UKC

Nice vid with some drop tests regarding sling use for lanyards.

https://youtu.be/DpWKrghSLao?list=PL9355CE73250ACA55

When they say 'tying knots in slings reduces their strength', they don't make any distinction between knots to join ends (not recommended) and tying knots to isolate. In fact straight after the knotted sling drop test, there's a section with a guy tying an isolation loop in a sling.

Tying isolation loops in slings is pretty normal, I assume there is still a reduction in strength, but a very different scenario to joining ends. Anyone care to comment?

J2V

In reply to Jonny2vests:

Ye're back.

Mick

In reply to Jonny2vests:
I assume a drop test will break any static item such as a sling, caribiner, nut or cam etc.

Which explains why you use them as designed with a dynamic rope to connect yourself to the anchor or runner in the rock face.

In reply to Jonny2vests:

You reminded me of some very similar tests done in 2006:

http://www.bethandevans.com/pdf/lanyard_tests_v6.pdf

Conclusion
Cow's Tails currently on the market that are entirely manufactured, whether they be single or double, symmetrical or non-symmetrical, are not appropriate for either caving or work on ropes. In particular, Cow's Tails made from sewn tapes, in widespread use by cavers and rope workers, can pose a real risk. The tests have, in effect, shown that a Fall Factor 1 shock load could exceed 15 kN (test 6) when the recognised maximum for work equipment according to the European Standards is set at 6 kN.

However, it is possible to use manufactured goods by linking them to the harness with a knot to specifically perform a shock absorbing role and thereby serving to keep the shock load for a Fall Factor 1 fall within acceptable bounds. Different manufacturers offer lengths of dynamic rope with pre sewn ends. With a 150cm Cow’s Tail, it is therefore quite easy to make a pair of non-symmetrical Cow's Tail, which is ideal for both caving and rope work. It can be joined directly to the harness tie-in point with a Figure of Eight Knot, an Overhand Knot or a Clove Hitch.

From the point of view of shock absorption, Cow's Tails made from dynamic rope and knots at both ends achieve the best results. The effect of the diameter and of the weave of the rope on this shock load is not significant. Furthermore, the results are similar for knots that are well tied and knots that are badly tied, that is when the ropes cross over each other, and also whether they have been pre-tightened or not. This method also allows the lengths of the Cow's Tails to be adapted to the size of the user. Figures of Eight Knots, Overhand Knots or Clove Hitches can be used at the harness end. At the other end, a Figure of Eight Knot or an Overhand Knot and also a Barrel Knot can be connected to the karabiner. The Barrel Knot is being increasingly used by cavers and has the advantage of holding the karabiner in place. It is, in effect, completely secure and furthermore is the knot that provides the best results in both the static and dynamic tests.

In reply to SenzuBean:

Thanks for that, really useful.

Also worth looking up " Purcell Prussik ", developed for this area of use.

In reply to Mick Ward:



More like posting from a galaxy far far away.

In reply to Jonny2vests:


That link doesn't work for me but this one does:
https://www.youtube.com/watch?v=DpWKrghSLao&feature=youtu.be

In reply to Jonny2vests:

Well, I hope you're OK out there. All these are anyway are flickering shadows on the wall, whispered voices on the ether. But it's good to have yours' again.

Mick

In reply to Jonny2vests:
Best to get info from IRATA as this is more covered in their methods of work.

Most slings are either to EN566 (mountaineering slings) or to EN765B. (general anchor devices). The mountaineering standard is an increasing load test & the other standard is a fixed weight test for a set time & a slow pull I think. (I used to know it off by heart). There is also EN354

Most mountaineering slings have 22kN breaking strain marked on them & in industry it is well known that if you sling (for a PPE anchor point) a horizontal beam & pass one end loop through the other to "choke it" the strength is now reduced to 16KN even if the loop is correctly placed. Place the loop wrong & it reduces further to 8kn.

So tying knots in a sling even a simple overhand to create a smaller loop will reduce the overall strength slightly if tied correctly.

In reply to Snowdave:
Yeah, thanks for that. My understanding has always been that any bend in any type of webbing or rope reduces its strength when compared to an unbent section. Fibres are loaded unevenly, the sharper the bend, the worse the effect?

