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climb_eng
Jun 5, 2007, 8:08 PM
Post #26 of 60
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whiskeybullets wrote: While an anchor does indeed see an approximately 2x increase in force under a slingshot belay, this is due to the weight of the climber and the belayer combined, not due to the rope configuration.
You are incorrect, and using the term mechanical advantage is pretty stupid and confusing here. Lets think back to gr.11 physics everyone... assuming a frictionless pully at the anchor, the tension in the rope will exactly be equal to the weight of the climber ONLY. The pully sees exactly double this force since the rope tension acts on it twice, once to the belayer and once to the climber. The force on the belay will be EXACTLY the same whether he is belaying from the top or the bottom.
In a real world situation (non-frictionless pully), the force felt in a sling shot belay will be the weight of the climber minus whatever the contribution of friction is (and in the scenario of a rope running over a carabiner, this is a noticable difference).
I think proof of competancy in gr. 11 phisycs should be a requirement for becoming a climber... seriously, and this goes to everyone, don't spew bullshit... this question could have been handled by one person who knew what they were talking about!
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pastprime
Jun 5, 2007, 10:04 PM
Post #27 of 60
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The circus never ends at this place.
I like how Ja1484, and climb eng, say whiskybullets is completely wrong and ".....stupid"; then to explain how wrong he is, they restate, in different words, exactly the same things that whiskeybullets said in his posts that they claim to disagree with.
It would be well, before jumping in to refute someone, to slow down, re read what they said, and ask yourself if it isn't just possible they may be entirely correct in their understanding of the principle under discussion, and just be wording the explanation differently than you have heard it explained before, and to realize that their different way of stating it may well make more sense, or add to the understanding, of some of those reading it than does your pet wording of the same principle.
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ja1484
Jun 5, 2007, 10:18 PM
Post #28 of 60
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whiskeybullets wrote: Don't refer to us as a special lot when you are confusing your situations. The OP clearly stated that he found a top-belay more difficult than a sling shot belay. Someone commented to him that was due to mechanical advantage. His differing belay experiences were certainly and clearly not due to a mechanical advantage, but rather to differing amounts of rope in the two distinct systems.
Who's confusing what situations? The bulk of my discussion has had little to nothing to do with the OPs statement. While this is, admittedly, thread drift, that's beside *the* point, which is the suggestion to add a redirect onto a single piece of the anchor.
In reply to: While an anchor does indeed see an approximately 2x increase in force under a slingshot belay, this is due to the weight of the climber and the belayer combined, not due to the rope configuration. This does change, however, if the top-belay is of a fixed style, as in a Reverso configured in an autolocking mode.
Actually, the rope configuration (i.e. it's a slingshot belay) is the exact reason why the anchor must bear 2x the force - and it's not just the weights of the climbers involved. Any fall force felt on the climber's end of the rope must be equaled (minus friction, of course) on the belayer's side to arrest the fall, so ALL forces put on the anchor via the climbing rope are doubled.
Furthermore, I again note that the above suggestion is to redirect through a single piece, not the entire anchor, thus doubling system forces on to a single unit of anchorage. Even if the rope is still run through the anchor's powerpoint, you're risking an unecessary "shock load" in the event that the redirect piece fails. Not to mention you've taken equalization out of the picture, and all of this is done needlessly.
In reply to: If the feel of a belay only has to do with how comfortable one is or is not with a given system, one has completely ignored the variable of rope length. If a rope is to absorb a set amount of force over a variable length, the belayer will "feel" less force in situations where there is more rope in the system.
I correct my previous statement: Comfort with the belay system and rope friction involved.
I'll concede that the additional forces to the belayer are dampened through a slingshot belay from the ground due to additional rope in service, but it still shouldn't be a problem belaying from the top. Belay directly off the anchor. Belaying at the top in any other fashion is, pardon my overbearing opinion, f*cking stupid.
In reply to: Change this analogy to lead belaying and you have the reasons for rating falls by factors.
More or less.
Anyway, to get back on track:
Belay from the top directly off the anchor. Don't redirect through a single anchor point. It's moronic.
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pastprime
Jun 5, 2007, 10:22 PM
Post #29 of 60
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climb_eng wrote: whiskeybullets wrote: " an anchor does indeed see an approximately 2x increase in force under a slingshot belay, this is due to the weight of the climber and the belayer combined," Then climb eng wrote "You are incorrect, ... " The [anchor] pully sees exactly double this force since the rope tension acts on it twice, once to the belayer and once to the climber. ". Just one example.
