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Sliding X revisited 2-Feb-2015 At 8:05:13 PM Jim Titt

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On 2/02/2015 BBSR wrote:
>
>> With
>>something like 8mm cord the load on each side of the X (the load split)
>>is 65%/35% and a dyneema sling ca 60%/40%.
>>The quad was developed to remove the wrap of the X and reduce the friction
>>but it isn´t hugely better really (8mm cord 62/38, 10mm Dyneema 58/42).
>
>Interesting to see the numbers, I would have thought the difference from
>removing the wrap would have been much higher. Perhaps we need to use
>those revolver draws with bearings in them = )
>
>When I 'researched' this a long while back, I seem to remember one of
>the more interesting things was John Long suggesting that perhaps in hindsight
>he put too much emphasis on SERENE Anchors, which can tend to take emphasis
>away from other considerations. For example, it may make sense to put
>the anchor somewhere than enables a low risk ascent to a bomber jesus nut,
>and it may be worth sacrificing some of SERENE to get to do it. Total
>anchor failure (or belay failure) is more likely when a leader falls directly
>on to the Anchor, creating factor 2ish forces, so perhaps protecting the
>anchor from this is as important as making the anchor itself as strong
>and perfectly equalised as possible.

One concern with introducing dynamic equalising (or any of the anchoring systems like cordalettes) to beginners in particular is that they will place gear which fits their visualisation of a text-book anchor so they can build their belay and ignore the bomber pieces which aren´t in the "right" place.

The load-split numbers in themselves don´t look too bad (though it should be noted they are the best case) but when climbers start creating multi-piece anchors things go haywire real quick. We tested a 4 piece setup posted on an American forum which was claimed to "perfectly equalise". Theoretically it actually has a load split of 12.9%/21.7%/24.5%/40.9% on the pieces.
We then built the anchor and tested it and measured 7.7%/18.2%/30.9%/43.2%. The test result is worse because as the karabiners slide under load the cord starts twisting.

Another interesting thing we saw was testing 3 piece anchors when one fails, in all internet videos the climber unclips one and shows how nicely the remaining 2 equalise. In reality there is a karabiner and a cam/nut or whatever still clipped into the sling and when this gets to the central karabiner some exciting things happen, none of which have anything to do with equalising.