A Knotty Problem Solved

https://www.npr.org/2020/01/02/793050811/a-knotty-problem-solved

"After that, they took what they'd learned and came up with basic rules that would let them identify strong knots and weak knots without having to do a bunch of rigorous calculations. "You should be able to look at a knot and how it's tied and guess how stable it's going to be," says Patil."

Concluding sentence in the story. As one who is hanging from tied ropes on occasion, what are these basic rules and what knots are best for different applications. Fascinating indeed.

Hanging around to learn more....

Some more details...

http://news.mit.edu/2020/model-how-strong-knot-0102

Unfortunately the paper is behind pay walls. DOI is 10.1126/science.aaz0135

Using special fiber cords that change color under strain is an interesting, but an ultimately silly thing to do.

I can tell you what their conclusions will be already, without needing a grant for extensive testing:

(1) Strain increases as the load increases
(2) Strain increases as the rope curvature increases
(3) Failure points will be at maximum strain points, and at points of preexisting damage or poor quality manufacture

More useful would be a study of knot security rather than knot strength.

My understanding is that in actual use for technical climbing, ropes do no typically break at the knots. Most often the rope is cut by being stressed across a sharp rock edge, etc. or fails at a point weakened by abrasion or something similar. Unfortunately, I am unable to cite any recent analyses. Does anyone have current info?

At least my ropes have not broken, at the knots or anywhere else, for that matter.

The only example of rope breakage in my experience was the deliberate sacrifice of a 9mm climbing rope to extricate a vehicle from a flooding stream. With abuse like that,it was not surprising when it popped. It did not break at the knot, as I recall.

Any knot is going to be a weak point compared to the rest of an undamaged and quality manufactured rope. But a damaged/poorly manufactured rope may have weak points (possibly not being obvious to an observer) that are worse than the knot weak point. The bends and twists (the stress points) that are inherent to a knot are never going to make it stronger than the rope it is tied with. It will always be weaker. Your rope that broke away from the knot may have been damaged by the previous knot at that location (that was later untied). Or it could have had internal flaws that were not noticeable.

The paper is about knot stability relative to other knots.

The colour changing thread was used to validate simulations.

Rope produced nd sod for climbing and mountaineering is tested ti UIAA standards,explained in some detail here:

http://itrsonline.org/wordpress/wp-content/uploads/2014/09/Weber-Hudson1999_ITRSPaper.pdf

It is not the stuff you buy down at the hardware store (and it ain't cheap,either). Of course in use, any rope is degraded to some extent, even with care, and sunlight and exposure to various chemicals also takes a toll. Still, when ropes fail, it is usually due to cutting; rocks become quite sharp when highly stressed ropes become in cntact with them.'

Prudent climbers retire ropes before they are seriously worn. I have used retired climbing ropes to successfully lift 1000 pound loads (mammoth fossils) with no failure. And that was after tying the rope in various knots which typically reduced the strength by about 40 per cent or so.

I wonder if this research might shed light on which types of rope construction might be better (that is stronger) when tied in various knots.

"For example, take the granny knot and the reef knot — two simple knots that look very similar but behave very differently."

This reminded me of one of the questions on the SAT test I took in 1964 -

Reef Is to Sailor as Square is to -

(a) Ship
(b) City
(c) Scout
(d) Highway

Old climbing ropes still very strong if not damaged in some way.

"These facts also hold for 10- or even 15-year-old ropes. This has been proved by many tests of such old ropes (not even 25-year-old ropes and one 30-year-old rope broke in tests in accor- dance with the standard; they still held at least one drop; this means that they will not break in practice, unless loaded over a sharp edge, in which case they may break)."

http://www.caimateriali.org/fileadmin/us...rnal_3-2000.pdf

1" Tube loses only about 1.5% per year too.

"This is about a ~1.45% decrease in strength relative to the original breaking strength per year."

http://itrsonline.org/wordpress/wp-conte...bbing-paper.pdf

I had a discussion about this paper with someone who has access to the original. They tested 6 knots, and ranked them. They didn't find the "6 best knots". The order of the knots are:

1. Zeppelin
2. Alpine butterfly
3. Reef
4. Granny
5. Thief
6. Grief (aka "Whatnot" in Ashley)

I would love to see comparative evaluations of a bowline, double bowline, and a rewoven figure eight, all knots employed in tieing in to a climbing rope.The bowline used to be the standard, but the figure eight is now considered superior.

In sixty years of technical climbing and rescue work, i have never had need to tie an alpine butterfly. How does it stack up against a figure eight?

The main reason for the Alpine Butterfly as I understand, is it's ease to untie after loading. Say some sort of crevasse rescue/raising situation where there is tremendous load on the knot. I haven't seen anyone use it for a tie in near the bitter end tho. Only for a mid point knot to form a loop.

I haven't used them, prefer a double bowline since it is also easy to untie and spreads the wear on two loops of rope. The double bowline is common when building a Banshee belay anchor too.

The double bowline, AKA bowline on a bight, is said to have the same quality. I have used the knot in rigging up the hoist for a mammoth skull fossil, which we later weighed at 1100 pounds. The knot untied easily, after being loaded for about thirty minutes.

I have used a sheep shank to create an easily untied after loading pair of loops for the trucker's hitch. You just have to run the moving line thru both loops to prevent the knot from rolling undone.

Never seen anyone else do this.

Wonder what are the strength/failure potential?

Even used it for a Tyrollean traverse, (with backup overhead line), over a small creek.