I find an easy way to make the purcell is to make the Prussik on an empty toilet paper roll, that way it's shaped nicely and easy to dress. then put the other end through and then pull out the roll and tighten. Yes other methods are easy enough, but especially on longer purcells its nice to get all the twists out and such before putting it through the prussik and this holds it all in place nicely.
Ryan brings up a very valid point against purcell prusiks, and i want to give my work around You cannot tighten a purcell prusik one handed. You have to completely unweight it and use 2 hands which really sucks if you're trying to tighten up on an anchor My solution is to get some paracord or something similar and make a small prusik loop on the 2 strands that feed back into the prusik, NOT the strands going through the prusik You can pull on your small prusik to introduce slack into the purcell, and use that same hand to pull the knot in and shorten everything up. Its not perfect but its very handy to know about
My takeaway is that for factor falls greater than 1.5 ish you really need a screamer of some sort. But that's not really a thing when climbing and walking around above the anchor is really common.
With dyneema woopie sling you can theoretically find the optimal length for "stuck through" part. It is also possible to make few such parts with pulled out parts of rope between "stuck through" parts. This can make gradually increasing stopping forcethat can be adjusted. Friction parts of rope will be distributed so heat problem should also be less of a worry
@@alandoak5146 I sort of knew that :-) I’m more on about the spread over time of load due to squishyness.. eg DMMs tests on slings showed they break with an 80kg factor 1 (IIRC) but nobody has had this happen. When Ryan tested it he got way, way lower forces
@@largeformatlandscape A lot of people have come to the completely wrong conclusion from that DMM video, a rigid mass is a very poor dynamic model for a human body. DMM even tied a knot in the sling to create the outcome they wanted, the vid was dishonest and deceptive. Or, maybe they don't understand physics, which is probably worse. Let's not forget that an arborist had a new DMM swivel disassemble itself on him, bigwallers and circus aerialists (I'm both) use swivels in non-redundant systems where failure is catastrophic. It's a lot harder to drive a nail with a rubber mallet (or with your fist) than a steel hammer, the peak forces are so much lower. And it's not just that the energy is spread out over time (F=ma, lower deceleration means lower forces), a lot of energy is absorbed in the body.
@@alandoak5146 yeah - I realise that. But I’m interested in the quantitative values. Is it possible to model a loosely connected squishy body using a ridged body connected to another weight via a dampened spring? The answer is yes so how to similar that on a drop tower? I might try to answer the question myself as I’m just helping my niece with her mech eng degree
This is interesting to get more into different type of personal anchors. Looking forward to seeing Petzl adjust and hopefully Kong slyde as well. I guess that would cover almost all common personal anchors.
@@thefack149 I never noticed eashook. That could be so handy in some applications and you can attach it to a sawn loop too (unlike some other similar models I have). In general use I tend to find triple locking carabiners or ball lock ones quite fast to use.
Glad I'm a caver, not a climber. We don't have to worry about shock-loading. All of our lines are static, most of them 11mm pit rope. Avoid sharp edges and you're fine. In fact, we have a couple of 13mm static ropes that will cut a groove in the limestone rather than get damaged themselves. We use those for fast and dirty recon of new sites. The only drawback is they're very heavy.
I appreciated this simply because of the knit tying tutorial. Then, additionally the shock absorption was quite interesting. I’m not a fall-geek, and still enjoyed your efforts.
Been using things like this purcell prussik for roof and chimey jobs for years. Never taught , but seemed good use of knot skills learned in my youth helping arborists. So glad to see testing on something I do. But yes, It is not my sole safety for steep pitch or other serious consideration where I may think a deadly whipper would be on the agenda before the next break.
Not sure if this is going to make sense, but there are two concepts I was given for the Purcell Prusik. 1st: You can tie it with the knot inside the prusik loop to maximize how short you can make the loop, but limits the extension a little. The std design with the knot outside of it limits how short you can make it. 2nd: This concept came from an OG SAR climber I know...you can make double Purcell Prusik by using a much longer cord (30'?), and tying a second Prusik on the tail end (where you usually connect to your harness) after completing the construction of the std Purcell. You then pass the first/completed Purcell Prusik through that second one and you can girth hitch the middle to your hard points. This gives you two adjustable tethers (and a mountain of cord).
