And you can make that point without relying on absurd claims that a belayer could experience a 9kN load in a TR fall.

And for what it's worth, I believe the 1.67 factor is usually applied to the force on the climber's end of the rope. If you are starting from the force on the belayer's end of the rope, I think a multiplier of 2.5 would be more appropriate.

Nevertheless, the basic fact that you can't seem to understand is that just because a belay device can apply a certain force to the rope, doesn't mean it will apply that force to the rope.

I just went ahead and bought some 11mm static rope to setup my anchors.

I know some folks don't like the clove hitch (it's adjustable!) and others don't like the two loops on a bite at the master point (it makes me happy), but all I really want is to prevent falling to my death! Hopefully this will do the job.

Opposite/opposed locking 'biners on two loops made from overhands on a bite. I know O and O doesn't matter for lockers, but it helps me remember to pay attention.

Very lively discussion guys. Thanks for the input. So I just went ahead and bought some 11mm static rope to setup my anchors. My rigged setup is pictured below.

I know some folks don't like the clove hitch (it's adjustable!) and others don't like the two loops on a bite at the master point (it makes me happy), but all I really want is to prevent falling to my death! Hopefully this will do the job. :)

Thanks again for your insight. It's been a real help and might have contributed to my long life!

Opposite/opposed locking 'biners on two loops made from overhands on a bite. I know O and O doesn't matter for lockers, but it helps me remember to pay attention.

[image]http://swatyy.webs.com/setup.jpg[/image]

One leg is a figure eight. The master point is made to length and the second leg is adjusted on a clove hitch to equalize the anchor.

For those of you who don't like clove hitches, what knot would you suggest and why is it better?

[image]http://swatyy.webs.com/legs.jpg[/image]

*edit: I bought *static* rope, not dynamic. ;p

Very lively discussion guys. Thanks for the input. So I just went ahead and bought some 11mm static rope to setup my anchors. My rigged setup is pictured below.

I know some folks don't like the clove hitch (it's adjustable!) and others don't like the two loops on a bite at the master point (it makes me happy), but all I really want is to prevent falling to my death! Hopefully this will do the job. :)

Thanks again for your insight. It's been a real help and might have contributed to my long life!

Opposite/opposed locking 'biners on two loops made from overhands on a bite. I know O and O doesn't matter for lockers, but it helps me remember to pay attention.

[image]http://swatyy.webs.com/setup.jpg[/image]

One leg is a figure eight. The master point is made to length and the second leg is adjusted on a clove hitch to equalize the anchor.

For those of you who don't like clove hitches, what knot would you suggest and why is it better?

[image]http://swatyy.webs.com/legs.jpg[/image]

*edit: I bought *static* rope, not dynamic. ;p

I not only made no "absurd claim" but made no claim at all. I merely quoted one of the most respected and most published rope force experts in the world in response to hugepedro's claim that his subjective judgement was based on "the math" - even though he never offered any mathematical substantiation and still hasn't.

Based on the above comparison, the maximum credible event (MCE) for belay loads with new ropes would be 12 kN for devices designed for all falls and 9 kN for devices limited to fall factors less than 1.0 (single pitch or top rope climbing).

And what you - and several others - fail to understand is that it makes sense to build a top rope anchor to be able to take what Attaway calls the "maximum credible force", which is less than the maximum possible force but a good basis for safety engineering.

The 9 kN that he calculated is the maximum credible force for all falls below fall factor 1. A maximum credible force (not the maximum possible) on the anchor for top roping is probably 5 kN.

Very lively discussion guys. Thanks for the input. So I just went ahead and bought some 11mm static rope to setup my anchors. My rigged setup is pictured below.

that looks totally fine despite what some "expert" may say

whether you opposed lockers or not is your choice ... but make sure they are both LOCKED if you dont ... and every locker eventually has its gate rubbed against rock when unsupervised ... as anyone with real top rope set up experience will attest to ... the climbers moves all over the place, the rope gets flipped here and there ... it wont destroy yr locker or make it dangerous, biners are tough ... and thats why you use TWO of em


from the american alpine institute ...

