Rebelay failure on skinny static rope (hownot2)

M

mikem

Well-known member
I saw that and it doesn't seem to be a thing UK caving does, and isn't on our types of ropes. I'm also not quite sure what they're replicating because the weight drop seems a lot higher than it would be if a rebelay failed? Just found it not very clear.

On the other hand always worth considering how frail our set-up can be - I know I'm guilty sometimes of rigging from p-bolts without too much concern of their failure.
 
I agree with your comment there. The drop test in the wood doesn't seem to match the set up on the wall at the start of the video so may be misleading. The actual test looks to be a larger drop.

It's a lightweight uncertified rope. Fair enough to warn against them.

The impact figure is under 6kn. That's worth considering.

Knots, as long at they are not over tight, do reduce impact forces.

Single anchor rebelays are used especially for lightweight pushing style trips.

In real rigging situations it is always worth considering what is the risk of failure? What is the likelihood that the anchor will fail? If it does fail what are the consequences of failure or the severity of failure. That is the question and I'm not sure how much this demo really helps.
 
I'd say it's a reasonable drop distance, to be compared with (from memory) the single bolt Y hang at the top of Sidewinder in Marble Steps which from memory is less than the traditional 5 m below the last Y hang? (although I could be mis-remembering, but there are definitely other examples out there). It looks like maybe 2 or 3 m in the video?

It's also not even remotely surprising to me as that's an 8.5mm polyester hyperstatic cord that would not be legal to sell in the EU/UK as rope as it is not stretchy enough (it is *not* a semi-static 'rope'). It's got 2% stretch at 136kg, so I guess it's stretchier than something like dyneema but less stretchy than an 11mm semi-static rope and a lot less stretchy than the 7mm or 8mm 'ropes' we might use in the UK (which are of course also not ropes, but are clearly just semi-static ropes in 'skinny' form) which are more like 4% to 5% stretch at 80kg (HowNot2 give a static elongation for Beal Spelenium 8mm of 6.5%!).

I think the best line in the video is 'a normal butterfly is better; you die either way!'. Taking a dynamic fall onto hyperstatic cord is Doing It Wrong and a few knots won't save you...

That rope breaks (according to HowNot2's technical specs) at 19.3 kN, but with figure 8 knots in will break at only 11.25 kN which is worse (as a fraction) than you normally get with nylon ropes I think but seems to be common for more static cords (a larger fraction of weakening due to knots). Obviously in the video it's breaking at 4/5 kN which is much less than the rated strength but shouldn't really be a surprise - falling on ascenders is bad.

I'd suggest that in most cases on expedition these days you can just put a second bolt in a rebelay if it's close to the one above... if your bolts are so expensive that you are trying to save money on bolting, maybe you'd _actually_ be safer with a bunch of cheaper bolts that you weren't afraid to use? I appreciate you can't always carry that much metalwork, but in that case I'd just try and avoid a single bolt rebelay too close to the one above.

Most of all - don't use single bolt rebelays with hyperstatic cords!
 
No argument from me.

Another point worth considering is that cavers are not lumps of cold steel. A caver in a harness will have less impact and the device would show a lower force. Cavers, being generally fit enough to get down and out of a cave, would also likely mitigate the severity of any fall compared to a lump of steel. Unfortunately it is not wise to use real cavers for these tests although I understand some have volunteered in the past.

I totally agree with the comment about not using this type of rope wherever possible. It's a similar argument to not using tape slings for cowstails. However, I would refer to my comment about assessing the risk. One well placed and solid rebelay anchor is far better than two dodgy ones for example. Two anchors in the same dodgy rock do have the potential for a common mode of failure. The likelihood of failure of an approved IC or P type hanger in the Dales, for instance, would be extremely rare, old type spits less rare of course.

I appreciate most on this forum know all this stuff about vertical work but it is good to air some knowledge when these sort of videos appear to put the risk in context. Cheers
 
Look at 53 seconds in their video, the load is onto a hand jammer (toothed ascender) and that's why they get failures.

Although they are doing some weird stuff with weird ropes. It's a sobering reminder that falls onto toothed devices are bad business and a rebelay failure while someone is ascending could cause that. Would need to be a perfect storm of weird bad conditions to replicate what they were trying to demonstrate
 
I would say americans seem to rig without any considerations to anchors, tending to use 11mm single hang, and rope protectors on bad rub points. they also dont seem to rig to avoid water. also seemingly dont rig tight if using reblays as we tend to in the UK and europe.
 
mikem said:
Who needs proper gear anyway!
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143K views · 816 reactions | Can you make a climbing sling with fiberglass reinforced tape? We did human testing with @climbingtaiwan Don’t do dumb sh*t! Just follow us if we made you laugh. Also, get your gear at https://hownot2.com/ | How NOT 2

Can you make a climbing sling with fiberglass reinforced tape? We did human testing with @climbingtaiwan Don’t do dumb sh*t! Just follow us if we made you laugh. Also, get your gear at...
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Click to expand...
That might be a tongue in cheek video, but I've read posts before about ermm.. "creative equipment use" from some of the more senior members here, mentioning "borrowing" their mum's washing line to go and explore something when they were kids 🤣
 
Well, I find that hard to believe. I was never much of a climber but I dabbled in it when I was a kid in the sixties. We had a 'proper' climbing rope (i.e. three-strand hawser-laid nylon); I can't remember how we paid for it, but I guess we must have put together our pocket money or birthday -present money or such-like.
 
mikem said:
Most adventurous climbers up to the 1980s started on washing lines (not rotary back then!)
Click to expand...
Rubbish. When I started climbing in the late 1960’s I used a hawser laid nylon rope, by the early 1970’s I had kernmantle ropes (bright orange as I recall).
 
.
mikem said:
Yes, it was a social commentary joke, apparently started by Joe Brown... ...
Click to expand...
But was it always a joke??

Not sure how to link a different thread.. but the 8th post on this page https://ukcaving.com/board/index.php?threads/huge-sinkhole-emerges-in-bexleyheath.29618/
includes

"...I went down a few of the ones near Coldblow and Stankey Wood (which we always called Sankey Wood) when I was a kid. Even in the late 50s/early 60s most were blocked. Usually it was ones with cut footholds - all we had to help was a clothes line..."

And I'm sure I've read other posts on this site discussing using washing lines. People were made of sterner stuff back then


.
 
Yes, it certainly happened (just not as often as legend suggests & more for handlines than lead climbing) - clothes lines were also tougher!
 
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