(This post was edited by pastprime on Jun 5, 2007, 10:24 PM)
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ja1484
Jun 5, 2007, 10:25 PM
Post #30 of 60
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pastprime wrote: The circus never ends at this place. I like how Ja1484, and climb eng, say whiskybullets is completely wrong and ".....stupid"; then to explain how wrong he is, they restate, in different words, exactly the same things that whiskeybullets said in his posts that they claim to disagree with. It would be well, before jumping in to refute someone, to slow down, re read what they said, and ask yourself if it isn't just possible they may be entirely correct in their understanding of the principle under discussion, and just be wording the explanation differently than you have heard it explained before, and to realize that their different way of stating it may well make more sense, or add to the understanding, of some of those reading it than does your pet wording of the same principle.
You are obviously no good at the internet. Allow me to explain:
If I post an opinion in a forum, it is the duty of anyone else reading to understand my position and the intention of any ambiguous sentences by mind reading, without any clarification whatsoever.
If they don't, one must simply call them stupid and repeat what they have said before until the other person figures out the intent of the words.
Yes, this applies even if the two parties are essentially agreeing with one another but talking unrelatedly about another subject that may or may not be the OP's question.
So, to come up with the net score:
Myself:
- State that a ridirect through a single anchor piece is not a good idea because of doubling of entire belay force on that piece.
Whiskeybullets:
- Agrees about doubling of force, but interprets mechanical advantage in a different manner and also slips in some items about belay comfort, comfort defined as forces felt by the belayer, due to rope in service of the system
Both:
- Call each other names and continue to agree but use words that are different enough but with the same intended meaning so as to escape detection by most readers and make it seem as though we are disagreeing about something.
And thus: The internet.
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climb_eng
Jun 5, 2007, 10:33 PM
Post #31 of 60
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Pastprime, my problem is with whiskeybullets that:
"this is due to the weight of the climber and the belayer combined"
This is incorrect. The weight of the belayer has absolutly nothing to do with the force in the rope. The belayer simply applies a counter force equal to the weight of the climber minus friction....
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majid_sabet
Jun 5, 2007, 10:40 PM
Post #32 of 60
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Ja1484
how did you come up with this ?
In reply to: risking an unecessary "shock load" in the event that the redirect piece fails. Not to mention you've taken equalization out of the picture, and all of this is done needlessly. |
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pastprime
Jun 5, 2007, 10:44 PM
Post #33 of 60
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Last comment, then I'm going home.
The notion of "shock loading" has been thoroughly refuted. If a piece fails and results in a fall being 3 feet longer than it would otherwise have been, the peak forces are basically the same as they would have been had the fall just been 3 fee longer to begin with, minus whatever was absorbed in pulling the piece.
If you are belaying off an anchor that bloody well better be built to handle a few thousand pounds, I hardly think it is "moronic" to avoid a configuration that might load the anchor to 400 lbs, in favor of one that will only load it to 200 lbs if you have any reason to desire the first configuration. It just doesn't matter.
Remember, we are talking about top roping here, folks. If we were willing to settle for the safety margins that are routinely accepted in lead climbing,
we'd be doing it on 5mm ropes. The margins are so huge that doubling the forces anywhere in the system is inconsequential.
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carabiner96
Jun 5, 2007, 10:45 PM
Post #34 of 60
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ja1484 wrote: I swear, sometimes I wonder why I don't just let people do themselves in from ignorance and save myself the trouble.
Because you are our savior and i throw myself down at your feet. Clearly.
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shockabuku
Jun 5, 2007, 10:49 PM
Post #35 of 60
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climb_eng wrote: Pastprime, my problem is with whiskeybullets that: "this is due to the weight of the climber and the belayer combined" This is incorrect. The weight of the belayer has absolutly nothing to do with the force in the rope. The belayer simply applies a counter force equal to the weight of the climber minus friction....
Not that this has anything to do with the OP really. I just couldn't resist adding my particular version of irrelevant stupidity to this thread.
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ja1484
Jun 5, 2007, 10:54 PM
Post #36 of 60
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pastprime wrote: Last comment, then I'm going home. The notion of "shock loading" has been thoroughly refuted. If a piece fails and results in a fall being 3 feet longer than it would otherwise have been, the peak forces are basically the same as they would have been had the fall just been 3 fee longer to begin with, minus whatever was absorbed in pulling the piece. If you are belaying off an anchor that bloody well better be built to handle a few thousand pounds, I hardly think it is "moronic" to avoid a configuration that might load the anchor to 400 lbs, in favor of one that will only load it to 200 lbs if you have any reason to desire the first configuration. It just doesn't matter. Remember, we are talking about top roping here, folks. If we were willing to settle for the safety margins that are routinely accepted in lead climbing, we'd be doing it on 5mm ropes. The margins are so huge that doubling the forces anywhere in the system is inconsequential.
