Monday, July 20, 2009

Triaxal Loading on Trees

Surprisingly, there is one mistake that both beginners and advanced climbers alike tend to make. Many people will wrap a tree with a sling and then clip the sling. Often the sling is wrapped around the tree in such a way that it is loading the carabiner improperly. A carabiner that is loaded from three directions is often referred to as being triaxally or tri-directionally loaded. This is very very bad...

In this photo the carabiner is radically tri-loaded.
An impact on such a carabiner could cause failure.

A tri-loaded carabiner is crossloaded. It will not hold a high impact fall. As such, it is important to use slings that are long enough to tie off. In the preceding example, there is not enough sling material to get all the way around the tree, but even if there was enough for the carabiner to hang more loosely, it could still triaxally load it.

One could tie the sling off with a pre-equalized knot, but this isn't required. The following photo shows one quick example of a tie-off that eliminates the possibility of triaxal loading.

Triaxal loading is a detail that a lot of climbers don't think about. But it is just these kinds of minor details that can get you in the end. The phrase, "the Devil's in the details," didn't come from nowhere.

--Jason D. Martin


Justin said...

Great little article, and timely for me, as I slung a tree like this just this past weekend. I was aware of the danger of cross loading, so the biner was much farther from the tree than pictured, reducing the cross loading somewhat, but your simple knot solution is clearly the way to go.

I'm wondering if the knot you have pictured (on overhand?) is preferred to girth hitching the tree. Why or why not? Thanks!

American Alpine Institute said...

The overhand is preferable to girth-hitching because the girth-hitch puts extra stress on the tree and on the sling.

That said, occasionally a girth-hitch is a better option. It is better if you sling a horn and you're worried that it will pop up off of it. In such a case, then it would be good to set the girth-hitch in an orientation where it is squeezing the tree.

If I can avoid using a girth-hitch, I usually will.