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Josh Beckner
climber
Tetons
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Topic Author's Original Post - Mar 7, 2016 - 03:39pm PT
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I'm looking for some feedback on a 'how-to' video that I recently helped create (unlisted on YouTube):
[url=" https://youtu.be/XpwY4vLEKYo"]
This video is aimed at students that are taking courses with SIET (advanced alpine mountaineering courses) and need a brush up on alpine anchors, need to get on the same page as one another in terms of vocab, etc, and need to understand current industry best practices before their course. The vid also serves as a resource for anyone interested in learning more advanced tech skills.
Thanks for the help!
jb
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GDavis
Social climber
SOL CAL
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Just booted it up, so far killer production!
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thebravecowboy
climber
The Good Places
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seems odd to prep for alpine with bolted anchors, right?
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Vitaliy M.
Mountain climber
San Francisco
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Bro you have a knot in the dyneema sling...
#NOOB
I'm glad that I am not the only one who brings a powerdrill onto alpine expeditions!
#WHATWOULDBRIDWELLDOTOYOU
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marty(r)
climber
beneath the valley of ultravegans
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Pretty slick production! Hope you and Marisol are doing well.
Are those portaledge shots from the Charakusa?
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the Fet
climber
Tu-Tok-A-Nu-La
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Good stuff!!
For the Magic X with Extension Limiter Knots
Your Cons
Knots are difficult to get out after use
Required 2 knots, thus more time to set up
Master point is not user friendly when loaded
I carry 2 of these pre-tied and just leave them tied. I tie them offset where one side is longer than the other. It works for side by side placements or up to about a foot difference between the two placements. So they work for 95% of placements as is, and if the placements are far apart I can extend one with a sling. So it negates the first two cons.
I use Metolius Monster webbing which is a mix of dyneema and nylon. They are a little thicker and wider than plain dyneema, but the nylon doesn't suffer from loss of strength from repeated bendings like dyneema. Plus they are easier to untie than plain dyneema. I take my time and dress my knots (overhands) and even after using these for dozens of pitches they are still easy to untie if needed.
For the third con, I clip a big locker in as my master point, then clip everything into this. It's two more biners to carry, but it makes it so easy to clip and unclip and stay organized, it's worth it to me. Some people are concerned with clipping two biners together, but these are all lockers and easy to keep an eye on, so it's not like two biners on a piece of pro that could unclip in a fall.
I leave a locker on each one for the masterpoint and for racking.
The SWAMP looks cool. I'll have to try it.
A Con you missed:
Doesn't distribute a variable direction load well
The Equalette
Is like a more redundant Magic X with Extension Limiter Knots. I like it for top rope anchors that I can't keep an eye on (in case something is abrading it and I can't monitor it) but is kind of overkill in multipitch climbing where someone is always keeping an eye on it IMO. Same things as for the X above apply. Tie it offset and just leave it tied. Take the time to dress the knots and they come out pretty easy, especially with monster webbing.
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rgold
Trad climber
Poughkeepsie, NY
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The video looks ok to me, but I wish that you would not characterize the increase in tension in the arms of your anchor sling as "exponential." (You say this and then repeat it in the text review that follows.)
I know, the term "exponential" is passing into popular parlance as a synonym for the Trumpian "yuge," but it does have a precise meaning, and sling tension does not increase exponentially with the power-point angle.
The increase is much more extreme than exponential increase---the load increases without bound as the power-point angle approaches 180 degrees. (The function in question is essentially the secant function.) The graph below compares exponential growth, the blue graph, to the tension in an anchor strand, the red graph. The 180 degree power point angle line is dotted green.
(The x-axis markings are degrees of power point angle, the vertical scale is a generic load scale. The power-point angle was converted to radians, and the plots use the radian value, not the degree value. In order to separate the graphs in a small window, it was necessary to use very different scales on the axes.)
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Josh Beckner
climber
Tetons
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Topic Author's Reply - Mar 11, 2016 - 11:49am PT
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rgold, thanks for that info! I'll have to take your word for it because honestly, I don't fully understand the physics here. I understand the take home point, that "the load increases without bound" when it's close to 180. But is it exponential when we go from 0 to let's say 90 degrees?
Regarding the bolts, we chose to use bolts so folks that are learning this stuff won't get distracted by the pieces. I mention pieces of varying quality (screws, pickets, etc) to address the best use of each type of anchor. If we showed each anchor on each type of piece that it could be used for, the vid would be way too long.
Regarding knots in spectra/dyneema, it's fine, though it does weaken the material, but all knots weaken the material they're in.
the Fet, thanks for the thoughts!
marty(r), yeah, that's the Charakusa...miss that place. Someday Pakistan will be safe again! Hope you're well too!
Thanks for the input everyone! More thoughts will be appreciated...
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rgold
Trad climber
Poughkeepsie, NY
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Mar 11, 2016 - 02:24pm PT
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I understand the take home point, that "the load increases without bound" when it's close to 180. But is it exponential when we go from 0 to let's say 90 degrees?
Well, the secant function is not the exponential function, to the answer is the growth isn't exponential anywhere.
But since you are looking for intuitive content, this isn't an easy question to answer. Moreover, I'd suggest that even if the growth over a finite interval was exponential, it wouldn't mean as much as you might think.
