Sunday, November 26, 2006

More on falling distances...

This discussion on falling distances with respect to clipping position is down there somewhere in the comments column, thought I'd post it as a new entry. I'm getting some email on this as well, it's been fun discussing it all, I hope the following helps people figure it out. Just for the record, it's generally safer to clip at waist level than over-head.

Anon wrote:

I've read your info regarding clipping and, while I didn't pull out the graph paper, I did use a string demo and am not seeing your logic.

Here's my scenario:
- assume a vertical face
bolt3 (30ft above ground - not clipped)
YOU (28ft above ground)
bolt2 (20ft above ground - clipped)
bolt1 (10ft above ground - clipped)

If you overhead mis-clip 2ft from bolt3 (ie. 8ft above bolt2) then you'll have 8+2+2=12ft of slack rope and a 24ft fall from 28ft above ground. (You better hope you got less than 4ft rope stretch!!). If you mis-clip at your harness then you have 10ft of slack rope and a 20ft fall from 30ft above ground.

Seems to be safer to clip from the harness at bolt height. What am I missing!?

Will Gadd said...

Hi Anon, you're definitely right that clipping at waist-level is often safer than clipping overhead. That's the main point of all of this, so you're not missing anything in my mind in terms of where it's generally safer to clip. But your math is wrong in your scenario for total fall distance. I've written a few explanations below that I hope will help you understand...

In your scenario you don't fall twice the distance of the amount of rope you have above the last piece. That's the error I made as well when I wrote my book. Seems obvious that you would and that's how we are often taught to think of lead falls, but it doesn't quite work that way when part of the rope is "above" you. We actually end up the same distance below a piece as the amount of rope we had above the piece when we fell...

It's funny, I too refused to believe the graph paper for some time until I really counted the squares and thought it through. In your example you correctly have 12 total feet of rope in the system above the last piece at 20 feet. So you'll definitely end up with 12 total feet of rope below the 20 foot piece after the fall, right? What's 20 minus 12? 8. If your harness starts the fall at 28 feet and ends at 8 feet how far did you just fall? 20 feet... It's fun to run this scenario using a "long armed" climber who can clip 6 feet over his/her harness; Now there's 16 (10 to the missed clip, six from the missed clip to the harness) feet of rope above the last piece and the climber will end up 16 feet below the last piece--four feet off the ground. But the fall is still 20 feet, the "extra" six feet of rope going from the climber's harness to his attemped clip hand doesn't increase the fall.

So in your scenario, you actually fall 20 feet and end up 12 feet below the last piece--the two feet of rope going from your harness to the clipping point doesn't "double" or add to the fall distance. Count your squares on the graph paper, or with the string--the fall distance is exactly 20 feet (ignoring rope stretch, belayer feed, etc.) The KEY difference in the clip at waist and clip overhead scenarios is that the starting point for the fall is higher off the ground when clipping at waist level (safer). Belayers also tend to feed more slack than absolutely necessary, and climbers generally also pull more slack, which adds at least a few more feet of slack in the system when clipping overhead...

Just for fun and 'cause I'm a nerd, think of a climber who has a bomber piece at 100 feet above the ground. He climbs up another 20 feet, rattles in a sketchy piece, and starts climbing down to get back to his bomber piece. Unfortunately, just as he gets his harness level with the bomber piece he falls, the top piece blows, and he goes for a ride. How far is he going to fall? 20 feet? 40 feet? 80 feet? He has 40 feet of rope above the last piece now, our "classic logic" would tell us he's going to go 80 feet... Nope, he's going to end up 40 feet below the "bomber" piece because he had 40 feet of rope above it. Total fall 40 feet... This is just an exaggerated version of the clipping overhead scenario.

I've had a half-dozen discussions on this now. I expect a non-climbing math student would figure this out very fast, but as climbers we have a very strong, almost religious belief that fall distance equals twice the rope above the last piece. In the last two weeks I've had three major beliefs I hold about climbing seriously revised: fall distance, half-rope impact forces, and the use of Cordelettes...


john said...

your statement "Just for the record, it's generally safer to clip at waist level than over-head."

its not safer if the clipping hold is realy small for a waist clip and there is a nasty ledge to crash on. Just clip high from the bomber jugs below to avoid crashing if you fall. Many route setters design routes to clip above your head. Which is a pain because I'm pretty short. I guess ice climbing the screws are always clipped at your waist.

Will Gadd said...

Agreed John, this whole discussion started when thinking about making "sketchy" clips. I often see people struggle to clip high overhead on sketchy holds, this is potentially more dangerous than clipping off sketchy holds with the gear at waist level.



Anna Malou said...

Thinking about what John wrote I like to add that maybe we should not be thinking so much about that the fall distance is the same if clipping above our head as when clipping the same bolt by the waist but what would it had been if we fell in the last bolt instead? Imagine we´re standing one meter above the last clipped bolt and the next is one meter above us. Falling when trying to clip next bolt over head makes a four meter fall (the same as when clipping the next bolt by the waist) but falling in without any extra slack gives a fall of 2 meters. So I guess that´s the reason for saying not to clip over the head to avoid a longer fall.