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aikibujin
Jun 2, 2004, 10:44 PM
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http://www.climbing.com/...ps/sport/ttsport216/
I'm still a relatively new climber, so far I've only climbed on TR, but I'm hoping to move into sport soon, so I'm trying to gain more theoretical knowledge to get a head start. I'm just looking through Climbing Magazine's Tech Tips on sport, and came across this tip on creating a "fast and safe" anchor on multi-pitch sport routes. Now like I said I'm still learning a lot about climbing, but with my limited knowledge I can see some problems with the set up they have.
http://www.climbing.com/techtips/sport-216.jpg
Basically, the leader is anchored into the bolts with an equalized anchor. He then belays the second, redirecting the belay using a quickdraw on one of the bolts. Here's my problem with this set up. If the second ever falls, or even just hang on the rope to rest, it would put (at a minimum) a force equal to twice the weight of the second on that single bolt. Granted, you hope you never have a second that hangdogs a lot. And a bolt is probably strong enough to take that kind of force. But, what if? If the bolt blows, it could ugly, since now the weight of the second is directly hanging on the belay device. What's the advantage of this set up anyway, speed? Would it be much slower to set up a SRENE anchor with a cordelette, then redirect the belay using the power point? At the very least, wouldn't it be better to clip another quickdraw in the second bolt, and redirect the belay through both quickdraws? These are my questions, I'd like to hear your thoughts.
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gds
Jun 2, 2004, 10:53 PM
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You always need to make judgements. In this case the ? is how good are the bolts. If I thought the bolts were bomber I'd have no problem with this set up. On a true sport route the bolts should be bomber. The load you mention is less than what a lead fall would be on any bolt on the route.
If you're nervous you could redirect the belay through the master point instead.
And the anchor does fulfill the requirement of SRENE.
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boss
Jun 2, 2004, 11:37 PM
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I've used this setup for a couple years now. Never had any problems or felt uncomfortable with it. If you are worried about just using one draw, then run your rope through two draws, one on each bolt. Still a judgment call thought whether or not the bolts are bomber.
Boss
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aikibujin
Jun 2, 2004, 11:43 PM
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Yes, you're correct. The anchor in the diagram is SRENE. Sorry, I wasn't very clear in my original post, so I have edited it to clear up my question. The anchor in the diagram lacks a master point, so I was wondering if would it be much slower to build an anchor using cordelette, which has a master point you can use to redirect the belay.
When belaying a leader, you really don't have a choice but to trust a single bolt (assuming he/she only clipped one bolt), but when belaying a second... seems like it wouldn't take more than a few seconds to clip a second quickdraw into the second bolt and redirect the belay through both.
Now suppose the bolts are bomber, which they should. The article mention "speed" as the reason for this setup, and I can see why. But now, with the assumption that the bolts are bomber, and speed as the objective, wouldn't it be even better to anchor the leader into only one bolt with a quickdraw, and then belay the second by redirecting the rope through a quickdraw on the second bolt?
Assuming a hanging belay, here are the forces in each scenario:
When the leader is hanging, and the second is climbing:
a) if the leader is anchored into both bolts, each of the bolt takes the force of (weight of leader / 2)
b) if the leader is anchored into a single bolt, that bolt takes the force of (weight of leader). The other bolt is not loaded.
When the leader is hanging, and the second is hanging:
a) if the leader is anchored into both bolts, one of the bolt takes the force of (weight of leader / 2), and the other one takes the force of (weight of seond x 2) + (weight of leader / 2).
b) if the leader is anchored into a single bolt, that bolt takes the force of (weight of leader), and the other bolt takes the force of (weight of second x 2).
When the second falls:
a) One of the bolt takes the force of (weight of leader / 2), and the other bolt takes the force of (the fall + weight of leader / 2).
b) One of the bolt takes the force of (weight of leader), and the other one takes the force of (the fall).
