skinny ropes - thoughts on failures and real world safety?

Question: I'm wondering about whether there is a real safety difference between, say, 9.5 or 9.1 mm or skinnier single-rated ropes, speaking generally. Specifically, it seems the real-world failure mode for ropes is cutting, not breaking. Given that under tension ropes seem to cut relatively (frighteningly!) easily, is there a real additional margin of error for a very skinny single-rated rope and a slightly fatter one? In particular, is there any evidence of skinny rope(s) having failed in real world in conditions that would not have failed were they a bit fatter?

Background:
I've steadily marched my way towards skinnier ropes over the past couple decades, from 11mm BITD to I think 9.5 or 9.4 or so now, I forget the exact g/m of my current cord but a step or two up from the skinniest singles available a couple years back.

I'm now considering going skinnier for longer trad and ice routes because weight and rope drag and I'm a weenie. This will be a rope quiver thing: I also have a couple sets of doubles/twins that I use a lot (8.1s) and will probably get some 7.whatevers for this winter. Would go with whatever the sheath technology is that keeps the rope from completely unraveling on a core shot, like some of the Beal ropes I have experience with.

Putting aside for now questions of cost, durability, and whether the benefits really matter (probably not that much for me), I'd like to settle my mind on the safety question above - is there a real compromise in using the skinniest ropes rated for single falls, assuming I replace them as they wear. For reference, these topics are discussed in other threads here here here and probably others.

I get that this is an unanswerable question, the outcome will depend entirely on the condition of the actual fall, and yes I'll end up selecting ropes based on the route, etc etc. But curious if others have thought it through from this perspective.

Thanks for any thoughts... 

I have been climbing on a mammut serenity for 6 years. I am on the 2nd on having replaced the rope last year.  My climbing is multi-pitch trad averaging 1 day a week.  I am very satisfied with the rope and it's durability seems on par with other ropes i have owned during the last 40 years.  

The previous rope was an edelrid 9.6 which was fine.  Before that a blue water lightening pro 9.7 which got cut all to hell by getting snagged on a sharp something while pulling the rappel.  Probably 20 feet of the sheath was sliced open.  The rope before that was an edelweiss 9.8 which wore out almost immediately.  There are MP threads about some problem with red thread being defective.  Previous was a 10.2 mm Sterling rope that some rodent chewed on. Pretty good rope but I don't know why the rodent chewed on it. Before that blue water ropes for a long time with no problems. One of the bluewater ropes got hit by a rock on its 1st day out and cut in half.  Before bluewater i own mammut back to 1978.  No issues with any of those ropes.

I have damaged ropes of all diameters except the skinny one.  I imagine that a damaged skinny rope is just a matter of time.

I am looking forward to next years release of the edelrid swift protect with the high tech cut resistant fibers in the sheath.  I might replace my rope early 

The thing that gives me pause is that I am worried about the Dunning-Kruger side of things.

Maybe 8.7mm singles are perfectly OK... for people who are better than me at avoiding swings over sharp roofs (and protecting their seconds from them).

Maybe 8.7mm singles are perfectly OK... for people who are better than me at choosing the appropriate rope for the objective.

My current thinking is that 8.7mm singles are OK for me on terrain where I am unlikely to fall or where there is little/no cut hazard.

Maybe I am being overcautious; they are presumably safer than just one 8.5mm half rope, and lots of people have seconded lots of routes on just one 8.5mm half rope.

Part A: Severing
1) All the ropes in question are constructed of the same nylon, and thus the material has identical fracture toughness, the material property that governs how easy something is to cut; therefore the question is about geometry and/or construction. High tech cut resistant fibers in the sheath would change this point.
2) When cutting in a pendulum fall, the resistance to cutting is proportional to the amount of nylon and thus to the cross sectional area of the rope (the diameter squared). There is no effect of rope construction. High tech cut resistant fibers in the sheath would complicate this point.
3) In a vertical fall over a sharp edge, things get more complicated and your mileage vary; that said, don't count on your skinny rope to do a better or worse job of not severing. For example, in one sharp edge test, the sheath severed, then bunched up at the edge permitting the core to slide without touching the sharp edge.