But considering the lengths we are sold stitched dyneema slings, is there not an assumption that knots will be used for anchor isolation and that knots are uncontroversial as long as you understand the shock loading pitfalls. These videos of dyneema drop tests provide useful info, but they never seem to add a rope in the system for comparison, static tests seem unrealistic for most climbing scenarios.

Am I right in saying that a knot used to join dyneema ends is much worse because of low friction properties causing ends to slip under load? Or did I pull that out of my arse?

Mick Ward, appreciate your words, thank you for the welcome back, you never quite know what kind of response you're going to get on UKC. I see the place has had a paint job, Paul Phillips handy work no doubt.

In reply to Jonny2vests:

I think the upshot Jon, is that while dynamic lanyards are 'safer', whatever lanyard you use, don't climb above the anchor point. And if you must, be aware or the consequent risks.

I wonder how many real world incidents have seen such failures? The drop tests are alarming, but I can't think of ever being in a scenario (in 48 years) where I could have replicated such an impact force.

Steve

In reply to SteveSBlake:


Yes


The only ones I recall involved slipping off at a multi pitch abseil station.
I bet there was a lot in the early days of via ferrata.
I once managed to clip the rope loop on a Whillans harness with a quickdrawer, dropping off pumped I was (very)shocked at the jolt of 200mm factor 1 fall.

In reply to Rick Graham:

But you are clearly (and thankfully) still with us!

I should have added, 'Keep it tight or use the right length'.

The drop tests we see always use a lump of iron, rather than an 11 stone bag of sand (or something suitable) tethered somehow into a harness. Your squidgyness is what may
have saved you.....

Steve

In reply to SteveSBlake:


Thanks for your concern, compassion and empathy




It was just a winding and fortunately at an age before bad backs. But as you say, if you took out the short length of rope, the knot, friction on the harness loops, my squidgy waist and a longer fall, it is easy to see how the shock load gets critical.

In reply to Jonny2vests:

So you would agree that knotting dyneema slings is uncontroversial? My north american friends are all a panic but they don't distinguish between knots to join ends and knots in slings for isolation.

In reply to SteveSBlake:

That last was meant for Steve Blake.

In reply to Jonny2vests:
Like much of what we do, it's a compromise Jon, less than perfect (That being a dedicated dynamic lanyard) but acceptable to most if you're aware of the dangers.

I've used it in the past, and will in the future. Meanwhile I'm exploring the utility of having a length of 8mm dynamic permanently attached to my harness, then with doubles or twins you get an instant 3 point equalisation and with a single, two.

It can also be rigged as shown in the vid for abseils.

Steve

In reply to Jonny2vests:
I'm quite happy to use a static sling for climbing, but would never do it for caving. Caving I use 9mm dynamic rope (you need two clip-in points for caving). The difference is that when I climb, I use the sling to secure myself statically - I am not moving around, I am just sat on my sling at a belay. I also never use longer than a 60cm sling so the fall will not be catastrophic anyway. If I do a silly thing and climb up and fall off, I may die horribly still though :P

Caving you are moving around, moving along traverse lines for example (and some are a bit sloping so you could slide down them). If you are moving your chance of slipping and falling into a hole is significantly increased, hence the chance of generating a high fall factor is greatly increased. You also can't maintain a tight rope in the same way you can at a climbing belay.

Incidentally most cavers use snapgates on their cowstails; I can see why (clipping into and out of traverse lines) and they are never attached by a single point (except a descender) but I still don't like it :P I use twist (not triple-action) locks for mine.

PPS I assume all knots (including isolation knots) weaken the sling by _roughly_ a half or so; I'm not sure distinguishing between different kinds of knots is really worth thinking about.

In reply to andrewmcleod:

Interesting contrast, cheers.

Yeah, about half strength. But with equalisation, you get multiple strands, so forces per anchor are reduced.

In reply to Jonny2vests:
(insert controversy) Equalization is a myth (discuss) :P

More seriously I think reducing extension is important, but the range in say a two-piece anchor where the anchor holds rather than fails because of equalization because the pieces were only strong enough to hold half the weight is so contrived as to probably never happen EVEN if the anchors are perfectly equalized, which they never are (even with something like the sliding X which is a disaster for extension anyway).

