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curt
Feb 22, 2006, 1:25 AM
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In reply to: A few thoughts. First, regarding the Gordolette: http://members.cox.net/...ordo-lette%20004.jpg I'm really impressed at the fact that Gordo came up with a solution that is self-equalizing, has redundant strands (meaning that not only is it okay if a piece rips, but also if the line is cut), and has almost no extension. A sort of holy grail. So those are the pros...
I haven't had a chance to play around with any of these things yet--but I really like the looks of this.
Curt
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daithi
Feb 22, 2006, 1:43 AM
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JL,
Thanks for posting the results and analysis thus far. I am sure the constant questioning (ranging from the profound to the inane) is getting a bit tiresome, especially in your current state with an eye infection.
I also understand that you probably just want to gain an understanding from the current testing and not necessarily perform the most scientifically rigorous testing ever performed, so apologies if you feel some, or all, of these points are extraneous!
1. Quantifying the effect of lost of ‘dynamicity’ of rope.
In reply to: Using the same piece of climbing rope increases the chances of a shock load since after repeated drop testing, the rope looses it's stretch and becomes little more than a piece of static line.
Is the same time between tests allowed for the rope to recover? I agree with the assumption that the chance of shock loading is increased. However, the repeatability of these data will not be great unless the loss of dynamic properties over number of falls can be quantified or at least estimated in some way. If it is not, repeating a particular data point will prove difficult. To have confidence in the numbers we need a degree of repeatability.
2. Trends in data.
In reply to: Half the time it's less--the rest it's the same or a little more--at most about .75 kN, or 168 lbs.
Why is it sometimes more, sometimes less? Are these data trend indicative of some physical phenomena or do they fall within the bounds of experimental scatter?
3. Limiter Knots.
What do the results look like without these? Is it possible to infer some optimums for the placing of these knots? I imagine the use of these limiter knots is going to make the experimental repeatability quite difficult and also lead to quite large scatter due to difficulties with their exact location, knot chosen, how tight they were tied etc.
4. Variables chosen in test.
Having not thought about it for too long I would imagine the variables for the peak force felt would be, rope fall-factor (how much ‘dynamic’ rope there is to absorb energy), fuse strength (how much energy is absorbed by the first piece before it blows), length of sling and angle it makes (determine the extra length of fall and how much ‘static’ material there is to absorb it) and the relative length of arms in the anchor. What variables have to chosen to test and do you have trends for them over a range of values.
One potential problem I would see is only testing a one fall factor. I imagine a crucial variable will be the ratio of ‘dynamic’ rope to ‘static’ material in the system. For example, let’s take a high fall factor, implying a small amount of ‘dynamic’ rope out and a long sling making up the anchor, implying a long fall on a ‘static’ sling as one of the anchor pieces blow with a small amount absorbed by the rope. In the limit as the length of the dynamic rope goes to zero and a piece blows it just becomes a fall on 'static' material with potentially high forces depending on the length of the sling. This is the limit at the worse case. What is the behaviour as the length of dynamic rope decreases?
At the test conditions you were testing there is no ‘force multiplication’, which although may be true at all test conditions, I can still imagine a case where extension of an anchor could produce potentially lethal forces. What are the experimental results at the limits of your test variables?
Thanks so much for taking the time to arrange and perform these tests. They are invaluable. The above questions are all rhetorical and are just some thoughts, from a theoretical perspective, for you and the people conducting the tests. I realise it is quite presumptuous of me since I have only seen four data points and only read brief descriptions of the test procedure! Hopefully something in here was of use.
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slcliffdiver
Feb 22, 2006, 2:17 AM
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In reply to: The belayer is 'falling' onto the anchor in how many situations? I can think of one main scenario. When the leader has fallen past the belay, ripping all pieces, and the belayer is catching the leader directly on his harness along with a failing anchor.
In reply to: If in this scenario, the belayer is belaying off his harness and the rope runs through the powerpoint (which more than likely is above him slightly), the leader falls and pulls the belayer upwards..... no?
The belayer not being tied down has actually has brought up scenario that hasn't occured to me before. Climber falls with enough energy energy to suck the belayer up to the power point. Remaining energy of falling climber rips out a peice and the anchor extends. Now the belayer is pulled down by gravity and the falling climber limited by the configuration of friction belay device sucked into the power point biners. I'm guessing either the force the belayer can appy to the anchors is most likely going to be limited to either how much he can hold with a belay device or at most free falling onto whatever anchor material he/she attached to the anchor. Something else to play around with. A bit to complicated for my brain to get around right now.