Ok, sorry if I'm over analyzing this. But I'm just trying to learn and build a good understanding of why things are done a certain way. It is a simplified force analysis, not taking into account the weight of the rope, frictional force, etc. But based on these scenarios, looks like it is faster to anchor the leader into a single bolt, AND the forces are spread more evenly between the bolts overall (which I assume is better than loading one bolt more than the other). Since we assumed the bolts are bomber, would you just anchor the leader into a single bolt then?
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coldclimb
Jun 2, 2004, 11:52 PM
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I'd use two draws. Always better to be on two bolts than one.
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rmiller
Jun 2, 2004, 11:53 PM
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Actually, the force would be around body weight if the belay is done correctly. You would have to factor in two things however: 1) impact force of the second falling given the amount of slack, which would be a positive force on the anchor and 2) impact absorbed by the elongation of the rope, which would be a negative force on the anchor. Thus, the force on the anchor should be around body weight, give and take a bit. If there is extreme on either end, of course, the force will be skewed in one direction or the other. There are some other factors, but I think they would be minor, i.e., dynamic belay, how far away the second is, etc. Either way, this is a completley safe set up if done right.
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alpnclmbr1
Jun 2, 2004, 11:58 PM
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scratch that
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sonso45
Jun 2, 2004, 11:59 PM
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As a leader, when I get to a 2 bolt anchor, I tie into both. Always. When I put the second on belay from 2 bolts, it is into my belay device. His weight may be redirected as shown on a single bolt, but it is my device that is the ultimate anchor for the second. Why would anyone ever want to tie into one of 2 bolts at an anchor, instead of both? M
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jt512
Jun 3, 2004, 12:01 AM
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In reply to: http://www.climbing.com/...ps/sport/ttsport216/ I'm still a relatively new climber, so far I've only climbed on TR, but I'm hoping to move into sport soon, so I'm trying to gain more theoretical knowledge to get a head start. I'm just looking through Climbing Magazine's Tech Tips on sport, and came across this tip on creating a "fast and safe" anchor on multi-pitch sport routes. Now like I said I'm still learning a lot about climbing, but with my limited knowledge I can see some problems with the set up they have. http://www.climbing.com/techtips/sport-216.jpg Basically, the leader is anchored into the bolts with an equalized anchor. He then belays the second, redirecting the belay using a quickdraw on one of the bolts. Here's my problem with this set up. If the second ever falls, or even just hang on the rope to rest, it would put (at a minimum) a force equal to twice the weight of the second on that single bolt.
The more serious problem would occur if you are swinging leads; that is, if the second you are bringing up will be leading the next pitch. If he falls, he'll be putting a lot more force on the one bolt than twice his body weight. Then, if that bolt fails, the remaining bolt will be shock loaded. When I lead above a belay anchor, I clip my rope through two draws, one on each bolt.
-Jay
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rmiller
Jun 3, 2004, 12:04 AM
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No, you would never anchor the leader into a single bolt if at all possible. If so, you just killed your redundancy and equalization. In an ideal world, say with a cordolette (sp?), the master point is the tied off loop. The leader would be tied into this point with the rope connected by 2 biners. Then you could put the draw supporting the second into the same point. This would keep the equalization on the two bolts for both the leader and second. Also, there is a master point in the diagram. The master point in the diagram is the clove hitch, although you could also argue that it is the figure eight tied directly to the leader and the clove hitch is an intermediate master point.
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aikibujin
Jun 3, 2004, 12:17 AM
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In reply to: Actually, the force would be around body weight if the belay is done correctly.
Are you sure? If I remember my college physics correctly, then I would say when the second is hanging on the rope, it puts a force twice the body weight on the anchor. And that was one of the scenarios I ran.
I'd draw a block diagram, but my photoshop isn't working right. So I'll try to describe how I come to this conclusion. When a climber is hanging on the rope, he puts a force equal to his body weight (W) on one end of the rope. Now if there isn't a force on the other end of the rope, the rope will slide freely through the anchor and the climber will fall; if there is a force < W on the other end of the rope, the climber will get lowered; if there is a force = W on the other end, the climber will hang right where he/she is. Now assume both strand of the ropes are hanging straight down, the force on the anchor would be W + W = 2W when the climber is hangdogging on the rope. (Not accounting for friction)
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rmiller
Jun 3, 2004, 12:21 AM
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Oh and to answer your question. Yes, the advantage of this set up is speed.
