por Davi Marski, agosto de 2007
Pois bem.. no livro "Rock Climbing, Mastering Basic Skills", da The Mountaineers Books (mesmos editores do Freedom...) diz que para unir duas cordas (quando vamos fazer rapel com corda dupla, por exemplo) devemos utilizar o nó simples. Aqui no Brasil normalmente o recomendado é utilizar-se nó de pescador duplo para unir duas cordas para o rapel (e novamente, o nó fica muito apertado depois..) , o livro entretanto diz que o melhor nó para isso é (pasme !) um nó simples (ou azelha) com um arremate apenas na corda *oposta* a que será recolhida ! Eu mesmo aprendi a usar o pescador duplo para unir duas cordas para o rapel... mas... hábitos não são para sempre !
Bom... o pessoal da Mountaineers a muito tempo recomenda o nó simples, com apenas a ressalva de utilizar-se cordas de diâmetros semelhantes e é claro, deixar uma boa folga (uns 30 cm) de sobra depois do nó..
Esse é o nó com menor probabilidade de enroscar-se em alguma fenda ou saliência e é o nó que mais facilmente desliza sobre a rocha quando a corda está sendo recolhida !
veja a foto abaixo :
Mas.. para resolver de vez o assunto, copio aqui a matéria do site da Black Diamond, onde eles comparam a resistências de três nós diferentes para unir cordas, e "é claro", acabam por recomendar o uso do nó simples (que eles chamam de "Euro Death Knot"... rsrsrs) :
http://www.blackdiamondequipment.com/en-us/journal/climb/trips/qc-lab-what-is-the-best-rappel-knot
I was climbing in Yosemite last summer and, while at a belay, was talking to a party from Bozeman, Montana. They noticed all the proto gear on my rack and deduced that I was from Black Diamond. My partner and I bailed (typical) and they were watching me like a hawk. I asked what they were looking at, and they said, "We want to see how the QA guy from BD raps.” In particular, they were eyeing my rap knot, since knot choice (Double Fisherman’s, Ring Bend or Euro Death/Overhand) has always been up for such a large amount of debate.
There are advantages and disadvantages to each type of rap knot, but is there one that is superior in strength to the others? I put all three knots (with three different rope diameter scenarios) through a quick-and-dirty series of pull tests and have provided below some basic strength testing data based on my limited testing of the three most common rappel knots. (Note: only two data points per configuration.)
THE OBSERVATIONS
• The Double Fisherman's and Ring Bend had similar strength results
• The Euro Death Knot was the weakest: ~20-30% less than the Double Fisherman's and Ring Bend.
• The Euro Death Knot slipped a bit before failure at ~4000 lbf with the 10.2 and ~2000 lbf with the 8.1 in the system.
THE BOTTOM LINE
The reality is that all three of the methods for joining two ropes for rappelling that I tested were PLENTY strong for the forces seen during a typical rappel (i.e., bodyweight-plus, taking into account some shock loading when bouncing around, jiggering with tangled lines, not smooth rappelling technique, etc).
For what it's worth, when I started climbing I always used the Double Fisherman's, but now I've fully converted to the Euro Death Knot—it's fast to tie, plenty strong, less likely to get hung up when pulling and easy to untie. And finally, no matter what rap knot I tie, I always leave long tails (like at least 12 inches).
Climb safe,
Kolin Powick
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Kolin Powick (KP) is a Mechanical Engineer hailing from Calgary, Canada. He has nearly 20 years of experience in the engineering field and has been Black Diamond's Director of Global Quality since 2002. Kolin oversees the testing of all of Black Diamond's gear from the prototype phase through continual final production random sample testing. If you have a technical question for KP, please email him at Este endereço de e-mail está protegido contra spambots. Você deve habilitar o JavaScript para visualizá-lo. and he will TRY to respond.