In reply to: Does that make sense? I'm just trying to think of a scenario where the leader falls onto the anchor, making it fail (ie. pieces pop) and the belayer also 'falls' onto the anchor while the leader is theoretically still falling due to an extended anchor. |
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billl7
Feb 22, 2006, 2:25 AM
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In reply to: * Getting truly equal loads is impossible from a practical perspective no matter the anchor system - the different angles will create different forces.
Also, as long as the masterpoint is in line between one piece and the direction of the falling force, the force on each individual piece will never exceed the falling force. This is pretty cool. However, if that in-line piece fails then one has to look at angles with respect to the remaining pieces - and forces on those remaining pieces can exceed the falling force just like when rigging off of two bolts with a large angle between the rope-point and the two bolts. Better descriptions of this are in almost any text on anchors.
Bottom line: on a dynamically equalized anchor such as the gordolette the force felt by any and each piece will be somewhere between
a) a max of the falling force (assuming poor arrangement of pro other than the "central piece") and
b) a min of the falling force divided by the number of pieces (assuming pieces all close together).
Again, this is not intuitive - never realized this until today because of this thread. Thanks!!
Bill
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gordo
Feb 22, 2006, 2:40 AM
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That's a hard two pages today!! :)
FWIW I've put my Gordolette into a vertical crack situation and it fails misserably. Also, in more than 3 placements, I can' t get much good out of it.
Given 3 placements horizontal and especially a Top Rope I think it's (the Gordolette) a good rig.
I've been working the Quad and Equalette and can really see the benifit in speed. We are all looking for a compromise since we know there is no perfect system. The Equalette seems to be the fastest, it stays set up on the rack, equalizes well, is fully redundant, and limits extension. It sets up very well in the vertical situation, and can handle the 4 pieces well.
The pursuit goes well. I'll get a chance to put some of this on rock this weekend and hope to get some better idea on how I like it in the real world.
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rgold
Feb 22, 2006, 3:14 AM
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I think one of the problems with "shock load" analysis is that "shock load" is an undefined term. People use it without a clear idea of what it means, and different users mean different things. A peremptory internet search turns up "definitions" such as, "a load caused by the rapid application of a force," without, of course, even a hint of what either "rapid" means by itself, or what "rapid application" means in the context of forces. It seems fairly clear from the industrial sites that "shock load," however it is produced, is taken to mean a load that will probably exceed the load rating of the object, and so in this way I suppose that shock load has come to imply something very severe.
From the perspective of anchors, I think the only thing "shock load" ought to mean is the load that results from arresting a free fall. It follows that all leader falls shock load the system. So do falls by the second, if there is any slack at all in the rope, which means that most falls by a second shock load the system. However, a rappeller whose foot slips on an ice patch constitutes a challenge to this definition. The rappeller is never free falling, but the slip causes a "rapid application of a force" to the rappel anchor. If you want to call this a shock load, then you'll need to specify how fast the load has to be increasing in order to qualify as a shock. Enjoy.
From the free-fall definition, a shock load may be moderate or severe, and does not by itself denote an event of catastrophic severity. So, if an arm of an equalizing system fails and the anchor extends, the subsequent load is a shock load by definition. To say that there is no shock load because high forces were not measured is to imply the existence of a further condition that only recognizes as shock loads those events in which the force increases with "suitable" rapidity. But it is hard to imagine any reasonable specification for such a condition that would not in any case certify most anchor extension events as shock loads, at least those for which a free fall for the belayer is a consequence.
The only conclusion I can extract from this is that the shock-load terminology should be abandoned, because its lack of real meaning allows everyone their own meanings, and in particular allows the concept to become undesirable by definition, rather than by virtue of its actual effect.
It would then follow that the potential for "shock loading" cannot, by itself, be a "drawback" of equalizing systems. It would be better to ask a more specific question rather than allow damning by the subjective connotations of an undefined term.