Part B: How far you're going to fall
1) Skinny ropes in general stretch more and slide more easily through belay devices. So in general you'll be falling farther.
2) Corollary: The good news is that skinny ropes also reduce the force and jerk on the top anchor during fall arrest, which might be reassuring for those ice screws in brittle ice.

Part C: Other stuff
1) Fat or skinny makes no difference in susceptibility to strong acids. Insert surface to volume ratio argument here if overthinking seems appropriate...
2) No dynamic climbing rope, fat or skinny, has ever severed because climbers took too many falls over nicely rounded carabiners or similarly benign surfaces.

mbk wrote: My current thinking is that 8.7mm singles are OK for me on terrain where I am unlikely to fall or where there is little/no cut hazard.

Maybe I am being overcautious; they are presumably safer than just one 8.5mm half rope, and lots of people have seconded lots of routes on just one 8.5mm half rope.

I don't see that "unlikely to fall" is a relevant issue. If that were the case you wouldn't even use a rope a lot of the time. Do you plan to have holds break? Not likely. You don't know when you will and won't fall so you should recognize that if you reduce your safety systems at any time you may be reducing them at the time you need them most.

dave custer wrote: 

Part B: How far you're going to fall
1) Skinny ropes in general stretch more and slide more easily through belay devices. So in general you'll be falling farther.
2) Corollary: The good news is that skinny ropes also reduce the force and jerk on the top anchor during fall arrest, which might be reassuring for those ice screws in brittle ice.

That "Skinny ropes stretch significantly more than fat ropes is not true".  The reduction in impact force is not very significant and probably overwhelmed by the extra slip through the belay device. It is very important to get a belay device that works well with your rope, skinny or otherwise.  I recommend the Alpine Up or the BD Alpine Guide ATC.

Impact force and rope stretch are one of many aspects of a rope that must be in a specific range for the rope to be certified for climbing.

Mammut Eternity 9.8 mm impact force 8.5 kN, 80 kg stretch 5.5%, stretch on first fall 31%

Mammut Gravity 10.2 mm impact force 8.3 kN, 80 kg stretch 7%, stretch on first fall 30%

Mammut Serenity 8.7 mm impact force 8.1 kN, 80 kg stretch 6%, stretch on first fall 31% used as a single.

Bill Czajkowski wrote:

I don't see that "unlikely to fall" is a relevant issue. If that were the case you wouldn't even use a rope a lot of the time. Do you plan to have holds break? Not likely. You don't know when you will and won't fall so you should recognize that if you reduce your safety systems at any time you may be reducing them at the time you need them most.

I don’t plan to have holds break but I do consider the quality of the rock when I assess how likely I am to fall.

And, FWIW, climbing well within your ability allows you to avoid suspect holds, to test holds before committing to them, and to weight them conservatively, etc.

Getting back to OP's original question:

Imagine a swinging-over-an-edge fall with a fat rope which cuts through the sheath completely and then severs 2/3 of the core strands, leaving you hanging on by a thread.

I guess in that scenario, a skinnier rope would have cut.  How common is that scenario?  Absurdly rare, to the point of it not even mattering.

Given that cutting is the most likely scenario for rope failure, it is disappointing that cut resistance is not a standard line item on dynamic rope specifications. As I understand it, the UIAA Sharp Edge Resistance test was suspended, and did not test a scenario that replicated a rope running over a sharp edge during a fall, anyway. I have noticed that some manufacturers, such as Beal, claim their bonded (AKA "unicore") ropes are sharp edge resistant, although it is unclear what tests they currently base that claim on, if any.

Sam Skovgaard wrote: Getting back to OP's original question:

Imagine a swinging-over-an-edge fall with a fat rope which cuts through the sheath completely and then severs 2/3 of the core strands, leaving you hanging on by a thread.

I guess in that scenario, a skinnier rope would have cut.  How common is that scenario?  Absurdly rare, to the point of it not even mattering.

http://www.climbingyosemite.com/portfolio/matthes-crest-fatality-july-30th-2017/

Gregger Man wrote:

http://www.climbingyosemite.com/portfolio/matthes-crest-fatality-july-30th-2017/

I'm not saying rope-cutting falls are absurdly rare, I'm saying that a fall where rope thickness makes the difference between living and dying is probably pretty rare.

