UKC

Sliding X: how far apart should the gear be?

In reply to dark_star:

Between 26cm and 34.5cm.

In reply to dark_star:

IMO the Sliding X is a great techinque for building self-equalising anchors. However care must be taken to ensure that the pro at the two ends are <bBomb-Proof. In the event of a single failure, the configuration will extend and shock load the other placement.

In reply to dark_star:

Depends on the kind of gear it is and the position of suitable placements. I know that's not very helpful, sorry.

In reply to chris tan:

I used to use this a bit, but tend not to nowadays. I simply don't put that much trust in a single piece of gear not to pop and shock-load the system. If I did have a piece that was that solid (like a tree), then I wouldn't use a second placement anyway.

In reply to dark_star: All depends on how long what you are extendig with is.You shold try to avoid an angle of over 90 degrees at your end,otherwise detrimental vector forces come into play,and act as a lever on the gear.

In reply to James G:

IMO the only time I would seriously use the Sliding X ( over a static equalisation point) is when my second is climbing up an arete, alternating faces. The configuration will then allow me to move with my partner, thus ensuring that the rope will always be above him.

BTW it is also a single rope situation.

In reply to chris tan: This can be easily minimiesd by tying an overhand knot about 2-3" either side of where the 'take off point' is. That way you get the benefits of the self equalizing belay, but at the lowest risk of shock loading the other piece should one fail.

In reply to D Berry:

See the Petzl catalogue for a diagram of this - is a nice method.

However ... the answer to the original question is as 'in-line' with each other as possible. The more 'in-line' they are the less force per anchor.

In reply to chris tan:

I can not see how it could shock load the system any more than a normal fall -- the clip point moves 30 cm lower that is all.

In reply to Tom Povey:

You're using a sling which is static - no bounce.

In reply to Tom Povey: The whole point of the self equalizing belay is that when both pieces are in contact with the rock it is exactly that, equalised. Should one pop due to a fall, the distance, what ever it may be, before the system locks on the remaining piece will shock load it. Not just by the force from the fall either; generally the belayer would be tied into it as well. That is why its in your interest to minimise any possibility of shock loading in your anchor.

In reply to James Jackson:

Yes, like any clip point. The point simply moves 30 cm or so lower (unless you climb on a tight static rope, which I hope you do not).

In reply to D Berry:
The whole point of the self equalizing belay is that when both pieces are in contact with the rock it is exactly that, equalised.

Yes.



Should one pop due to a fall, the distance, what ever it may be, before the system locks on the remaining piece will shock load it.

Sounds quite a lot like a normal fall to me. If in a normal fall you use the same terminology I agree with you.



Not just by the force from the fall either; generally the belayer would be tied into it as well. That is why its in your interest to minimise any possibility of shock loading in your anchor.

Yes - the reaction force at any anchor is generally greater than the upward force on the climber, but this holds in any situation where you load a rope looped though a carabiner.

In reply to Tom Povey:

You're missing the point (unless we're both talking about different things...)

In a self equalizing belay belay with two bits of pro, if one bit rips you will fall, say, 30cm as the sling comes tight on the remaining bit of gear. This force is 'transmitted' to the gear by the static sling - it has very little give so the force on the gear is very high (force = momentum / time).

In a leader fall situation, say of the same distance, you're falling on a bouncy rope, and you've also got a hell of a lot more rope out than the distance you're falling (unless you're falling off a belay) so the time taken to slow the fall is a lot more, the force on the gear is therefore a lot less - no shock load.

In reply to James Jackson:

I'm sorry, I must have misunderstood. You seem to be talking about a system with no dynamic rope in it, just static slings, like, for example, a belay to which a climber is clipped directly. If so, I withdraw my comments.

If you are talking about a normal lead situation, however, where a leader chooses to use two equalised pieces of protection (with a sliding 'X' type sling) in place of a single placement, then the comments I made above apply.

In reply to Tom Povey:

Ah I see. You were talking about runners, I was talking about at a belay. Confusion sorted! Even so... At a runner placement equalised in the same way, if one pops the other will still have some element of shockloading as there is now a slack static link in the chain.

In reply to Tom Povey: From reading further posts, I too thought you were talking about anchors rather than runners. Though I would still say minimising the distance that is run through, should 1 placement fail, is a good idea whatever the application.

In reply to James Jackson:

And where did the dynamic element go? Has the rope miraculously dissapeared.

In reply to Jon Greengrass:

No of course it hasn't, hence I said an element of shockloading. Nothing compared to a belay going, but there will be some nonetheless.

In reply to James Jackson: think about what you are saying. how can there be any shock loading? The load is applied to the runner by an elastic (the rope) connection.

You are confusing impact force with shock loading.

In reply to James Jackson:

Yes, I shared your misaprehension that Mr. Povey was talking about a belay at a stance rather than a runner, and was making a big mistake in his "mental modelling" of the situation. One protection point "ripping" on a simple twisted sling equalised belay at a stance would be a much more serious situation.

Consider also that a fall may generate considerable forces in the system BEFORE the gear rips.

The resulting situation of the belayer is then comparable to someone "protecting" themselves on via ferrata with a simple sling and krab, instead of the recommended (actually essential) friction brake system.

Even worse, actually.

I think Petzl provide a graphic illustration of the dangers of this in their catalogue, and possibly also on their website

So, unless you are TOTALLY certain that both anchor points are "bombproof", it is best to clip into them separately if at all possible.

In reply to Jon Greengrass:


It's all just force and energy.

In a system with highly elastic component (e.g. the rope) the graphical representation of the application of the force (over time)would be an extended, smooth "hump".

In a system with a low elastic component, (e.g. falling directly onto a slack dyneema sling)it would be a steeper, higher, much shorter "spike".

The "peaks" of these two graphs are the significant points.

IIRC the total energy absorbed is the area under the graph.

The differences are quantitative, not qualitative.

A failure of one anchor of an equalised running belay would result in a higher fall factor. The resulting longer fall would be held by the same length of rope. That's how you define fall factor.

That is exactly right. As I said above, the only difference in the case of running belay anchors between a single point and equalised points that then fail is that in the second case the fall is longer, so you have a (normally slightly) higher fall factor.

In reply to dark_star:

Excuse my ignorance but what is a sliding X? Do you just mean a good old sling with a twist in it?

In reply to Wibble Wibble:

It isn't a technical term, just a good description of a way of twisting a slig.

In reply to dark_star:
Here is a qoute from the American Safe Climbing Association:

Many climbers use a "sliding X" to equalize two pieces - ususally beginner climbers with bolt anchors. You should NEVER use this except in two specialized cases (see below). While the sliding X does equalize the pieces, it assumes that neither could break, since if one does break, there is severe extension in the system - enough that it would likely cause the carabiners to break. Since it assumes neither piece would break, it's a stupid system - if neither would break, there's no need for equalization. If one might break, then there is WAY too much extension. This is why many call it the "death X." Instead, use one sling off of each bolt or piece. You can tie one shorter to approximately equalize the pieces if needed.

The two cases where the sliding X is used:

1. equalizing tenuous pieces in a larger anchor - for instance, two poor nuts in a large natural pro anchor. The nuts are equalized, then the sliding X is equalized with other pieces through a cordelette, webolette, or other non-extending method.
2. equalizing two very tenuous pieces in extreme aid - for instance, a hook and a bashie on A4 terrain.

In reply to Paddy Duncan:

Damn.

I just typed out a post making almost exactly the same points.

In reply to Tom Povey:

Thanks. Haven't used that for years, always independently equalise stuff with the rope or a long sling with an overhand knot in it.