I think the following question is an appropriate one: Given the fact that a non-equalizing system can, in many cases, transfer the entire load to a single piece, one might ask whether an equalizing system that suffers the failure of an arm will load up the remaining piece (or pieces) with more than they would have experienced if they had to bear the entire load originally. If the load after arm failure is the same or less, than the equalizing system would seem to be the better bet in spite of the "shock" loading. If the load is more, than the non-equalizing system might be a better choice. It appears from the data John has mentioned that it is the former possibility that obtains, and on this basis the sliding X looks good regardless of what you think "shock load" means.
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rgold
Feb 22, 2006, 3:17 AM
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I think one of the problems with "shock load" analysis is that "shock load" is an undefined term. People use it without a clear idea of what it means, and different users mean different things. A peremptory internet search turns up "definitions" such as, "a load caused by the rapid application of a force," without, of course, even a hint of what either "rapid" means by itself, or what "rapid application" means in the context of forces. It seems fairly clear from the industrial sites that "shock load," however it is produced, is taken to mean a load that will probably exceed the load rating of the object, and so in this way I suppose that shock load has come to imply something very severe.
From the perspective of anchors, I think the only thing "shock load" ought to mean is the load that results from arresting a free fall. It follows that all leader falls shock load the system. So do falls by the second, if there is any slack at all in the rope, which means that most falls by a second shock load the system. However, a rappeller whose foot slips on an ice patch constitutes a challenge to this definition. The rappeller is never free falling, but the slip causes a "rapid application of a force" to the rappel anchor. If you want to call this a shock load, then you'll need to specify how fast the load has to be increasing in order to qualify as a shock. Enjoy.
From the free-fall definition, a shock load may be moderate or severe, and does not by itself denote an event of catastrophic severity. So, if an arm of an equalizing system fails and the anchor extends, the subsequent load is a shock load by definition. To say that there is no shock load because high forces were not measured is to imply the existence of a further condition that only recognizes as shock loads those events in which the force increases with "suitable" rapidity. But it is hard to imagine any reasonable specification for such a condition that would not in any case certify most anchor extension events as shock loads, at least those for which a free fall for the belayer is a consequence.
The only conclusion I can extract from this is that the shock-load terminology should be abandoned, because its lack of real meaning allows everyone their own meanings, and in particular allows the concept to become undesirable by definition, rather than by virtue of its actual effect.
It would then follow that the potential for "shock loading" cannot, by itself, be a "drawback" of equalizing systems. It would be better to ask a more specific question rather than allow damning by the subjective connotations of an undefined term.
I think the following question is an appropriate one: Given the fact that a non-equalizing system can, in many cases, transfer the entire load to a single piece, one might ask whether an equalizing system that suffers the failure of an arm will load up the remaining piece (or pieces) with more than they would have experienced if they had to bear the entire load originally. If the load after arm failure is the same or less, than the equalizing system would seem to be the better bet in spite of the "shock" loading. If the load is more, than the non-equalizing system might be a better choice. It appears from the data John has mentioned that it is the former possibility that obtains, and on this basis the sliding X looks good regardless of what you think "shock load" means.
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rgold
Feb 22, 2006, 3:23 AM
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A number of people have mentioned that John's drop tests do not have a belayer in them. If we ignore the effect of the rope connecting the falling climber to the leader and just think about the combined weight of the falling leader and belayer (each weighing 80 kg), than an arm failure is going to involve arresting the their combined fall. Consider the case of a sliding X rigged from a two-foot sling with equal arms and stopper knots placed 3 inches from the carabiner. suppose that the belayer is clipped directly to the power point, in which case, if an arm fails, the pair fall 3 inches on a total of 15 inches of sling and so suffer a fall with fall factor 0.2. I don't know what the modulus of spectra webbing is, but the UIAA Journal devoted to equipment quoted the UIAA Impact force for a nylon sling as 18 kN. Using this value, our falling pair loads the remaining piece with about 9.9 kN---a pretty nasty jolt. Without the stopper knot, the pair falls 12" on 24" of rope for a fall factor of 0.5, producing a load of 14.6 kN on the remaining piece. Not good.
Now suppose the belayer is tied to the power point with 3 feet of sling. The fall in the limiter knot case is 3", stopped by 41 inches of sling, for a fall factor of 0.07. The anchor load is about 6.6 kN in this case. With no limiter knots there is a 12" fall on 60" of sling for a fall factor of 0.2, and the anchor load is 9.9 kN
Finally, suppose the belayer is tied to the power point with 3 feet of rope with UIAA rating 9 kN. Treating the sling as completely rigid, the fall in the stopper knot case is 3" on 3 feet of rope for a fall factor of .08, and the resulting anchor load is 4.5 kN. With no stopper knots, the fall is 1 foot on 3 feet of rope for a fall factor of 1/3, and the anchor load is 6.8 kN.