That's why "shock load" was in quotes. It's well known it's not a true additional load.
Now, because I tire of this game, let's get some things in the clear:
1) We're talking about belaying a seconding climber, essentially a tope rope situation, through a redirect that applies force to only one component of the anchor, per Dr. Feelgood's suggestion.
2) Should that anchor piece fail, peak forces wouldn't be expected to be higher, no, but the rapid change of position (that is to say, short fall) of the belayer and changing configuration of the belay anchor may in fact cause the belayer to lose control of the rope. Unlikely, but possible.
3) Significantly more possible than say, if the belayer would simply belay directly off the anchor which allows for near-equalization of forces between all anchorage pieces (assuming the anchor is well constructed) and the use of the full strength of the anchor, rather than a single piece.
4) Re-directing here serves no purpose other than to put a greater than needed load on a portion of an anchor. There is no reason to do it. Will it matter in the long run? most likely not - climbing gear is so overbuilt that this situation is likely a nonissue, but why form bad habits, and why go about climbing safety and anchorage half-assed?
5) People are using the term "mechanical advantage" in this thread to both describe the doubling of force that occurs through the use of a redirect and in the "technically correct" sense of a system multiplying the force put into it, which doesn't come into play here.
6) It may be a bomber anchor as a whole, and if so, there's no point in re-directing to something less bomber, as mentioned above.
7) My issue is only with Dr. Feelgood's suggestion of a re-direct, and I really couldn't care less about "comfort" with a belay system or anything related to it. I mainly spoke about it because it was there.
Are we a little more up to date now?
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ja1484
Jun 5, 2007, 10:58 PM
Post #37 of 60
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carabiner96 wrote: ja1484 wrote: I swear, sometimes I wonder why I don't just let people do themselves in from ignorance and save myself the trouble. Because you are our savior and i throw myself down at your feet. Clearly.
Bout time somone recognized 
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ja1484
Jun 5, 2007, 10:59 PM
Post #39 of 60
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God I miss the killfile.
Majid, per normal, posting information that has little to nothing to do with the discussion at hand. We're not discussing a leading situation here, and the linked article gives no information on how the redirect was constructed.
You're also apparently missing the point that a direct belay off the anchor meant the belayer would not have had to deal with rope pull AT ALL, but rather simply let the anchor do its job whilst ensuring the rope was very much locked off.
:sigh:
(This post was edited by ja1484 on Jun 5, 2007, 11:07 PM)
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majid_sabet
Jun 5, 2007, 11:07 PM
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ja1484
read and learn what redirectional does and how it works.
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ja1484
Jun 5, 2007, 11:07 PM
Post #41 of 60
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That's good advice. You should follow it. Done yet?
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ja1484
Jun 5, 2007, 11:58 PM
Post #42 of 60
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Almost forgot: Here's that Attaway Rope System Analysis in case anyone was waiting with baited breath. Sorry it took so long. Been busy this afternoon.
The PDF exceeds the attachment limit, so you'll have to settle for a link:
http://www.amrg.org/...analysis_Attaway.pdf
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patto
Jun 6, 2007, 12:39 AM
Post #43 of 60
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Back to the problem at hand.
While a re-direct will make belaying easier I don't like the sound of that. Holding a top roper is still MANY times easier than catching a lead fall. If you belaying isn't top notch it is better to get used to firm belaying when top roping than getting surprised by a lead fall.
Learn to grip firmly and lock off well and a top belay shouldn't be an issue. If your belaying off your waist ensure that the belay biner is clipped into the anchor as well so that the weight of the climber does not go through your harness. This is important for your comfort.
The reverso isn't the grippiest of devices but it is more that sufficient for top roping with all but the thinnest ropes. I regularly use my reverso for this on multipitches without any issues on a 10mm rope.
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binrat
Jun 6, 2007, 11:58 AM
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ja1484 wrote: binrat wrote: OK: From what Dr FG said is basically a change of direction not a 2:1 MA, unless things have changed in the last little while. Binrat binrat wrote: Okay: Here we go. So what you are saying it that it is a 2:1 MA which means that as the climber climbs 1 ft, the belayer takes in 2 ft of rope. Totally disagree. First, this has nothing to do with rope movement, and secondly, please stop talking about things that you are obviously clueless about. I can't get to the file right now (it's on my home PC), but Steve Attaway (sp?) did a great write up on how traditional roped safety systems work and why redirects are best avoided. Rather than summarize it for you, I'm going to pass the info along and hope you can make sense of it. In the meantime, please don't belay me (or set up an anchor for me) any time soon.
