Hacker News Reader

I was a bit surprised to learn this as well. I might have thought at a minimum that the assumption:

>This analysis is meant to show the relative stresses in the ice and ice screw placed at different angles and not to predict pullout loads.

would have invalidated the analysis but apparently not under a lot of circumstances. I suspect the positive angle comes from experience with nails and screws where pullout tends to be the dominant failure mode.

As an aside, ice is a really interesting material on all sorts of dimensions--solid usually being less dense than liquid, typically used near its melting point, etc. As the post notes, the US Army has done a lot of research on ice. My thesis advisor ended up establishing an ice lab partially funded by the Army CRREL and has a lot of papers on the topic. (I worked on high-temperature metallic alloys however.)

I think this is it: http://mra.org/wp-content/uploads/2016/05/Beverly_IceScrews_... It's been a while since i've thought about ice climbing, but i think most/many ice climbers are using twin and double ropes, which significantly softens the impacts, while the Ouray study is primarily single ropes (from my quick reread)

this is another: http://hmga.gr/storehouse/word-acrobat/Ice%20Climbing%20Anch...

I used to climb at the gym in Salt Lake adjacent to BD's headquarters, and remember meeting equipment designers and testers. They seemed pretty fanatical about testing and had rigged up all kinds of equipment to, among other things, destroy carabiners at different angles, which made me feel good about their climbing gear. The most important factor is that you always rigged to load biners along the length, never near or on the gate.

BTW self rescue is a critical skill for all climbers, but the years i lived in the Bay Area, i remember only a handful of clinics for this (the ones I went to were in Davis)

The MRA.org PDF references the article I was thinking of:

> Craig Luebben1 and Chris Harmston did some drop testing on ice screws and found poor results in aerated ice. Using a solid mass of 185 pounds of iron, Luebben reports having “pulled out entire lengths of ice screws” in some tests resulting in a ground fall from the top of the climb.

It appeared in the November 1997 issue of Climbing magazine.

Found it: http://imgur.com/a/uEzCF

Note that this study uses the opposite convention when talking about the angles - original article calls screws screwed down "positive" but the MRA study calls them "negative"

> Their initial fall test actually broke some carabiners! So they adjusted it to be a smaller load.

I'm surprised they didn't go by the UIAA standard of 80kg factor two falls; it's been in effect for a while and makes comparisons easier.

> if the long screw hits rock before going all the way in, the exposed tube creates a lever arm. In those situations the generally accepted practice is to use a webbing runner to tie off the ice screw at the ice, instead of using the hanger.

This goes for pitons as well. There's a nice illustration in "Mountaineering: The Freedom of the Hills" which I can recommend picking up as a good introduction to climbing and mountaineering. The supplemental resources listed also are good if you want to go into more detail.

I'm surprised "Mountaineering: The Freedom of the Hills" even mentions pitons as it's all about the non-destructive ethics of climbing. Honestly I don't remember it ever mentioning pitons at all but granted I read it last time few years ago.

It was more an overview, a "well, if you're going to use pitons, here's how to use them safely" at least in the case of the tie-off loop with a piton that had bottomed out.

They might have--I don't remember. I think I still have that magazine in the basement somewhere; I'll try to find it this evening.

Found it. Here are pictures of the magazine pages:

http://imgur.com/a/uEzCF

> I'm surprised they didn't go by the UIAA standard

... for testing dynamic ropes. That's because they weren't testing dynamic ropes. All the other UIAA standards—the ones for harnesses, nuts, camming devices, static ropes, and so on—tell you to apply a set force, usually 10kN, and see what breaks. To be pedantic, all this stuff is specified in the CE standards that the UIAA ones incorporate by reference.

If you're in a lab, you apply 10kN in a precise way that uses a whopping great hydraulic ram. If you want to avoid hauling a whopping great hydraulic ram halfway up an ice cliff, then you improvise, but the aim is still to control the force acting on the gear and measure what happens. I'm using "control" and "measure" in the technical sense here.

Dynamic ropes are different because they determine the forces that act on everything else. In a dynamic rope test, the conditions of a fall are controlled as well as possible, and the peak impact force it generates is one of the variables to be measured. If you did that in the ice screw tests, the results would depend on which rope you used, and that isn't what you want.