Although these calculations are very crude (the right way involves the equations for a pair of coupled damped harmonic oscillators), they do suggest the effect of a falling belayer might raise the impacts in the case of arm failure to alarming levels. Although I'm not a fan of absolutes, I'd say it is imperative that extension be limited in some way, that the belayer tie into the anchor with as long a length of climbing rope as is feasible, and that using slings to connect the belayer to the power point is a truly bad idea.
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kachoong
Feb 22, 2006, 3:30 AM
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In reply to: The only conclusion I can extract from this is that the shock-load terminology should be abandoned, because its lack of real meaning allows everyone their own meanings, and in particular allows the concept to become undesirable by definition, rather than by virtue of its actual effect. It would then follow that the potential for "shock loading" cannot, by itself, be a "drawback" of equalizing systems. It would be better to ask a more specific question rather than allow damning by the subjective connotations of an undefined term.
....I wish I could write like that.... I also wish I could give trophies today....
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cracklover
Feb 22, 2006, 4:58 AM
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In reply to:
Does that clear it up?
JL
I'm sorry, but no it does not clear up my question. I appreciate the work you're doing, but without adressing this issue, I think you'd be doing a little disservice to any conclusions you draw.
The issue is: what happens to the climber at a hanging belay when that piece blows and the tech cord anchor extends the 10 inches you said was possible to a limiter knot. What happens when the belayer falls 10 inches directly onto spectra cord - known to have less elasticity even than one inch nylon webbing. What kind of force does that create on the body, and on the remaining piece(s) in the anchor.
Sorry if my last phrasing of the question was unclear (or you may simply not have time to read all of the posts here).
Thanks!
GO
---
Here was my original post on the subject, if that might help clarify my question at all:
In reply to: JL, have you had them test the hanging belay? In other words, in addition to the 80kg weight on the dropped end of the rope, hang another 80 kg weight directly (or with a short piece of "tie-in" rope) on the anchor. I'd be curious to see what happens to the force on the remaining anchor when "fuse" breaks and the 80kg weight drops to the end of the limiter knot. This should create a true, but very small, shock load. A true test of each system is whether the shock load from this fall is within reasonable bounds (both for the climber and the remaining anchors). |
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cracklover
Feb 22, 2006, 5:47 AM
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In reply to: cracklover wrote In reply to: The standard sliding-x becomes redundant the minute you put a limiter knot on each side. You don't need to double it over for this to occur [and in the very next post...] Let's separate the breakage issue from the issue of having a cord sliced/crushed. In most cases, I would not be comfortable with an anchor that requires 20 feet of cord which, if it is sliced anywhere along the length, would cause catastrophic failure of the entire anchor. This failure mode is not implausible. think systems here. the ends are not redundant, there is only one loop.
No. Each sliding-x can be cut on either end, and will remain attached to the other end. If you don't believe me, try it yourself. The only part of a limited sliding-x that's not redundant is the part in between the two limiting knots. My definition of redundancy being - you cut a strand, the whole anchor falls apart.
In reply to: the sliding x part is sort of redundant - cut either strand and you have basically an american death triangle - so if EITHER piece rips you are done. the basic sliding x is not sufficiently redundant.
Sorry, you lost me there. I don't believe it is possible to make an AT out of a limited sliding-x. In a limited sliding-x, cutting any strand produces the same result as pulling that piece.
GO
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curt
Feb 22, 2006, 5:58 AM
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In reply to: In reply to:
Does that clear it up?
JLI'm sorry, but no it does not clear up my question. I appreciate the work you're doing, but without adressing this issue, I think you'd be doing a little disservice to any conclusions you draw. The issue is: what happens to the climber at a hanging belay when that piece blows and the tech cord anchor extends the 10 inches you said was possible to a limiter knot. What happens when the belayer falls 10 inches directly onto spectra cord - known to have less elasticity even than one inch nylon webbing. What kind of force does that create on the body, and on the remaining piece(s) in the anchor. Sorry if my last phrasing of the question was unclear (or you may simply not have time to read all of the posts here). Thanks! GO
Too bad you don't understand the fundamental conservation of energy concept.
