can someone point me in the right direction please.

Having a hard time finding the thread that talks about impact forces on last piece relative to the amount of rope payed out. I've got to school some fool.

Ryan N wrote:Having a hard time finding the thread that talks about impact forces on last piece relative to the amount of rope payed out. I've got to school some fool.

Fall factor?

en.wikipedia.org/wiki/Fall_…

Alright! Way to step up, 20 kN. That's a great link.

Freedom of the hills book

Force on the top piece should be roughly 2X the impact force on the climber due to the pulley effect.

Impact force on the climber is limited by the impact rating of the rope (10kN or less) as well as other variables on the belay side of things (belay device, weight difference between climber/belayer, etc).

I'm sure there are a few more factors I'm forgetting at the moment but that's a starting point.

Not fall factor.

The question was asked if paying out more slack on a sketchy piece of gear would lessen the overall force of the fall if the distance between last piece was constant?

20kn I was going to call on you, but you beat me too it.

I did attempt a google/mp search and found the wiki link but nothing on mp.

Benjamin what happned to you links?

If h is the height of the fall before the rope comes taut, l is the length of the rope between belay and climber, and p is the amount of slack paid out, the fall factor changes from h/l to (h+p)/(l+p). Therefore, if h/l is greater than one, paying out slack decreases the fall factor, and if h/l is less than one, paying out slack increases it.

OK, here are some threads to look at:

mountainproject.com/v/how-c…

mountainproject.com/v/rope-…

mountainproject.com/v/soft-…

Are you asking if paying out slack would decrease the force on the top piece? If so, then the answer is no for fall less than a FF=1 and it is easy to calculate by using fall factors. If the FF is greater than 1, then paying out slack would theoretically decrease the force on the upper piece.

if catching a fall "softly" then the force on the gear should be less, rather than being caught with a grigri etc.

Ryan N wrote:The question was asked if paying out more slack on a sketchy piece of gear would lessen the overall force of the fall if the distance between last piece was constant?

No, that is an urban legend that has been discussed a number of times on rockclimbing.com. Feeding slack out only increases the impact force.

Let's look at an example.

- 100' between belayer and climber
- 3' slack in the system
- Climber is 10' past last piece
-- Total rope out, 103'; total fall distance, 23'
-- Fall factor, 0.223

Now let's add in 3' of extra slack to "soften the catch."

- 100' between belayer and climber
- 6' slack in the system
- climber is 10' past last piece
-- Total rope out, 106'; total fall distance, 26'
-- Fall factor, 0.245

However, this rule is only true when the fall factor is below one. Once the fall factor increases above one, adding slack would technically reduce the fall factor.

- 10' between belayer and climber
- 3' slack in the system
- climber is 7' past last piece
-- Total rope out, 13'; total fall distance, 17'
-- Fall factor, 1.307

Now let's add in an extra 3' of slack.

- 10' between belayer and climber
- 6' slack in the system
- climber is 7' past last piece
-- Total rope out, 16'; total fall distance, 20'
-- Fall factor, 1.25

So technically, if you are in a multipitch environment and the leader takes a fall with a fall factor over one, if you wanted to limit the fall factor as much as possible you should let go of the rope and allow the leader to fall the full 60m of the rope. But that said, I wont be dont that anytime soon, even if it is a FF2 I am still going to lock off. ;) Lest what the UIAA would have you believe, the impact force on the top piece is actually a function of more than just the fall factor, in the real world. Outside, fall distance does play a role in the load on the top piece, as well as rope drag, carabiner efficiency, the rope's coefficient of friction and a million other things.

Allen Corneau wrote:Force on the top piece should be roughly 2X the impact force on the climber due to the pulley effect.

