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jt512
Jun 17, 2010, 6:21 PM
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I think that most experienced climbers believe that if two carabiners with gates opposite and opposed are used for the master point of a top rope anchor, then neither carabiner needs to be a locker. However, over in this post, cleethree writes:
cleethree wrote: I state that one biner [in the TR master point] needs to be a locker only because that's what is written in books and is the main source of guildlines here. You all speak about limiting the chance of failure at the power point with use of 2 biners, why not always use a locker here for additional safety?
So, presumably, the reason that one biner should be a locker is to eliminate the possibility that both biners are simultaneously loaded with their gates open in a fall. Well, the worst carabiners that meet the CE standard have open-gate strength ratings of 6 kN, giving 12 kN, or 2700 lb, of open-gate strength when used in pairs. To see if this is enough strength, let's calculate the peak impact force in a wost-case top rope fall. Under common assumptions, the peak impact force on the anchor can be calculated as a function of the climber's weight, the fall factor, the UIAA impact force rating of the rope, and the friction between the rope and the anchor. In order to come up with a worst-case fall scenario, we'll use reasonable upper bounds for each of these parameters in our calculation. We'll also assume that the belayer is anchored and gives a static belay.
Upper bounds for impact force parameters
Climber's weight. The heaviest climber I have ever personally climbed with was a guy from the gym who weighed 290 lb. (I, who weigh 135 lb, belayed him, and it wasn't pretty, even on toprope, with me anchored.) Now, if someone who weighs 290 lb can toprope, it is likely that at some church outing or office "team-building" event somewhere, a 300+ pounder has or will get on a toprope. The two fattest people I have ever personally known were Jerry and Marvin from my karate class in high school. Jerry and Marvin were taking karate to lose weight. Jerry, the lighter of the pair, weighed 360 lb, and I think if he set his mind to it, he could struggle up an easy TR route. But Marvin, at 440 lb, just wouldn't get off the ground. So, I think that 400 lb is a reasonable upper bound on the climber's weight.
Fall factor. Fall factor, of course, is the length of the fall (before the rope begins to stretch) divided by the amount of rope out between the belayer and the climber. If the belayer has zero slack in the rope when the climber falls, the fall length will be zero, and hence so will the fall factor. But there often will be at least a small amount of slack in the rope, and if the belayer is inattentive, there could conceivably be a lot. So to come up with an upper bound on our fall factor we need to put a reasonable upper bound on belayer inattentiveness. On a top rope, the largest fall factors can occur when the climber falls from the anchor on a short route. So, let's say that the climber falls from the anchor on a 25-foot route, and the leader is so inattentive that he has let 12.5 feet of slack build up in the rope. The fall would then be 12.5 feet onto 37.5 feet of rope, for a fall factor of 1/3.
UIAA impact force rating. The largest permissible impact force rating for a dynamic rope under UIAA guidelines is 12 kN. We'll use that value.
Friction. Friction is calculated as a fraction of the tension in the climber's side of the rope. It's almost universally taken to be 1/3, so we'll use that value.
So, to recap, our parameters will be the following:
Climber's weight: 400 lb.
Fall factor: 1/3
UIAA impact force rating: 12 kN
Friction factor: 1/3
Now, we plug these values into my on-line impact force calculator¹, and here are the results we get.
The bottom line of figures, the force on the anchor, is what we're interested in. Depending on which impact force model is used, the calculated peak impact force is between 15 and 17 kN, which, regardless of model, is substantially greater than 12 kN, the combined open-gate strength of two UIAA-certified carabiners.
So, is the n00b right? Do we need a locker in the master point of a TR anchor after all?
Jay
¹ The impact force equations that this calculator uses are documented here and here.
(This post was edited by jt512 on Jun 18, 2010, 1:06 AM)
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hafilax
Jun 17, 2010, 6:31 PM
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What is the probability that both carabiners will be open? If it's not infinitesimal then I think at least one locker is a good idea.
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ptlong
Jun 17, 2010, 6:37 PM
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Maybe so, if you're belaying a climber with a mass of 400 lbs and all of your other carabiners are crappy ones.
(This post was edited by ptlong on Jun 17, 2010, 6:39 PM)
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uni_jim
Jun 17, 2010, 6:38 PM
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"oh noes! my fat friends are all going BLOW UP THE ANCHOR!!!"
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gmggg
Jun 17, 2010, 6:49 PM
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uni_jim wrote: "oh noes! my fat friends are all going BLOW UP THE ANCHOR!!!"
But what if they* have cracks.
But +1 for having a locker in the top rope anchor. It is safer, it is generally equipment on hand, and it is just as easy to rig.
For me it comes down to: There's no reason not to.
*Intentionally ambiguous they
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reno
Jun 17, 2010, 6:50 PM
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gmggg wrote: For me it comes down to: There's no reason not to.
