/ Shock loading equalised nuts

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Kevin Woods - on 01 Sep 2012
I'm having a discussion with a pal.

You have 4 micro-nuts lined up, they're the only gear on this silly-badly protected route.

2 nuts are solid but 2 are definitely wobbly and will probably pop if you fall on them.

Do you equalise them with a sliding x? (his argument)
Do you equalise them with an overhand knot? (my argument)

I imagined pre-equalising with an overhand knot on the sling will mean if one pops (likely), the others will not get shock loaded. He's saying the same thing, except that a sliding x will solve it.

Or can you suggest anything more effective?

Please settle this one! Reasons why would help, too. Thanks.
Jonny2vests - on 01 Sep 2012
In reply to Kevin Woods:

Overhand knot, surely its a no brainer. A sliding x is about the worst thing you could have if one of the pieces fails, as shockloading is guaranteed.

Incidentally, a sliding x is about the most pointless thing ever. Ok, so it self equalises, but in tying it you effectively assume the anchors are beyond reproach, therefore there is little point worrying about minor equalisations.

I've heard arguments about using a sliding x when you have a lot of shite anchors, but I'm not convinced. And I've seen people use them but with overhands at the gear end, but that seems like a big faff.
payney1973 - on 01 Sep 2012
In reply to Kevin Woods: When using a sliding x on two nuts, should the pair shock load and one pops, there will then be a subsequent greater shock load on the remaining nut, bad!!!

Overhand-good
Purple - on 01 Sep 2012
In reply to jonny2vests: Seconded. The sliding x is the sliding death-knot. Don't use it.
Ben Sharp - on 01 Sep 2012
In reply to Kevin Woods: Never used a sliding X myself but largely agree with what has been said already. There's not really any place for it at a belay imo but could be used with two poor runners: if you have two anchors that you're certain will pop on their own but may just hold together, i.e. two really shit runners or directional anchors. There's no point using an overhand because if one goes, so does the other. Using a sliding X still means that if one goes, so does the other, but it gives a greater chance of them both holding.

Still worthy of being called the sliding death knot and pretty desperate but like everything else in climbing it has it's place. Don't see much use for it as a main attachment to a belay though, if the belays bad enough to warrant tactics like that it's not much of a belay.

Ben
Ben
jezb1 - on 01 Sep 2012
In reply to Kevin Woods: but is the sliding x the only way to truly equalise anchors?
Fraser on 01 Sep 2012
In reply to jezb1:

Must admit, I often use a sliding X at a belay and am happy to do so. To my mind, it's the best way to equally distribute any load likely to come on the placements. If the 'shoogly nut' is that bad, I'd not rely on it at all. (I appreciate the OP is talking about runner-protection on route, whereas I'm referring to a belay / anchor.)

Let's say a fall occurs, the climber drops a certain distance, loads the placements/anchor, and one piece rips. The load may or may not have been properly spread equally between the pieces of gear. With a sliding X it's more likely to have been equally spread than with an overhand. In the event of a piece ripping during the initial fall however, the climber will drop a bit further, but it's going to be less than the original 'full height' distance. The climber is roped, so its a dynamic fall they're taking anyhow. That's my tuppence worth.
m dunn - on 01 Sep 2012
In reply to Kevin Woods: Overhand is a good way of equalising a load in ideal circumstances. However it is likely that in practice one piece will be loaded disproportionately, possibly leading to failure. A sliding X almost guarantees the load will be shared equally. But if despite this one blows .... !!

Rory Shaw - on 01 Sep 2012
In reply to Kevin Woods: if you are leading its pretty hard to equalise so just clip a quick draw to each as you normally would. I often use longer draws on the better bits so the poorer ones take the force first.
Michael Gordon - on 01 Sep 2012
In reply to Rory Shaw:
> (In reply to Kevin Woods) if you are leading its pretty hard to equalise so just clip a quick draw to each as you normally would.

That's probably what I'd do onsight but it sounds as though the OP is headpointing and wants to stack things as much in his favour as possible.

