"sliding X with limiter knots"

[counterfeitfake]

Engaging noob mode...

 

There was some discussion here about anchors, precipitated by this thread over at rc.com (before our thread devolved utterly into spray).

 

Glancing at the RC.com thread, I wondered: what is this "sliding X with extension limiting knots" that they mention? I did a little searching but only came up with references back to various other RC.com threads. I tried to envision the system and couldn't. Can someone illustrate?

[G-spotter]

You tie off the sliding X so that the power point biner(S) can only slide a little way in either direction, sort of like a cordelette. That way if one anchor piece blows you don't get a massive shock load on the other one, just a tiny little shock load.

[Alpinfox]

Sorry, that image was just too great to not post.

 

Here is an illustration that is a little more serious:

 

You can read some drama-queen gear wanking about the "deathX" HERE

[catbirdseat]

I'm not a good illustrator, but assuming this is not a troll, the purpose of the knots is to limit extension should a piece of the anchor fail. You are trying to balance the useful angle over which self-equalization will work against the potential for extension.

 

The closer the knots are tied to the power point, the less extension, but also the narrower the useful angle. If the pull comes from outside that useful angle, no equalization will occur and all the force will come on that one leg of the sling.

[counterfeitfake]

Okay, I had envisioned that drawing but thought that those knots would make it no longer a sliding x. Thinking harder I realize that it can still slide some. Le doi.

 

Thanks!

[catbirdseat]

Time for you to do a little experimenting and see for yourself!

[billcoe]

Interesting that while reading John Long postulating on all this at RC.com, one of his buddies on supertopo just outed him for TR belaying him and some other friends back in the day by just holding the rope with his HAND

 

Too funny.

 

Still, there's some interesting ideas out there.

[Toast]

One of the point JL was trying to make was that the touted danger of shock load of the sliding X is overblown. He refers to testing by Blue Water that illustrates it's not as significant as some make it out to be. This is espcially the case if you further mitigate the danger by tying off the legs. He goes onto point out that something like a cordalette rarely actually equalizes all points. I may have read too fast, but my read on it is he likes the sliding x.

[catbirdseat]

One of the point JL was trying to make was that the touted danger of shock load of the sliding X is overblown. He refers to testing by Blue Water that illustrates it's not as significant as some make it out to be. This is espcially the case if you further mitigate the danger by tying off the legs. He goes onto point out that something like a cordalette rarely actually equalizes all points. I may have read too fast, but my read on it is he likes the sliding x.

One way of looking at extension is that you can compare it to your hypothetical 20 foot FF2 fall. How is an extra 2 feet of extension going to make it any worse?

[catbirdseat]

Interesting that while reading John Long postulating on all this at RC.com, one of his buddies on supertopo just outed him for TR belaying him and some other friends back in the day by just holding the rope with his HAND

 

Too funny.

 

Still, there's some interesting ideas out there.

If you consider that JL was, at one time, strong enough to pick up a climber with one arm, maybe belaying by hand would not have been so dangerous after all.

[underworld]

One of the point JL was trying to make was that the touted danger of shock load of the sliding X is overblown. He refers to testing by Blue Water that illustrates it's not as significant as some make it out to be. This is espcially the case if you further mitigate the danger by tying off the legs. He goes onto point out that something like a cordalette rarely actually equalizes all points. I may have read too fast, but my read on it is he likes the sliding x.

One way of looking at extension is that you can compare it to your hypothetical 20 foot FF2 fall. How is an extra 2 feet of extension going to make it any worse?

 

would it not be a very low shock to the system if you are belaying off of the anchor. so the big fall pulled one piece and there's x amount of rope out. the peice fails, and it extends 1 foot. that is 1ft/amount of rope out factor fall, since the rope is stil absorbing the shock.

[Dechristo]

it does't matter how strong you are when the rope burns through and starts burnishing bone.

[Alpinfox]

[ ] One might argue that the elasticity of the rope is largely exhausted at the time maximum force is applied and therefore would be acting more like a static rope at the time of first piece failure/subsequent extension/subsequent loading of second piece. [/]