In order for equalization to save you for say an 6kN load, both anchor points (ignoring the triangle thing) need to hold between 3 and 6 kN. If equalization is (as it always is) imperfect, and one leg is taking twice the load of the other (not unreasonable I suspect?) then you need one anchor to be able to hold between 4.5 and 6 kN while the other holds between 1.5 and 6 kN. That's also assuming the load comes onto the strong anchor first, otherwise the whole anchor fails. If either anchor holds more than 6kN then the equalization is not important (the strong anchor saves the day singlehandedly). It all just sounds awfully contrived to me...

I would never put a piece in a belay that I didn't think could potentially hold the entire weight of a fall. Note carefully that's 'could' rather than 'definitely will'

In reply to Jonny2vests:

Did anyone watch the other videos, particularly the one about how to descend multi-pitch? How many errors can you spot in that video? There's at least 5 things I would do differently and they're supposed to be the experts.
youtube.com/watch?v=l_5z6A5Z1h0&

In reply to Jonny2vests:

Equalisation is not quite detailed as most people think this clipping a big sling between the anchors & placing a krab in the middle open loop of the sling & pulling on it until the pull on both anchors is ok..

There are several factors;- the main one being the angle between the anchors, this determines how much load is placed on each anchor, or how much is dumped on one. The closer together the more the force is "straight pulled" & shared, so a 60deg angle between the anchors approx. 58% of the total load goes to each one, a 120deg angle & 100% total load goes to each anchor.

And yes you read that correctly 58% + 58% = 116% you have created more load than you actually have because you positioned the anchors to far apart, so each anchor is acting more like a single point & the load is not shared 50% 50%.

The anchors can be at different heights & can be joined in different ways, BUT the most important is that the angles between the anchors when viewed from the single point which the load is attached to. (I am not considering good & bad placements in this scenario).

I would be more worried about knotting the middle of a sling & clipping against the knot & them being above said knot as high fall factor ratio situation, which is why etriers & the like people sometimes mis-use. I know some manufactures have created high strength versions with each pocket being bartacked with stronger multiple tacks, but you still have the fact those will rip at a certain load until you end up with a full length open sling, but your krab still retained. In the case of knotted slings what happens is that the knot can break the "loop" of the sling resulting in your krab falling out!

In reply to andrewmcleod:

Given everything is always a compromise of sorts........ Equalization isn't doomed to imperfection; while with a single rope and equalette (of some sort) it may be, that's not the case with doubles and twins. Add a third 'tether' and you can deal with most real world equalisation scenarios you're likely to encounter.

I can never figure out why it's become so complicated!

Steve

In reply to SteveSBlake:



I do agree, some of the way I do things at belays etc will vary depending on leader belay, or bringing up the second or abbing off, & might be deemed "not best practice". I prefer to K.I.S.S. (keep it simple stupid) as this not only reduces TED (time exposed to danger) when on a climb, it also reduces the chance of bad set-ups which can cause more problems with en-tanglement & load forces.

I have studied loads & forces & used to sell & advise on rope access & climbing gear, & the main point which I feel people forget is that gear development moves on & you need to understand each piece in your kit & what it's own limitations are. I have had people tell me "you can't use that piece of gear that way", so state back to them, it is designed to take Xkn load to an end to end pull, the current situation is putting less loading than that in the same direction, so it can take it. All because they were not taught a certain way or because it is not the standard rule book.

Thankfully in IRATA they do state that you can use any piece of gear in any situation, so long as you can prove that no other currently available piece can do the same job! So this is why certain non EN rope was used for making tree surgeons prusik loops as it was a specific make up of rope & totally different to single rope & EN cord & it's performance was way beyond that of the EN stuff, so it was used.

Understand forces & loading & the limits of each item then the possibilities of better gear handling is increased!

In reply to Snowdave:

I think the drop test videos we see, such as the one in the OP and which have also been produced by BD, and DMM are useful reminders that equipment is far from unbreakable. But they are (to me ) worst case scenarios, when what we actually do in the real world is try for the best possible compromise.

I guess you could never say that someone couldn't replicate these impact forces, but using common sense I've managed to avoid it for nearly fifty years.

You're right that the variety of gear with their attendant strengths and weaknesses is ever growing though. All the more reason for simplicity.

Regards,

Steve

In reply to SteveSBlake:

Danger! you used two words there which are being erased from the English language....hehe


Yep!!