To be honest if 2 of the bits are solid I'd probably be tempted to just use those and not bother with the others.
wivanov - on 01 Sep 2012
In reply to Kevin Woods:
> You have 4 micro-nuts lined up, they're the only gear on this silly-badly protected route.
>
> 2 nuts are solid but 2 are definitely wobbly and will probably pop if you fall on them.
>
> Do you equalise them with a sliding x? (his argument)
> Do you equalise them with an overhand knot? (my argument)

It's unclear to me whether you are trying to 1) equalise all 4 nuts, 2) equalise one solid nut with one wobbly nut that would probably pop or 3) equalise just the two wobbly nuts.

For #1, why bother? You have two solid nuts.

For #2, I'm not sure I'd bother with the wobbly nut if I had a solid nut. But, if I did, I'd probably use two slings or one sling with an overhand knot.

For #3 I've used a sliding X with pre-tied limiter knots. The logic was that if one blew the other would probably blow anyway... and the sliding X MIGHT equalise enough so that both would hold.

I've also done it with limiter knots but without the sliding X. Just clipped into one strand between the limiter knots. The logic being as above and that I MIGHT get better equalisation without the nylon/nylon friction. True, the single strand is not redundant but I figure it's breaking strength was greater than the micro nut placements anyways. In this case, I suppose I could have simply looped a sling between the two pieces and clipped it without the limiter knots. But, you never know. With the limiter knots, if one piece blew, the other MIGHT hold despite any "shock loading".

Happily, I didn't fall to test this.

I'm kind of thinking that, in this case, "shock loading" doesn't quite happen the way we might think - because of the dynamic rope in the system and the very small distance between the limiter knots. But, someone like Jim Titt might correct me on this...

Milesy - on 01 Sep 2012
In reply to Kevin Woods:

Is this hypothetical? It cant be that badly protected if two nuts are solid? In which case I wouldnt use the bad nuts on the belay.

If I had to use just the two bad nuts I would be thinking about how can I make them more secure.

If you are standing in a single position then there is absolutely no reason why I wouldnt use a overhand knot. No brainer to me. A sliding X gives you redundancy but definately shock loading. You can stick overhands above the sling X to reduce the extension and shock loading but there will still be some. I have never felt the need to use either.
David Coley - on 01 Sep 2012
In reply to Kevin Woods: I'm probably not going to explain this well, but I hope you get the point. There is no advantage in using a sliding x unless the force the weaker arm can take is at least half the force the force generated. If the fall creates 10kn say and this is shared equally between the arms we have 5 on each. If the weak arm can't take this it will blow and nearly 10kn will transfer to the other arm. If this can't hold 10kn then game over. If it can then there was no need for the weaker arm. It only makes sense to equalize reasonably good, similarly strong pieces. Equalizing a good with a poor is not logical.
gethin_allen on 01 Sep 2012
In reply to Kevin Woods:
How about using a sling with 2 overhand knots, clipping the end loops to the gear and the middle to the rope. This way you share the initial load on both nuts but if one rips you don't extend the fall significantly.
jimtitt - on 01 Sep 2012
In reply to Kevin Woods:

Well itīs quite simple really, Iīm somewhere on about page 130 of an article about equalisation and 700 or so tests and 18 months work and the answer it probably doesnīt matter what you do.
A 4 point sliding system with limiters wonīt in any way even begin to approach equalisation, in theory youīll be getting 12.9%/21.7%/24.5%/40.9% load split on the pieces with nylon and the 4 pieces set up as two sliding pairs equalised by another (the normal way to set this up and the most efficient). Using sliding Xīs will make this worse.
Testing I get 7.7%/18.2%/30.9%/43.2%. as in reality the lowest sliding karabiner twists and binds (using 8mm cord, this might be better with tape).

But a fixed equalised system with 4 pieces is even worse as you cannot tie the central point accurately enough and at least one and usually two pieces wonīt feel any load at all. It is also impossible (and I do mean impossible despite what some authors may write) to compensate for the different stretch in the legs due to their varying lengths. Marc Beverly has done loads of testing on this and his conclusions are you are lucky if two pieces do anything.

The shock-loading issue is unresolved as usually we are looking at belay systems where there is no rope or a limited amount involved when the increased forces become enormous, with the amount of rope available in a lead fall situation the additional forces from extension will be reduced but must always always higher than if no extension occured.