Cool to see these results! I use a 60cm nylon sling (girth hitched) for my PAS when single pitch climbing and when I am multipitch climbing I always clove in using my rope. Seems like regardless of what method you use, the basic gist is don't go above the anchor and if you do then don't fall onto your PAS
I've been using the klemheist version of this for years with a 6mm cord. Not sure I'd ever go to anything else for the price. I've got mine set to a fully stretched arms length. I'd love to see what you could get if you fell with your super long one. Haha
Yeah, fewer wraps generally means it slips at a lower force. That's good if you're trying to get a bigger ratio between the slipping force (ideally ~4-5kN?) and the breaking force (ideally 15kN+).
@hownot2 Thanks for the video. I do rescue so we use Purcell Prusiks all the time. Are you familiar with the Aztek Edge Kit? We use them as personal anchor, travel restraint and for patient rescue and a million other things.
This is all super interesting!! But, I'd also love to see some less "extreme" fall examples. Yes, I know these fall factor ~2 falls are interesting to see, and it's always fun to see gear break. However, I think some "sensible" falls where the person isn't really above the attachment point (FF < 1) would be very informational!! It would be amazing to be able to see the different forces one would feel if one fell on pas (dyneema loops), dyneema sling, nylon sling, purcell, connect adjust, etc.
Great stuff. I use a Purcell prusik as a personal anchor, but I place the double fisherman close to the prusik knot to maximise the length adjustability. Probably doesn't effect the strength much but a friend had the double fisherman get partially inside the prusik when the prusik got loose, so that's a risk to be aware of.
I use this as an adjustable manual handbrake on a temporary rope zip line on my property. It trails behind the zip line pulley with no weight on it. You lightly wrap your hand around it (with gloves on of course) and as you’re approaching the end of the line you take your hand off. As the prusik is trailing the pulley and all of your forward momentum and weight are on the pulley which is clipped into your harness as the prusik starts to engage it starts to shift your weight from the pulley to having your weight on the prusik giving you a soft catch. Work’s beautifully! As the pulley then naturally travels back to you as it has less resistance, it shifts your weight back onto the pulley at which point you can easily reach up and tend the prusik with your hand again. The system also does a wonderful job at not turning you into a human pendulum. I know this is not ideal zip line setup but for a line that gets moved around the property and setup with dramatically varying levels of speed and height the system works extremely well. Way better than trying to rig and re rig tire, compression spring or bungee breaking systems all the time.
I know it's an old video but the updated way of tying a purcell does not have a bfk; just a double fish, a prusik and the girth hitch to your hard points. If you need a shelf you can add or remove an overhand. It's much more simple to tie and can be easily converted to a loop of cordalette.
FYI: spine breaking is probably what you worry about when talking about the body taking the force. The part of the spine that is probably most worrisome can resist about 2kN before accounting for soft tissue that'll absorb some force. (in vitro) When they studied forces on patients in vivo, it seems that the back can take about 3.4/3.7 kN before ~50% of folks will break their low/mid back (granted, the studies include older folks, avg age ~50 since that's who gets most back fractures in the medical world). Younger folks can tolerate ~4-6kN and part of that depends on how much time the force is spread over (as Ryan mentions), but also other factors like if you're upright/vertical vs horizontal when you the rope catches (e.g. horizontal = more torque and force on weaker parts of the spine vs vertical = more compression on the parts of the spine that are used to seeing some compression... same concept as compressive vs shear forces when you're talking about breaking bolts... except on your spine...). Also, in the physics/biomechanics world, the technical term for force over time is "impact". Force spread out over more time = less impact. Concentrated into less time = more impact. Makes sense if you think about a whip. Barely any force, yet cracking a whip hurts because it's such a short time = more impact.
