8mm acc cord

Here's another one-

Would you use 8mm accessory cord with a strength rating of 15.6kn for a top rope anchor not doubled up- single strand on each leg?

Assuming that the masterpoint is redundant this is fine, and there is no reason why you would ever generate this amount of force in a top rope situation. With that being said, there are many situations in which I would not find it acceptable. Most notably, I would not us 8mm cord if it was running over a sharp edge. In this case I would prefer a beefy static. Use your discretion and assess each anchor individually and make decisions on a case by case basis.

I am curious, in what situation are you trying to use 8mm cord as a single strand for each anchor leg? That may provide for more specific advice.

Sure, why not? Each leg is to a bolt or a tree, right? Redundancy through your fig-8 on a bight masterpoint. Not over any sharp edges? Sounds good to me.

Dylan B. wrote: no leg will take more than ~ 33% of the force of the fall.

Well, I guess I'll go ahead and get this started...

"john long john long john long, craig luebben craig luebben, john long..."

"some tests in soviet laboratories in the 80's..."

On a more serious note, these are kind of interesting:

petzl.com/en/Sport/Forces-a…
petzl.com/en/Sport/Influenc…
petzl.com/en/Sport/Conseque…
petzl.com/en/Sport/Fall-com…

edennis wrote:Here's another one- Would you use 8mm accessory cord with a strength rating of 15.6kn for a top rope anchor not doubled up- single strand on each leg?

I use it all the time. If you are using a dynamic rope and you can generate 15kN, or even 7kN you are the man.

I'm not one of those people that likes to make my anchors just good enough, usually I like to be able to drop a bus off them. but you do have to have some concept of the forces before freaking out.

Two independent strands equalized is a rundundant anchor, the failure point would most likely not be the 8mm cord but the anchor point itself, or heck, even the carabiners before the 8mm cord if the anchor is well equalized.

If the cord you are describing has the rating that you state, there should be no reason to believe it would not be adequate for a top rope anchor.

I believe that with the question being asked, you should make sure to have someone who is safe and experienced to double check your setup.

Climb safe, double check yourself/partner, and have fun.

I think his data showed the forces on the anchor, climber, and belayer were far below 15kN.

Thanks for the replies-
I am competent at setting up top-rope anchors, just curious because the 15.6kn in a funny middle ground between smaller cord/webbing which would be used doubled up, and true static line which is used single strand. The anchor I am imagining is a simple, 2 leg anchor.

Also, someone mentioned that cordellette is dynamic- which is untrue, yes?

The statement that cord is static or dynamic is generally relative to your definition of what's dynamic or not..

Generally, all nylon cords are dynamic, and will stretch between 8-15% at 100lbf, where polyester and dyneema/spectra cords will only stretch 1-5% under an equal load.

Dylan -

Nope, doesn't say anything about forces on top rope anchors, but it does show that forces on a lead fall will rarely even be above 6 kN, which is pretty much the same thing that John Long says:

rei.com/media/cc/a4955f32-3…

The other three links are only quasi-relevant. The rope drag one is relevant in that on top rope, there shouldn't really be any rope drag, and so you have the entire rope in the system. The other ones were just kind of interesting, especially the gri-gri vs. reverso one.

As far as I can tell, yeah, you're totally right about the force distribution in those ideal conditions, but, we don't engineer for the ideal conditions, we engineer for the worst case scenario. Like others said, it's abrasion that I would worry about. I think you'll break your belayer before you break your cordellete.

A couple interesting articles from the UIAA about the impact of abrasion on ropes:

theuiaa.org/upload_area/fil…
theuiaa.org/upload_area/fil…

(Yes, I realize a kernmantle rope and cordelette are not the same thing). Just interesting to see the UIAA say that a modern rope, even a 10 or 15 year old one, will not break unless loaded over a sharp edge. Made me realize that SRENE / EARNEST / WHATEVER really has nothing to do protecting the anchor, but instead is all about protecting the placements. Even force multiplication due to wide angles probably won't generate enough force to break any of the components (assuming that the carabiners stay loaded on their major axis). I always think about a slackline, where your angle is nearly 180 (forces on the anchor approach infinity), and you're girth hitched to a tree several feet up the trunk (lots of leverage); you can bounce your full body weight on it repeatedly, and everything is fine.

akscrambler wrote: I always think about a slackline, where your angle is nearly 180 (forces on the anchor approach infinity), and you're girth hitched to a tree several feet up the trunk (lots of leverage); you can bounce your full body weight on it repeatedly, and everything is fine.

You may want to consider that everything is fine because the forces on the anchors, in fact, don't approach infinity...if they did, the anchor would necessarily fail.

Max Forbes wrote:The statement that cord is static or dynamic is generally relative to your definition of what's dynamic or not.. Generally, all nylon cords are dynamic, and will stretch between 8-15% at 100lbf, where polyester and dyneema/spectra cords will only stretch 1-5% under an equal load.

Yep. Polyester doesn't absorb water and it doesn't stretch.

Nylon absorbs 44% of its weight in water and it does stretch. All nylon is technically dynamic, but not truly dynamic in the sense we talk about dynamic climbing ropes. That little stretch will reduce impact forces, however, vs Titan cord or polyester cord.

Xam wrote: You may want to consider that everything is fine because the forces on the anchors, in fact, don't approach infinity...if they did, the anchor would necessarily fail.

Obviously. I'm just saying that you're applying the worst force multiplication possible.

Would assume cyclic loading upon a single strand of the anchor is more relevant in a TR setup than the breaking force possible in a fall.

From an article by Bigfoot Mountain Guides
Anchors built for a group (more than a party of two that will each take one lap) also need to be durable. We call the repeated loading and unloading seen in a group toprope environment “cyclic loading”. This cyclic loading causes all the materials in our safety system to stretch. As the material, which is generally out of sight to the climbers on the ground, stretches and rubs over an edge repeatedly it can become abraded. In extreme examples anchor materials or climbing ropes have been almost entirely cut or abraded as they rub over edges during the course of a single climbing session. Using durable materials (static rope or 1” webbing are the standard) and wisely choosing anchor locations will prevent material wear.

Source Article

edennis wrote:Here's another one- Would you use 8mm accessory cord with a strength rating of 15.6kn for a top rope anchor not doubled up- single strand on each leg?

Top-rope? Sure. Even if I take a 50% strength loss on each leg, and I get minimal load distribution, a TR fall isn't going to approach that.

As others noted, have to watch out for sharp edges, sawing action, etc. But that's always a good idea.

A 8mm static cord will hold a factor 2 fall as a lanyard even with an alpine butterfly in the middle

It will hold the forces found in TR climbing, especially as you have two legs

To make it extra secure folds the loop back onto itself and tie the knot ... This way the amount of material through the weakest point is doubled, clip the loose bight in to the biner

;)