OK, this is where my n00bness really comes through: how dynamic is this compared to other dynamic ropes?

why 8.4kn is appropriate for a dynamic rope? I always thought what made a dynamic rope was it's ability to stretch and that the kn was more for falls and durability.

Geez, Greg! You are such a damn noobie! I would never climb with you!! Oops! Too late! Come to think about it, don't you ever listen. I'm always spouting this stuff. I hope at least half of it is correct. Let's hope rgold is in the house!!!

In general, the lower the impact force the stretchier, or more dynamic, the rope. For example, an rope with an impact force rating of 8.0 kN is more dynamic, stretchier; than a rope with a 9.5 kN rating.

As to why 8.4 kN is appropriate for a dynamic rope, think about the limitsl both high and low.

Climbing ropes are subject to UIAA testing standards. They must hold at least 5 falls, __ number of minutes apart (rgold will fill in the blank), of a 80 kg weight with a fall factor (FF) of 1.74 or so (rgold?) with no more than a 12 kN impact force. This is for single ropes.

The test is designed to approximate the highest FF of 2. Fall factor is the distance of the fall divided by the amount of rope out. The design of the testing apparatus precludes achieving FF 2.

Why this 12 kN upper limit? Putatively it comes from Air Force testing of the impact of g forces on humans. It is said that beyond 12 kN impact force you will very likely suffer serious injuries. Most ropes are in the 8 to 9.5 kN impact force. They are "over engineered" with regard to the standard of 12 kN for safety and because not every climber weighs 176 lbs or less. http://www.cwu.edu/...rints/cmj135-140.pdf

My recollection impact force does increase relatively significantly with increasing climber weight. Stay on the program Ed! Too lazy to look for my program to calculate what weight it would take to generate 12 kN on a 8.4 kN rope. (rgold?)

Regarding falling on static ropes, I haven't done the calculations (and yes I'm too lazy to weed through my files to find the program) but I don't think you have to fall very far to significantly exceed 12 kN impact force with a static rope. (rgold?)

[Regarding FFs and impact forces in actual climbing situations, I have done a fair amount of sport and trad climbing and have caught a lot of falls. To the best of my recollection the most severe fall(s) I have caught were about .5 FF with a 200+ lb partner. They were pretty nasty. I was sore for a few days afterwards where my harness runs across my back and hips. I would guess the very great majority of falls I have caught or taken are significantly below the .5 FF level. I don't think I want to be doing the bucket test or worse yet experiencing a bucket test situation on a climb!!!!]

What is the lower practical limit? Not sure how or if it has been "established". Ropes are stretchy. Dynamic ropes will stretch about 30% under UIAA conditions. I suppose you can make a rope with a very low impact force but it would be very stretchy. I think they call them bungee cords. You want to stop with a safe impact force level but the further you fall the more chance you get to hit something.


For any given set of fall conditions a "stretchier" or more dynamic rope will generate lower impact force which is measured in kilonewtons (kN) than a less stretchy rope. Thus kN and stretch are directly and inversely related.

Regarding durability, how do you define it? Time to the sheath getting really stiff, the development of squishy spots, abrasion of the sheath, number of falls before it rips in two, etc.?

Ropes are made with different materials, designs and construction methods. I assume these variables impact any number of rope specifications in an interrelated manner. Durability characteristics are certainly one of them. Regarding number of falls, ropes are specified as to the number of UIAA falls experienced before failure. In general, this is a measure of the robustness or strength or the rope. For the most part, heavier, not necessarily thicker, ropes have higher fall ratings.

Bonus question for you Greg. Why would one tend to sew up a pitch coming out of the belay and then might run it out a bit towards the end of the pitch?

Sorry I didn't translate this into Spanish. Perhaps BEC can do it.

To navyguy, back to the original topic, yeah I think you are right. Be interested in what is learned from the Beal rep.

Bill

My recollection impact force does increase relatively significantly with increasing climber weight.

Too lazy to look for my program to calculate what weight it would take to generate 12 kN on a 8.4 kN rope.

That's not something you should have to recollect.

running it out higher up was better than down below was because the amount of rope out = lower fall factor

That's not something you should have to recollect.

[…]

Jay

I keep hearing that that lighter weight climbers face a higher impact vs. heavier persons. You, Jay, and Bill seem to have a good understanding of the matter, so can you confirm/debunk this?

It seems somehow plausible to me that I, a skinny 60 kg, may feel a stronger impact in the same fall than, say, a 80 kg climber.

Would that change at the rope's limits (100 vs. 150 kg climber)?

I'd love to hear some thoughts on that. Might be nonsense, as your calculator seems to prove.

What I forget is the actually numerical, or shape of the curve, relationship

I keep hearing that that lighter weight climbers face a higher impact vs. heavier persons. You, Jay, and Bill seem to have a good understanding of the matter, so can you confirm/debunk this?

It seems somehow plausible to me that I, a skinny 60 kg, may feel a stronger impact in the same fall than, say, a 80 kg climber.

Would that change at the rope's limits (100 vs. 150 kg climber)?

I'd love to hear some thoughts on that. Might be nonsense, as your calculator seems to prove.

Lighter climbers whose belayers don't give them dynamic catches go through their climbing careers getting slammed into the wall by their belayers, who don't get lifted into the air automatically when they catch the fall. Conversely, when these same heavy belayers are themselves the climber, they always get soft catches because they pull their lighter partner up into the air when they fall.

Most theoretical models of impact force assume that the belay is static, in which case, the heavier the climber the greater the impact force, all else equal.

Jay

Based on the collection of quoted people above and not at all on what was actually written, I declare this the best thread ever on RC.com.

Gee Greg you may not be up on the physics but you have the very important practical implication down pat! Good job rapping on the EDK. If all else fails just remind yourself that "Life is an adventure or nothing at all".

Bill

FYI to all on this thread. Beal just announced their first OUTDOOR rope with UNICORE.
http://bealplanet.com/...plete.php?idnews=370

Sounds awesome. Will wait and see...

[M]axim ropes have the highest impact force of any rope on the market . . .

Really? Even higher than Mammut?

Jay

Really? Even higher than Mammut?

Jay

My main project rope is their 9.5mm version of the Glider which has an impact force of 10.3 kN. But with a good belayer that knows how to give soft catches, it will still provide a nice smooth stop.

On some of their ropes, yup. The rest are at least as high. The lowest impact force i found on their single lines was 9.4kn- most were 9.8kn-10.3kn. They have a double that sits @ 6kn, but the rest are super-high. Mammut even drops into the 8s occasionally...

i assumed that a ropes impact force would actually rise with age, as it looses elasticity...but i dont actually know. i'd be curious to see that...