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rmiller
Jun 3, 2004, 12:26 AM
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In reply to: In reply to: Actually, the force would be around body weight if the belay is done correctly. Are you sure? If I remember my college physics correctly, then I would say when the second is hanging on the rope, it puts a force twice the body weight on the anchor. And that was one of the scenarios I ran. I'd draw a block diagram, but my photoshop isn't working right. So I'll try to describe how I come to this conclusion. When a climber is hanging on the rope, he puts a force equal to his body weight (W) on one end of the rope. Now if there isn't a force on the other end of the rope, the rope will slide freely through the anchor and the climber will fall; if there is a force < W on the other end of the rope, the climber will get lowered; if there is a force = W on the other end, the climber will hang right where he/she is. Now assume both strand of the ropes are hanging straight down, the force on the anchor would be W + W = 2W when the climber is hangdogging on the rope.
I am not sure about this. Good thought! Does anyone know if the locking off of a belay creates a force (of course without it there would be no force, so that is not what I am asking)? Or is it the second that creates the only force? In a sense, does the statement "it is all about the second" apply here?
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mandrake
Jun 3, 2004, 12:44 AM
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In reply to: The more serious problem would occur if you are swinging leads; that is, if the second you are bringing up will be leading the next pitch. If he falls, he'll be putting a lot more force on the one bolt than twice his body weight. Then, if that bolt fails, the remaining bolt will be shock loaded. When I lead above a belay anchor, I clip my rope through two draws, one on each bolt. -Jay
That I agree with. The other option (sometimes your only option if you're rigged close in to your belay) is to belay directly off your harness and risk catching the factor 2 on your body. Yi-yi-yi! On a bolted line, the leader is pretty much in a Don't Fall Zone before the first bolt on the second pitch (which is hopefully pretty close).
From what I understand, the OP's more or less right on the doubling of forces on the right-hand bolt if you bring your second up as diagrammed (there's a bit a friction, so it's not quite doubled). I thought I saw a tech tip somewhere outlining just that recently... and recommending belaying directly off the anchor with a reverso...but I can't find it to link to it just now. I don't usually redirect and just bring the second up with my belay device. It's a strain if he's hanging a long time, though. Not a big deal, just uncomfortable.
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bsignorelli
Jun 3, 2004, 12:57 AM
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In reply to: And the anchor does fulfill the requirement of SRENE.
It does not fulfill all of the SRENE requirements...specifically the 'Never/Not Extending' requirement.
If the right hand bolt blows then the quickdraw will fall until the 'dog eared bowline' fully extends and thus will shock-load the left hand bolt.
Agree?
Bryan
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slobmonster
Jun 3, 2004, 1:01 AM
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The full TechTip includes the following:
"Also, you should not use a Grigri with this set-up, as the locking mechanism can fail if sucked up against the quickdraw."
If you have brought your Grigri along, clip it to the master point of your masterfully-tied Doggie Woof Woof Bowline and belay directly off the anchor. Your SRENE concerns are solved. Similarly, you can use a Reverso (or Plaquette, or Munter hitch, or TRE) in the same fashion. You'll find that belaying directly off the anchor saves you mucho energy, and if you're at all savvy you can haul your schlep partner without too much difficulty.
I remember seeing this and trying to "Learn the dog" as it suggests. I found it annoying. It's far easier, I think, to tie a two-eared Figure-8. I use this all the time when swapping leads.
