How strong is it? ANCHORS (Part 1)
Premium Members can read the entire article here:
This section of my website is where I satisfy some of my curiosities (and hopefully some of yours) about the actual breaking strength of anchors, gear, and knots.
If you're new to this part of my website , I suggest you start at the overview page, and then bounce back here.
What's on this page?
What are the forces on the anchor when rappelling?
How strong is an overhand knot anchor in a nylon sling?
How strong is an overhand knot anchor in a Dyneema sling?
How strong is a girth hitch master point anchor with Dyneema?
How strong is a girth hitch master point anchor with Dyneema, if one strand gets cut?
How strong is a girth hitching a Dyneema sling to a carabiner?
How strong is a girth hitching a Dyneema sling to a bolt hanger?
1 - What are the forces on the anchor when rappelling?
If you bounce around on the rappel rope like a special forces cowboy, you can generate between 2 and 3 kN as a temporary peak load.
When you rappel smoothly, the load to the anchor is pretty much your body weight.
Source / testing: Youtube: What can go wrong when connecting two ropes? [dubbed]
Something we've all wondered when leaning back on a rappel anchor that’s Less Than Ideal . . . How strong does this thing really need to be? The gear experts at Edelrid did some testing, here's the answer.
Takeaway: rappel smoothly without bouncing to minimize force on the anchor.
2 - How strong is an overhand knot anchor in a nylon sling?
About 26 kN.
Source / testing: YouTube, You aren't supposed to tie a knot in this, Start around 15:50
One of the most common ways to make an anchor. Simple, easy to check, fast, redundant, and probably hard to untie.
3 - How strong is an overhand knot anchor in a Dyneema sling?
About 21 kN.
Source / testing: YouTube, You aren't supposed to tie a knot in this, Start around 11:00
While many people prefer to avoid tying knots in Dyneema, many folks think it's no problem. Again, this is a common and simple way to make an anchor.
Dyneema is less strong than nylon, but it's still #SuperGoodEnough for climbing. (Just don't expect to ever untie it . . .)
Takeaway:
If you double a sling like with the basket hitch, you get double the strength.
When you tie a knot in the doubled sling, you reduce the doubled strength by about half. So in the end, that leaves you with something close to the MBS for the original material.
We see this in both the nylon and Dyneema sling in the last two examples.
4 - How strong is a girth hitch master point anchor with Dyneema?
About 27 kN.
Source / testing: YouTube, Are climbing master points made with a girth hitch or clove hitch REDUNDANT??? Start around 7:00
The girth hitch master point is a modern standard for many climbers. Good to know it's super strong! And yes, it's redundant if one strand gets cut. Read my whole article on it here.
How strong is a girth hitch master point anchor with a cut strand?
How strong is a girth hitching a sling to a carabiner?
What about girth hitching a sling to a bolt hanger?!
