UKC

Question, do people use the Sliding X anchor and if so in what situation, I.e as protection on the lead or as a belay anchor ?

In reply to drsdave:

no.

It's pretty rare due to shock loading on gear failure.

In reply to drsdave:

I'd consider it as a belay anchor if I thought that neither individual placement was strong enough to hold the anticipated load but they will do if the load is shared, and if they're of about equal strength. So that's not very often at all and it assumes you're able to judge your placement strengths to an unlikely degree of accuracy. Things really aren't looking great if it's the best option you can think of but in that case it might just save your bacon.

In reply to AdrianC:

For a belay...

So you have 2 poor anchors. Bang on the sliding X with an alost sattic sling. One anchor fails. The second is then shock loaded and therefore more likely to fail.
or
you have 2 poor anchors. Equalise and tie off with your dynamic ropes. Even if one fails, the other is not shock loaded. Better system.

If on a route, then clip one to each rope, share that way.

Sliding X, maybe if my slings are too small to equalise with a good angle. Otherwise I struggle seeing the benefits.

In reply to drsdave:

no, much better to tie the overhand in - it's perfectly adjustable if it's not loaded too much and much safer than the slding X.

In reply to drsdave:


I think it caught on with some climbers because it looks a bit sexy. It's fundamentally flawed, though, for the reasons stated above - I don't believe its use is remotely justified with weak anchors, either. Just anticipate the direction of loading correctly; then tie the whole belay together to get effective redundancy.

In reply to drsdave:

I sometimes (very rarely) do an 'equalette' (using a 2.4m sling), which as far as I know is the modern replacement for sliding X, and is just as easy and much safer. Only really do it if I know the anchor loading will shift, or if I can't quite figure out the direction of loading.

In reply to drsdave:

I've done it on bolts. You can also do an isolating version that reduces the shock loading.

Normally I'll equalise and create independent anchors properly with a tied of sling or the ropes.

It's worth noticing that tests show it's pretty much impossible to equalise anchors evenly.

In reply to drsdave:

Thanks for all input, consensus seems to be, not to bother. But then if the anchor points are solid and a nylon sling is used, the ability to tweek the directional load somewhat can be gained. I confess I've never used one but did wonder whether others had. Thanks.

In reply to Kevster:

Yep - understand that thanks. That's why I said I'd only consider it in a very specific situation.

Slightly off the OP's topic but this video youtube.com/watch?v=X0SP85S1m4Q& is worth a watch - particularly the bit from about 12:20 in relation to load sharing when the angle at your focal point is small.

In reply to drsdave:

It's ok on bolts, have used it a few times. But then its main advantage is equalising two bolts, and when building anchors on 2 (well normally 3 on multipitch routes) I'm not that fussed if my anchor isn't perfectly equalised so it's kinda redundant.

In reply to drsdave:

I read some research / tests somewhere (I could find it if I could be bothered) with the following results:

- Using an equalette or the rope: when people think that they have equalised the anchor it is rarely ever actually equalised even when assuming the load direction is constant, when the load moves direction it becomes unequalised further;

- Using a sliding X results in the much better equalisation, though it is subject to shock loading if a piece of gear fails;

- Using a sliding X with limiter knots reduces the shock loading significantly, to make shock loading inline with other anchor methods.

Therefore it appears that the sliding X with limiting knots is a winner in tests but in practice I find it takes longer to set up, requires a big sling/cord and has the usual static sling problems. I only use it if climbing as a group of 3 and expect to swap around rope ends - keeps the rope separate from the anchor.

In reply to drsdave:

As far as I'm concerned, sliding X is an answer to a problem I don't have.

In reply to drsdave:

Yes, if it's two small runners close together. I can't tie and equalise an overhand knot one-handed

In reply to drsdave:

I've used it on lead before when I've had 2 bits of gear close by to save some extenders for higher up. Faff putting limiter knots in. To be honest, on lead I don't think the 'extension' (if one piece fails) is an issue because you've got rope in the system, so you won't wholly dynamically load the sling, you would just fall a bit further.

In reply to drsdave:

I use it now and then if connecting 2 belay anchors that are close together but still some distance from the edge (instead of 2 long bights of rope to each). I'm aware of the shock loading issue and so only use on good anchors. I find it quicker than tying an overhand and more reassuring than just clipping both strands of the sling.