Photos
Recent Talk (1)
Em julho de 2009, a Samantha Chu, diretora técnica da FEMESP, publicou um artigo muito didático sobre este assunto :
http://www.femesp.org/seguranca.php?dica=200907
Nesta dica de segurança recomendamos e analisamos alguns nós que podem ser utilizados na união de duas cordas para o rapel.Há diversos nós que podem ser utilizados para se unir duas cordas distintas para o rapel. Cada nó possui suas vantagens e desvantagens e nós diferentes podem ser escolhidos dependendo das circunstâncias em que você se encontra. Todo e qualquer nó que seja executado em uma corda irá fazer com que ela perca parte de sua resistência, sendo o nó o ponto mais fraco da corda e provavelmente o local aonde a corda irá romper caso sofra a ação de forças extremas.
Entre os nós mais comuns e recomendados para a união de duas cordas para o rapel estão o pescador duplo, o azelha e o oito recosturado. O nó oito duplo, feito com as duas pontas de corda na mesma direção (foto 1), é considerado inseguro e não deve ser utilizado para unir duas cordas para o rapel pois sua configuração não distribui a carga pelo nó criando pontos de tensão extrema e o enfraquecendo, podendo até romper.
De acordo com o experiente guia e escalador Americano Craig Luebben em seu livro ‘Nós para Escaladores’ (Knots for Climbers; 2a edição, p. 1) a força de resistência relativa de uma corda seria:
- Sem nó >> 100%
- Oito recosturado >> 70-75%
- Pescador Duplo >> 65-70%
- Azelha >> 60-65%
Oito Recosturado (foto 2): é um nó bastante seguro, especialmente se as pontas forem arrematadas com um pescador simples. Fácil de desatar porém bastante volumoso, podendo entalar em fendas e blocos de pedra quando a corda estiver sendo recuperada.
Pescador Duplo (foto 3): ainda bastante seguro mas fácil de ser executado incorretamente e mais difícil de verificar se feito corretamente. Possui menos volume mas também pode enroscar quando a corda estiver sendo recuperada. Pode ser difícil de desatar uma vez que tenha sido tensionado.
Azelha (foto 4): apesar de ser o menos resistente é ainda extremamente resistente para suportar o peso de um escalador em situações normais (peso do escalador + equipamento + choque resultante de um rapel não-suave). É fácil de executar e pouco volumoso sendo pouco propenso a enroscamento (chamado nó ‘cavalgante’) mas sendo necessário deixar 40-60 cm de chicote (sobra) na ponta da corda; um segundo nó de azelha pode ser executado ao lado do primeiro como arremate.
A técnica mais recomendada, técnica esta aprovada pela UIAA, é a utilização do azelha pela sua praticidade, facilidade de uso e por ser cavalgante, mas todas as técnicas acima mencionadas são seguras.
-
Independentemente da técnica que você irá utilizar lembre-se dos seguintes fatores:
- independente do nó que você irá escolher, saiba executá-lo corretamente;
- deixe no mínimo 30 cm de chicote em cada ponta da corda para caso o nó deslize;
- certifique-se de que o nó está alinhado e os tramos de corda não se sobrepõem criando pontos de pressão;
- tensione o nó puxando cada tramo de corda individualmente antes de utilizá-lo;
- lembre-se de sempre fazer nós limitadores nas pontas da corda que estarão mais próximas ao chão na hora de rapelar.
Escale com segurança!
Samanta Chu
Diretora Técnica
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Comentarios
um bom nó para emenda não seria o 8(nó oito) ?a resposta é "sim" e "não"...
sim pois é um excelente nó para unir duas cordas, e não pois especificamente para o rapel, é um nó volumoso e fácil de "enganchar" em fendas, etc... e pior, se o bolo do nó for forçado contra uma quina (ou mesmo o olhal de um grampo P), ele de forma relativamente fácil pode se desmanchar.... inclusive esse forma de unir os nós é chamada de "european death knot for rapel".... A Black Diamond já fez alguns testes mostrando que mesmo com pequenas forças, por exemplo, 3KN, o nó vai se "desenrolando" sobre sim mesmo e se desmancha...
Outro excelente nó seria o pescador duplo, mas é claro, demora mais tempo e ainda pode ser feito de forma errada (por alguém desavisado).... e também fica volumoso....
Enfim... a recomendação nem é minha... é do pessoal do Mountaineers, American Alpine Club, Petzl, Black Diamond...