Iīd clip them all one after the other and hope something held working on the theory that hanging around arranging a poorly equalising runner cluster would make it more likely that I would run out of strength or stop concentrating on the climbing and increase the chances of me falling in the first place.
don macb on 01 Sep 2012
In reply to Kevin Woods:

random guess: walk on the wild side at the 'starry?
Robert Durran - on 01 Sep 2012
In reply to jimtitt:
> As a matter of interest, I presume it still makes sense to equalise an abseil anchor with an overhand knot.
Michael Gordon - on 01 Sep 2012
In reply to don macb:

On that the gear is one after the other as you go up the crack (after the initial bold section). On his route the gear is all clustered together before presumably a tricky bold bit. I'm guessing its also a bit harder than HVS!
jimtitt - on 01 Sep 2012
In reply to Robert Durran:
All the tests show with 2 pieces you can make a reasonable stab at equalising an anchor, you get better results if you tie the centre knot first and then clove-hitch into the points as you can get the tensions more equal (though still only `reasonableī since once you start measuring climbers ability to equalise the results are depressingly poor).
The advantage of the central knot system is you are always joined independently to both pieces no matter what happens and donīt increase any possible loading which is where the sliding systems all fail. Generally it seems the concept of treating an anchor as a primary piece and back-ups is the way to go (and the thinking of the DAV these days) since you rarely achieve the levels of equalisation one hoped for and donīt in fact know whether you want to equalise in the first place anyway.
Michael Gordon - on 01 Sep 2012
In reply to Milesy:
> (In reply to Kevin Woods)
>
> Is this hypothetical? It cant be that badly protected if two nuts are solid?
>

If they're micros they could be solid (as in well-placed) but small enough that there's a risk of the wire breaking. Personally I'd usually still just go with the two good pieces though.
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Kevin Woods - on 01 Sep 2012
In reply to don macb: Nope! Try again :)
don macb on 01 Sep 2012
In reply to Kevin Woods:

doh!
Kevin Woods - on 01 Sep 2012
In reply to Milesy: Real situation. French grade feels about 7a. The two good nuts are very hard to place and until you do so, about 7m up, it's a solo/highball.
don macb on 01 Sep 2012
In reply to Kevin Woods:

ooft. waaaay harder than WOTWS then...

how about just busting the move and hoping to not fall off? ok, i'm not helpng and will return to my pizza and beer to observe the thread's progression with interest :D
Kevin Woods - on 01 Sep 2012
In reply to Kevin Woods: Goal for the moment is just to TR it. But if things fall in favour of leading then it will be good to have a shot.

A sick twist is that the two wobbly nuts are (awkwardly) easy to place, 1 relatively good one is hard to place, and the other is near impossible. There's a possible micro-cam in a solid flake in the same area, but if that doesn't work then the ground is the next point of contact.

Another guess? :)
john arran - on 01 Sep 2012
In reply to Kevin Woods:

As it's for a headpoint you may as well just rig a correct length equalised knotted sling on abseil and keep your wires clipped to it so they will be perfectly equalised already as soon as you've placed them.
don macb on 01 Sep 2012
In reply to john arran:

... or as perfectly equalised as an overhand can be, i suppose. this is the worry, isn't it? at least your suggestion avoids faffing while in the thick of the moves.

to kevin: i'd just stack them and hope for the best, but i think john's suggestion is by far the wisest so far for a headpoint scenario and- as per the above posts from a bunch of folk who know much better than me- i'd suggest your mate's argument in favour of the x is a bad idea.

ps- as for another guess: nope! i just wondered- based on your profile grade and location- if it was this route. i'm fancying WOTWS and have been pondering about the benefits of faffing around equalising the small pro' versus just swiftly stacking them on seperate draws and going for it, especially given that the moves are a little thin but basically easy, so a psychological buffer at the half way mark would really help.
Skip - on 01 Sep 2012
In reply to Kevin Woods:

what is a sliding x?
Kevin Woods - on 01 Sep 2012
In reply to don macb: Ah right that's cool. My route is Hamilton's Arete, Craigmore. E4 6b and higher if the other E4 there is anything to go by. I'll check out WOTWS next time I'm at Auchstarry.

