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moose_droppings
Mar 26, 2006, 11:45 PM
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In reply to: I have read through pages 7 and i am questionning the efficiency of the sliding X with limiter knots anchor in the situation of a traversing route where the a leader fall could bring the master point all the way to the limiter knot loading only one arm of the anchor ?
Then why would'nt you build it for that direction?
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fingertrouble
Mar 27, 2006, 2:19 AM
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In reply to: Your sloppy sliding-X is no solution at all; IMHO it's dangerous. The master biner mightn't be stopped by (edit: right before) a limiter knot. Depending on the amount of slop in the longer strand, the limiter knot could pull through the master biner and drag a carabiner with it. Worse, it might drag part way through. Don't "try it;" you could get unlucky. In reply to: You would have to tie the loose strand very long for that to happen In reply to: if you tied the troublette with one strand longer than the other this could happen as well. In reply to: You shouldn't bring John Long's name up to support a proposal that he might not agree with. |
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fingertrouble
Mar 27, 2006, 4:06 AM
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[I've done it again, wasted a few days ski mountaineering when I could have been glued to this thread.]
After I posted some observations from my master point sliding friction tests charlesjmm raised the question as to the effect of friction at other points in the anchor design where strands make U turns around carabiners. I basically blew him off:
http://i1.tinypic.com/rumwb9.jpg
but I didn't stop thinking about that issue. Recently I gave a little more scrutiny to the AstroGlide--which I had pointed out is basically a pair of z-pulleys equalized together. I happen to know a bit about z-pulleys from research I did for The Mountaineering Handbook. Z-pulleys are a core technique for mountaineers, and should be familiar to trad climbers, too, I would think. The punch line is that they don't actually deliver their theoretical 3:1 advantage, due to rope friction; the reality is more like 2.3X or even less when carabiners are used instead of real pulleys. Carabiners used as pulleys have roughly 67% efficiency, depending on rope diameter, rope history, carabiner load bearing diameter, pull rate, etc, etc.
In reply to: Aye, there's the rub.
As an example of friction at U turns around carabiners, here is yet another variation of the alpine equalizer:
http://i1.tinypic.com/sce6v6.jpg
Since the cord is fixed at the master carabiner, equalization might require 5 U turns. When I measured the distribution of a load to one of the side placements I got significantly less than 10% (you'd hope for 33%). I'd also hazard a guess that abrupt loading makes the imbalance worse, not better. (You can see that tying a limiter knot in the center leg defeats equalization, despite Trango's apparent recommendation.)
Applying the same physical measurement to Craig Short (or the double sliding-X, or sliding W, or whatever you want to call it) suggests that only about 20% of the load shows up at a placement when strands must slip to achieve equalization. Again, 33% is what you would hope for. Craig Short doesn't require that cord slip around every carabiner to equalize; you can tie a limiter knot in one of the side legs (but that wouldn't solve the extension problem). This implies that the many other designs (all the 3-placement proposals?) that use equivalent equalization configurations would be similarly impacted; the friction effect might make some 25-50-25 designs even worse than they appear, or better, It All Depends (TM).
Now for the AstroGlide. The friction analysis of a z-pulley is tricky (and necessarily coarse), but making the same measurements as before showed me that glowering's proposal delivers a bit over 20% if you measure at the center placement and about 40% when measured at a side placement. This could be improved upon somewhat by using a troublette-like master point. Since the other carabiners are essentially "troublette-like" i.e., the load slides on a single strand, why not use that approach at the most critical (highly loaded) sliding point? I've already pointed out that the equalette-type master point measures half the sliding friction of a sliding-X and the troublette-type master point measures half that of the equalette. The conclusion is obvious if you're going for best equalization.
What could be done to reduce the effect of carabiner friction? I doubt if it could be reliably addressed geometrically (sorry, charlesjmm), but those with excess time on their hands may chose to soldier on. John Long has already suggested using big, anodized HMS carabiners, but probably the biggest effect would come from using a Spectra/Dyneema runner for the equalizing components (runners made with the slippery Spectra/Dyneema on the outside, not on the inside like Trango Ultratape or high modulus cord). That would be a big constraint, since there are no commercially available Spectra/Dyneema runners that are long enough for most designs and also because no one recommends for--and every recommendation is against--relying on knots or hitches to hold in Spectra/Dyneema tape (or convince yourself with some simple tests)--so that precludes knotted equalizer designs, whether the knots are used as limiter knots or as length-adjustment knots. The only design that isn't impacted by these worries, IIRC, is that (those) of rgold.
