Terrifying bit of ropework

[peds]

 

This popped up on my feed and it made we wince and grit my teeth to imagine the catastrophes it could cause. A non-redundant, rope-on-rope, temporarily-self-equalising-to-destruction anchor?

 

47 K vues · 478 réactions | Incredible rope skill. #tyingropeknots...

WWW.FACEBOOK.COM

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Incredible rope skill. #tyingropeknots #zeppelinknot #siberianhitch #knottying...

 

The version on Facebook had 47k views when I first saw it. Scary.

Edited July 17 by peds

[Will C]

If it had of been tied with a ring in the centre it would have been fine to climb on in principle but he ain’t tieing my knots

[peds]

Yep, put a ring or a biner on that sliding butterfly instead of doing rope-on-rope, and it's a fairly clever way to join two marginal anchors together and split the load equally.

 

But it would be interesting to test to destruction the inner tip of the bight after the load has shifted position a few times... how many swipes do you get at different weights?

[Will C]

More than you think based on seeing some right cluster fcuks with rigging and climbing lines crossed over the years

[Mike Hill]

That would be fine.

 

If you fell hard enough onto that setup to find a weak point,the fall would be the least of your worries.

 

 

[Will C]

6 minutes ago, Mike Hill said:

That would be fine.

 

If you fell hard enough onto that setup to find a weak point,the fall would be the least of your worries.

 

 

I don’t worry about the fall it’s the sudden stop at the end I don’t like the sound of - quote Fed dibnah ( I may have miss quoted but the  meaning is there! ) 

[Dan Maynard]

Is it equalising though? If you neglect friction (say put a pulley on the top right and a riding pulley on the midpoint) then there are two ropes top right but only one on the left.

[peds]

Erm... I'm happy to be corrected here... but the number of ropes on each leg doesn't affect the kN on each anchor point... assume a load of 8kN, each leg will carry 4kN, that 4kN will be split 2 and 2 for each leg on the top right, but all 4 through the single leg on the top left...

It would be interesting to see a load cell put on each anchor point to see what variation there is as the load shifts around, it would probably wobble a bit, but it wouldn't be 33-66 as I think you might be suggesting? 

 

Now, if the sliding knot wasn't there to split the load, and instead transferred it to a non-moving single strand and a double strand, you'd absolutely get a difference in the kN at each anchor point, as the rope would stretch (even what most people call "static rope", which is in fact semi-static)... twice as much on the single strand as the double, because there's half the rope. It only matters when loads get big enough to worry about, but it's still a potential weak point in the system. So in that case you'd definitely want either a pair of single legs, or a pair of double legs; unless you were using truly zero-stretch materials (or as close as possible,  aramid, spectra, dyneema etc).

[Dan Maynard]

10 hours ago, peds said:

number of ropes on each leg doesn't affect the kN on each anchor point... assume a load of 8kN, each leg will carry 4kN, that 4kN will be split 2 and 2 for each leg on the top right, but all 4 through the single leg on the top left...

I thought that, but the other rule of thumb is that without friction the tension will be the same all the way along the rope, else it would move where the tension changes. This is how you can work out mechanical advantage in 3-1 or 5-1 systems by counting ropes.

 

My suspicion here is the friction at the alpine almost locks that point, so the tension is not the same along the rope.

 

I haven't really thought it through though, was just musing. 

Edited July 18 by Dan Maynard

[peds]

2 hours ago, Dan Maynard said:

I thought that, but the other rule of thumb is that without friction the tension will be the same all the way along the rope, else it would move where the tension changes. This is how you can work out mechanical advantage in 3-1 or 5-1 systems by counting ropes.

 

My suspicion here is the friction at the alpine almost locks that point, so the tension is not the same along the rope.

 

I haven't really thought it through though, was just musing. 

 

Hmm. Complicated really, isn't it. It would definitely be interesting to build it with a load cell on each anchor to check the numbers. Anyone on here got a pair? We've been tempted to buy one on the MRT for a while, they are hugely useful. 

 

But I guess the real lesson here though is don't incorporate random twit-toks of unknown origin into your rigging repertoire, especially when it doesn't really solve any problems.