Im a boulderer and about a month and a half ago fell 25 feet, thus breaking my spine exactly where you just said (L1 burst fracture) I’ve been curious about how many kilonewtons the fall was but it’s hard to tell. I’m assuming it was somewhere in the 6-8kn zone. Got surgery and am doing better now, soon to return to climbing
Just out of curiosity, why would you or anybody else need/want a measurement of energy here? It's not a very useful metric for the use of this kind of equipment, which is why everything is rated in terms of force. Theoretically you could get a rough approximation of the energy by slapping a meter stick to the drop tower and using E = m*g*h where m is mass, g is 9.8 m/s^2 (gravity on earth) and h is the total distance traveled from the beginning to end. This would only work with really static lines though, like dyneema. If you wanted to find it with a more dynamic system you could do a simple pull test to find the spring constant k via hooks law (F = k*x) and then use E = 1/2*k*h^2. That said, your value for k will be very different when the system has knots that slip, deform, etc. and hooks law would still be a rough approximation at best. My point is you *could* roughly calculate the energy and power with relative ease, but it doesn't give you any useful information so why would you bother? It's appropriate that force is the primary metric to consider here. Energy is kind of an abstract measurement for assessing safety in these kinds of systems, force is all we need to make well informed decisions. It's like wanting your car speedometer to measure energy; sure you can do it but it's kind of irrelevant as speed is a much more useful thing to know.
@@BridgetWirth A spring is poor model for textiles (cordage, webbing, rope, etc) in destructive pull tests: energy is dissipated in the frictional heating and melting of the weave, plastic deformation of the fibers, chemical bonds being stretched and broken, etc. Once a metal spring experiences plastic deformation, you can throw Hook out the window. The human body is incapable of generating the same forces as a rigid mass, especially for shorter drops and less elastic/dissipative textiles, a rigid mass is a poor predictor. But, like you said, gpe is trivial to calculate, and it might be interesting to compare that to the Joules/meter that a textile can dissipate during failure.
@@BridgetWirth For example, we know that a 1m rope will survive the 700J of energy in a 1m fall. The complication I guess with doing the same exercise with dyneema, a larger portion of that 700J is going into the climber's kidneys and spine.
@@BridgetWirth Energy is a measure for how much of a fall it can hold on its own before it's fully extended (or breaks). A shock absorber that can absorb 6kJ over 1.5m of distance before it is fully extended can hold an 80kg person that fell 6.14m (from start of the fall to the first point where the shock absorber is under tension), assuming there are no other shock absorbing parts in the system.
You already covered a lot but I feel like if people are really worried about shock load they could just do one less wrap when setting up the Purcell Prusik.
Did you clip the end of the daisy or shorten it? If you clipped the end it’s equivalent to testing the fully extended Purcell. A (correctly) shortened daisy seems more useful to test and might absorb better
Love the Purcell Prusik on a loop! I've been using them for over 10 years as my primary anchor system. I use 2 of them as my PAS for sport climbing and 1 when multi-pitch climbing. 6mm accessory cord tied with a double fishermans knot girth hitched to my harness hard points It's so nice to be able to easily get into the most comfortable position at an anchor. Great video, thanks for testing!
I'd be interested if the friction of the Purcell Prusik could be tuned with a lower friction material lining the knot or a sheath. Granted it would either have to melt during the slide as to not slip too much or the sheath would need to have a gradient where the friction would increase the farther the knot slips.
i've heard people say that the cord used for a prusik cord should be -3mm, but shouldn't it be a percentage? seems like a 1mm prusik on a 4mm rope would act differently than an 8mm prusik on an 11mm rope..
Great content Ryan. Regarding the long high line one you used. I found it more practical to use a climbing rope or section of rope tied in with a standard tree climbing system. Weave it through/around the anchor, clove hitch one side to a biner/harness, and leave a tail for a Blake's hitch. Super practical and you can have about as long of a system as you want while being able to wrap it around things like trees and poles if you want. Perhaps even more practical with a split tail or eye n eye. Idk maybe one more thing to play with.