Anyone can repeat these simple measurements and are encouraged to do so, but as
In reply to: Absent tests that simulate fall forces, we just don't know.
I reached this same point in writing my book when, after spending considerable ink pointing out that true equalization is unachievable and extension isn't such a big deal and that SRENE needs to be rethought, I asked in a subchapter "What's a Mountaineer to Do?" My conclusion was to focus on Anchor #1 (John's soon to be birthed "Jesus Nut") and to worry about security and direction of forces more than strength (which is what equalization addresses). Exploit redundancy. I wrote, "Your primary focus should be to connect the placements of Anchor #1, not so much in hopes they all share the load (mutual strength), but so that they work together to ensure mutual security."
Not a perfect recipe, but that was the best I could come up with two years ago when I wrote the book.
Craig
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glowering
Mar 27, 2006, 4:11 AM
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Craig,
Are you saying the sliding-X with limiter knots is inherently dangerous? If so this is the first time I've heard it and you should be making it heard beyond this thread if it is true. People tie the Sliding-X the way I'm describing all the time by accident due to differences in the length of the strands when you tie the limiter knots.
Even if I tie the sliding-X with more than twice the slack I showed in my picture (which itself was exagerated to at least twice what is needed or wanted - because the excess slack could interfere with the weight bearing strand) it's not an issue.
The slack resulting from the wrap around the biner is taken up by the wrap around the biner. I don't see how it could contribute to the limiter knot pulling through the biner.
Maybe you could post some photos demonstrating what you are describing and how much slack it would take to happen.
If you tied the strands between the limiter knots exactly equal and tie the Sliding-X then the weight bearing strand will be the strand with the X in it, and the other strand will remain loose. Do you see the same issue with this setup?
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hemp22
Mar 27, 2006, 6:09 AM
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In reply to: In reply to: You would have to tie the loose strand very long for that to happen Not really. The slack resulting from a wrap around a biner is plenty enough to pull the limiter knot into the master biner and potentially wank its carabiner. Even exactly equal lengths will, under tension, result in the limiter knot being on the opposite side of the main carabiner's bend from the upper limiter knot.
At least, I hope that's what he's talking about, because I can't imagine how he'd picture this happening on a normal sliding X with limiter knots.
also, Craig, it's possible to buy a 4 meter x 10mm sewn dyneema sling from Wild Country. They seem a bit hard to find, but are a cool piece of gear.
link
it's true that you're not supposed to try to tie 2 strands of dyneema together because there's not enough friction. But, it holds a knot just fine when the knot is a limiter knot in a sewn sling (like in the basic limited sliding x) - unless, of course, you have some data that suggests that using a standard sliding X with limiter knots made from a skinny mammut dyneema sling is somehow dangerous.
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fingertrouble
Mar 27, 2006, 11:04 PM
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glowering, I didn't say or mean to imply that the sliding-X is unsafe. I doubt if a limiter knot pulling through the master carabiner would be a problem either. hemp22 put his finger on the issue where I should have been more clear: your method of clipping into a limiter knot (figure-8 "clipped in its butt") when there are significantly different strand lengths in the sliding-X appears to me to guarantee that that clipped carabiner will get pulled into the master carabiner, maybe a little, maybe a lot. I couldn't predict what might happen then, but I'd certainly want to avoid such a possibility, particularly when it seems easy to do so.
http://i1.tinypic.com/se7xqo.jpg
Why not just go with a troublette-type master point and simplify things?
In reply to: If you tied the strands between the limiter knots exactly equal and tie the Sliding-X then the weight bearing strand will be the strand with the X in it, and the other strand will remain loose.
http://i1.tinypic.com/rths1x.jpg
What I meant before when I said the AstroGlide was a moving target is that the photos I've seen are each somewhat different. Some show an equalette-type master point and two master carabiners, for example.