I'm thinking a pre-equalised set of nuts is therefore the way to go for me. Imagine dropping them!
John1923 - on 01 Sep 2012
In reply to Kevin Woods:

I have heard that sliding x is a bad idea as, when it is shock-loaded the webbing on the sling sticks, which shock-loads the two pieces in rapid succession, so one of the pieces is subjected to the full force of the fall.

Overhand knot is the best plan, but tying one on lead can be tricky.

Generally if I am using gear rated over 5kn, I just place 2 completely independent pieces just before or after a big runout.

don macb on 01 Sep 2012
In reply to Kevin Woods:
> (In reply to don macb)
>
> I'm thinking a pre-equalised set of nuts is therefore the way to go for me. Imagine dropping them!

yeah yeah... you can always purify the style of ascent later if you really feel like you have to, but maybe bag the headpoint this way first. good luck and let us know how it pans out man.

in all seriousness: an e4 tick is a cracking headpoint, but balancing risk, consequence and possible benefits is hugely important before stepping up to the challenge. i've seen the outcome of a broken neck this year and it is seriously not good. but you know that :)
nniff - on 01 Sep 2012
In reply to Kevin Woods:

Sliding X (or two if there are 4 nuts) for two reasons.

If they're runners they're not going to be shock loaded per se because there's a big dynamic rope to absorb the impact. Ergo, you're not significantly worse off than if you just had a longer sling on the one nut if the other fails, but your chances of spreading the load successfully are significantly better.

Secondly, your chance of tying a decent overhand knot in the right place one handed is slim. If you're got both hands then what's the fuss about.

One the other hand, if the poor nuts really are poor, stop messing about and crack on without them.
jkarran - on 01 Sep 2012
In reply to Kevin Woods:

Clip the two good bits one on each rope, long draws and rollers. If the poor bits are shit then skip them and save your arms. If they're passable clip them below the good gear so they don't rattle/lift it out as you rip em. Quick, simple one handed and equalises well.

jk
David Coley - on 02 Sep 2012
In reply to David Coley:
If anyone has the time, please comment on my previous comment, which ended with the statement: "Equalizing a good runner with a poor is not logical."

This is something Jim Titt taught me and I would like to see what others think of this as a general rule of thumb.

Thanks.
Kevin Woods - on 02 Sep 2012
In reply to David Coley:

jkarran: What are rollers - I did a Google and came up with a pulley?!

David's comment: I'd imagine that if the poor runner is not too poor then where is the harm, as long as the potential failure of the poor piece doesn't shock load the strong piece?

Does it make more sense to equalise strong not-full-strength pieces than poor full-strength pieces?
rgold - on 02 Sep 2012
In reply to Kevin Woods:

First of all, as has already been said it makes no sense to "equalize" good and bad pieces. Second of all, the chance that you can get anything that even remotely resembles equalization with four pieces is nil, regardless of the rigging method. (But I also don't understand Jim's theoretical load distribution to four pieces with three sliding X's. In the absence of friction---which is never absent---that set-up should genuinely equalize.)

The situation you describe calls for double-rope technique. I'd rig the two good pieces together and clip one strand to that and rig the two bad pieces together and clip the other strand to that. I'd do it this way even if you are headpointing and have the slings pre-rigged. The double-rope set-up, if the belayer knows what they are doing, imposes no penalty on the faller if the bad gear blows.

As for rigging, I use something fixed (as opposed to sliding) if the situation made it feasible---that would typically be a no-hands position on a ledge. Unpredictable as sliding X's are, you can install them quickly one-handed, and so for a hard leading situation they are probably the best you can do.

But then again just putting quickdraws on everything may well be as good an option.
wivanov - on 02 Sep 2012
In reply to Kevin Woods:

Are the 4 nuts at a belay anchor?

I took it that they were protection pieces along the route ("they're the only gear on this silly-badly protected route.") but some of the responses seem to be for a belay anchor.