Um abs !
davi marski
9 Jul 2009, 3:33PM
have you tested the barrel knot? how does it stack up?
with the barrel knot and the others, did you ever take into consideration the effect a back-up knot has on preventing slippage? for instance, i often back-up a barrel knot with a euro death knot.
10 Jul 2009, 4:05PM
This is the first time I've ever heard of a Barrel Knot, or Blood Knot for use in climbing applications. Usually this is for fishing line and very small diameter cord. I have used this to tie tippet to leader for dry fly fishing applications with very small (7X) tippet. We can sure give it a shot when we have time and see how it stacks up against more typical knots for climbing/rappelling applications. Stay tuned for a future post on this test. There are some knots that benefit from back-up knots. The EDK benefits from another back-up EDK (overhand) right behind the first knot to prevent the "un-rolling" of the knot that occurs under high loads. In most cases, however, the back-up is merely for management of the tails and redundancy at any load ranges that are foreseeable in most climbing applications. Tails slipping through the knot are never the failure mode for a properly tied knot with long tails. In all cases we've tested, the knots fail rope @ knot where the rope cinches down on itself. With proper length tails I don't foresee a tail slipping through the knot making a back-up overwhelmingly necessary from a strength standpoint, but rather for the redundancy factor. Cheers
12 Jul 2009, 3:19PM
First off I'd like to say that it's great to see some scientific testing being brought to the debate about the strength of climbing knots. However, with only two data points it's difficult to say that there is any difference between any of these knots. And this is made even more difficult for the reader as there is no mention of the variability in the results. It would be nice to see reports like this with a statistical work-up of the confidence in the results. If this became the norm, climbers would undoubtably become used to interpretting these results. Besides, the majority of climbers I know actually have a technical background and would expect this type of data in a report they read outside of climbing.
Again thank you for the testing and for posting.
13 Jul 2009, 1:01PM
All of us in the QC Lab would love to develop this test and other "curiosity tests" further, but as I wrote in the original post these tests are done "quick and dirty" and mostly to satisfy my own curiosity. I agree that climbers would benefit from the additional understanding of the results which come from larger sample groups. Lack of time, not interest is the main reason we can't. We use statistically significant sampling in all of the testing for Raw Material, Work-In-Process and Batch Testing of our gear and we statistically analyze and report results with regard to mean, standard deviation, and 3 sigma for all our production testing. What all that means is that in most cases, we just can’t devote all the time we would like to these other interesting experiments. My goal with these QC Lab posts is to get some basic ideas of the answers to common climbing questions, usually focusing on the breadth of possibilities without drilling to great depth on any particular one. Thanks for your interest and understanding!
13 Jul 2009, 5:31PM
Thanks for the tests - always good to see some quantitative data to back things up. Some other things to think about as well:
1.) Ease of getting your knot undone once you've done the deed.
2.) How many flakes/slots/etc.... will the knot get hung up on on retrieval? Some do better than others.
Maybe you can come up with some quick and easy tests for these issues. Thanks again. Cheers!
14 Jul 2009, 11:17AM
Good to see some common sense overcoming cheese-headed paranoia. Why it's nicknamed the "Euro Death" knot is anyone's guess. Same with the "Yosemite Death Triangle" when attaching two perfectly good bolts - it's quick and saves some sling. The overhand knot has been the worldwide standard for decades for tying rappel knots. The "best" is definitely not equal to the "strongest" in climbing applications. Scrape off the cheese and do what works.
Just don't use the overhand for tying two ropes together for a two-rope lower where the knot will run over rock or you might wear through the sheath or worse...
23 Jul 2009, 12:05AM
I like these QC Lab posts -- thank you!
Ring bend = water knot, right? I thought that wasn't a good knot for a rappel -- insecure in rope, only good for webbing. I thought the 3 common choices were double fishermans, EDK, or square knot with backups. Maybe I'm remembering incorrectly. I switched from double fishermans to EDK and never looked back.
3 Aug 2009, 4:19PM
I still think the best not for rappelling is the Triple T-Fisherman's Knot. It is easy to know and is always in a good position if you pull down the rope.
Take a look at http://www.gudelius.de/spst.htm
Maybe you want to make some tests again.
