is the slope of the graph that describes the force needed to stretch the rope a certain amount the fall factor is a ratio of the distance the climber Falls before the Rope catches to the total length of the rope available to stretch and stop his fall there's a link in the video description to a paper that shows the derivation of this equation a fall factor if there is no slack in the rope is zero and the max force equation simplifies to weight plus the square root of the weight squared or just double the climbers weight this is the mathematical reason that you should avoid having slack in your climbing line now let's imagine a scenario where a 180 pound climber is free climbing above their tie-in point and they slip fall a few feet and are caught by their climbing line disregard the wisdom of free climbing above your tie in point and let's imagine that a climber is 60 feet high in the canopy on an SRT line that is basal hangar they climbed three feet above their tie-in point slip and fall a total of six feet before they are caught by the rope the fall factor is 6 divided by 63 or roughly 0.1 from the equation for the force on the rope we calculate a force of about 1500 pounds well below the breaking strength of the rope or the zigzag and right at the point at which the zigzag has been shown to slip another scenario involves a fall resulting from a broken limb holding the climbers tie-in point for example a climber unknowingly installs an srt access line over a sketchy tie-in point 60 feet high and anchors it at with a basal anchor as the climber gets 250 feet on the rope the tie endpoint breaks and he falls 20 feet before the Rope catches on a lower branch the fall factor is 20 divided by 70 or 0.3 the total force exerted on the rope is 2,400 pounds or 10.5 kilonewtons this ignores the possibility of the zigzag slipping which we have shown is likely to occur the slippage is likely to start at 1,300 pounds of force and continue until the remaining roughly 900 pounds or fill 4 kilonewtons of force is dissipated from the analysis mentioned earlier in this video we estimated that a slipping zigzag dissipates about 1.9 kilonewtons per inch of slip that means that the climber will probably stretch the rope to the point associated with 1,300 pounds of force and then slide down the rope about two inches before coming to a stop at no point is the rope or the zigzag in danger of breaking now let's say there's a climber who loves to bungee jumps so they climb to the same height of 60 feet pull out 40 feet of slack in their high mning lineman and then jump off the limb they will fall 40 feet and the total length of the rope available stop their fall is 100 feet in this scenario the fall factor is 40 divided by 100 or 0.4 and the total force exerted on the rope is 2,800 pounds or 12.3 kilonewtons that means that the climber will probably stretch the rope to the point associated with 1,300 pounds of force and then slide down the rope about three and a half inches to dissipate the additional force before coming to a stop as you may be beginning to see it's actually quite hard to imagine a scenario where there is a fall factor greater than 0.4 especially when an SRT line is basal anchor falls on a canopy anchor could be a bit more impactful for example if our bungee jumping arborist climbs to a canopy anchor of 80 feet let's out 70 feet of slack and then jumps the fall factor would be 70 over 70 or one a fall factor of 1 for a 180 pound climber on a nearly static rope such as blue moon or Vega will result in a force on the rope of 4,300 pounds or 19 kilonewtons not really the kind of forces a bungee jumping thrill-seeker would enjoy being subjected to the theoretical maximum fall factor is 2 the only way I can imagine a tree climber experiencing a fall factor of 2 would be if he basil anchored to a tree on the edge of a cliff free climbed up some distance say 20 feet without tying in at all and then fell off the tree and down into the cliff he would fall 40 feet on a 20-foot rope before the rope caught him that is a fall factor of 2 and in our scenario of a 180 pound climber on Yale Blue Moon mostly static line the fall would exert a force of 6,000 pounds or 26.5 kilonewtons that is enough to get dangerously close to the breaking strength of a rope assuming there is no slippage of the zigzag more importantly forces of that magnitude are likely to lead to a broken back when only restrained by a harness around the waist as I've already outlined in the previous scenario the zigzag is almost guaranteed to slip under these forces and if it did slip once the first 1,300 pounds of force was exerted on the rope the remainder of the force of this factor to fall would be dissipated by the zigzag by the zigzag sliding down the line about 11 inches you may be thinking and rightfully so that vertical drops are not as common in tree work as taking a bad swing toward the trunk from an unsecured limb walk let's talk for a minute about the forces exerted on the rope during a bad swing in a swing the maximum force on the rope is at the bottom of the swing when the radial acceleration and the force of gravity combined together the largest force would result from a swing that started when the rope is perpendicular to the ground such as in johnny pro's infamous swing off the construction crane in this scenario the maximum force is equal to three times the weight of the climber so if Johnny weighed 180 pounds the force on the rope at the bottom of the swing would only be 540 pounds or about two kilonewtons nowhere near enough to strain the rope or the hardware and nowhere near the forces generated from a fall that has a freefall component it's the sudden deceleration force when the climber hits the tree trunk that is the real danger with a bad swing but that force is not felt by the rope or the mechanical ascender here's another interesting point of discussion how much force can the human body withstand what would happen if a climber in a waist harness alone experienced a decelerate 'iv force of eight or twelve or 26 kilonewtons rapid deceleration experiments with cadavers anesthetized primates and conscious human subjects have actually been done believe it or not a force of 12 kilonewtons is considered the upper limit of what a human body can endure with minimal chance of injury when supported by a full torso harness 12 kilonewtons is the average force that a military trooper experiences when they land with a fully loaded pack in a combat parachute jump the fall rate for paratroopers and the design of military parachutes are actually calibrated to get the jumper to the ground as fast as possible while not permitting a force greater than 12 kilonewtons the highest known impact force experienced by a living person who survived to tell about it was about 32 kilonewtons the person was John Stapp a pilot and scientist who in the 1950s voluntarily endured many crash tests in a rocket-powered sled to determine the forces that could be tolerated by fighter jet pilots in his last and most famous test mr. staff was wearing a compression suit to keep his vital organs in place his head was in a helmet that was strapped to the reinforced cockpit seat his arms and legs were also strapped in place he was rocketed to 630 miles per hour on a horizontal track by nine solid fuel Rockets at the end of the track was a pool of water that caught scoops on the underside of the rocket sled and stopped its movement in about one second mr. Stagg survived the test but he broke both wrists and a few of his ribs he was badly bruised by the restraint system and all the capillaries in his eyes burst clearly a force of the magnitude mr. Stagg and dirt couldn't be survived by someone in a tree climbing harness it's even debatable whether the human spine could survive a 12 kilonewton impact force when supported by a tree climbing harness fortunately as shown in the first half of this video the force is likely to be experienced by tree climbers even in the worst fall accident are going to be less than 10 kilonewtons the take-home points are no different from what climbers already know always keep tension on your climbing line and choose your tie-in point wisely in conclusion I give it as my opinion that the three-way pairing of the putzel zigzag the singing tree rope fringe and the zag wrench tether is a strong high-performance choice for SRT climbers the zigzag automatically Tunes to every arborist climbing line I've ever tried it on and it acts predictably on wet or dry ropes new or old ropes and dirty or sappy ropes slack tending is effortless and the built-in swivel makes it easy to keep your climbing system in your preferred orientation the single piece construction of the zag wrench tether eliminates the fluffiness inherent in a two-piece connection like the chicane and it's required carabiner and the built-in tending point on this a Grunch tether let's your hands focus on grabbing the rope wherever it works for your height and posture instead of using one hand to advance the zig zag plus you
