Core shots


Original Post
Mark Hudon · · Lives on the road · Joined Jul 2009 · Points: 0

This may have changed but when I learned to climb (early 70's) we were taught that the strength of a rope was all in the core, that the sheath was merely to protect the core and did not contribute much, if any, strength.

Is that still true?

Stich · · Colorado Springs, Colorado · Joined Jan 2001 · Points: 1,240

That is primarily where the strength is, yes. It would be interesting to see what a core without a sheath can hold as opposed to a regular rope and also a sheath alone.

Michael Schneider · · Unknown Hometown · Joined Apr 2014 · Points: 85

As I recall the arrival of the "STRATOS" sheath 1st pioneered by Edelweiss was the start of
Designed to prevent cutting and increase sheath strength.

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And as always critically important information!

The Wall Master rope!
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20 kN · · Hawaii · Joined Feb 2009 · Points: 1,128

It is somewhat true, but irrelevant. Tensile strength is not a concern with dynamic climbing ropes as the most harshest of falls (FF2) on the most worn ropes wont produce enough force to exceed the tensile limit of the rope. You'd have to weigh 300+ lbs and take an FF2 for that to happen.

However, it is a common misconception that the sheath is just there to protect the core. That is a large portion of it's job, but it does play a critical role in the integrity of the rope as well. When ascending a rope with jugs, a large portion of the weight is held by the sheath and a failure of the sheath can, and on several instances has, resulted in the rope failing entirely. While rappelling the sheath holds quite a bit of weight as well, and a failure of the sheath can result in the failure of the rope. I can cite several examples, including an incident that happened to me on El Cap. Climbers have been injured or killed as a result of a failed sheath. This is why Unicore technology is important--it helps prevent this issue.

This video demonstrates the issue quite well:

https://www.youtube.com/watch?v=CtURlhPssQI

Furthermore, the sheath plays the largest role (out of the core and sheath) in determining if a rope can resist loading over a sharp edge. For a given diameter, a rope with a thicker sheath and thinner core is less likely to fail when loaded over an edge than a rope with a thinner sheath and thicker core. This is why some half ropes and single ropes designed for multipitch "generally" have thicker sheaths where as light ropes designed for sport climbing focus more on thicker cores.

MacksWhineturd · · Squaw · Joined May 2016 · Points: 0

Damn that's a pretty crazy video.. I guess that when you're jugging you're pretty much all on the sheath? I always figured the sheath is nothing and the core is everything.

So is the unicore sheath woven into the core or something?

Kevin Mokracek · · Burbank · Joined Apr 2012 · Points: 50

I took a ride a few years ago while ascending fixed lines above Heart Ledge when the sheath separated and slid down the rope with me and my jugs on it. I slid about 7-8 feet until the sheath bunched up. Quite the wake up call.

20 kN · · Hawaii · Joined Feb 2009 · Points: 1,128
MacksWhineturd wrote: So is the unicore sheath woven into the core or something?
Yes.
Mark Hudon · · Lives on the road · Joined Jul 2009 · Points: 0

The vid is interesting. Mostly they show the sheath being cut and the rope not breaking, which would jive with my old understanding of the sheath/core relationship. At one point though, the rope breaks. If the strength is all in the core, and this test is not over and edge, why does the rope break?

I'll dig up the photo of it but I took a fall on Zodiac a couple years ago and core short the rope, over a pretty rounded edge, that got real close to being the end of dear, old, loveable me!

Yikes!

Chris treggE · · Madison, WI · Joined May 2007 · Points: 8,590

Beal the only one who makes ropes with the Unicore, or is this now the standard across all companies?

John Wilder · · Las Vegas, NV · Joined Feb 2004 · Points: 1,500
Chris treggE wrote:Beal the only one who makes ropes with the Unicore, or is this now the standard across all companies?
Just Beal and Edelweiss, to my knowledge.

I think another brand (i want to say Mammut) has something similar, but its not standard.
Daniel Joder · · Boulder, CO · Joined Nov 2015 · Points: 0

In the video, one or two of the tests apparently showed the rope failing entirely once the sheath was cut--which jives with what someone in an earlier comment said. I am still not clear on why this should happen. Anyone care to explain.

Jason Young · · Los Alamos, NM · Joined Jul 2009 · Points: 1,000

I don't think the core is failing. Rather, the sheath is failing completely and sliding off of the short section of rope being tested. The "rope clamp" only adheres to the sheath, and when the sheath fails the clamp pulls it off of the core of the non-unicore rope. If there was a knot in the end of the rope being tested then the sheath would just bunch up and the test weigth would be caught.