After you video on cow's tails, I was wondering, "OK, but how does a Purcell-Prusik anchor do in similar conditions?" I had not gotten around to asking directly, but here you are, anyway, with a video on the Purcell-Prusik. As if you'd read my mind... Background: I come from a world that is not generally populated with rope-climbing knowledge but nevertheless fall protection is of great interest: namely square-rigged sailing ships. The things we climb are intentionally designed to be climbed and, in general, falls are actually pretty rare. In the old days of wooden ships and iron men, there was no fall protection at all. If you fell, you fell. End of story. But as this world has moved on, over the course of the last 120 years, evolving from commercial shipping into sail training and historical interest, there is a greater emphasis on safety. Fall protection has taken a higher priority due to insurance and the desire of organizations not to damage their volunteers/employees. These organizations have, slowly, evolved various systems to protect (at least, in theory) their sailors. But in many ways, this world is still a long way away from the climbing world. A common way of thinking is that, as long as the gear doesn't break and you stop the fall, life is good. Climb down and have some tea. Not a lot of thought is given to shock loading or what a fall factor 2 can do to a human body if abruptly arrested. You would absolutely shudder if I told you what was being used for fall protection 20 years ago. We've evolved since then, and currently, in my organization, we are using a Purcell-Prusik as a personal anchor (we say "lanyard" because, well, it's nautical...). It's made 10mm dynamic line. I'm told that it was tested and deemed "plenty good enough" if one were to fall on it. And perhaps it may be, but I have always been thankful that I have never found myself putting the theory to the test.
Hi! Maybe for the "not adjustable end" you could try a... Double bowline... I'm not sure how call it. I mean the same knot which is used by Stefano for example. Anyway, thanks for this one, I really enjoyed it
I've been using this setup for multipitch rock climbing with 5m of 6mm cord, but I use a double fisherman's and add a butterfly above for an extended rappel!
I can appreciate the skill, knowledge and consideration of so many factors demonstrated in these tests. The one thing missing, I think, is an explanation of the relevance/meaning for the "average climber". Is one sling construction significantly better/safer than the others? Or are these sling variations just for use in 'advanced' climbing and not relevant for the rest of us? Yes, I did watch the last few minutes of this video. But telling us to go watch other videos and blogs and suggesting (sort of) that we shouldn't use "personal anchor systems" (at all?) because the tests seem to show that they aren't safe doesn't seem like a satisfactory conclusion to a 18 minute 'technical analysis'.
Have you tried this with Robert Chisnall’s Modified Tarbuck Knot? Intended for anchoring rope to a tree or post. Requires at least 3 wraps around the tree before tying the knot.
Is there an official name for the "figure of 8 bfk flemish sort of a knot"? It looks like a safe variation of the flat 8. Also, why the two specific options for the bend. Wouldnt any critically safe bend be ok?
While the double fishermen's knot is incredible for making a loop, we all know that if loaded they can be near impossible to untie. I prefer a reever knot because it's still super strong and easy to tie, but can still come undone if you want it to You may think "if you want to untie it why not do the Flemish"? I have 2 reasons. the versatility of a completely open loop is more useful to me than the Flemish, and a reever uses considerably less rope than a flemish
Is it a try worthy to make the Prusik (witch is by the way named after a Nazi~time for a renaming) only with 2 tourns? It will Slip much quicker but will hold a person?
pre-watch thoughts: the biggest issue i see with using a friction hitch for "shock absorption" is that the shock is just going to lock the hitch. it you want shock absorption, you either need something elastic or something mechanical which will always slide at a specified load, no matter how off-center or angled the applied load is.
We’ve made Purcell prusiks out of 8mm dynamic half/twin rope with the thought that it will provide even lower forces in a fall. I’d be curious how that compares and if there’s anything we’re overlooking making that a bad idea.
"it all depends on how fast you are getting to [high force applied to you]" No, it's not. It seems your measuring equient is just not fast enough (or has too large integration time) for catching those short-time overloads
i made my Prucell out of Edelrid Aramid cord sling. been working amazing for years. since the aramid is a lot stiffer its a lot easier to handle and adjust, but id love to know how it compares to nylon or dyneema that you tested here.
hi, I was wandering... close to4:30min, is there any reason why not to do first the prusik and after the figure 8 knot? isn't it be easier to go through the pursik knot if we have the tail free? thanks for the video, by the way :)
Hey, would You test via-ferrata kits eg. compare fall on dynamic rope vs kit with absorber. More interesting is how to carabiner lay on the steel line anchor, during the fall on vertical route, it makes the carabiner is cross loaded and side way loaded when hit the anchor point and the steel line is pre-tensioned high - I think this is the weakest point.
