UKC

As I've climbed more widely and expanded the range of my gear a lot more of my pro is what you might call marginal, by which I mean rated under 7KN. My micros range between 2KN and 5KN, the superlight rocks from 4KN to 6KN.

I suppose the force varies according to how much rope is out, so for 5m, 15m and 25m of modern low impact half rope, something like a Mammut Phoenix or Genesis, and for a climber weighing 80kg with a full rack, how far above gear will that climber need to ascend to generate a force equal to 4KN and 6KN on that gear?

Presumably there is a formula but I'm a linguist, not an engineer. Can anyone help?

In reply to BnB:

Now I know these things are always controversial, but there are a few fall force calculators around that can give you a rough idea: http://junkfunnel.com/fallforce/

So for an 80kg climber (inc rack), with dynamic rope with 32% dynamic elongation you would have fall from this far above your last[0] piece of gear to generate 4KN of force on your top piece of gear:
* 5m of rope out: 2.7m
* 15m of rope out: 8m
* 25m of rope out: 13m

[0] I'm not sure if/how this calculator handles it, but additional friction will be introduced at each piece of protection that alters the flow of the rope (hence why extending placements is important). This will increase the forces in question by reducing the stretch of the rope.

This also doesn't take into account a good soft catch from a belayer which could be crucial with such falls on marginal gear.

DISCLAIMER: I have no clue how accurate this calculator is, I was just curious and wanted to see for myself.

In reply to hipyhop:

Could you define your parameters please
I am unsure, is it

15m of rope out, fall 8m, fall to ground/below belay

Or 15m of rope out, fall 8m, fall to 7m

In reply to 3leggeddog:

I didn't think about it like that, but in all 3 cases you'd hit the ground before shredding the gear, if this calculator is accurate AND no other friction is introduced anywhere else AND your belayer is as dynamic as a tree

In reply to 3leggeddog:

I assumed from the post that you can effective run out 1/4 of your total rope length above your last piece of gear in this theoretical scenario, e.g. if you have 25 m of rope out, then your last piece of gear would have to be within 6.5 m of you, allowing you to fall up to 13 m, and therefore the gear not to break.

I haven't thought about at what point your rope stretch is involved and therefore how this affects the fall distance, and obviously this assumes vertical (no obstruction to falling), no friction in the system, belay plate, no rock strength limitations etc. as mentioned previously, however I don't know any of this for sure

In reply to BnB:
The calculator linked to is rubbish, particularly when talking about the real forces a climber will experience.
The numbers on your gear are how strong it is when tested in a fixture designed to allow its ultimate strength to be tested, they bear no relationship to how strong the gear you place is. Plenty of people have been killed pulling gear marked with 10 or 15kN.
If you get perfect placements then 7kN is generally considered adequate, 4kN is potentially miserable but also potentially wonderful if it keeps you off the deck.
Trad gear is like house selling, location, location, location.

In reply to jimtitt:
Yes, 3 bits of gear in 3 different locations and I'm happy

In reply to jimtitt:

I understand what you say about the quality of the gear, but if we stay in the realms of the theoretical for a moment and assume the gear WILL hold our 80kg climber:

The calculator suggests that a fall factor of less than 1 will not generate a force on gear in excess of 5KN, nor is it likely that the merest slump will generate a force much lower than 3KN

Is this accurate (in theory at least)?

In reply to BnB:

The factors which influence the force on the climber are intermediate friction, method of belaying and rope condition, none of which you can put into that (or any other current) force calculator.
Your also doing something wrong if you can´t get more than 5kN using that calculator, an 80kg, FF1 with a 7% rope and .66 karabiner factor gives 6.77kN but it´s still rubbish anyway.
Like it says:- Note: This is a simplified calculation that ignores many important parameters, such as dynamic belays, wet or icy ropes, and local gravity perturbations. It's complicated.
This is intended for educational purposes only. Not rated for actual climbing use.

In reply to jimtitt:

I'm assuming 29% stretch as per Mammut's specification. I wouldn't use a rope with only 7%!!

In reply to BnB:

That´s why it´s claptrap, it works using the static elongation value of the rope not the dynamic one. This assumes the elongation is proportional to load which is incorrect.
You can try for yourself with your rope specs and put in a FF2 and see if the numbers match those from Mammut. For my rope the manufacturers tested impact force of 7.9kN magically goes to 3.59kN.

In reply to jimtitt:

no chance of ever understanding this stuff then?

In reply to jimtitt:



According to wikipedia:
Apparent gravity on the Earth's surface varies by around 0.7%, from 9.7639 m/s2 on the Nevado Huascarán mountain in Peru to 9.8337 m/s2 at the surface of the Arctic Ocean.

So I think we can safely focus on the other sources of error...

In reply to John Kelly:

Realistically only as huge generalisations like `the further you fall the more likely it is you die´.
Trying to put numbers on impact forces especially using fall factors is an exercise in futility most of the time since the belayer force alone varies in normal circumstances by several 100% and then accounting for friction through the entire system is difficult or impossible. There have been a number of reasonable attempts but half the parameters we use are still guesswork and always will be. Most protection failures are when the gear rips, it very rarely breaks.

In reply to jimtitt:
`the further you fall the more likely it is you die´ - that makes sense and vindicates my cowardly approach to climbing, like

I think the value of the models may not be in giving definitive numeric answers rather highlighting the most important factors within the system so modifying our behaviour.
for example I extend runners more now i understand that the friction is a significant factor knowledge i gained from looking at simple examples

In reply to jimtitt:

So is my (securely placed) 4KN wire good for a run out or not?

In reply to BnB:


Maybe, maybe not. Better place 2

In reply to BnB:

Maybe?

In reply to BnB:

From general climbing experience we know that a piece rated 10kN will almost certainly never fail, Black Diamond have never seen one so it´s reasonable to assume that´s around the top limit for the forces normally felt. The number of open-gate karabiner failures tells us that climbers often achieve 6-7kN and a number of companies make their karabiners with an open gate strength of 9kN for this reason. It´s reasonable to run it out a long way over a 4kN piece but unreasonable to expect it to always stop you.

In reply to BnB:

It's certainly better than nothing

In reply to BnB:

I would say that you are looking at this the wrong way.
As so many other people have said, calculators are not going to give you much useful information about how small gear performs.
What you want to know is whether _you_ can trust _your_ placements to hold in the event of a fall and there are only two ways to find out:
1) Fall on your placements (the Darwin approach).
2) Test placements you put in just for practice (the Newton approach).
For 2), get an old rope you retired and a rucksack full of rocks and go do a bit of testing with the rope tied off to a ground anchor. If you test 1 or 2 small pieces to destruction (use old, retired biners), you should be left with a solid understanding of exactly what your small gear placements will or will not stand up to. 20 or 30 quid is a small price to pay for a confidence boost that might mean an extra trad grade or two.

My personal experience: Other than very rusty in situ gear, the only gear I remember actually breaking was an RP 0. I have, on the other hand, pulled placements out on a number of occasions, sometimes when the rock broke, sometimes just when the placement wasn't very good.