An 80kg static load would not cause the core strands to break. The load does become dynamic when the sheath slips, but I don't think it would be enough to break the core strands either in a <FF1 situation.

That being said, the sheath DOES add some strength to the rope and a lot of integrity.

Jake Jones · · Richmond, VA · Joined Jul 2011 · Points: 748

Most of the strength does come from the core. However, the scariest thing for me is knowing that whatever caused the sheath to rip open, if the rope remains in the same position as when it failed (i.e. if the fall was arrested and the core shot was due to being loaded or sawing over a sharp/abrasive edge) the core is now subject to whatever ripped the sheath open- and the core, although strong, is much less resistant to being cut/abraded than the sheath.

Chris treggE · · Madison, WI · Joined May 2007 · Points: 8,590
John Wilder wrote: Just Beal and Edelweiss, to my knowledge. I think another brand (i want to say Mammut) has something similar, but its not standard.
I want a Beal or Edelweiss bi-pattern 70m dry treated, unicore rope.

What do I buy? Looking at websites reveals a dizzying array of things I don't want, or things that I cannot tell if it is what I want.
Mark Hudon · · Lives on the road · Joined Jul 2009 · Points: 0

And, BTW, that core shot in my photo was cause by a rounded edge, as round as your finger.

Jess, yes, I think you are correct.

J. Albers · · Colorado · Joined Jul 2008 · Points: 1,228
Mark Hudon wrote:And, BTW, that core shot in my photo was cause by a rounded edge, as round as your finger. Jess, yes, I think you are correct.
The old "edge cut" test that they used to perform on ropes a few years back (I don't think it's done anymore...this is when mammut made their Supersafe rope and edelweiss was advertising the edge resistance of their fat Stratus rope) was performed on a rounded piece of metal that was about the diameter of a pencil if I recall correctly. The rope cuts because of heat (and consequent heat transfer between the individual strands of the core) not because of some sort of sawing action. Thus all you need is to have a small enough edge (sharp or not) and you can cause the rope to cut. This is why the way the made edge proof ropes was to coat each individual strand of the core with an insulating coating that cut down on the heat transfer and hence the failure of the whole core. Not sure what happened to this idea. Too expensive? Consumers didn't care? Not possible on skinny ropes?
Jim Titt · · Germany · Joined Nov 2009 · Points: 0
J. Albers wrote: The old "edge cut" test that they used to perform on ropes a few years back (I don't think it's done anymore...this is when mammut made their Supersafe rope and edelweiss was advertising the edge resistance of their fat Stratus rope) was performed on a rounded piece of metal that was about the diameter of a pencil if I recall correctly. The rope cuts because of heat (and consequent heat transfer between the individual strands of the core) not because of some sort of sawing action. Thus all you need is to have a small enough edge (sharp or not) and you can cause the rope to cut. This is why the way the made edge proof ropes was to coat each individual strand of the core with an insulating coating that cut down on the heat transfer and hence the failure of the whole core. Not sure what happened to this idea. Too expensive? Consumers didn't care? Not possible on skinny ropes?
More like radius 0.75mm if my memory hasn´t failed. The test gave erratic results and was abandoned anyway.
The mechanism of failure was described by David Smith at Strathclyde University.
20 kN · · Hawaii · Joined Feb 2009 · Points: 1,128
Jim Titt wrote: More like radius 0.75mm if my memory hasn´t failed.
Correct. The test jig was not round by any means. It basically represented dropping the rope over the edge of the edge of your desk, except your desk is made out out of steel. It is possible for a rope to fail if loaded over an abrasive but round edge. I've seen a rope desheath when a guy fell and his rope got caught between the main rock face and a stalagmite-like formation. The distance between the ends of the stalagmite was probably 10" long, so plenty round, but the rock where the rope touched was highly abrasive which was enough to desheath the rope.
20 kN · · Hawaii · Joined Feb 2009 · Points: 1,128
Chris treggE wrote: Looking at websites reveals a dizzying array of things I don't want, or things that I cannot tell if it is what I want.
Edelweiss only makes some ropes with Unicore tech. They call it something else also. Best bet is to call them or look more on their website. I just wish the tech was available on ropes that dont stretch so damn much. Beal ropes like wet noodles. I want something with a bit less stretch.
Guideline #1: Don't be a jerk.

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