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Chockstone Forum - Gear Lust / Lost & Found

Rave About Your Rack Please do not post retail SPAM.

 Page 2 of 2. Messages 1 to 20 | 21 to 26
Author
Sliding X revisited
kieranl
28-Jan-2015
11:51:39 AM
Got my vector lines muddled in my head. So yes it does equalise.

But the second point still holds. If your anchors are bombproof it doesn't matter, but if they're not then it might.
johnpitcairn
29-Jan-2015
10:18:07 AM
I've often used a sliding X made from a single extendable draw (60cm) plus one extra biner (grabbed from anywhere convenient) to equalize 2 small or dodgy wires close together. It's pretty damn quick to rig and extension is quite limited anyway due to the shortness of the sling.

If I need to span a larger distance between the pro where extension might be a problem, I don't shag around with knots unless I have a great stance, I'll add an additional extender to the top of one or both legs of the sliding X. I might clip into one of those while I'm building the rest of it. Again, it's fairly quick to rig. The only caveat here is the extra biners in the system, whether they might contact the rock, what happens if one piece pulls and hits a biner*, etc.

* I'd finished a route recently and was bringing a second up when he fell and put a lot of sideways tension on my last hex. It popped, hit its own biner attached to the rope, opened that and fell the length of the pitch. Wow.

Jim Titt
31-Jan-2015
10:51:28 PM
On 28/01/2015 Dave_S wrote:
>
>Incorrect. The only degree to which magnitude of load on the anchors can
>differ with a sliding-X is due to friction between the carabiner and sling,
>which is negligible in comparison with the load force. The carabiner simply
>cannot exert force on one end of the sling more than the other, which would
>be required in order for different magnitudes of force to be placed on
>the anchors. The only way in which forces on the anchors can differ is
>in direction.
>

The friction isnīt negligable, itīs roughly 1/3rd of the load force. 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 isnīt hugely better really (8mm cord 62/38, 10mm Dyneema 58/42).
BBSR
2-Feb-2015
3:18:21 PM

> 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 isnīt 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.
Jim Titt
2-Feb-2015
8:05:13 PM
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 isnīt 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 arenīt in the "right" place.

The load-split numbers in themselves donīt 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.
rightarmbad
2-Feb-2015
9:33:53 PM
Take home answer is simple.
Doesn't really matter much what way you rig, bomber pieces equals good anchor.
Just don't do dumb things.

 Page 2 of 2. Messages 1 to 20 | 21 to 26
There are 26 messages in this topic.

 

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