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aikibujin
Jun 3, 2004, 1:02 AM
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In reply to: As a leader, when I get to a 2 bolt anchor, I tie into both. Always. When I put the second on belay from 2 bolts, it is into my belay device. His weight may be redirected as shown on a single bolt, but it is my device that is the ultimate anchor for the second. Why would anyone ever want to tie into one of 2 bolts at an anchor, instead of both? M
I agree with you totally, I wouldn't anchor into only one bolt if I have the choice. And I would redirect the belay through both bolts also. Problem solved.
But in case of the set up Climbing Mag is suggesting, what I'm proposing is, at least in theory, a faster way that spread out the load more evenly in the case of a second falling or a hangdogging second, by clipping into only one bolt as the anchor. I know this is definitely not a SRENE anchor, but we are assuming bomber bolts, and please look at the force analysis I did in all three scenarios, because I find something interesting. If I didn't make any error in my analysis: a) with the leader anchoring into both bolts and redirect the belay using a single bolt, one of the anchor bolt will always take the force of (weight of leader / 2), while the other bolt will have the highest force when the second falling: (fall force + weight of leader / 2); b) with the leader anchoring into a single bolt (I know, not SRENE, but hear me out), one of the bolt will always take a force of (weight of leader), while the other will take the maximum force of (fall force), which is less than what it would take if leader is anchored with both bolts. So it seems that by clipping into one bolt at the anchor, you're evening out the force more in the worse case scenario.
I'm not saying that's what people should do, but it seems no worse than the method proposed in Climbing Mag, except for the non-redundant anchor. As far as the non-redundant anchor goes though, if the single anchor bolt blows, the leader and the second will be hanging from a quickdraw clipped to the second bolt. Not pretty. In the Climbing Mag's set up, if the bolt used for redirecting the belay blows, the leader and the second will be hanging from the other bolt, with the second hanging on the leader's belay device. Not pretty either. But by spreading the force out more evenly in case of a fall, there will be a less chance of a bolt blowing out, no?
Again, I know now the problem is easily solved by redirecting the belay using two quickdraws on both bolts. My current question is if people feel safe using the setup as described in Climbing Mag, why wouldn't you feel safe to use the setup where you use one bolt as anchor and the other to redirect the belay (apart from the instinct to always use redundant anchor)?
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bsignorelli
Jun 3, 2004, 1:05 AM
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In reply to: Does anyone know if the locking off of a belay creates a force (of course without it there would be no force, so that is not what I am asking)? Or is it the second that creates the only force? In a sense, does the statement "it is all about the second" apply here?
"Every action has an equal and opposite reaction."
In order for you to hold the second still you have to pull down with a force equal to the weight of the second.
So in our little example you would have the weight of the second (X) pulling down plus the equal and opposite force the belayer creates by holding the second (also X). So, if we balance the equation, the anchor would be holding 2X because 2X = X(the second) + X(the belayer).
But as someone said...friction in the system will reduce the weight you have to hold to keep the second still while he hangdogs. So it won't quite be 2X.
Bryan
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aikibujin
Jun 3, 2004, 1:37 AM
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In reply to: The more serious problem would occur if you are swinging leads; that is, if the second you are bringing up will be leading the next pitch. If he falls, he'll be putting a lot more force on the one bolt than twice his body weight. Then, if that bolt fails, the remaining bolt will be shock loaded. When I lead above a belay anchor, I clip my rope through two draws, one on each bolt. -Jay
Makes sense. Thank you.
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overlord
Jun 3, 2004, 6:44 AM
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in this case i wouldnt worry about the second falling. bolts should easily handle a second falling (consider what kind of force a leader fall puts on the top bolt). were talking about a small fall with a small factor. no biggie.
but i would rerig the anchor were swapping pitches.
so this is only usefull if youre the leader for the next pitch, because if youre not, than you have to rig this anchor and then rerig the thing to be able to belay the leader safely.
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jt512
Jun 3, 2004, 4:40 PM
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In reply to: From what I understand, the OP's more or less right on the doubling of forces on the right-hand bolt if you bring your second up as diagrammed (there's a bit a friction, so it's not quite doubled).
