Ice Anchors

Mark Nelson wrote:Ah yes, threw that Jesus-screw term out there. Based on the Long's rock definition. The Jesus screw would be the first screw placed off the anchor.

thanks Mark (:

Yeah Mark thanks for the info and Kirra for the video feed. I was also curious about a v-thread in a vertical position rather than a horizontal one. Also in the video it didn't look like they made the v-threads very deep. In peoples experience or is there stats about v-threads of varying depths, such as using a 16cm screw compared to a 22cm screw. I would think a longer screw (deeper hole, more ice that needs to be displaced in case of failure, also placing screws farther apart) would produce a stronger v-thread. Any thoughts or numbers out there? Have a day.

Juan

Juan:

here's their site with download papers near the bottom -- under Research:
strikerescue.com/downloads/

Ice Climbing Anchor Strength, I believe is their latest ITRS presentation. There are a couple of angles that give optimal results.

(ps -- don't thank me; I'm not the guru -- but it sure does help to incorporate actual results with climbing styles when considering anchors)

Mark Nelson wrote: Matt, with the screw back-up on a v-thread rap, the failure plane of a thread is actually above the thread. You want to put the back-up screw below the thread. I usually do that and rig with a screamer.

Good to know since I have not had a v-thread fail. I wonder what the average range of failure is. I am usually 2ft above my v-thread with my back up screw. Also with a failing v-thread and the block of ice that comes off I wonder if with a screw below if it increases the load more so than with it above due to the greater range of motion. I guess it would need to be tested.

Good read: thanks, Mark! I wonder why they recommend that one should maximize the area enveloped by the anchor, but they recommend an equilateral triangle. The maximum area is obtained with an isosceles triangle with 45 degree angles.

Interesting video, but no numbers and rather vague qualitative conclusions.

Very nice Petzl banner flying near the test site and petzl ice screws shown. The overall impression one is left with: buying and using Petzl equipment is substantially safer than something that you can make with a coat hanger and some cord. If you are going to rap off something and leave it behind, make sure it's a petzl ice screw and then go out and buy some more.

Disclaimer: I own quarks, aztars and even one of those nice v-thread tools. I am on board with the program ;)

mattb19 wrote: Also with a failing v-thread and the block of ice that comes off I wonder if with a screw below if it increases the load more so than with it above due to the greater range of motion. I guess it would need to be tested.

Two things you'd have in your favor would be the screamer and the ability of the rope to absorb energy, not a static loading situation on the screw (don't really have a range of motion??) -- would you even activate the screamer with about a 1 footer? maybe a stitch or two.

The one hazard you could introduce is a block of ice connected to your rope .... on it's way down ..... bonk.

All this anchor talk is very interesting. Again everything comes down to ice quality and how to properly assess things. The data is good to know that if things are done properly they can work. Mark Nelson way to get a great thought provoking topic going.

What do you guys out there think about belaying in autoblock mode on ice verse off your harness (for the second)? From the data that I saw on Mark Beverly's website I would stick with the rock adage, "it depends". Just curious as to if anyone had any different data or input.

mattb19 wrote:All this anchor talk is very interesting. Again everything comes down to ice quality and how to properly assess things. The data is good to know that if things are done properly they can work. Mark Nelson way to get a great thought provoking topic going. What do you guys out there think about belaying in autoblock mode on ice verse off your harness (for the second)? From the data that I saw on Mark Beverly's website I would stick with the rock adage, "it depends". Just curious as to if anyone had any different data or input.

Oh, yes, a minor update -- one of the SAR teams did some testing in glacial ice; found similar results, they were a little stronger in averages, but not anything surprising. They were basically consistent in their findings to what Beverly had.

ITRSOnline Archive : Smith, Gordon, Allen, 2009, "Strength of V-Thread Ice versus A-Thread Ice Anchors"

It seemed that if you really wanted the strongest setups, load-distribute two A-threads that are threaded with 1" tubular.

But everyone I talked with or results I saw, the V-thread with cord is totally adequate from test result standpoint for a climber descent anchor; though it doesn't really take much more effort if you start the orientation to A-thread and it will give you a better anchor anyway.

mattb19 wrote:All this anchor talk is very interesting. Again everything comes down to ice quality and how to properly assess things. The data is good to know that if things are done properly they can work. Mark Nelson way to get a great thought provoking topic going. What do you guys out there think about belaying in autoblock mode on ice verse off your harness (for the second)? From the data that I saw on Mark Beverly's website I would stick with the rock adage, "it depends". Just curious as to if anyone had any different data or input.

Agreed with all here that the Beverly article (though I wonder how analogous lake ice is to vertical water ice) and the testing done by Craig Luebben is about the best quantitative data out there. I did find Beverly's conclusions regarding v or a threads for anchors interesting. I've used them plus one screw in the past for an anchor when I come up short on screws (and it's certainly better than just one screw to be sure).

In good ice with a team of 2, I normally anchor off of 2 screws "equalized" with a sliding-X (long leg, if there is one, tied off). In less good ice or with 3 people, I use 3 screws (or more if I got 'em and the ice is less than good). If the ice is really sketchy, I will belay off my harness and try to chop a very good stance if one doesn't exist already, otherwise I auto-block off the anchor.