In reply to StuMsg:



This is not necessarily true! There was a very interesting discussion on this at Mountain Project (www.mountainproject.com/v/knot-limited-sliding-x---failure-mode/111739687) with results on some tests with sliding x. Basically it says you should avoid using the sliding x.

In reply to Eciton:

Followed your link up and also,Mike Barter the Canadian climber (does some nice stuff) comes down to getting your basics sorted, I don't think there's a magic energy saving belay system, you've either got your anchors sorted, angle right and climbing well or you've haven't. Bit simplistic explanation but that's how I'm seeing responses and the real time practicality of the X system.

In reply to drsdave:

Nope. Use a 3-piece quad and be done with it.

In reply to StuMsg:


But it's exactly that "if a piece of gear fails" situation that we're looking to insure ourselves against. It's only "much better" equalisation if both anchors hold - in other words when it's just sitting there looking pretty If one anchor blows it's suddenly totally crap equalisation, just at the precise moment when it really matters!

In reply to drsdave:

Sliding X does not adhere to redundant in my eyes, so I never use it for anything.

In reply to drsdave:

I've used an X on runners in the past but usually to put two pieces onto one sling-draw when I'm running out of kit rather than for the equalisation performance. A stretchy rope in each piece 20+m out from the belayer (where I'm typically running out of gear and brave) probably equalises better than an X anyway.

Don't see much point in them for a belay.
jk

In reply to AdrianC:

2 out of 10. Must try harder.

If your anchors are that crap then you really, really need to ensure there is no sudden extension in the system if one anchor fails.

In reply to bpmclimb:


I think the idea was that it was really funky if you had to bring a partner up on one side of the stance and then they led through from the other side. And I can see it being quite cool in that context - if you are clipped into stonking big bolts

In reply to jkarran:


You know, I've never, ever thought of using a sliding X to equalise two runners. Never mind the fact that you've run out of kit it just might be a good way of producing a possibly viable protection point out of two rubbish ones!

I must go away and play with some ropes.........

In reply to Andy Say:


Isn't that exactly what you just gave me 2/10 for a couple of posts higher up?

In reply to atypic:


That's a very sweeping statement, so tell me more of 'redundancy' - how far does that go, and what defines the divide between a need for redundancy and one is enough?

For the sake of argument, let's start at one end, perhaps with the belayer's belay loop, the krab and belay device, or perhaps the belayer's hand. Or the belayer, for that matter.

In reply to AdrianC:


No it isn't. What you posted was 'I'd consider it as a belay anchor if I thought that neither individual placement was strong enough to hold the anticipated load but they will do if the load is shared, and if they're of about equal strength.'

Different?

In reply to Andy Say:

Yes. In other words, "a good way of producing a possibly viable protection point out of two rubbish ones!"

In reply to AdrianC:

Whatever.

In reply to Andy Say:

Come on Andy, fair dos. If you're going to write stuff like "2/10, must try harder," then you could at least engage with the debate. Especially when you contradict it two posts later.

In reply to AdrianC:

OK. I'll bite. But if you cannot see the difference between thinking about trying to maximise the holding potential of runner placements through improvisation and using a sliding X 'as a belay anchor if I thought that neither individual placement was strong enough to hold the anticipated load but they will do if the load is shared, and if they're of about equal strength' then I felt that maybe we don't have a lot of common ground to debate.

I stick with my point made above - 'If your anchors are that crap then you really, really need to ensure there is no sudden extension in the system if one anchor fails.' If 'it's the best option you can think of' then you are making a decision that could cook your bacon in my opinion. There are far better ways of sharing the load between a couple of marginal belay anchors that won't produce half a metre of slack into the system if one fails don't you think?

In reply to Andy Say:

Thanks for coming back to this, Andy. But no - I don't agree!

In the situation specified, extension doesn't matter. Neither point on its own is good for the whole load so if one fails, the whole thing fails whether there's shock-loading or not. The thing you need to ensure is the best load sharing that you can possibly get. Whilst the sliding X isn't perfect, putting an overhand in the sling makes it very unlikely that you're going to have equal load on both points, especially if they're both closely aligned with the load direction. (That makes it hard to keep load on both points when there's even a slight change in direction - see the video I linked to above.)

I thought your comment about making one *potentially* good point out of two crappy ones summed it up well.