Curt
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cracklover
Feb 22, 2006, 5:59 AM
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In reply to: regarding the Gordolette: http://members.cox.net/...ordo-lette%20004.jpg
Here were the cons:
1 - I found tying the biners in a bit finicky. You have to get the cloves in the right spot, or you lose some movement. With practice this could be pretty speedy, as I'm sure Gordo could attest at this point. ;)
2 - At times, self equalization is pretty limited. You only have the biner's range of movement. In practice, this *might* not be a problem. I haven't used it on the side of any cliffs yet.
I want to apologize. When I built the Gordolette yesterday, I did so incorrectly, with the biners going across to the other side, such that when one strand went up the other went down. So I was mistaken about how finicky the placement of the biners was, and I was mistaken too about the limited equalization. Both issues are fine when you make the thing right.
GO
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dr.ed
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Feb 22, 2006, 6:34 AM
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Richard poses a good question. Think of funking out a piece, it is the fact that you get the hammer moving before the connecting cable comes tight that generates the force to pull the piece. If you extend the cable tight and then pull on the piece you won't generate enough force to get the piece out.
Why? because the force is generated by stopping the hammer in a short period of time. What you are stopping is the momentum (the product of mass and velocity). Divide this by the time to stop and you get the force. Given a set mass, you can do two things to reduce the force: 1) reduce the velocity and 2) increase the stopping time.
If you put a bungie on the funkness, you spread out the time to stop the hammer and greatly reduce the force. If you use a short cable you reduce the hammer velocity, also reducing the force.
So the worry with a system which extends is just that it could result in increased forces.
However, if we look at the "system", the belayer and the leader are connected by a damped-spring system. The force of the fall starts to accelerate the belayer, but also extends the rope, increasing the time and reducing the force. So the full force of the falling leader is not transmitted to the belayer. If the connection to the anchors is also elastic, and even less force is transmitted.
As Richard points out, the belayers position is an important factor in determining the force on the anchor. John points this out in the Anchor books.
I can't quite understand the test results, hopefully a technical description of the setup, the tests and the data will appear here.
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vivalargo
Feb 22, 2006, 4:39 PM
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Hey, I wish I had time to address all of these important questions but I can't. Richard G. went far on many of them.
So far as the belayer's weight causing a shock load (slippery term to be sure) during extension--there's now a golden rule: Always tie into the anchor with the climbing rope (stretchy), and NEVER with tech cord or a tech daisy (often seen). The Sterling tests replicatd the results of a belayer falling directly onto the belay on a piece of dynamic climbing rope because during the factor 1 fall, the dynamic rope in the system was not belayed, it was simply tied off to an inflexible anchor. There was no load multiplication when the fuse blew and the second piece caught after the extension. But that's with nylon rope--NOT tech cord, which would really jack up the impact forces.
JL
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cracklover
Feb 22, 2006, 5:29 PM
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In reply to: The Sterling tests replicatd the results of a belayer falling directly onto the belay on a piece of dynamic climbing rope because during the factor 1 fall, the dynamic rope in the system was not belayed, it was simply tied off to an inflexible anchor. There was no load multiplication when the fuse blew and the second piece caught after the extension.
You're mixing apples and oranges. Basically, there are two falls happening within the same time frame. The main one is the leader fall - the factor one fall. In your test setup (as I understand it) the secondary one is a much smaller factor fall within that fall. Let's say the anchor extends ten inches when the fuse blows, and the tests are performed on 2 meters (just a random number thrown out for the sake of argument) then you're looking at a factor .13 fall on the rope. In other words, the test may have been regarding a factor 1 fall, generating say 5kN of peak force on the anchor, but within that fall is a much smaller fall - only factor .13. And it's made more complex by the fact that during that factor .13 fall the rope is relaxed slightly and then tensioned again, so it's really not as severe as a true factor .13 fall.
But this is not analagous to the question I'm asking, in which, within the factor 1 fall, there is *another* factor 1 fall (say 10 inches of rope tie-in on an anchor that extends 10 inches when the fuse pops) when the belayer drops onto the anchor.
Does that make sense?