7 Aug 2009, 9:50AM
Nice Q&D, Kolin. I'm surprised you show (and more surprised you USE) a "single" EDK. Tie a friggin' backup knot on there, and it blocks the knot from rolling out.
If the ropes are similar in size and character, then the backup knot is not required, but if the ropes are dissimilar (or not nice, soft climbing ropes), then the backup knot is pretty much required for security and peace of mind.
Keep up the good work.
Tom
9 Sep 2009, 12:39AM
[WARNING: rockclimbers can post a gazillion pages on musings about equalizing anchors, but the sight of more than 5 lines about knots makes them queasy. And more than just climbers; the stupidest things can be said -- and printed/echoed/re-printed -- for decades and even centuries about knots.]
On the testing reported here:
0) Good to see it! But, OTOH, the relevance of knot STRENGTH to abseiling is pathetically small; the testing that should be done concerns security and ease of moving over rough surfaces, of any vulnerability to being untied in hauling. NEVER is strength an abseil issue; unfortunately for that, it is an easily generated datum (at least if superficially regarded).
1) How were the ropes/knots configured? E.g., for the two photos center & right, it COULD be the case that the knot joined a single rope into a sling and was pulled as such between pins; this would, btw, tend to exagerate the strength of the knot, as material fed out of it during compression would leave the unknotted side to assume more load/tension -- i.e., it really could be the case of adding 100% to and dividing by 2 ! (Which I surmise is how there are some reports of Grapevines or Dbl.Grapevines (Trip.Fish) being "stronger than the rope".)
But for the mixed-ropes cases, clearly one cannot just make a simple sling.
So, how were the test specimens configured?
2) People don't usually realize this (and books ignore it), but there are FOUR possible loadings of that "Ring Bend" structure, two of which fall under that name: the one shown here, where the loaded strands reach to the far sides of the knot; and the reverse where the loaded strands turn interior to the far ends -- here, if the ends were loaded.
The other two loadings make the knot "offset", and note the difference between the loading of the upper two strands vs. the lower two strands **in this case shown of diff.-diameter ropes**: in the former case, the thinner rope makes the choke at the entry point; in the latter case the thicker rope (blue, here) makes the choke. It should be easier for loading to pry the thicker rope (possibly more elastic, in dynamic + haul-line pairing?) around the thinner than vice versa.
3) The orientation of the 8mm+10mm ropes in the case of the Offset Ring Bend are not revealed -- no photo, no report wording. I can only guess that this (important!) aspect wasn't considered. It should be.
It should also be noted that upon tying the ORB/EDK/OOB and setting it lightly, one can rotate the knot over a range of about 180deg in plane perpendicular to the offset axis of the knot (i.e., stretch ropes so knotted across a desk/table-top and the knot can be *dialed* a half rotation from where one rope will be entering and making a backwards circle to where that same rope will be making a forwards arc to the opposite rope's backwards loop. The difference can be noticed in which direction the ends point.
In the image shown for the EDK, the position is about the middle of this 180deg range: grasp that knot by the left hand and turn it knuckles away, and the ends will come towards perpendicular w/axis of tension, towards the viewer; and one could rotate it 90deg in the opp. direction, with ends pointing away from viewer. I've not played around with the different orientations enough to know which might be more vulnerable to "rolling". I'm unaware of anyone who has remarked at this orientation variance -- but that doesn't make it unreal.
Yes, ages of practical usage suggest that likely all orientations have seen duty and survived.
(Regarding the left photo, of the Ring Bend, as given offset loading by pulling the 8mm end to the left --as it points-- and the blue 10mm one rightwards, you can clearly see the 8mm making a "forward arc" in the knot, and the blue rope making a backward loop.)
-------- comments on comments
Re "Why it's nicknamed the 'Euro Death' knot is anyone's guess"
Because that must've been the reaction to those Americans who first encountered it in use by Europeans, and felt --naturally, IMO-- that it was a most ungainly, dubiuos knot (a Ring Bend gone bad). And one still gets this sentiment, hence the efforts to remove doubt by some securing mechanism, such as a simple Overhand stopper.