OK, got your propeller caps on? I made some tests by linking a series of loops with carabiners and pulling on them with a 3-ton comealong. The loops included one made with 11/16 webbing tied with an offset (flat) overhand, one made with 7 mm cord tied with an offset (flat) overhand (European Death Knot), one made with 8 mm Dyneema tape (Mammut runner) tied with an offset (flat) overhand, one made with a figure-8 "clipped in its butt," and one made with either ratty old 3 mm accessory cord (my dog's old training leash) or old 4 mm accessory cord, both tied with a Yosemite bowline and ring loaded. That's the knot I recommend in my book as a better choice than the conventional rethreaded figure-8, including for tying in to the rope. I pulled until the 3 mm cord loop broke (at a carabiner, not at the knot); I figure that amounted to not much more than 2 kN. At this point the knotted Dyneema runner had started to roll over on itself (slip) and it appeared that the figure-8 "clipped in its butt" was starting to slip. I then put in the 4 mm cord loop and pulled on the loops again, but not to breaking (which would have been maybe 6 kN). At that point the Dyneema runner was rolling over on itself and the figure-8 "clipped in its butt" was obviously slipping. No other knots, including the Yosemite bowline, slipped or rolled.
From these few tests I conclude: do not rely on knots in Spectra/Dyneema tape; no not use the figure-8 "clipped in its butt" in anchor designs until better testing confirms its suitability; the Yosemite bowline is strong and is immune to the ring loading concern that applies to the figure-8.
Note that a troublette configured as illustrated above does not "rely" on the limiter knots. Even if a Spectra/Dyneema runner is used the distance slipped would be very small and would be stopped by a carabiner. Rigs where extended slip in Spectra/Dyneema runners might occur, especially under abrupt loading, could result not only in knots slipping but also the potential of the cord melting.
Thanks for pointing out a source for a long Spectra/Dyneema sling, hemp22. I note that the sales pitch on your link says "This huge and hugely useful sling makes perfect use of 10mm Dyneema: compact enough to carry easily, the Cordelette is the simplest way of safely equalising any belay. Ideal for all mountain environments. Comes with instructions." Instructions! :shock: We've obviously been wasting our time.
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charlesjmm
Mar 28, 2006, 3:07 AM
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As happy as I was with the AstroGlide and after reading Craig’s posts, I set out to better understand the effects of friction on the load balancing qualities of this design; something I should have done before shouting Eureka….
At the heart of the AstroGlide lie two independent pulley systems which handle the load balancing duties by means of a 3:1 mechanical advantage created on each side of the anchor. The performance of a 3:1 pulley system is governed by the efficiency of the two pulleys that comprise it. In ideal conditions, i.e., absence of friction, rope elongation, inter-fiber friction, etc, a 3 to 1 mechanical advantage is achieved; as the quality of the pulleys decline so does the mechanical advantage and hence the overall load balancing qualities of the AstroGlide.
Let us translate this into numbers; the following tables show the behavior of the AstroGlide as the efficiency of the pulleys declines from ideal (100%) to what biners can offer (around 60% - if you have better data I would appreciated it).
http://i49.photobucket.com/...ficiencyanalysys.jpg720x540 - 52 K
Table 1 assumes that a load of 100 is shared equally on each side of the anchor. With 100% pulley efficiency, we get a load distribution of 33,33 / 16,67 / 16,67 / 33,33 for 4 pieces and 33,33 / 33,33 / 33,33 for 3 pieces….what we would all aim for. Now, look at how the results deteriorate as quality of the pulleys goes from 100% to 60% : 24,49 / 25,51 / 25,51 / 24,49 for 4 pieces and 24,49 / 51,02 / 24,49 for 3 pieces. Curiously, the 4 pieces anchor starts showing equalizing behavior while the 3 pieces anchor shows a 25 / 50 / 25 behavior, exactly what we were avoiding!!!!!!
Moreover, remember that the master point also suffers from friction problems, which means that the total load will be shared unevenly by the two sides of the anchor from the start. This is simulated in Table 2 with a 10,52% (47,5 vs 52,5) difference on each side.
Without a doubt, FRICTION is the monster to defeat. Anchor designs incorporating many U turns or biner contact to achieve equalization definitely embed the seed of their doom, it’s in their DNAs!!!!
The number of biner contacts within an anchor could be a good indicative of performance, in that case the Equalette and Mhabitch´s definitely stand out.
I need a break from this anchor design roller coaster :D ......