GO
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healyje
Feb 22, 2006, 7:09 PM
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John,
A brief aside for a moment. I know the emphasis of your book is on the more technial concepts behind constructing anchors, but one thing I've increasingly noted over the years is a lack of appreciation for, and understanding of, the importance of a good stance and its contribution to a safe belay. Those of us here that go back to the old days of passive pro have no shortage of experience on marginal belays and I bet still instinctively put the energy into establishing and "detailing out" the best possible stance. Or at least I know I still do. Effective stancing is a distinct set of skills/judgments that almost rise to the level of craft and one that I think is seldom acknowledged as such or given due consideration these days. Stancing is also an integral aspect of the application of anchors.
If you're revising your book I'd encourage you to at least touch on the subject as I think it is getting lost in the shuffle today. I've also seen a couple of accidents go by recently that were compounded by a lack of stance and tensioning against the anchor. In these accidents the "jolt" associated loading the belayer caused them to let go of the rope or caused them to let it slide rapidly. So sorry to diverge from the topic but it is something that has been on my mind of late.
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jeremy11
Feb 22, 2006, 7:47 PM
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cracklover wrote
In reply to: My definition of redundancy being - you cut a strand, the whole anchor falls apart.
Now I see where you are coming from. I consider redundancy to be if you cut a strand that side is still intact, for example two piece anchor - piece A piece B. standard limited sliding x, cut strand on piece A side - same as pulling piece A - the anchor does not totally fail, but I dont consider it fully redundant as mine is. The basic limited sliding x is more redundant than equalizing setups like my butterfly alpine equalizer setup where if the cord is cut, the entire anchor fails.
In reply to: Sorry, you lost me there. I don't believe it is possible to make an AT out of a limited sliding-x. In a limited sliding-x, cutting any strand produces the same result as pulling that piece
ok. the limited sliding x has three loops - one end clipped to piece A the other clipped to piece B. The one in the middle has the powerpoint. cut one of the middle strands and you are still ok, so it is sort of redundant, but if either piece pulls out, there is total failure since the powerpoint is not inside the middle loop, it is just resting on it. Make sense?
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jeremy11
Feb 22, 2006, 8:06 PM
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would using dynamic cord for an equalizing anchor (sliding x, gordo, equalette) be a help in the proposed case of hanging belay, climber falls ripping a piece out of the belay, then the belayer falls with the extension, applying a second force to the anchor. We now see more clearly the need to tie in with the rope and not clip in, but this belayer fall would be better cushioned with dynamic cord holding everything together.
With that in mind, does anyone know if 8-9mm dynamic rope is sold by the foot anywhere?
Sidenote - how/where can screamers be used as a part of the belay most effectively?
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slcliffdiver
Feb 22, 2006, 9:34 PM
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In reply to: If we ignore the effect of the rope connecting the falling climber to the leader and just think about the combined weight of the falling leader and belayer (each weighing 80 kg), than an arm failure is going to involve arresting the their combined fall.
But ignoring the rope connecting the falling climber to the belayer in direct belay the results are very different than if you don't so you can only do this for a redirected belay.
For a direct belay if the anchor fails while the leader has tension on the rope but is still moving they belayer is going to be accelorated by the falling climber in addition to gravity at least until he matches speed with that climber or is decelorated by the anchor. If you take Johns number of 600 lbs of max force wouldn't a 200 pound climber be accelorated at approximatly 4g at least for a time in a worse case senerio? 3g for the rope 1 for gravity. Isn't the 200 lb as the weight of a climber actually the force a 200 lb person feels under 1g? So acceloration for gravity
f = mg 200 lbs. = mg
Acceloration for rope 600 lbs. = ma.
Multiplying terms 600 lbs. X mg = 200 lbs X ma
divide both sides by 200m gives 3g =a or a = 3g
Or a general form total acceloration in terms of g is
a(total) = g X 600 lbs/(climber weight) + g
Edit:Note this give about 6 g if you are a 100 lb for max felt acceloration in your body (you don't count the free fall). Which means I'm probably missing something vital honestly I hope I screwed up other wise it may mean it would really suck to even before you hit the anchor to be a light belayer if you have significant extension.
If I got this wrong I'm probably in trouble for the rest but I haven't cracked a book yet so maybe there's hope. I'm sure my model is correct. Attach two equal mass rubber balls A and B by a string throw A. B is going to speed up when the string comes under tension and A is going to slow down how fast this happens depends on the tension/elasiticity in the sling.