Are all 4 all together? Or two sets of one strong nut and one wobbly one?
jimtitt - on 02 Sep 2012
In reply to rgold:
The theoretical values are calculated with the friction in the sliding parts (I used single strand with limiter knots rather than Xīs which have even more friction), however when I practically tested this setup I found that the lowest (central) karabiner insisted on twisting which caused the cord to twist and rub on itself making things worse. Whether this was a peculiarity of the cord I used who knows, since it occured it could always occur. Tape of course might be better but since the overall result is so bad anyway it hardly seemed worth testing.
Kevin Woods - on 02 Sep 2012
In reply to clifffhanger: It is for running protection about half way up the route. The nuts are spaced about a metre apart up a vertical crack, and will deffo be place one-handed.
Ramblin dave - on 02 Sep 2012
In reply to Kevin Woods:
Thinking aloud here, if they were close enough together (or could be extended with quickdraws to be close enough together) could you extend them all with screamers? The idea being that they sort-of self equalise as they all start taking load sequentially but while the screamers are still screaming...
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Ramblin dave - on 02 Sep 2012
In reply to Ramblin dave:
Not falling off would be the other obvious solution.
jimtitt - on 03 Sep 2012
In reply to Kevin Woods:

If they are vertically above each other then a sliding system is the only way to get any load sharing whatsoever (fixed equalisation is useless in this orientation) but if they are a metre apart then then extension is going to be appalling so limiter knots are going to be needed which all sounds like a lot of faffing around actually climbing the route.
The best would be find another belayer and use four strands of rope, if nothing else youīve got two spotters to land on (or carry you to hospital)!
rgold - on 03 Sep 2012
In reply to Kevin Woods:

A meter apart? I wouldn't bother with "equalizing." Put a quickdraw on each one and use double-rope technique.

Tests have shown that when a piece pulls, the rope snaps back, which means that extracting a piece absorbs some fall energy and so has at least some use. The situation is even better with double ropes properly clipped, since the second catch will be on a strand that has not been stretched by the first failed catch.
Fraser on 03 Sep 2012
In reply to Kevin Woods:
> (In reply to David Coley)
>
> jkarran: What are rollers - I did a Google and came up with a pulley?!

These:

http://www.supertopo.com/inc/photo_zoom.php?dpid=Mjo8OTg8ICcn


jkarran - on 03 Sep 2012
In reply to Fraser:

I actually meant these but words clearly failed me. Nevermind.

http://dmmclimbing.com/products/revolver/

jk
Ciro - on 03 Sep 2012
In reply to jkarran:

Does a roller not actually cause a slight increase the peak load on the runner? (reason being that friction reduces the component of the total force coming from the belayers mass)
Milesy - on 03 Sep 2012
In reply to Ciro:

I have always been under the impression that the revolver is good for marginal gear. I have one on my rack and have used it on a dodgy ice screw before.
lithos on 03 Sep 2012
In reply to Milesy:

really a revolver not a screamers (tapes which rip under load) ?

I'd use a revolver to reduce rope drag usually.

we havent even started on screamers on this thread yet !
Fraser on 03 Sep 2012
In reply to jkarran:
> (In reply to Fraser)
>
> I actually meant these but words clearly failed me. Nevermind.
>
> http://dmmclimbing.com/products/revolver/


Aah, sorry. (I've got a couple of those Revolvers - they're great.)
David Coley - on 03 Sep 2012
In reply to Ciro: Yes, but it also allows one to access the full dynamic properties of the rope the belayer side of the krab, and this side of the rope is normally much longer.

Imagine 100% friction at the knot, i.e. a clove hitch. Any fall would be a factor 2, so even if the force is reduced as it is not doubled by the rope to the belayer, it is still a nasty fall because you have little stretch. Remove the friction at the krab (i.e. untie the clove hitch) and you have a nice, say, fall factor 0.1 fall.

Does that make sense?
gethin_allen on 03 Sep 2012
In reply to lithos: using a revolver allows the force to act on a longer length of rope so reduces the force on the last gear.
Robert Durran - on 03 Sep 2012
In reply to David Coley:
> (In reply to Ciro) Yes, but it also allows one to access the full dynamic properties of the rope the belayer side of the krab, and this side of the rope is normally much longer.
>
> Imagine 100% friction at the knot, i.e. a clove hitch. Any fall would be a factor 2, so even if the force is reduced as it is not doubled by the rope to the belayer, it is still a nasty fall because you have little stretch. Remove the friction at the krab (i.e. untie the clove hitch) and you have a nice, say, fall factor 0.1 fall.