Some examples of times I'd consider it:- Any time there were several poor anchors available, e.g. on the slope at the top of a sea-cliff with lots of scrubby vegetation - link up pairs of stems with sliding Xs. At a stance with one decent bit of gear and two crappy ones - link the two crappy ones with a sliding X then equalise that point with the decent piece (especially if the two crappy ones were in the same vertical crack.)

Are these situations common? No - they're probably once in a blue moon. But like a blue moon, they're not unheard of so I think it's another of these things where there isn't a single rule that fits all circumstances and there are times when a sliding X is worth considering.

In reply to AdrianC:

This never happens in practice. The range of strengths in which this is true is tiny, especially once you account for imperfect equalization (even with a sling), and even then it would only be true for a limited range of fall sizes. Even if somehow all these things came to pass, you would have no way of knowing that (and how would you know how much force an upcoming fall would produce anyway). Gear is either good enough or not, 99% of the time (probably).

In reply to AdrianC:

Why a sling. Why not use the rope and include an element of dynamism which would enhance gradual sharing?


Well, if you will forgive me, I think you have shifted your stance. Your first post seemed to suggest that you only had two poor anchors. 'if I thought that neither individual placement was strong enough to hold the anticipated load but they will do if the load is shared'. Now you've got loads! Including a decent one..... (Pairs of stems? You're using sliding X's to equalise the vegetation? You've climbed in North Devon obviously. Wasn't it Screda Point that required threading rabbit holes. But I digress......)


Totally agree.

In reply to Andy Say:

Rabbit holes are bona fide in situ gear.

In reply to AdrianC:


The sliding X is terrible at equalization anyway - tests were done (by BD IIRC, but just checked and can't find any from BD) that found it hardly shared the load at all (there's too much friction from the wrap is the hypothesis). Have a look at the equalette/quad, which provides far better equalization, and gives almost zero extension.

Another idea that gets toted around in cases where it does not apply is the idea of "shock-loading" an anchor. An actual shock-load is only possible if you're connectly directly to the anchor with a basically non-stretch material (i.e. dyneema, which has only 3% stretch). The moment there's rope in the system, is the moment a shock-load becomes impossible. The rope physically cannot apply a true shock-load - it is a force low-pass filter. The additional acceleration of a climber over 30cm (the amount of extension for example) is negligible too, and quite possibly wholly counteracted by the rope recoiling (and thus being able to absorb more energy when it comes tight onto the second piece). Personally I still prefer to minimize extension, but if there is possible extension it's not the death sentence people talk about it as, if there's rope in the system.

In reply to SenzuBean:


That may be absolutely true. But isn't it semantics? If dyneema slings stretch 3% then using them also prevents a 'shock-load'. You'd probably need a steel cable clipped direct to the anchors? I would completely agree that using a dynamic rope, and an indirect belay, might reduce the impact force hitting the system but there will still be one?


We can over-think, it is true. I can't think of more than a handful of incidents in the UK where anchors have failed over the last three decades.

In reply to Andy Say:

I don't think it's semantics. The 3% stretch is basically useless in terms of energy absorption and force reduction. Also dyneema stretches plastically (i.e. it will not recoil).
I'm pretty sure (with my physics hat on) in most scenarios (excluding stuff such as the rope catches on a flake during the fall), the force on the second anchor will at most be approximately the same as that on the first anchor, if not far less due to the absorption of energy from the rope stretch.
The "force over time" graph of dynamic rope (the area under the curve is the total energy) is basically a wide bell curve - it's pretty harmless relatively speaking compared to say the same fall on a dyneema sling (all the area of a wide bell curve squished into a tiny narrow spike that is far higher - thus far higher peak forces, thus placements exploding).


I don't know of any, but I've found a few examples in the accident reports from rockandice.
There's also a very scary website called 'jive ass anchors' too.

In reply to SenzuBean:



The benefits of changing to an equalette style rather than sliding X are somewhat limited, we saw a load split of 1.685:1 for an equalette rise to 1.89:1 for a sliding X which is not exactly wonderful. the amount of extension is purely a function of how close one ties the limiting knots, too close and the self-equalising is negated anyway. In practice it´s hard to get anything less than 20cm to be usable.
Used for joining two protection pieces the increased impact force from extension is irrelevant so a sliding X is probably the most convenient if not the best way.
Extension in a belay can have shocking results and is to be avoided at all costs, the belayer may be clipped directly in or with a sling/PAS and anyway there is both the belayers weight and the dynamic effects of the falling climber to take into account. The benefits of a short length of rope are overestimated and the forces involved with both a faller imposing perhaps 4kN on the belay PLUS a belayer being accelerated downwards are often underestimated.
i would never belay using a sliding X or equalette.

