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Half rope route line choices. What's safe?


Original Post
anotherclimber · · Unknown Hometown · Joined Apr 2016 · Points: 70

I'm wondering when using half ropes that are only rated for half, or half and twin like the Mammut Genesis 8.5mm...  Is it safe to use each rope to protect only a portion of the climb in an effort to reduce friction and drag? Or should I be looking for half ropes like the Beal Opera 8.5mm that are also rated for single rope use for this application? Some theoretical examples:

A route that has a vertical crack up until halfway then there is a short traverse and another vertical crack continues to the top. In this example one rope protects one of the cracks and the other rope protects the other crack. 

A route that has a substantial traverse in the middle where one might want to use one rope for the initial section going straight up to the traverse in addition to the traverse, and the other rope for the final straight up section to the end of the climb. Or maybe split the difference and one rope is used all the way to halfway into the traverse, and then the other rope finishes the climb. 

A route where the majority of the  protection is straight up, with the exception of a few pieces of protection significantly off to one side in one area such that you'd want one rope clipped into the majority of the protection that is straight up, and the other rope only for those few pieces that are way off to the side. 

Thank you in advance for your insight.


wivanoff · · Northeast, USA · Joined Mar 2012 · Points: 472
anotherclimber wrote:

I'm wondering when using half ropes that are only rated for half, or half and twin like the Mammut Genesis 8.5mm...  Is it safe to use each rope to protect only a portion of the climb in an effort to reduce friction and drag? 


Yes. The examples you give are exactly how double ropes are used. https://www.ukclimbing.com/articles/page.php?id=2737

Gunkiemike · · Unknown Hometown · Joined Jul 2009 · Points: 2,745

Yes, you can do what you're asking about.  Doubles make such schemes quite practical where a single rope would have inherent troubles.  And I wouldn't worry about the various ratings; all half -rated ropes will hold a real fall (just not lots of them in the UIAA's most severe testing scenario).

anotherclimber · · Unknown Hometown · Joined Apr 2016 · Points: 70

Am I misunderstanding the rating for half ropes that are not rated for single use, that they are not designed to be used where you are relying on only one rope, or mostly on one rope to catch your fall? This is why I asked the initial question. 

Edit: Thank you gunkiemike. I didn't see your post until after I commented this.


Ryan Hamilton · · Orem · Joined Aug 2011 · Points: 20

I believe the main idea behind half ropes is that a single half rope is rated to catch falls, just not as many as a rope rated as a single rope. The sheath is thinner so durability less and protection against being cut on an edge is increased. However, the nature of using the two ropes is that you can use the two ropes to avoid having to run a rope over a bad edge as well as reduce rope drag. Plus, they tend to provide a softer catch so you are less apt to pull gear when you fall. I think Europeans must think Americans are strange for not using half ropes because of all of these benefits, and maybe they are right. 

If I'm climbing multi-pitch ice I always use a set of half ropes, mainly for the softer catch (less likely to pull a screw). I also like them for the ease of double rope rappels which are faster, but also reduce the need for v-threads or leaving gear in case anchors are covered in ice or non-existent. 

dave custer · · Unknown Hometown · Joined Nov 2010 · Points: 790

All rope choices are trade-offs. More nylon is heavier; in general though, there will be less stretch and less feed through the belay device during fall arrest; and more resistance to cutting/sheath abuse. Less nylon is lighter, permits more stretch/feed-through, reduces the force on the top anchor, and tolerate less abuse. All rope "severing" failures are the result of loading the rope over a sharp edge/protrusion or acid exposure.

BErnst & WVogel

Determination of the redistribution shock load in climbing double rope systems

http://www.sciencedirect.com/science/article/pii/S1350630708001246

Nick Drake · · Newcastle, WA · Joined Jan 2015 · Points: 483

Half rope technique like you describe is REALLY helpful on friction slabs when the route traverses a lot. Case and point, only green clipped first half of pitch, big traverse right and then only yellow clipped top half of pitch. https://www.instagram.com/p/BKUIz36BhTd/?taken-by=nurkdurk&hl=en

Last pitch of that same route I took a longer fall (well run) which was caught on the one 8mm mammut genesis. I've also taken complete vertical falls on that same 8mm rope as a single strand. 