[image]http://3.bp.blogspot.com/_ejAk42p7jdY/SoRXesza9kI/AAAAAAAAEAo/h4U-UVY68Mw/s400/Op%26OP+Locker+1.JPG[/image]

One of the commonly quoted rules for toproped climbing is that one should always use two opposite and opposed lockers at the master point.

The idea is that there is no way that the rope could possibly jump out of two opposite and opposed lockers. And while it may be possible -- however unlikely -- for movement in the system to cause the one of the gates to become unlocked and to open, it would be nearly impossible for the both lockers to become unlocked and to be opened.

In the guiding world, two opposite and opposed lockers are considered to be industry standard. The liklihood of a single locking carabiner becoming unlocked and opening is incredibly low. However, this is one of the rules that you learn when you start to climb and it has become so integral to outdoor groups throughout the world in toproping that it has become the industry standard across the board.

Industry standard is one of those phrases that we should pay attention to in climbing. There are very few things that can be considered industry standard in the climbing world.

http://alpineinstitute.blogspot.com/...-at-power-point.html

while i personally think that 2 opposed non-lockers is fine as is common in most sport climbing areas i know of ... i dont really question the AAI's emphasis on absolute safety ...

2 opposed lockers is what they use for their clients ...

who would you rather trust ... the AAI that guides clients and has liability and whose guides are all certified and trained ...

or some "rc expert" who goes off about 9 kn falls at belays on TR, and cant read a simple study ... and, as is typical with "rc experts" can never admit to be wrong

Well it’s about time you admitted you were wrong.

Not worth much. But I overstated that factor. The force on the belay device would be .67 times the force on the climber, and the force on the anchor would be the sum of the two, or 1.67 x the climber's impact.

Calculating from the belay force, the climber's impact would have to be 1/0.67 or 1.5 x the force at the belay, not 2.5 times.

Seriously, dude, read the dang report again and see if you can figure this out for yourself.

In fact, it is you who has failed to either read or comprehend the data and conclusions in this report. Or, rather, who chooses to use it selectively to support your own position.

I had earlier posted this image from the Attaway report, which is specific to impact forces in top roping and gym climbing:

[image]https://lh4.googleusercontent.com/-tkGLQhbUWis/TlM6-Efcy5I/AAAAAAAAAE8/ja2fX93vkbU/s512/Max%252520Impact%252520force%252520on%252520Top%252520Ropes.jpg[/image]

While it may be true that most TR falls are of low FF, low impact and low consequence, failure of imagination to include the entire range of "credible" events that might cause a more significant impact force is what leads to disaster.

For instance, I've seen top ropers top out beyond the top anchor for a variety of reasons. I've seen climbers wandering off route - or onto another route from the same anchor - and sometimes getting the rope caught on a rock feature and climbing above the snag until it can be freed. There are, in fact, many credible scenarios that can cause much higher FF falls. And, as I mentioned earlier, rope drag and friction between the belayer and the anchor effectively increases FF by reducing the effective rope length that can absorb energy.

Though you earlier disparaged my emergency management experience, the algorithm that all risk management and disaster mitigation is based upon is the Risk Matrix, or probability vs. consequence matrix.

We don't put much effort into trying to plan for or mitigate low probability events with low consequence. We put effort into planning for high probability events of high consequence, though those are the ones that most people consider and try to avoid. We put some effort into planning for high probability events with relatively low impact because they happen so often. But the most effort often has to go into planning for low probability events that have high consequence, because those are the ones most people never bother considering or preparing for ("it can't happen to me", or "it's a one in a million chance").

[image]http://eight2late.files.wordpress.com/2009/06/riskmatrix22.gif[/image]
We put lightning rods on our barn roofs, not because we expect lighting to strike often, but because we don't want to deal with the consequence of losing the barn.

Those who set up top rope anchors thinking that nothing can go wrong or be out of the ordinary, are the ones I, as a wilderness EMT, will end up evacuating and transporting to the ER (or the morgue).

Ok, but... 1.5X is just the force on the climber's end of the rope. The force on the anchor will be the sum of these: 1 + 1.5 = 2.5... don't delude yourself, or anyone else, into thinking that you have a firm grasp on the actual numbers.