So the question is: For given effective coefficients of friction between rope and the two types of krab, for what fall factor and below is it beneficial (ie lower peak force) to be using the lower friction (ie revolver) krab? I have a feeling the analysis could get very messy. maybe Jimtitt will have some experimental data!
David Coley - on 03 Sep 2012
In reply to Robert Durran:

DMM might have the data. They did have some I think when it was launched.

I would guess the peak force is lower in all cases when it gives rise to more rope to stretch. Therefore the only time when it might not work is if there is another high friction point just before the top krab, e.g. the rope is struck in a crack or pulled tight on a lip.
jimtitt - on 04 Sep 2012
In reply to David Coley:
Iīve never seen any test data.

If you change the friction value at the top piece using the standard rope model we see an inexorable rise in impact force on the top piece as the friction is reduced. It would appear that the increased rope stretch is not enough to compensate for the increase in the pulley effect on the top piece.

However the standard model doesnīt consider the complexities of integrating a belay device into the system which may or may not have an influence and this would probably change anyway depending on the length of the fall and the device used (and the belayer).

Without a good deal of somewhat difficult (expensive) tests all we can say is that in a simple system reducing the friction increases the load, in real-world situations this may not be so but there is no evidence for this (nor do DMM make any claims either way).
David Coley - on 04 Sep 2012
In reply to jimtitt:
Jim, if that is true in the real world, and regardless of the amount of rope to the belayer, it could really change things. It would mean clove hitching a poor piece before the crux move is a good thing. Totally rad. Could I test this in any meaningful way with a spring balance?
jkarran - on 04 Sep 2012
In reply to David Coley:

> I would guess the peak force is lower in all cases when it gives rise to more rope to stretch. Therefore the only time when it might not work is if there is another high friction point just before the top krab, e.g. the rope is struck in a crack or pulled tight on a lip.

Or where the krab pinches the rope against a high friction surface like a gritstone bulge. Also I suspect when heavily loaded the bearing bush binds up and they act like a normal krab.

They're still worth having on small gear, being heavy and slippery they're less likely to lift it out.

jk
jimtitt - on 04 Sep 2012
In reply to David Coley:

Think of it this way round. Take a rope which has an impact rating of 8kN with a standard drop test. Tied to the karabiner this is the force the top piece will encounter so 8kN. If you use exactly the same setup but replace the karabiner with a frictionless pulley and tie the rope to a fixed point directly (so with an infinitely short extra length of rope) before the pulley the force is now doubled to 16kN. Clearly if your are going to take FF1.77īs then high friction is better.
The question is whether there is a fall factor at which having more rope on the belayer side to stretch outweighs the increased pulley effect and the standard model says there isnīt.
David Coley - on 04 Sep 2012
In reply to jimtitt: I still can't get my head around it. If I take a near ff2 from a tied off bolt it is going to hurt. If I add 50 of rope tied off to the ground on the orbs side of the krab I would hardly notice the fall.
jimtitt - on 04 Sep 2012
In reply to David Coley:
But we arenīt discussing whether you feel the fall, were talking about the top piece. With a 100% friction top point you and the top piece will feel the same force and the belayer none, with zero friction your belayer and you will both feel a lower force (than you felt in the first case) but the top piece feels the sum of the two which it appears is greater than in the 100% friction scenario.

However itīs worth noting that both this and the friction adjusted standard model are crude approximations in that they assume the load on the top piece is the sum of the maximum force felt by the climber and the maximum force felt by the belayer. This assumes in turn that both maximums occur at the same time which regrettably we see is not the case if we look at drop-test force curves. So without some real test results itīs hard to be absolutely sure either way whether or not adding a pulley is beneficial or not. Since the reduction in the friction over the top piece isnīt going to be enormous with something like a Revolver I doubt in normal circumstances it makes much difference at all.
David Coley - on 05 Sep 2012
In reply to jimtitt: I would have thought that if the falling climber and the belayer feel very little force and a nice soft fall, then the top piece can't be seeing much force either. I still find it hard to get it in my head that a FF2 fall on a tied off piece creates less force on the piece than a FF0.1 fall with the rope tied to a bolt 30m below.