CharlesJMM
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glowering
Mar 28, 2006, 6:27 PM
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As far as the AstroGlide being a "moving target" I don't think a certain named configuration (equalette, AstroGlide, etc.) has to have all aspects of the anchor the same everytime you make. The AstroGlide is just an anchor configuation with biners at the limiter knots acting as pulleys and overhand knots with one strand pulled loose to control extension and equalization. I believe I mentioned when I first posted it you could put limiter knots in all 4 arms for a four point anchor, I would still consider that an AstroGlide. If I put a sliding-X, or two biners, or one biner (ala troublette) for the powerpoint, it's still an AstroGlide IMO. I guess we're splitting hairs here. If you back up the troublette with a quickdraw to the other strand is it still a troublette? I also mentioned (mhabicht's) figure8 in the butt knot was an untested knot as far as I know and you could use another knot (bowline, two overhands, etc.) in it's place. I like it because it holds the biner firmly in place, but don't trust it yet.
So back to my proposal for the powerpoint (the sloppy-X). If you don't use the 8-inthebutt is there any reason not to use it? I have only tried it maybe 6 times so the more we all try it the more we will see if it proves useful. Craig you might say the itch (redundancy needed at the powerpoint) doesn't exist, but one principle many of us live by is don't trust your life to one piece of gear. If you do, that better be one bomber piece of gear (e.g. multiple strand rope enclosed in protective sheath, a LOCKING biner). Would you trust hanging 3 people and all your big wall gear off a single strand of a sling? Do they pull test all slings? Maybe if it's your powerpoint AND you use a special/bomber sling I would be ok with it. A good analogy is the belay loop on harnesses. Yes it's one piece of gear you are trusting to hold you life, but it's doubled around itself and sewn more extensively than a runner. Manufacturing defects DO happen. I'm not willing to throw redundancy out the window in the one link of the chain that can possibly take more force than any other I can think of.
Maybe the profile of the sliding-X changes depends on how it's tied. i.e. if you tie the X before of after you tie the limiter knots, or if the relative lengths of the strands effect how it sits. I'll have to play with a few times and see.
As far as friction and efficiency go, we will need some better tests before we can come to any conclusions. e.g. Craig's informal test showing the troublette has half the friction of two biners on the strands (ala Largo's equalette) doesn't see plausible to me unless there is some additional friction generated somehow (the biners interfering with each other?).
But I also go back to Largo's earlier statement. To paraphrase - equalization isn't so much about getting all forces perfectly equal, but redundancy. Redundancy isn't true redundancy if you experience cascade failures, it's backup. I think most people will end up using combinations of slings to build anchors (and that's probably the way it should be). But the reason I like the AstroGlide is because I can set it up faster than anything else (besides a direct rope tie in, or a static tied coredelette) and get rough equalization among 3 pieces with limited extension.
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fingertrouble
Mar 29, 2006, 3:13 AM
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In reply to: The AstroGlide is the same no matter what the design of the master point configuration.
Adding a backup feature to the troublette does not affect its equalization performance. In fact, those who are paying attention can see that, given the difficulty of tying precisely equal strands between the limiter knots, the equalette master configuration is basically a closely backed up version of the troublette.
My understanding of this thread has been that it is a search for a cheap way to achieve true equalization, particularly of a 3-placement anchor. It appears to me that, all things considered, there is no cheap way, probably not even an unconscionably complex way. This is the same conclusion I reached two years ago as I was writing my book. That's not the end of the anchor design story, but it does seem to mean that building good anchors can't be boiled down to any simple recipe.
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glowering
Mar 29, 2006, 1:36 PM
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Craig, I think you need to read this thread from the beginning, you're still not getting it and repeating things that have been stated.
As I suspected, the sloppy-X will cause the biner to hang perpendicular to the anchor, while an X tied with equal strands will cause it to hang parallel (at least in cord). I guess if you had actually tried my powerpoint proposal before commenting you would have seen this. Why use a "troublette" without redundancy if there's a better option available?
In reply to: Adding a backup feature to the troublette does not affect its equalization performance. In fact, those who are paying attention can see that, given the difficulty of tying precisely equal strands between the limiter knots, the equalette master configuration is basically a closely backed up version of the troublette.
I though you said the equalette has twice the friction of the "troublette?"
The only way I could get a biner in the butt of a 8 into the master biner like you have shown was to manually place it there with my hands...