In my worst case model (couldn't get it out of my head last night) the anchor leg cuts loose and extends the anchor at the point the rope is slipping through the belay device and hits the end of the anchor while the rope is still under enough tension to be slipping to the belay device. Basically the belayer is being pulled by the max force possible the whole time and when the belayer bottoms out on the anchor the force the climber adds to the system is still at maximum.
I'm planning on doing my modeling first on the board in a single post and editing in the math and factors that may be relevant as people contribute or I figure things out in the same post. I can use as many eyes as I can get looking over and correcting my work. Anyway I'm sure I'm not the best person to do this but I just don't recall seeing a model or test that answers the questions I want. What forces result on an extending anchor with a direct belay? And I don't have any volunteers so far. If this has already been modeled or I'm off my gord then please enlighten me.
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vivalargo
Feb 22, 2006, 9:47 PM
Post #221 of 915
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I say go for it, David. You're concern is a real one and also one that would be VERY difficult to test in the lab. Common sense tells me that this is yet another factor in favoring A) always clippping the anchor off with the dynamic lead rope, and B) using 7mm nylon to rig with. If you have the belayer dropping 5 inches (10 inches is too much--this means the limiter knots are 20 inches apart whihc is way too wide) straight onto the anchor, you get more flex and give if the anchor is rigged with stretchy nylon than you do with tech cord. I think it's also important to understand that this is a worse case scenario that happens VERY INFREQUENTLY in real world climbing--perhaps only a handful of times a year.
JL
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robdotcalm
Feb 22, 2006, 10:23 PM
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In reply to: would using dynamic cord for an equalizing anchor (sliding x, gordo, equalette) be a help in the proposed case of hanging belay, climber falls ripping a piece out of the belay, then the belayer falls with the extension, applying a second force to the anchor. We now see more clearly the need to tie in with the rope and not clip in, but this belayer fall would be better cushioned with dynamic cord holding everything together. With that in mind, does anyone know if 8-9mm dynamic rope is sold by the foot anywhere? Sidenote - how/where can screamers be used as a part of the belay most effectively?
J11:
That’s what I’ve been wondering about. It appears that JL has answered part of your enquiry by suggesting the use of 7 mm nylon cord. From what’s been written in ths thread it is clear that tieing in with the rope is safest, i.e., it mininizes the force on the anchor. However, it’s often convenient just to tie in with slings. E.g., the first belay stance (on a multi-pitch route) has two good bolts properly spaced. Clipping into them with locking carabiners and 2 slings girth hitched on the belay is speedy and provides a platform for draping the rope as the second ascends. If both slings were 7 mm cord, would there be any significant advantage of tieing in with the climbing rope?
Many of the systems suggested here seem innovative and safe (and my admiration to those who devised them) but very complicated and time consuming to implement. As one who could never bring himself to carry a cordelette or even a daisy chain, I can’t see myself using them. Mostly I tie in with rope and occasionly just use slings as mentioned above. A question is, What percentage of climbers would be willing to implement these more complicated schemes? Making the best possible placements, choosing a good stance, being tight against the tie-in, and tieing with the rope or stretchable slings summarizes what is the most one could expect from the majority of climbes.
Cheers,
Rob.calm
_______________________________________________________
‘Tis better to have trad and failed then not to have trad at all.
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slcliffdiver
Feb 22, 2006, 11:16 PM
Post #223 of 915
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In reply to: I say go for it, David. You're concern is a real one and also one that would be VERY difficult to test in the lab. Common sense tells me that this is yet another factor in favoring A) always clippping the anchor off with the dynamic lead rope, and B) using 7mm nylon to rig with. If you have the belayer dropping 5 inches (10 inches is too much--this means the limiter knots are 20 inches apart whihc is way too wide) straight onto the anchor, you get more flex and give if the anchor is rigged with stretchy nylon than you do with tech cord. I think it's also important to understand that this is a worse case scenario that happens VERY INFREQUENTLY in real world climbing--perhaps only a handful of times a year. JL
Thanks for the encouragement. I'll do all modeling in this post. You're probably correct I'm guessing there is only a very small chance this will effect conventional climbing wisdom and likely will only eftect the fiefdom of my mind but worth a shot I guess.
