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I was out ice climbing with a group today and they were using three-point anchors using two vertical v-threads (abalakovs) with one backup ice-bolt. They said the vertical v-threads (one hole over top of the other) were superior and stronger than the horizontal ones (holes side-by-side).

How much stronger are vertical v-threads compared to horizontal ones?

V-Thread:

enter image description hereSource

ShemSeger
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  • I suspect they're just wrong. Otherwise why do experienced climbers make them horizontal? –  Jan 08 '17 at 16:37
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    @BenCrowell The UKC guys aren't completely inexperienced and the agree after testing. And experience climbers using a certain technique over another does not necessarily mean it is better (that would kind of inhibit any progress at all). – imsodin Jan 08 '17 at 16:42
  • @benCrowell I was climbing with some of the most experienced climbers in my region. They were the ones preaching the vertical abalakov. – ShemSeger Jan 08 '17 at 18:46
  • I suspect at the time mr Abalakov invented and popularised the thread no one was testing much of anything climbing related. it worked very well and so the horizontal thread became dogma. I've never made vertical thread but I imagine it would be a bit trickier, not the best reason to avoid it but surely a factor. – aaaaargZombies Jan 09 '17 at 01:26
  • @aaaaargZombies Everyone says it's easier, which makes sense, anyone who shoots targets knows it's easier to hit a vertical axis than it is a horizontal one. When you make a vertical Abalakov then the holes are on the same axis as your eyes even if you're making it above or below eye level, and you don't have to try to make the left hole with your left hand. – ShemSeger Jan 09 '17 at 02:08
  • I don't ice climb, but I would certainly expect vertical to be easier, as getting the cord through can be helped by gravity. – Rory Alsop Jan 09 '17 at 07:56
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    @BenCrowell People regularly do stupid shit all the time. Hence "American Death Triangle". – Lagerbaer Jan 09 '17 at 18:40

2 Answers2

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TL;DR

Vertical oriented V-threads (A-threads) are significantly stronger than horizontally aligned V-threads. The following numbers should not be taken at face value: Different test configurations were performed, but it is not clearly stated which are used to come up with these numbers.
Tests by Beverly and Attaway showed an increase in mean failure load of 27% with standard deviation of 12%. Both are strong enough for abseiling (mean 11.3kN and 14.4kN, minimum 5.2kN and 10.9kN) but not suited as single anchor point for a belay.

Experiment Description

There were several experiments performed regarding rebored ice screws and ice screw angle (in case you wonder: positive angle is teeth pointing upwards). The here relevant experiments were sever slow pull tests on V- and A-threads. For reproducibility and ease of access, the tests were performed on lake ice (few tests on waterfall ice were done as well, but only in one configuration). Three to seven measurements per configuration were performed and the ice area included by the thread measured for each. The configuration varied not only by being horizontal or vertical, but also by the orientation of the thread. These variations were unfortunately not addressed in the discussion of the results. I can only assume, that they could not determine any significant differences. All these configuration seem to be evaluated to compare A- and V-threads.

Results

In general they found an expected, but nevertheless nice relation between the area surrounded by the thread (in the following just area) and failure load. As mentioned the comparison of V- to A-threads suffers from varying configurations and potential skewing by different mean areas. It can be assumed that these factors were simply failed to disclose, but were taken into account.

The following values (all units kN) were obtained: 

[kN]      V-thread A-thread
mean:     11.3     14.4  
std err:   0.8      0.7  
min:       5.2     10.9  
max:      16.8     17.5

This means that A-threads are about a forth stronger than V-threads. However looking at the 95% confidence interval of 1%-53% should make it clear that any claim more precise than "A-thread is very likely stronger" is rather adventurous.

Discussion

Both variants are suitable to use, but as vertical A-threads are stronger, it is advisable to use them. However they cannot be trusted as single anchor for multi-pitch climbing. Ropes are tested to not exceed 12kN in a UIAA fall, which can be assumed as worst case scenario. So a single A-thread may hold such a fall, but not reliably. Always back it up by a second thread or an ice screw.

Source

Many thanks to J. Marc Beverly and Stephen W. Attaway for this hands on test with good documentation and to George McEwan from the UKC for publicizing this.
J.M. Beverly and S.W. Attaway, Ice Climbing Anchor Strength: An In-Depth Analysis, 2017-01-17, http://itrsonline.org/wordpress/wp-content/uploads/2015/03/Beverly.AttawayIce-Climbing-Anchor-Strength_-An-In-Depth-Analysis2.pdf
G. McEwan, Ice Climbing Anchor Strength, 2017-01-17, http://www.ukclimbing.com/articles/page.php?id=4315

imsodin
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5

One could argue its a mute point, unless you are taking Factor 1's on V Threads. A factor 1 fall generates about 5 kN - you should be no where near this, possibly if you screw up badly subjecting your anchor to half that.

This is a 'debate' we (me and fellow instructors agreeing on a consistent approach) had years a go when instructing students - the outcome was given vertical V threads, in lab testing in ideal conditions are shown to be stronger, the preferences is for vertical. But building the best anchor you can, in the best location, at the best speed, using the best ice will beat the vertical/horizontal debate every time (Except under laboratory conditions)