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sandstone
Mar 31, 2006, 12:26 AM
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In reply to: ...The only way I could get a biner in the butt of a 8 into the master biner like you have shown was to manually place it there with my hands...
Glowering,
That's the same result I got every time I tried the "sloppy X" -- both the knot and the 8 biner were consistently held clear of the interior of the master biner. I had the rig tied with just enough slack on one side to make one wrap around the master point biner. Getting the length right was easy, I just clipped in the master biner before tightening the 8 knots.
I have more concern with strange loading of the upper biners if the middle pro fails. In that case the overhand limiter knot and possibly even the carabiner on the pro can get pulled through the (8 in the butt) biner. You pointed out this possibility when you first posted the design.
Hopefully someone with the right equipment will do some thorough testing of the Astroglide. It would be interesting to see how close the friction preditions are to real world.
Even if the Astroglide doesn't test out to be a good solution overall, it's a clever piece of work, and your photos and posts have been consistently clear and thoughtful.
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fingertrouble
Apr 3, 2006, 2:44 AM
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I have posted what I consider to be a wrapup of the conclusions of this thread here on the "Solution to John Long's anchor challenge" thread. The punch line is there is no solution to John Long's anchor challenge, only compromises. The "solutions" will all be killed by friction. I proposed what I think is a reasonable compromise.
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charlesjmm
Apr 11, 2006, 2:28 PM
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The fight against the Friction Virus has led anchor designs to the reduction of sliding biner-cord contacts throughout the anchor elements, the Equallete being the most representative of this concept since it only incorporates 2 sliding biner-cord contacts at the power point. Other designs have addressed this issue in different ways :
http://i49.photobucket.com/...trandPowerPoints.jpg
Minimizing biner-cord contact at the power point would mean having only one strand supporting the clip-in biner, something very few people would feel comfortable with. An obvious remedy would be to duplicate power point elements (double ELET, double Troublette, double Equalizer), but this would defeat the initial purpose.
Here is a proposal that would minimize biner-cord contact at the power point while providing a backup strand for failure scenarios :
http://i49.photobucket.com/...TroubletteBackup.jpg
1) Using a 48 inch sling, begin by setting up a Troublette.
2) Add two overhand knots to the bottom strand.
3) Clip the top strand and in between the overhand knots with a HMS biner.
There you have it : a Troublette with a safety net using only 1 sling. The biner will slide on the top strand while the bottom one will provide for safety duties when required. Picture 4 illustrates when the top strand is cut; picture 5 illustrates failure of the right side. One concern might be the overhand´s ability to hold if abruptly loaded, however, slippage in contained to a few inches.
[Edit] An additional bonus: If you are lucky enough to experience failure of both strands on one side, the backup strand will still handle this most unfortunate/rare incident.
It could be argued that only one overhand knot would suffice, however, if the loop below the overhand is left sufficiently big, failure of one side could force the failed placement biner to go through the master biner producing an unpredictable clash. The second overhand knot eliminates this concern.
This idea provides enhanced performance over the Sliding-X-with-limiter-knots while making the Troublette more appealing for use in power points.
[Edit] It could also serve to further reduce friction in Equalette type power points (MHabitch´s, AstroGlide) : instead of placing a biner on each strand, the second strand could be made longer to implement the safety device and lab results would look even better!
Here is the Equalette with the enhanced power point.
http://i49.photobucket.com/...jmm/EqualetteNPP.jpg
Comments / issues welcomed.
CharlesJMM
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superbum
Apr 15, 2006, 5:38 AM
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christ almighty. Remind me never to climb a long multipitch w/ you guys. I forsee 30 minutes at each belay station setting up the anchor. Your skills will come in handy however, when we are constructing an anchor for our hanging bivy...
That said, good on ya for being thinkers. Nothing wrong with a little over analizing from time to time.
I suddenly realized I have no point...
bye.
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karlbaba
Apr 15, 2006, 6:25 AM
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First let me condemn myself for posting to this thread without reading all the posts.
Second I suck for cross posting this to the John Long anchor thread
Naturally everybody already knows that very few anchors are poor enough to need ultimate geek solutions.
And all solutions need to consider the additional risk that comes from having to carry extra gear to build elaborate anchors. Time equals safety on some routes too.