I've taken a number of such falls whilst rope soloing and they have been very soft, whereas, the idea of falling just above the belay onto the tied off anchor leaves me in a cold sweat.
martinph78 on 05 Sep 2012
In reply to Kevin Woods: I had used the sliding x quite a bit until I started climbing on UKC ;)

It was taught to me when ice climbing/glacier travel in South America and I actually like it (yeah yeah, I've read the above and had people tell me at the crag how wrong it is...)

In your case I would treat the two wobbly nuts as one anchor, using a sliding x to join them.

Most of the above presumes one piece failing causes shock loading on the other which will then fail. But if you are equalising them your treating them as one anchor so if one part fails the whole anchor has failed. The two equalised with the sliding x are now one.

I'd probably then do the same with the solid nuts, but only because they are microwires (otheriwse I'd clip them seperately). Equalising these with a sliding x you've equalised the load between then so each wire is sharing the force. If they are solid and not going to pop then why all the talk of shock loading the other if one does?

I look at a sliding X as equalising the load between two marginal bits of kit, so that both share the force to create one good one. In that case they re not two seperate bits of protection, but one (you've only clipped the rope into one crab afterall.

If all four of your pieces were wobbly I'd equalise them all with a sliding x creating one again. But in that case I'd probably have bottled and backed off the climb!!


I would like to see someone equalise four pieces of gear with an overhand knot using one hand. I know I could do this with an overhand. Again, gettting away from if one piece pops you're shock loading the other(s). You only have one piece, made up of four. Or if one piece is definiately going to pop, leave it out.

Of course I'll be in the minority here.


I would also like to see any evidence that proves the sliding x is the instant death method of equalisation that many uk climbers seem to think that it is. I'm always happy to change my thinking. None of the above has done that for me yet though.




martinph78 on 05 Sep 2012
In reply to Martin1978:

"I know I could do this with an overhand"

Of course I couldn't, I could do this with a sliding x is what it should have read :)
jimtitt - on 05 Sep 2012
In reply to David Coley:

Well yes, this does seem a bit wierd so Iīve checked a bit more. There does seem to be a break point in either FF or friction at the top point where the force on the top point exceeds the force it would feel if you tied in direct.
For my data (weight and rope and standard karabiner friction 0.333) it looks to be above about FF0.4. Around this FF there seems to be no advantage in reducing the friction at the top point.
The problem is also that according to the model for each fall factor and rope modulus there is an optimum friction at the top point which gives the lowest force (on the top point) and either side of this the force on the top piece rises.
For a FF0.1 with my parameters this is with a friction factor of 0.58, FF0.3 this 0.69, for a FF0.5 it is 0.85 and so on.

Interesting but a bit complex as there are so many variables like weight and rope modulus as well as the fall factor and friction, I shall see if it is easier if I do it graphically. There is probably an area enclosed by the various curves which would be the sweet spot and outside of this regions where less friction is better or worse.
David Coley - on 05 Sep 2012
In reply to jimtitt:

Thanks Jim, you're a great asset to UKC.
David Coley - on 05 Sep 2012
In reply to Martin1978:
>I would also like to see any evidence that proves the sliding x is the instant death method of equalisation that many uk climbers seem to think that it is. I'm always happy to change my thinking. None of the above has done that for me yet though.


For a runner, it isn't (although in might not have much purpose, as outlined in other comments). For an anchor is could be if there are no other dynamic elements in the chain. For example if the belayer clips in with a daisy. Failure of one side of the x might then drop the belayer off the ledge and cause a very high force on the remaining piece (Jim has some numbers). Hence most people would use an overhand as a power point. It might not load share as well as an X, but failure of one side results in only a small perturbation to the belayer and a much lower loading on the remaining piece. The use of limiter knots would help here, but the closer these are to the X the less likely the X will still function over the range of angles it has to as the seconds come up toward the belay and remove pieces near the top of the pitch.
Robert Durran - on 05 Sep 2012
In reply to David Coley:
> (In reply to Martin1978)
> >I would also like to see any evidence that proves the sliding x is the instant death method of equalisation that many uk climbers seem to think that it is.

With the sliding X, any one of the two pieces is less likely to fail (good equalisation), but, if one does fail, there will be a further drop before the other is loaded, increasing the chance of it failing. With an overhand (or indeed if the pieces are clipped independently), it is more likely one will fail, but then less likely the other will also fail since there will not be a further drop before it is loaded. So, you make your judgement and take your chances.