+1 for that.
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jt512
Jun 17, 2010, 6:54 PM
Post #7 of 89
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gmggg wrote: +1 for having a locker in the top rope anchor. It is safer...
I get the feeling that the italicized "is" means that this is a belief not based on any evidence; that is, you are assuming the conclusion of the argument.
In reply to: ... it is generally equipment on hand, and it is just as easy to rig.
And that is not true in a typical sport climbing scenario.
Jay
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gmggg
Jun 17, 2010, 6:54 PM
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reno wrote: gmggg wrote: For me it comes down to: There's no reason not to. +1 for that.
I would like to add though that I would not tear my hair and beat my liver if I came up and found I had been risking my life on two non lockers.
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kjaking
Jun 17, 2010, 7:01 PM
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jt512 wrote: gmggg wrote: +1 for having a locker in the top rope anchor. It is safer... I get the feeling that the italicized "is" means that this is a belief not based on any evidence; that is, you are assuming the conclusion of the argument. In reply to: ... it is generally equipment on hand, and it is just as easy to rig. And that is not true in a typical sport climbing scenario. Jay
How is it more difficult to rig a toprope with a locker? because that one befuddles me.
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jt512
Jun 17, 2010, 7:04 PM
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kjaking wrote: jt512 wrote: gmggg wrote: +1 for having a locker in the top rope anchor. It is safer... I get the feeling that the italicized "is" means that this is a belief not based on any evidence; that is, you are assuming the conclusion of the argument. In reply to: ... it is generally equipment on hand, and it is just as easy to rig. And that is not true in a typical sport climbing scenario. Jay How is it more difficult to rig a toprope with a locker? because that one befuddles me.
I only mean that when sport climbing, it would be unusual to have a draw with a locker on it with you. Hence, top ropes on sport routes are usually comprised of just two ordinary draws.
Jay
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reno
Jun 17, 2010, 7:16 PM
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gmggg wrote: reno wrote: gmggg wrote: For me it comes down to: There's no reason not to. +1 for that. I would like to add though that I would not tear my hair and beat my liver if I came up and found I had been risking my life on two non lockers.
Agreed. I put my liver through enough abuse as it is.
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kjaking
Jun 17, 2010, 7:26 PM
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jt512 wrote: kjaking wrote: jt512 wrote: gmggg wrote: +1 for having a locker in the top rope anchor. It is safer... I get the feeling that the italicized "is" means that this is a belief not based on any evidence; that is, you are assuming the conclusion of the argument. In reply to: ... it is generally equipment on hand, and it is just as easy to rig. And that is not true in a typical sport climbing scenario. Jay How is it more difficult to rig a toprope with a locker? because that one befuddles me. I only mean that when sport climbing, it would be unusual to have a draw with a locker on it with you. Hence, top ropes on sport routes are usually comprised of just two ordinary draws. Jay
Okay, that makes more sense. While most people resist this, it should become less unusual to have a couple lockers and shoulder slings with you anyways - maybe that bolt would be better extended, and who knows what the anchors look like if its a long pitch - its not always perfect for two draws.
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j_ung
Jun 17, 2010, 7:28 PM
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Well, that's warning enough for me. I'm not climbing with anybody above 300 lbs.
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edge
Jun 17, 2010, 7:33 PM
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I am completely fine with two non-lockers with gates opposite and opposed on a top rope.
If I happen to have a locker, I may use it to get it off my harness unless I foresee a better use for it later, say perhaps after lowering/rapping and then using it to anchor to the ground, where I would deem a single locker and a clove hitch sufficient.
Now, having said that, I will also say that if one of my partners at the time freaks out and insists on a locker at the top, then it is really not worth my effort to argue the minutiae ad nauseum to get them to come around to my personal way of thinking. I would just throw a freaking locker on the set-up and get about the business of climbing.
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gmggg
Jun 17, 2010, 7:49 PM
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jt512 wrote: gmggg wrote: +1 for having a locker in the top rope anchor. It is safer... I get the feeling that the italicized "is" means that this is a belief not based on any evidence; that is, you are assuming the conclusion of the argument. In reply to: ... it is generally equipment on hand, and it is just as easy to rig. And that is not true in a typical sport climbing scenario. Jay
I don't know that I'm assuming the conclusion of #1. If your safety concerns are predicated on the possibility of open gates, then a device that mitigates that likelihood is safer.
Good point for #2; but that is why I included "generally".
I would dispute #3 given the availability of the equipment.
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jt512
Jun 17, 2010, 7:55 PM
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gmggg wrote: jt512 wrote: gmggg wrote: +1 for having a locker in the top rope anchor. It is safer... I get the feeling that the italicized "is" means that this is a belief not based on any evidence; that is, you are assuming the conclusion of the argument. In reply to: ... it is generally equipment on hand, and it is just as easy to rig. And that is not true in a typical sport climbing scenario. Jay I don't know that I'm assuming the conclusion of #1. If your safety concerns are predicated on the possibility of open gates, then a device that mitigates that likelihood is safer.