This is because, over any finite interval, the exponential function can be approximated with high accuracy by a polynomial function even though, in a critical technical sense, polynomial growth is "much slower" than exponential growth. So for a finite interval, we may not "in practice" be able to tell the difference between polynomial growth and exponential growth, which means that calling growth in a finite interval "exponential" conveys little or no information, regardless of the intuitive content.
Forgetting about the mathematical niceties that preclude the use of "exponential" for things that aren't, you are looking for a suitably ominous term to characterize what happens when the power point angle approaches 180 degrees. I'd say the arm tensions (and so the anchor load) "increase catastrophically" and let it go at that.
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TLP
climber
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Mar 11, 2016 - 02:35pm PT
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Rgold, another good post with useful info and a bit of wry humor to go with it. Your graph is actually pretty reassuring about angles of 120 degrees or less, unless one of the pieces is a tiny cam or wire, or it's in crummy rock or a flexi flake. On the other hand, you really can't be doing a lot of hard falling in the alpine anyway. Too many sharp edges and things to hit.
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rgold
Trad climber
Poughkeepsie, NY
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Mar 11, 2016 - 05:56pm PT
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Please be careful about interpreting my graph for any real anchor, as I used a "generic" y-axis scale, not one with the actual loads for a particular anchor situation on it. To get those values, the y-axis values have to be multiplied by the anchor load. Also note that for ease of viewing, the axis scales are very different!
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David C
Trad climber
UK
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Mar 16, 2016 - 02:31am PT
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If we are on the topic of angles and anchors, it is worth pointing out that things are normally not as bad as sometimes portrayed.
1. it is almost impossible to create angles >120 or so once the system is loaded. This is because rope stretches. Even when using slings, the need to be able to clip the sling to the bolt, or tie a master point knot (which will create slack in the sling as it is tightened under load), or because even dymemma slings stretch a little, mean angles >150 are extremely hard to make happen. This means that getting the load to be >100% is next to impossible (see the nice diagram above).
2. The load is not often straight down. There might be a piece below to one side, or the belayer/hauler will be weighting the anchor to one side. This means one arm takes more force. Again this means it is hard for the force in one arm to be greater than 100%.
3. With small angles it is extremely unlikely the force is shared between the two arms at all, but will switch from nearly 100% on one arm and zero on the other to 0 on one and 100% on the other as people more around on the anchor. This means that small angles create MORE force on anchor pieces than slightly larger ones (but not as much as really big angles).
Re the video. What is missing is a banshee belay of some form; a belay using just the rope; a sling-based powerpoint that uses a butterfly rather than an overhand. Petzl seem to like using a clovehitch on a locker to form the powerpoint, so you could show this, but as those in the USA might be used to using the shelf, this could be a very bad idea as the shelf is a time bomb on a clovehitch powerpoint.
However adding new material to a video like yours will be expensive.
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overwatch
climber
Arizona
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Mar 16, 2016 - 07:29am PT
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Mr. C, I love multipitch climbing.com. Great resource.
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David C
Trad climber
UK
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Mar 16, 2016 - 07:59am PT
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Out of interest, did you buy the book as well?
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overwatch
climber
Arizona
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Mar 19, 2016 - 06:06pm PT
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Out of interest, did you buy the book as well?
No. I almost pulled the trigger on the Rope soloing book but have held off so far because of the price. most of my climbing is rope soloing. if I had the extra funds I would probably buy both of those books just because tweaking on books and gear is one of the pleasures in the sport for me
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bluering
Trad climber
Santa Clara, CA
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Mar 19, 2016 - 07:18pm PT
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Good vid for training people. Those rigs are essential to have in the grand bag-of-tricks.
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rgold
Trad climber
Poughkeepsie, NY
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Mar 20, 2016 - 10:08am PT
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it is almost impossible to create angles >120 or so once the system is loaded. This is because rope stretches. Even when using slings, the need to be able to clip the sling to the bolt, or tie a master point knot (which will create slack in the sling as it is tightened under load), or because even dyneemma slings stretch a little, mean angles >150 are extremely hard to make happen.
What happens in the worst-case scenario is a matter of high-school trigonometry. The graph below plots the amount the material stretches (remember you have to include what happens when the knot tightens) against the resulting power-point angle, if the initial (worst case) configuration essentially lies on a straight line between the anchors.
The 120 degree power-point angle is basically the cutoff between rigging equal arms and changing over to a "banshee" configuration with all the load going (initially) to a single piece.
This isn't the whole story, because (at least as a first-order approximation---Hooke's Law) the percentage stretch is proportional to the load, and is not a fixed property of the rigging material. Plus, remember that these figures are for a starting configuration---slings along a straight line between anchor points---that would never be the case in practice. But even in this worst-case scenario, the graph says that loads that stretch the slings more than 15% can never result in a power-point angle greater than 120 degrees.
The the more realistic effects resulting from starting a a specified power point angle less than 180 degrees do not turn out to be very dramatic, but for anyone who is interested, have a look at the version of the graph I posted above at http://www.desmos.com/calculator/ie2fbknbor. That version has a slider with values between 120 degrees and 180 degrees. The slider position determines the graph corresponding to the initial (unloaded) power point angle given by the slider setting.
For example, with the initial angle at about 145 degrees, a 10% stretch in the rigging would result in a 120 degree power point angle.
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