It would be interesting to attach an accelerometer to the dummies to estimate the deceleration in G's. A smartphone's accelerometer has a sampling rate of 100 to 200 Hz - perhaps enough to get an estimate?
I use the Purcell Prussik as my personal anchor/leash with a 7mm nylon cord but I drop one of the loops on the load side of the prussik knot. This (in theory) will reduce the friction in the prussik knot and maybe reduce the peak loads on your tree drop test.
it would be cool if you got a thermal camera to monitor the friction heat during slow pull tests, if not for actual data then just for the visual aspect
I've broken out of a tree twice and was saved by my rope without my split tail slipping. The bounce in my True Blue made both events comfortable so my opinion is that whether or not your fiction knot slips doesn't matter.
We tie this differently in fire department and I am wondering what the shock absorption would be if tied like so in the following video. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RAyrw-uLcnc.htmlfeature=shared this comes from a rope guru out of Arizona named Reed Thorne. Instead of wrapping the Purcell 3 times you would have 3 towards the anchor and 2 on other side. There is basically 1 less wrap on one side of the prusik. I would love to see that drop tested.
08/02/2023 Hello How. This video was very interesting. I did not know about using this rope knot on a rescue basket. The second point is what if you use one additional loop in the prusikis. I have used this knot but not very often because I do not do tree work. My weight is over 300 lbs when loaded to work. My naked weight is just under 250 lbs. The four loop prusiks are both for climbing and movement in the tree. I do enjoy watching the profession plan for a fall. That tales BALLS Thanks again, DON
So call me crazy, but the only application I've ever considered for the PP is for rope soling (on lead) a bolted route where finding a ground anchor (boulder, tree, good low crack) is not an option. The idea being: climb to the first bolt, clip a PP to it, then clip the end of the rope to the sliding end of the PP (having pre-connected other end of rope to my grigri on my belay loop). Crazy? Indeed. But potential advantages: (1) if you fall shortly above the 1st bolt, the PP should keep the fall force below factor 2 (but seeing the video, I'd keep the PP on 6mm or less to get more slippage and lower forces), and (2) once clipped into the 2nd bolt, the PP would add a little bit of dynamic quality for a fall (not much due to friction thru 'biners, but more is better in this case IMHO) and so that's good. I do loads of rope-solo leading and don't bother with a PP if I have a good ground anchor, as there's plenty of dynamic quality in the system once several meters of rope are out and the first piece has been placed, especially given that I'm not (and no one should) ever taking big whippers while rope soling... So I'd love to see the PP tested in this kind of application...
Recreational tree climber Arborist climber Bushcraft enthusiast I start your videos without enough time to finish them, but I usually look forward to and do come back … I love your videos Thank you for making them!
I've been using the purcell for years, I "feels" better/safer than a daisy chain and is cheaper than anything else. And I've never planned to have a F2 over over, so I guess it's.... good? The only difference is that I never take it our, so instead of doing a girth I just tie the 8 in the loop, so it's an "extra" loop in the loop (but I don't use it as an extra loop).
So what do you guys consider the best for a good fall absorbing personal anchor device? Thinking in a scenario, where we are developing a Highline Permarig space, with space nets, where people can stand, and therefore can take a Fall in Factor 2? And as "normal" weights here, people are around 60kgs - 90 kgs We want to advice of safety and good practices around Highline, and notice new generations to keep playing, rigging and highlining safe
With the dyneema you tested near then end, with it slipping well below 1KN, we shouldn't even expect it to slow you down, only make you accelerate slightly less quickly. That slight drop in the rate of acceleration is completely counteracted though I would suspect from the additional travel distance of the fully extended prussik. Meaning it basically it is worse than nothing and you are taking a hard fall on static protection.
The effect you describe with the maximum force is called jerk or jolt, thats the change of acceleration over time (da/dt). Love your videos, great job!