Sam Skovgaard wrote:

I'm not saying rope-cutting falls are absurdly rare, I'm saying that a fall where rope thickness makes the difference between living and dying is probably pretty rare.

Fair enough. The Yellow Spur accident in 2010 was a Beal 9.7

http://caves.org/section/vertical/nh/56/YellowSpur2010v6.pdf

Sharp things are bad.

I think a saw a post on mproj about upcoming dynamic climbing rope with aramid ( Kevlar) sheaf. The rationale - aramid fibers are more resistant to cutting than nylon or polyester.
The rope is going to be called "Edeldrid Swift Protect Pro Dry 8.9mm"
Here is "review" from gearjunkie - click me

Disclaimer - unfortunately, Edelrid did not provide me with this rope for evaluation purposes :(

amarius wrote: I think a saw a post on mproj about upcoming dynamic climbing rope with aramid ( Kevlar) sheaf. The rationale - aramid fibers are more resistant to cutting than nylon or polyester.
The rope is going to be called "Edeldrid Swift Protect Pro Dry 8.9mm"
Here is "review" from gearjunkie - click me

Disclaimer - unfortunately, Edelrid did not provide me with this rope for evaluation purposes :(

I'd be interested to hear how the aramid fibers impact the friction in a standard tube style belay device.

Yes sharp aretes make me nervous, especially when I am climbing with very skinny ropes. I'm not worried about a skinny rope wearing out faster over time with repeated falls, fuzzy spots, or dragging across rough rocks. You can spot this and buy a new rope. Who cares. Same with big falls, I think everyone agrees skinny ropes are fine and the UI ratings back this up.

But skinny ropes and sharp edges do make me nervous. I recall a sharp granite arete on Birds of Fire where one 8.5 mm double was keeping me from a long fall onto slabs below and the rope would have come tight right across a very sharp arete. I considered it no fall terrain.

Pat, I'm not buying that skinny ropes stretch the same as fat ropes, I think they definitely stretch a lot more. Hanging on one of my double ropes the thing gets really skinny and stretches like crazy below the point where I started taking. A 9.5 stretches too, but definitely not as much and doesn't seem to be as tightly compressed. Maybe in a big fall they end up stretching about the same but just hanging on them you can tell a difference.

When you think about it, both ropes as a whole are under the same tension in a fall. But the skinny rope is made of less strands (or smaller strands) so the tension per strand (or cross sectional area) is higher to support the same overall tension. A skinny rope would be easier to cut because the individual fibers get cut a few at a time and are under higher tension than when using a fat rope.  

Sam Skovgaard wrote: Getting back to OP's original question:

Imagine a swinging-over-an-edge fall with a fat rope which cuts through the sheath completely and then severs 2/3 of the core strands, leaving you hanging on by a thread.

I guess in that scenario, a skinnier rope would have cut.  How common is that scenario?  Absurdly rare, to the point of it not even mattering.

This sums up nicely the main thought that motivated this post. It's the delta that seems relevant. 

David Appelhans wrote: 
When you think about it, both ropes as a whole are under the same tension in a fall. But the skinny rope is made of less strands (or smaller strands) so the tension per strand (or cross sectional area) is higher to support the same overall tension. A skinny rope would be easier to cut because the individual fibers get cut a few at a time and are under higher tension than when using a fat rope.  

Is this true? Meaningful for real world application? 

mbk wrote: 

Maybe I am being overcautious; they are presumably safer than just one 8.5mm half rope, and lots of people have seconded lots of routes on just one 8.5mm half rope.

Actually I would say you're nothing about how the obscure UIAA testing plays out in real life. The big part to passing a skinny single is the fall test, you're asking the rope to basically hold 5 factor 2 falls in the same spot with only 5 minutes to recover in between. Does that have any bearing on the reality in which we climb?
What is usually our concern for alpine/adventure routes where we are bringing the skinniest cord? Usually abrasion resistance, not ability to multiple factor 2 falls right off the anchor repeatedly, that's just a stupid way to judge a rope in 99.99% of use (I don't know where the .11% would be, I'm just covering my ass because someone is going to have a goofy obscure scenario to try and prove me wrong).