I've had formal training in rope rescue and rope systems have you? and could you please post this report.
Binrat
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binrat
Jun 6, 2007, 12:02 PM
Post #46 of 60
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BTW
If I top rope top belay, I'm always not part of the system, meaning not using a redirect. Belay right off of the anchor built, on a personal safety system so I can see the climber.
Binrat
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petje
Jun 6, 2007, 12:52 PM
Post #47 of 60
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It's very easy, i didn't read al that yada, but in the start the original poster talked about using a reverso for belaying on the ground and belaying a second climber to a belaypoint somewhere higher up (multipitch so to say)
1. RTFM !
2. look it up on http://en.petzl.com/...roduits?Produit=204#
there is even a film on there that showes using a reverso for belaying for a second person to climb towards you.
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ja1484
Jun 6, 2007, 2:13 PM
Post #48 of 60
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It's already *up*. Read back a few posts.
Formal training doesn't mean much. I've heard plenty of nonsense come out the mouths of guides and instructors over the years. The problem with the body of knowledge in climbing in general is that it tends to be passed person to person orally with no sourcing or test data whatsoever.
This is how we end up with dumbass rumors like "microfractures" and "belay through the tie-in points for redundancy" (the second is something I have heard a local AMGA certified guide espouse multiple times. People should get their money back).
Get me the source science and data and I'll care...until then, having simply been trained by *someone* means nothing to me.
Anyway, the section on "leader fall analysis" may be the most pertinent to the (ridiculous) disagreement that occurred previously, but anyone who takes a look at that document should read the whole thing. It's good for 'em. High fiber.
(This post was edited by ja1484 on Jun 6, 2007, 2:20 PM)
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csproul
Jun 6, 2007, 3:02 PM
Post #49 of 60
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Not trying to be a smart ass here, and I agree that redirecting off of one piece is generally a bad idea...but where in that paper are they discussing anything but leader falls (not the OP's question)? I am sure there is useful information on avioding redirects for a leader, but I see nothng that would lead me to believe that belaying a second through a redirect (and I most always would use the entire anchor and not just a piece) is unsafe. And if given the choice between belaying a second redirected off a single solid piece and the leaving them with a pendulum (a traverse is the only situation I can think of offhand where I may redirect off a single piece), I think I would still rather redirect off the single piece.
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cracklover
Jun 6, 2007, 3:11 PM
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So this is why people bash on rc.com. Good god. This thread reads like an eight-car pileup. A moronic question, followed by a series of moronic answers.
JT512 is right, the people who actually know what they're talking about (actually, there are many nice posts by the likes of Blueeyedclimber and others) are drowned out by those who don't, but love to hear their own voices.
Sheesh.
A few notes:
1 - To the OP: The Reverso, while a perfectly adequate device, has the worst holding power when used in simple tube-style manner, of any device on the market. Certainly worse than the original (untoothed) ATC. It's not surprising you had a hard time holding your second if you were belaying off your harness from above. There are many solutions to this issue, some of which have been mentioned already in this thread.
Also the confusing business of "mechanical advantage" was introduced by the OP. If this was a troll, it was a masterful one. But as many have said, there is no mechanical advantage anywhere in any of the systems being discussed. All that's at issue is friction and pulleys - no MA. Ja1484, Westbend and DRector - learn what a mechanical advantage is before you embarrass yourselves further.
Also, climbeng: climb_eng wrote: Pastprime, my problem is with whiskeybullets that: "this is due to the weight of the climber and the belayer combined" This is incorrect. The weight of the belayer has absolutly nothing to do with the force in the rope. The belayer simply applies a counter force equal to the weight of the climber minus friction....
Nonsense. The weight of the belayer has a great deal to do with it. The only reason the belay side of the anchor can ever equal the force on the climber side is two things: Friction over the anchor, and the weight of the belayer. Ask a 50 lb climber to belay a 100 lb climber with a pulley at the top point, and the 100 lb climber will fall to the ground the moment their entire weight goes on the line. Period. In some very real cases, the weight of the belayer is not sufficient to hold the climber. That's why you see belayers get lifted by lead falls. Also, with some belay devices, the force needed to lift the belayer is more than the force that belayer can hold in the belay device, so some rope slips through the device. That friction "absorbs" force. And the rope slippage is the only reason the belayer (due to their weight being < force on the other side plus friction in the system) doesn't get pulled up.
GO
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