In reply to Phil Payne:

holy cow - f08 to join !

not sure how many i spotted a few others but none so worrying as that

In reply to Phil Payne:


Things that will kill you (in approximate order)
Not tying knots in the end of the rope
Not testing the abseil system before unclipping
Fig 8 to join ropes (the 'instant death' knot)
Taking hand off the brake rope without tying off the plate (i.e. completely relying on the prussik to save you, which initially is untested)

Things that won't kill you (but I wouldn't do)
Larks-footing to the tie-in loops rather the belay loop (not such an issue, particularly since at least one of them is using a sewn rope lanyard rather than a sling).

In fairness, things which will kill you which won't kill them
Anchor failure (replace dodgy tat, test pegs, backup). Probably much more important than joining with a (good) Fig 8 or trusting a prussik...

In reply to Jonny2vests:

I have nothing productive to add, but just wanted to say that the guy in the video (the one this thread is about) is awesome. My wife used to babysit for them when she was younger and my daughter was in the same class as his youngest. Turned up to pick my daughter up from a birthday party and found him throwing kids off the balcony on a zip line that he had set up going into the woods below. He also gave up a day of his time and took the whole school out climbing at les gaillands, whuch involved another zip line across the little lake, starting from the window of the old ruin, for those of you that know Cham.

In reply to all:

I've been using dyneema slings at top belays for years, in situations where using the rope is less convenient; I'm aware of the limitations (particularly with knotted slings) and I always try not to unload the anchors (normally possible, but not always).

However, I recently bought myself a couple of Beal Dynaclips (pre-stitched dynamic rope lanyards), which I think are great. I have a 50cm one (a good length for sport climb lower-offs), and a 75cm one too.

In reply to Jonny2vests:
many moons ago I did testing of various equipment as part of bmc technical committee and others using equipment at Lyon equipment's old Dent place. I came to the conclusion that if you can generate enough force in a normal climbing or falling while climbing to break even a knotted sling, then there are many other things that will fail first, including blowing your hips to smithereens.
Rope for short lanyards or Purcell prussiks is just common sense.

In reply to lithos:

What are people's objections to using a fig8 to join abseil ropes, and what knot would you use instead? Thanks Neil

In reply to nb:

it can roll off the end. Use an overhand instead.

This has been done over and over on here (just search for abseil knot)
and there are some videos as well.

also see http://www.needlesports.com/content/abseil-knots.aspx

In reply to lithos:

Interesting, however this goes against recent tests by the French mountain rescue which showed that the fig 8 would roll once and then block whereas the overhand knot could roll multiple times. The fig8 is also ultimately stronger although this is unlikely to be an issue on the vast majority of abseils (maybe the possibility of getting hit by a wet snow slide while abseiling might make this worth taking into consideration). The fig 8 is also easier to untie after multiple abseils. In the vast majority of cases both the fig8 and the overhand will do the job just fine as long as they are tied with sufficiently long tails (although not long enough to inadvertently abseil off!) and are tightened by hand before loading.

Of more concern are the choice of knots for tying dyneema cord. The slippiness of dyneema makes the knots fail at startlingly low loads. To make a loop of dyneema cord (eg for a prussik) it is recommended to use a TRIPLE fisherman's!!

Concerning the technique of tying knots in the end of abseil topes to stop yourself abseiling off the ends, this is obviously the safer option on relatively short descents with little objective danger. However, as anyone who regularly makes multiple abseil descents in the Alps knows, it's just not practical to pull the ends of the ropes up after each abseil, tie a knot in them, then untie it again before it gets pulled through. Also the knot can easily become jammed and further complicate the descent, or it can be forgotten about and block the abseil rope. Most alpinists will simply try to remain focused on the ends of the ropes while abseiling and then tie a knot in them if they see they are getting close.

Everything in Alpine climbing is a compromise. The most important thing is to avoid formularized solutions and know why you're using any given technique.

In reply to nb:

you got the reference for that french mr test be interested to read it.

not wanting to open this up again, a web search has plenty of discussion & tests
(eg http://user.xmission.com/~tmoyer/testing/EDK.html ) with plenty to think about.

In reply to lithos:

Don't have a reference for the original tests but they were replicated by ENSA youtube.com/watch?v=N-jE-Da4P1U& . The overhand/fig8 tests start at 3.30. This video is only in French for the moment but should be released in English in the near future.