In reply to AdrianC:


I'm with Andy on this one. It's very hard (let's be honest, impossible) to look at a placement and think that'll hold x kN which is y% of the load I may apply in direction z. What you're really doing is feeling your bum twitch a bit while looking at a little nut, bendy flake or a rusty peg. The judgement doesn't get much better than 'I don't like that much'. Now if you equalise a couple of those for a belay* using your rope or an in-extensible sling arrangement there's no risk of shock-loading either of them. They may not be taking exactly equal loads as you fidget about or your falling partner swings but if they're both a bit marginal and one rips there's still a good chance you get to live, there's still that big unknown as to how strong each piece actually is but there is not a huge shock load being applied. Now if that happened with the sliding X you're falling the extension distance 30-60cm directly onto one bit of gear you didn't much fancy to begin with. The primary energy absorption is your body deforming (ignore the meager sling stretch, it's a red herring) which isn't ideal. That's a big load onto bad gear! Yes, the first failure may be fractionally less likely to happen than if you'd equalised poorly with rope but the post initial-failure situation is much more likely to kill you.

*you'd be a fool, there are almost always better options

Used as a lead runner the X is ok since the primary energy absorbing member in the event of one piece failing remains the rope and which it's rather better at it than your butt in a sling.

Even in the situation you later alluded to, a nest of crap is better equalised in-extensibly if imperfectly, there's no chance of choosing say 5 pieces that are each exactly 1/5th as strong as you need them to be, that can only work when absolutely perfectly extended. Far better to guard against a cascade failure by limiting extension.

jk

In reply to jimtitt:




Thanks Jim for your input.

Was your loading ratio test measured with static or dynamic loading? I think I remember the sliding X only faring badly in the dynamic loading tests.



So just to clarify you're saying that if the extension is on a single runner it's fine to use an equalette/sliding-x, but in a belay system where the belayer could be shifted and thus when they are arrested there is very little dynamic rope out to absorb their energy - that's super dangerous?

If I do use an equalette (which I've only done 2-3 times ever) - it'd only be as long as I had enough rope to the anchor (1.5m+), and if the space between the limiter knots was small (in practice I use about 8-12cm). I've used it for a top-rope setup once too (on bolts) where I couldn't figure out the direction of loading, and again was quite happy using it.

In reply to AdrianC:


Usually the rabbit holes and tufts of grass I'm equalising in this scenario (Carn Gowla springs to mind) are way further apart than the longest sling I'm carrying and in any case most of the effectiveness, if effectiveness is the right word, of this system is predominantly driven by how well I have my arse and feet planted and on the rope dragged across the slope.

I don't think a sliding X obveates the need for tight buttocks

In reply to GrahamD:

Lol.

In reply to SenzuBean:





I´ve tested with three ways of dynamic loading and one static, there´s no real difference between the results one obtains.

On a group of small nuts as protection there´s by definition rope between the belayer and the faller so any extension if one piece fails is going to make little difference to the impact force so there´s no reason not to use a sliding X, it MIGHT help a couple of marginal pieces hold and anyway it´s about the only practical way to join them up one handed/hanging on thinking you will die etc.

In reply to drsdave:

I've heard of the sliding-x with limiter knots used on bolted multi-pitch routes. Basically you keep the belay sling/krabs rigged all the time, and just clip it in to the belay bolts when you arrive and it's ready to go. The 'sliding' element allows for variation in the distance between the bolts from one belay to the belay, and the limiter knots reduce the degree of shock loading should a bolt fail.

In that case it's to save time, and the chance of a bolt failing is very low. I've personally never used it, but have heard of it being used in that context to save time. On a bolted route like where time was critical I would certainly consider using it.

In reply to NottsRich:


It is a lot easier to be slick, quick ( and safe ) with tying knots than the actual climbing.

Keep it simple and do it right.

In reply to NottsRich:

There's a number of ways you can rig that, it doesn't have to use the sliding X. But agreed, leaving a belay rig constructed is a good way of making things a bit more slick and efficient on big bolted multipitch.