Nope. You guys are all wrong. The force on the piece if the second falls will be in excess of 3 times body weight if there is no slack in the rope, and can be much higher if there is slack in the rope (up to 7.5 times body weight with 4 feet of slack according to a recent R and I article).
Even though there is no slack in the rope, when the second falls a breaking force at least equal to his body weight must be applied in order to arrest the fall. Thus the maximum tension in the second's side of the rope must be at least 2 times the second's body weight. If the carabiner were a frictionless pulley, the tension in the belayer's side of the rope needed to produce this force would also be 2 times the second's body weight, and so the maximum force on the carabiner would be 4 times body weight. However -- and here's where the "3 times body weight' figure comce from -- friction across the carabiner reduces the tension in the belayer's side of the rope, by about 35%, to about 1.3 times body weight. Thus, the maximum force on the carabiner is 3.3 times the second's body weight. However, this assumes no slack in the rope. Even a small amount of slack will greatly increase this force.
-Jay
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brianinslc
Jun 3, 2004, 5:08 PM
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In reply to: In reply to: I'd use two draws. Always better to be on two bolts than one. Ditto. How much time is really wasted in clipping a 2nd draw or sling to a bolt & running the rope through it? In the context of safety/redundancy vs speed this seems like a no-brainer to me.
Not ditto always for me.
I think I like the leader and their potential factor two fall on just one bolt. If the bolt fails, then the force is on the belayer via the belay device on the harness. I prefer taking the force of the lead climber after that single bolt fails on me (I'm assuming a non-hanging belay station where I'm standing on my feet). Then the single bolt I'm anchored to is the backup, and I'm holding my partner whilst on my feet, off my harness. Seems like it would add a more dynamic shock reduction to the whole system.
If the leader fell and the force was on both bolts, and they both failed, yikes. At least by only clipping one, the force will only initially be on one, then transferred to the belayer, whilst the single remaining bolt would be the last ditch back up with a much lower force coming on it should the belayer's knees buckle.
I almost always only clip the leader to a single bolt off a double bolt anchor for the above reason. And, after the leader gets in a bomber piece of gear or three, I'll unclip them from that single bolt.
YMMV...
Brian in SLC
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jt512
Jun 3, 2004, 5:13 PM
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In reply to: I almost always only clip the leader to a single bolt off a double bolt anchor for the above reason. And, after the leader gets in a bomber piece of gear or three, I'll unclip them from that single bolt.
You won't be clippin' my lead line through just one bolt of a two-bolt anchor.
Your mileage might be 200 feet straight down. I think you need to rethink this.
-Jay
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j_ung
Jun 3, 2004, 5:21 PM
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In reply to: In reply to: And the anchor does fulfill the requirement of SRENE. It does not fulfill all of the SRENE requirements...specifically the 'Never/Not Extending' requirement. If the right hand bolt blows then the quickdraw will fall until the 'dog eared bowline' fully extends and thus will shock-load the left hand bolt. Agree? Bryan
I suppose. However, SRENE, SIREN or whatever acronym you prefer is not the be-all end-all of anchor construction. It's a guide and should not be substituted for the anchor builder's judgment in a unique situation... which describes every situation.
This goes for every anchor and no anal-retentive thread like this one can adequately cover every qualifier ("assuming both bolts are bomber...", "if it's a hanging belay...", if the belayer is asleep with too much slack in the system...", etc.).
If Climbing's Tech Tip bothers anyone that much, clip another draw to the second bolt, a la jt512, and climb on.
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alpnclmbr1
Jun 3, 2004, 5:28 PM
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In reply to: I almost always only clip the leader to a single bolt off a double bolt anchor for the above reason. And, after the leader gets in a bomber piece of gear or three, I'll unclip them from that single bolt.
Gotta go with Brian on this one. (people are overdoing the theory side of things)
Jay,
Assume a two bolt anchor. What type of anchor system are you using? Do you place the lead draws above or below your anchor system and to which side?
What happens if you start climbing on the right side of the anchor and move to the left side before you can place any gear?
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