If you were falling on a pulley that was 100% efficient, that would be true. But carabiners are quite inefficient and so the load on the top piece is more like 1.6:1 instead of 2:1. Normally the breakdown is that the belayer will see 60% of what the leader sees and the top piece will see 160% of what the leader sees. But that is highly dependent on how much friction is produced on the carabiner attached to the top piece.

keep in mind that when people on the intrawebs talk about "fall factors" and the theoretical effects on gear, etc ... they are talking about PERFECT scenarios

in the real world you generally dont have an absolute clean frictionless straight line path for TRAD climbs ... the illustration below from the DAV illustrates this rather clearly

without some serious testing or theoretical models that can account for this, and not just simple math ... all this intraweb discussion IMO is basically a cr@pshoot when compared to real world scenarios

look at the nice fun stuff from beal to make it even more complicated

add in the different types of ropes and belay devices and it gets even more fun

what a bit of slack can give you is allow you the time to react ... ive had people basically sit down when ive fallen on a tight rope and blow out gear (with an ATC) ... vs. people who let themselves get pulled up a bit and the same gear in the same exact placement held (with a gri gri) ... of course this is all anecdotal ... but youll find all this out when you whip over and over again on gear ... not through intraweb arguments

to add fuel to the fire ... imagine a case where there is a decent amount of friction due to bends in the route and/or the rope rubbing against the rock ... there could be an argument that in such a case the letting a bit of slack run through could help on the top piece ... similar to how a bit of slack can run through an ATC

heres a real life example ... the route comes from the left through the overhang onto the face crack ... when the climber whips at the crux the belayer often DOES NOT GET PULLED UP at all due to the rope drag (bends in the rope and friction on the rock) ... in fact many of my belayers have told me they barely felt my fall ...

this of course increases the forces on the gear ... i usually use a stetchy rope to offet this, and get my belayers to give me some slack

this is the crux piece that everyone falls on ... over and over again ... probably 30+ whippers on it by now ... i carry a hammer to get it out ... it hasnt pulled yet

i encourage people to go out and take clean, backed up whippers on their own gear and find out if theres any difference

especially micro gear

now im not saying real experts cant account for most these real life factors ... they absolutely can and probably have models for it ...

what i AM saying is that most of the intraweb "experts" wont be able to answer your question in real world applications ... they can only give you a very basic "perfect" scenario theoretical simplified answer


;)

Thanks guys

Heres this baby for you.

myoan.net/climbart/climbfor…

Eli Buzzell wrote:Heres this baby for you. myoan.net/climbart/climbfor…

That thing is way off.

Greg D wrote: That thing is way off.

For starters, it computes the fall factor as

instead of

Just wanted to expand a little on what 20kN said above, and point out a small arithmetic error. 20kN forgot to add 3' to the fall distance on the fourth example, so it should be 16' total rope out, 20' fall, giving a fall factor of 1.25 on the last example. What he (she?) said after that is true about a fall with a factor over one and feeding out slack. Here's a generalized version to demonstrate how the concept works rather than a few discrete examples.

If:
X1 = feet between belayer and climber
X2 = slack in the system
X3 = feet past last piece

Assume:
{X1,X2,X3} > 0
X1 > X3

Then:
Fall factor = (2X3+X2)/(X1+X2)

From that we can conclude 3 things:
- Changing nothing but feet between belayer and climber will always yield an indirect relationship with fall factor
- Changing nothing but feet above last piece will always yield a direct relationship with fall factor
- Changing nothing except increasing slack in the system will move fall factor closer to 1 (in special case where feet between belayer and climber is exactly 2X feet above last piece, then fall factor is one no matter how much slack)

Here's a preview image, since the subscripts didn't post properly. Why you no allow subcripts, MP?

here's a question for Bearbreeder - (with all the real world experience) how much force does a femur shave off?

If my partner uses a munter (direct from harness!) and runs to take up slack on my crossed over double 8.5's (stored near my battery), and I am 10 feet above a roof thrutching for a cam placement, when I bounce twice giving up a femur to the cause, will my no 5 stopper below the roof hold? What if he used a Gri-gri?

And should he attempt CPR? :)

MountainProject nerds strike again!
Hurray nerds!

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