But yes, with a belay a sliding X is madness (unless you are using a direct belay, but that is usually madness anyway!)
martinph78 on 05 Sep 2012
Thanks guys, good comments (was expecting a slating :p ).

jimtitt - on 05 Sep 2012
In reply to Robert Durran:
> (In reply to David Coley)
> [...]
>
> With the sliding X, any one of the two pieces is less likely to fail (good equalisation), but, if one does fail, there will be a further drop before the other is loaded, increasing the chance of it failing. With an overhand (or indeed if the pieces are clipped independently), it is more likely one will fail, but then less likely the other will also fail since there will not be a further drop before it is loaded. So, you make your judgement and take your chances.
>
> But yes, with a belay a sliding X is madness (unless you are using a direct belay, but that is usually madness anyway!)

Thatīs about the crux of the matter, the potential downside of using a sliding X (or any other self-equalising system) far outweighs any possible benefit except in fairly uncommon circumstances. For this reason this way of arranging belays isnīt taught any more by people like the AMGA, DAV and many others.
The other problem which worries many, including some of the previous `high priestsīof dynamic equalisation is that less experienced climbers have siezed on trying to achieve of good equalisation and neglected the absolute essential which is good gear. You canīt make a silk purse out of a sows ear is very apt regarding belays!
jimtitt - on 05 Sep 2012
In reply to David Coley:

Well Iīve made plenty of curves and boring it is too!

If we only consider the rope dynamics then it is clear that reducing the friction at the top point is never going to reduce the load on the gear, thatīs the case for any reasonable climber weights, rope characteristics and all Fall Factors.


There is an optimum desirable friction on the top point for the lowest force which varies with all the other parameters but seems to be in the region of 0,5 up to 1 depending.
For example with a FF of 0.1, 100kg climber and an 8kN rated rope the forces on the various parts are:-
No friction (0) Climber 3.11kN Belayer 3.11kN Total 6.22kN
Normal Karabiner (0.333) Climber 3,44kN Belayer 2.29kN Total 5.73kN
Optimum (0.58) Climber 3.89kN Belayer 1.63kN Total 5.52kN
Fixed (1) Climber 9.05kN Belayer 0kN Total 9.05kN

Iīm seeing the same effect with different rope factors and climber weighs, just the optimum point moves around a bit, for the same as above but a 50kg climber the optimum friction is 0.51.

Over Fall Factors of about 0.5 youīd be better off tied to the top karabiner rather than have the rope slide through it!

HOWEVER!!!! This doesnīt take into account the belay itself, in the example above the 3.11kN felt by the belayer is certainly in the range of force one could apply through a normal device but for higher fall factors Iīd have to start changing the forces felt at the belayer end as he couldnīt normally hold them.
For examplöe if the belayer in the case above gave a soft catch or used a weak plate and held only 2.5kN then with a frictionless top point the force on the top is only 5kN which is better than the optimum friction value of 5.52kN (unless of course there is too much slip and the belayer drops you with rope burns or you hit the ground).

So with soft belaying reducing the friction may well be beneficial (covering myself here a bit) but with hard belaying reducing the friction is of no benefit. Time to find a fool to jump off a cliff a few times I guess!

David Coley - on 08 Sep 2012
In reply to jimtitt:
Jim, what would be ideal I think (but if the physics says this can't be done, so be it) is some kind of rule. I.e. if the length of rope on the belay side is less than twice that on the climber side, you might as well clove hitch the rope as reducing the friction is unlikely to improve the situation.
jimtitt - on 08 Sep 2012
In reply to David Coley:

Eek, that means youīd have to climb back down to change it once the run-out got too much!
And wouldnīt be able to top-out either:-)
David Coley - on 09 Sep 2012
In reply to jimtitt: I was thinking rope soloing. Therefore not a problem.
jimtitt - on 09 Sep 2012
In reply to David Coley:
Right, I was thinking in a normal lead context. Still sounds a bit of a drastic measure though, surely itīs easier to allow a bit of slip at the belay end? I rig an HMS with a couple of metres slack and my rucksack as a weight similar to the way the aid guys use the pig as a counterweight.

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