If people pm me with contributions I'll try try and give credit (unless requested otherwise) I'd prefer not have to many posts for this one question because their seem to many other good seperate post on this thread and I'm guessing there is limited interest in this and this will probably take me a good while. Help comments on "any" aspects of this post would be highly appreciated.
Edit 2/23/06: I'm starting to look at this from the perspective of learning to manage a cooperative web based engineering project. Any suggestions along these lines welome. I have almost zero experience in this. I like projects that start out almost completely over my head (without time pressure) because I enjoy learning new skills and I'll learn somethings about myself I have interest in.
Question 2/23/06: Recomenedations for coordinating a pc work space and making thing legible on this board.
MODEL (FACTOR 2 FALL FROM A HANGING BELAY ON A DIRECT BELAY WITH AND EXTENDING ANCHOR)
A: Final velocity of belayer when they hit the end of the extended anchor
Find velocity of falling climber as rope goes tense.
Note neglecting all influences but gravity: May want to account for possible push of rock later especially for short falls.
As climber falls tension in rope increases given by
(formula)
Acceleration of falling belayer is given by
Acceleration(total) = Forces(total)/Mass(of belayer)
Forces(total) = Mass (of belayer) X g + Ft(force from tension in rope) - Ff (force of friction from exendending anchor)
Note: I'm neglegting flex in the climber body here an would like to account for this later as close as I can. Look for seatbelt, parachute other data to get some reasonable data to better aproximate short extensions.
Worst case modeling:
Note: I'm takeing 600 lbs. as the maximum tension in the rope to account for slippage through the belay device.
Note: I'm speculating that the worst case in terms of accelerating the belayer is when extension occurs when force on the belayer starts applying enough force to start slippage.
If you take Johns number of 600 lbs of max force wouldn't a 200 pound climber be accelorated at approximatly 4g at least for a time in a worse case senerio? 3g for the rope 1 for gravity. Isn't the 200 lb as the weight of a climber actually the force a 200 lb person feels under 1g? So acceloration for gravity
f = mg 200 lbs. = mg
Acceloration for rope 600 lbs. = ma.
Multiplying terms 600 lbs. X mg = 200 lbs X ma
divide both sides by 200m gives 3g =a or a = 3g
Or a general form total acceloration in terms of g is
a(total) = g X 600 lbs/(climber weight) + g
Edit:Note this give about 6 g if you are a 100 lb for max felt acceloration in your body (you don't count the free fall). Which means I'm probably missing something vital honestly I hope I screwed up other wise it may mean it would really suck to even before you hit the anchor to be a light belayer if you have significant extension.
B: Final tension in rope when belayer hits the end of the extended anchor
C: Final velocity of climber when belayer hits the end of the extended anchor
D: Force on anchor as a result of stopping climber and belayer
Note: Some knott tightening and harness deformation occur durring A and B and may not be available to contribute as much to energy absorpion when climber hits the end of the anchor.
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flyinglow
Feb 22, 2006, 11:20 PM
Post #224 of 915
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reading through all this has brought something to my mind.
A possible worst case scenario:
belayer is at a hanging belay on a "gordolette" set in a horizontal crack. belaying off the master point, which belayer is tied in at also.
climber climbs 10 feet, places a crummy piece of pro, climbs another 20 feet and falls.
Belayer is pulled up to the top of the extension of the gordolette at which point the one piece the climber has in fails.
belayer factor 2 falls 6 feet onto static anchor at the same time as climber reaches the end of their rope.
result: 6 foot fall, factor 2, static(belayer) + 60 foot fall, factor 2, dynamic(climber)
that seems like a really scary situation(also really unlikely, as both would have to hit the anchor at the same time). the climber would have been considerably slowed down by their piece that blew, but the force remaining would be applied to the anchor in addition to the belayers factor 2
anybody care to add up those numbers? how bad would it be?
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cracklover
Feb 22, 2006, 11:36 PM
Post #225 of 915
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In reply to: You're concern is a real one and also one that would be VERY difficult to test in the lab. JL
I'm sure you know the testing setup, but wouldn't it just be a matter of connecting two weights in sequence, and then doing the same drops you've been doing?
So if you're doing something like the first pic, could you do some like the second?
http://www.gunks.com/...0/677two_anchors.JPG
What am I missing?
GO
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