The downside here is that to make that fall test pass the manufactures have to run thicker cores with less sheath. Taking two ropes from Mammut for example:

• 8.7 serenity single/triple
  51gm
  sheath 36%
  ~18 gm per meter of sheath mass
  
  
• 8.5 genesis half/twin
  45gm
  sheath 45%
  ~20 gm per meter of sheath mass

So even going to a skinnier half rope we would end up with more sheath than in the triple rated skinny single. I've taken 15-20 foot falls on a single strand of 8mm half rope (traversing route, other ropes pro was far below). They work fine.

That said, personally I've gone all over from using an 8 as a single on a moderate route, lugging a 9.8 to the bugs once (never again) and used a variety of low 9 ropes. I've gone back up to using a 9.4 for the harder alpine routes closer to the road, but I'll use the 9.0 when falls are less likely. I'd still use a single half rope for >5.9 in the alpine.

I bought a 60M Sterling Fusion Nano IX (9.0mm) for F&L missions.  While rapping toward's Wolf's Head off of Pingora (Wind River Range), my buddy went over a small roof a little too fast.  When we pulled the rope it was puking core.  Now granted I never saw the exact edge that did the damage, but I was shocked at how easily that rope got sliced.

That all being said, a few days later I used an 8.0MM on the Grand Traverse and it felt completely fine.

David Appelhans wrote: 
Pat, I'm not buying that skinny ropes stretch the same as fat ropes, I think they definitely stretch a lot more. Hanging on one of my double ropes the thing gets really skinny and stretches like crazy below the point where I started taking. A 9.5 stretches too, but definitely not as much and doesn't seem to be as tightly compressed. Maybe in a big fall they end up stretching about the same but just hanging on them you can tell a difference.

• 7.3 gully (beal)
  9.8% static
  35% dynamic

• 7.5 twilight (mammut)
  6.7% static
  29% elongation first fall

• 8.0 Unity (maxim)
  9.6 static
  29% elongation first fall

• 8.1 ice line (beal)
  11.5% static
  37% dynamic

• 8.5 genesis (mammut)
  7.3% static
  29% elongation first fall

• 9.5 Infinity (mammut)
  6.5% static
  30% elongation first fall

• 10mm virus (beal)
  8% static
  35% dynamic

Sorry David, you may have a skinny rope that stretches more than your particular fat one, but the statement that skinny cords stretch more is just blatantly false. You can pick out skinnier cords within the same manufacture that actually stretch less, look at the 7.3 gully vs. 8.1 ice line from beal for example.

Individual ropes will have a different target use and have different elongation and impact forces, pick what matches your end use. It pays to look at different manufactures and not be set on one also. 

If you want low elongation because of ledge terrain and don't mind high impact forces go with something from maxim.
Ok with taking bigger falls and want a fluffy cloud of a catch even when your 300lb gorilla belayer doesn't step into the catch with a grigri? Get a beal.
Want something in the middle? Go with Mammut or Sterling. 

David Appelhans wrote: Yes sharp aretes make me nervous, especially when I am climbing with very skinny ropes. I'm not worried about a skinny rope wearing out faster over time with repeated falls, fuzzy spots, or dragging across rough rocks. You can spot this and buy a new rope. Who cares. Same with big falls, I think everyone agrees skinny ropes are fine and the UI ratings back this up.

But skinny ropes and sharp edges do make me nervous. I recall a sharp granite arete on Birds of Fire where one 8.5 mm double was keeping me from a long fall onto slabs below and the rope would have come tight right across a very sharp arete. I considered it no fall terrain.

Pat, I'm not buying that skinny ropes stretch the same as fat ropes, I think they definitely stretch a lot more. Hanging on one of my double ropes the thing gets really skinny and stretches like crazy below the point where I started taking. A 9.5 stretches too, but definitely not as much and doesn't seem to be as tightly compressed. Maybe in a big fall they end up stretching about the same but just hanging on them you can tell a difference.

When you think about it, both ropes as a whole are under the same tension in a fall. But the skinny rope is made of less strands (or smaller strands) so the tension per strand (or cross sectional area) is higher to support the same overall tension. A skinny rope would be easier to cut because the individual fibers get cut a few at a time and are under higher tension than when using a fat rope.  

Gotta go with the number.  The internal construction of skinny ropes is different.