And, of course, the purpose of all your useless verbiage is merely to prove me wrong, which you failed to do since you merely quoted the one statement of my own that you agree is correct. So, in fact, you have proved me right.

But that's not the point. I don't give a shit who is right. As a professional technician and instructor in the field of rope rigging and rescue, I care only about what is right and, in this discussion, about what is safe.

But among climbers (especially sport climbers), there is so much testosterone-fueled ego that it's always about who can tear down someone they perceive as a challenge or a threat to their superiority. This is what makes a place like RC.com so damn ugly.

No, my purpose was to counter false information that an ignorant douchenozzle was posting in the beginner forum.

You claimed the rig the AMGA is teaching is dangerous...

One of the most important qualities one looks for in a mountain rescue candidate is the ability, even desire and drive, for honest self-assessment post-incident, so that they can correct mistakes and improve skills. Not seeking to cover one’s errors to save face – it’s called integrity.

But, for those who are interested in statistical analysis, Attaway's use of large population survey data and random combinations of mulit-variant survey results to estimate actual field experience is how science works in this world. Attaway also includes several disclaimers with conditionalities that could either increase or decrease his statistical results. But, unlike bearbreeder, he knows what he's doing and his results are published by the AMGA among others.

I didn't catch that discussion in his paper (I only skimmed it), but I can think of several reasons that his Monte Carlo approach could be flawed. Mainly, it seems like he assumed the distributions of the various factors were independent.

Well, we seem to share a common purpose.

Only if you need a straw man argument. I stated that the convention of opposite and opposed carabiners, a holdover from the non-locking days, can be dangerous when applied to top rope anchors extended over the edge - the subject of this thread - and I explained why.

You cherrypicked the information from Attaway's report, you either inadvertently or deliberately misrepresented its conclusions and misrepresented my own comments

you claimed that "28 years on the sharp end" (talk about "puffery") gives you a better handle on rope system physics than my multi-discipline rope work and my teaching it for 12 years (I also teach math and statistics and the vector mechanics of rigging), and (unlike me) you have refused to acknowledge any mistakes on your part and continue to insist that you are always right and more knowledgeable than an internationally-recognized expert in the field (no brag, just fact).

I completely agree with you on this. But you need to look into the mirror. You would never even make the cut onto my rescue team, since you are far more interested in arguing than in learning.

None of us can make a determination about Attaway's assumptions without asking him or looking more carefully at his methodology. I suspect his randomizing of the three factors adequately covers any interdependencies.

But, perhaps, we can at least agree that Stephen W. Attaway, PhD, of Sandia National Laboratory, has some pretty respectable credentials for research in this field.

His publications include:

Rope System Analysis (1996, published in Nylon Highway, No. 41, a special publication of the Vertical Section of the National Speleological Society, and in the proceedings of the NATARS meeting of November 1-3, 1996 in Las Vegas, Nevada)

The Mechanics of Friction in Rope Rescue (presented at the International Technical Rescue Symposium, 1999)

Analysis of Rope Impact Force Equations Predicting Rope Impact Forces (ITRS, 2002)

Hang 'Em High: How Far Can You Trust Your Belay Device? (Nylon Highway, No. 52, 2006)

Measurement of Dynamic Rope System Stiffness in a Sequential Failure for Lead Climbing Falls (AMGA, 2007)

Ice Climbing Anchor Strength: An In-Depth Analysis (MRA, 2009)

But, perhaps, we can at least agree that Stephen W. Attaway, PhD, of Sandia National Laboratory, has some pretty respectable credentials for research in this field.

None of us can make a determination about Attaway's assumptions without asking him or looking more carefully at his methodology. I suspect his randomizing of the three factors adequately covers any interdependencies.

We computed the CLIFF distribution as follows. Random draws from a climber population with a weight distribution shown in Figure 2 and a maximum fall distribution shown in Figure 4 were used to construct the distribution of fall impact force, shown in Figure 7. The rope modulus was also varied to match the impact force distribution shown in Figure 1.

I wouldn't pick either of you guys for my fantasy rescue team.

Stephen Attaway does appear to have respectable credentials. But I don't like arguments from authority.

I didn't catch that discussion in his paper (I only skimmed it)...

We can indeed make determinations about his assumptions by reading his report more carefully.