As for " Same with the 'Yosemite Death Triangle', that comes in part from a simplistic view of mechanical advantage (seeing "2:1" pulley effects where in actuality the effects are well less). This is a structure I would like to see some calibrated testing on, just to see how much force amplification DOES occur IN THE USUAL SITUATIONS (tape or cordage around bolt rings). I think that such testing might reduce the alarm about it, but that's just my surmise.
Re the Blood knot: Why ... ? You have the Grapevine for ropes. And how could a Blood knot need any backup -- getting it UNtied would be the challenge.
UNLESS ... : there are many depictions of this knot carelessly showing it formed by what Stanley Barnes (1951) called "the outcoil" method -- the ropes respectively coil around the other going away from the center, and then the the ends are brought back in a big arc to dive through the center and be nipped. One well-known knots site, Grog's Animated Knots, has this mistaken imagery. In nylon fishline, this form during setting will transform into the "incoil" form -- ropes running past each other to the ends of the knot body and then wrapping back until meeting at the center and being tucked. Damn secure in the incoil form, but if tied in climbing rope by the outcoil way, YMMV: the transformation might occur, or might occur partially occur; where it is resisted, it is so by the friction-gripping mechanics of e.g. Blake's hitch or French Prusik and this impedes the setting/tightening of the knot. Why deal w/this?
The "Triple-T Fisherman's" -- Jost's (& Prohaska's) alternating Offset Fisherman's knot with Overhand tie-off (or guard, depending on perspective: as putting this *extra* one in front or at end amounts to similar results) is hardly simpler or even as simple as the Offset Ring Bend, and if anything it's a bit less stable in holding a good offset form. (Here is where some will want to take ONE testing of the knot as PROOF ... !) Tying off the ORB as I suggest below in reply to Tom can be seen as just one of the several ways that three Overhand knots in the two ropes can be arranged (that tie-off can be cast to come before the ORB).
To those wanting "scientific" over-analyzed statistical number crunching, you need to first consider how many factors can be at work here (lots of "unknown unknowns", in Rummey speak); banging the heck out of a few simple tests is of scant value, esp. when considering how much the testing might model actual usage (slow-pull vs. dynamic, or one-time vs. multiple loadings, say). We could report the data to 20 decimal points, for show ... .
NTJones wrote: "I'm surprised you show (and ... USE) a "single" EDK. Tie a ... backup ... and it blocks the knot from rolling out."
I'm surprised Tom wrote this, as he once showed (and presumably used) the notoriious Offset Fig.8 bend (but was intimately aware of the Mt.Zion tragedy) ! touche', Tom ?!
-- and sans backup on that.
As for "rolling out", has that ever happened, IN PRACTICE (vs. at absurdly high loads from a test device)?! In any case, Tom, I'd in mind suggesting that your Canyoneering site present the slightly trimmer (think "obesity is bad") single stoppered knot. There is some good reason for this: you show gold & patterned ropes joined in the OOB; the patterned rope's end will be what is pried out by loading, so IT is the end that should be tied off with an Overhand around the gold end -- no need to bulk up the knot further (but for user simplicity I'll admit that repeating the tying done initially (making the OOB (ORB) is simple).
It matters another way: in joining different-diameter ropes, you want the thinner rope to be in the position of the patterned one AND stoppered.
www.canyoneeringusa.com/cusapress/knots/index.php
Re "If the ropes are similar in size and character, then the backup knot is not required,""
Not so fast. The factors that make the Offset Ring Bend (and some other such offset knots) vulnerable to failure (coming untied) are stiffness & elasticity -- the former frustrates getting the knot snugly set, the latter provides for greater deformation on loading -- ; differences in diameter at least among the likely ropes employed by rockclimbers / cavers / canyoneers should make little difference. Also, a rough / frictive (think old & gnarly) rope can give more grip to prying parts than a slick one, and be resistant to setting tight ; then, slickness has some of its own risks.
------- re terminology:
"Offset", that's what the EDK is an example of: the knot is offset from the line of tension; and here we can see it as an Offset Ring Bend -- the commonly known knot loaded in an offset way. The site referred to for that mis-named "Triple T-Fisherman's" shows e.g. an Offset Grapevine, something Franz Bachmann thought worth trying.