But it seems to me that if you want equalization without worrying about direction or extension, you could build an anchor utilizing screamers so that when forces were really great enough to stress things, the screamers would start to rip at a certain force and automatically provide an even force on each piece connected to it's screamer until the force was dissapated or the length of the screamer reached. Pieces that immediately fail below screamer activating forces aren't going to help in a bad situation anyway
Just an idea
Peace
Karl
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dirtineye
Apr 15, 2006, 11:14 PM
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HAHA, well, you know, that ain't bad karl.
Now someone will go on for 40 more pages about how to set up the screamers in proper geek fashion.
Don't hate me, I'm a recovering math geek myself. 2,172 days and 18 hours of good, clean, math free living!
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charlesjmm
Apr 16, 2006, 12:12 AM
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Take a look at this variant of the improved Equalette type power point :
http://i49.photobucket.com/...oubletteBackupII.jpg
A more elegant approach which requires calibration of only one overhand knot and keeps both strands spaced out. When a placement fails or the main strand is cut, the load will fall on a bight instead of the overhand knot. The backup strand controls sliding range and the amount of extension. Make sure extension is kept to a few inches.
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jakedatc
Apr 16, 2006, 12:21 AM
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charles how's that work with 3+? 2 points has never been an issue since modified sliding x works pretty darn well
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charlesjmm
Apr 16, 2006, 1:35 AM
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Jakedatc, the issue being addressed concerns friction problems on Equalette type power points. The master biner of a Sliding X experiences unwanted friction since it is sliding over two x´d strands. This could be a contributing factor in the 10 +% equalization difference that John Long has reported. What I’m proposing is an improved Sliding X in which the second strand is given better use as a backup instead of contributing to superfluous friction. Fingertrouble has posted regarding the benefits of reducing sliding biner-cord contact to only one strand at the power point.
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jakedatc
Apr 16, 2006, 3:12 AM
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gotcha.. thanks for explaining
whats that scaffolding that you set your anchors on? if that was semi full strength i'd be campusing and roof climbing all around on that haha
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elvislegs
Apr 17, 2006, 3:57 PM
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In reply to: christ almighty. Remind me never to climb a long multipitch w/ you guys. I forsee 30 minutes at each belay station setting up the anchor. Your skills will come in handy however, when we are constructing an anchor for our hanging bivy...
heh, nice vic, no doubt man.
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healyje
Apr 24, 2006, 9:00 AM
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Charles,
Haven't looked at all this lately, but on catching up I noticed your latest. With cloves instead of overhands this rig is essentially a modified version of half of mhabicht's rig.
http://i49.photobucket.com/...TroubletteBackup.jpg
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adnix
Apr 24, 2006, 11:58 AM
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In reply to: christ almighty. Remind me never to climb a long multipitch w/ you guys. I forsee 30 minutes at each belay station setting up the anchor. Your skills will come in handy however, when we are constructing an anchor for our hanging bivy...
I've done hanging bivy with two pitons and no cordalettes whatsoever. One of the pitons popped out in the morning once my parner pulled the cord wrong direction. The other one got "shock loaded" but held just fine. We were tied in with our climbing rope. It's always my policy.
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charlesjmm
Apr 24, 2006, 9:40 PM
Post #874 of 915
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Registered: Jan 25, 2006
Posts: 75
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In reply to: Charles, Haven't looked at all this lately, but on catching up I noticed your latest. With cloves instead of overhands this rig is essentially a modified version of half of mhabicht's rig.
Certainly Healyje, I had the same impression myself although I worked up the solution from a Troublette in search of making it more appealing for use in master points; betting your skin to only one strand is way too thrilling for my taste.
In the end, it served the stage for a better solution that really shines when carried pre-set:
http://i49.photobucket.com/...TroubletteAnchor.jpg
Abstractively, you could also view it as a Sliding X (with limiter knots) in which you make one strand longer (the back up strand) and move the limiter knots near the placements, so maybe the ancestor of all these ideas could be attributed the to Sliding X.
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jimdavis
Apr 25, 2006, 5:51 AM
Post #875 of 915
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Registered: May 1, 2003
Posts: 1935
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If you could rig this with one overhand on 1 biner, and a clove hitch on the other...it'd be a lot easier to adapt from anchor to anchor. You could leave the biner closed and locked...then just adjust the clove to length, and tie your backup strand knot of choice.
Jim
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