Only if the combined open-gate strength of the two non-locking biners can be exceeded. So, the conclusion you are assuming, is that they can.
Jay
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tomtom
Jun 17, 2010, 8:03 PM
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jt512 wrote: I only mean that when sport climbing, it would be unusual to have a draw with a locker on it with you. Hence, top ropes on sport routes are usually comprised of just two ordinary draws. Jay
I have a couple partners who carry two quickdraws with lockers on both ends. If you need two quickdraws for the anchor, carrying two with lockers is just as complicated as carrying two with non-lockers.
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cleethree
Jun 17, 2010, 8:07 PM
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Maybe I'm completely off here but let's take a step back...
The rational behind having 2 opposite and opposed biners at the power point was so that the rope can't work itself out by accident. Not that 1 biner is strong enough for the task.
In a perfect scenario, 1 biner should suffice as it's strength is rated higher than any of your cases can generate. But we don't have perfect scenarios, gates can get pressed open and lockers can become unlocked.
So in my opinion, based on what I've read here and in literature, having a locker or two at the power point is safer, at least initially.
Although lockers are prone to coming unlocked from time-to-time. During the period that is it locked, which could be the entire time, it would impossible for the gate to be pressed open and have the rope come out.
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jt512
Jun 17, 2010, 8:21 PM
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cleethree wrote: Maybe I'm completely off here but let's take a step back... The rational behind having 2 opposite and opposed biners at the power point was so that the rope can't work itself out by accident. Not that 1 biner is strong enough for the task.
That's part of the rationale. The other part is the open-gate strength of a single biner is not high enough, but that of two biners is (possibly). The rope cannot come out of two reversed and opposed biners; therefore, the only logical rationale for including a locker is to prevent simultaneous open-gate loading.
Jay
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bill413
Jun 17, 2010, 8:23 PM
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It's an interesting analysis. I'm curious as to how "quickly" as we move away from the maximum assumptions (lighter climber, lower FF) we get to the "safe zone" of two open gate biners.
I wonder sometimes if the protrusion of the locking sleeve on a locker could put enough sideways pressure on a second biner as to cause gate failure. Would you actually be safer with two non-lockers than with two lockers?
As for using lockers at the top of sport climbs - if all you will be doing is TR, OK. However, if you will occaisionally be pulling the rope for someone else to lead up, having a locked biner at your anchor is a pain. Give me two non-lockers there.
I'm perfectly comfortable climbing to a two biner anchor. But, part of that is predicated on the assumption that
- They won't both open at once
- I weigh much less than 400 lbs
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jt512
Jun 17, 2010, 8:26 PM
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bill413 wrote: It's an interesting analysis. I'm curious as to how "quickly" as we move away from the maximum assumptions (lighter climber, lower FF) we get to the "safe zone" of two open gate biners.
There's a link to the on-line calculator in the OP, so you can play with those parameters, if you are so inclined.
Jay
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cleethree
Jun 17, 2010, 8:31 PM
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So to cover the worst case scenario, the power point should include 3 biners or 2 steel biners, lockers or not.
(This post was edited by cleethree on Jun 17, 2010, 8:32 PM)
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kjaking
Jun 17, 2010, 8:37 PM
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bill413 wrote: As for using lockers at the top of sport climbs - if all you will be doing is TR, OK. However, if you will occaisionally be pulling the rope for someone else to lead up, having a locked biner at your anchor is a pain. Give me two non-lockers there.
I still don't get how a locker is a pain. Its the same thing, it just doesn't open unless you want it to. Or do we need to argue about what a locker is?
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csproul
Jun 17, 2010, 8:42 PM
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kjaking wrote: bill413 wrote: As for using lockers at the top of sport climbs - if all you will be doing is TR, OK. However, if you will occaisionally be pulling the rope for someone else to lead up, having a locked biner at your anchor is a pain. Give me two non-lockers there. I still don't get how a locker is a pain. Its the same thing, it just doesn't open unless you want it to. Or do we need to argue about what a locker is?
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cleethree
Jun 17, 2010, 8:42 PM
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kjaking wrote: I still don't get how a locker is a pain. Its the same thing, it just doesn't open unless you want it to. Or do we need to argue about what a locker is?
Imagine you lead the route and put 2 draws with lockers at the anchors and lock them. Then pull the rope and have someone else lead the climb. That climber will get to the final 2 draws and have to unscrew the gates - that's a pain.
Also, for me at least, clipping lockers (even unlocked) require much more effort than a wire gate or bent gate biner.
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