Consider using two biners through rope and ATC when using half rope technique to make it easier to arrest lead falls.

rocknice2 · · Montreal, Quebec · Joined Nov 2006 · Points: 3,038

1/2 ropes do NOT necessarily provide softer catches than a single.

http://willgadd.com/single-and-half-rope-impact-forces-data/

1/2 rope data

Rope A. 80kg-7.35kN, 55kg-5.39kN, published with 55kg-4.85kN

Rope B. 80kg-8.15kN, 55kg-6.23kN, published with 55kg-6.3kN

Rope C. 80kg-8.23kN, 55kg-6.25kN, published with 55kg-6.5kN

Rope D. 80kg-9.22kN, 55kg-5.88kN, published with 55kg-6.1kN

Single rope data

BD “Joker” 9.1mm: 8.2kn
BD “Booster III” 9.7mm: 7.3Kn
Bd “Apollo II” 11mm: 7.7kN
Sterling “Nitro” 9.8mm: 9.0kN
Sterling “Pro”10.1mm: 8.6kN
Sterling “Mega” 11.2mm: 8.7kN

 

Guy Keesee · · Moorpark, CA · Joined Mar 2008 · Points: 310

anotherclimber..... good luck with the Doubles thing. A bunch of people will laugh at you for using two ropes.... don't worry- one day the reason for using them will be quite obvious.


Nick Drake is correct.

coppolillo · · Unknown Hometown · Joined Sep 2009 · Points: 70

Hey another---You're right to think this through. Kudos for the folks posting data---half and twins do not significantly reduce impact forces--I don't think there has been a study showing that they do. It's a common idea to use half ropes to reduce forces on sketchy gear/ice screws. RGold, I believe, is pretty knowledgable about these tests. 

The Beal Opera (as well as the Edelrid Corbie and others like the Mammut Serenity) carry all three certifications--so, no to muddy the waters further (which I'm now going to do), you could consider a rope like this---it makes sense, because often you'll see guys carry a half or twin on a glacier route with some rock climbing (think Cascades). When on rock, they'll double the twin rope and use it as it's intended to be used, but now you only have 30m of cord to use. A great strategy for some uses, but other times it's too limiting. The thing you don't want to do is get put into a situation during which you're leading substantial sections of rock on a single twin or half. Having a triple-rated rope solves that problem--the Beal or Corbie would be cool. That said, you don't want to end up leading a ton on a super-skinny single rope, mainly for durability reasons. No easy answer and often the solution (buying a few ropes!) is expensive! 

I own a couple Edelrid Swifts (8.9mm) and they've been remarkably durable for using them as singles. So far, so good--maybe 25 days on each of 'em, some of those trailing the rope to two climbers. The Mammut Serenity (8.9mm) is a phenomenal rope, too--super durable for its weight. Haven't used the Beal Opera, but knowing Beal, it's an awesome company and the cord's probably good. One suggestion is to compare sheath percentages in the ropes---you'll see the Corbie and Beal have lower sheath percentages to save weight--but that reduces durability, too. 

Anyway, hope that helps, rather than confuses! A buddy and I have a book coming out in a couple weeks, The Mountain Guide Manual, and it goes into some of this stuff in detail and situations in which you choose one rope over another. Shameless plug, but maybe give it a look if it seems in your wheelhouse:

http://www.vettamountainguides.com/the-book/

anotherclimber · · Unknown Hometown · Joined Apr 2016 · Points: 70

Rocknice2, that's good information. Thank you for posting it. This shows it's still important to give a soft catch on half ropes. Particularly if you are falling on less than full strength rock pro.

Not to side track too much from my original question...  

Regarding the sheath thickness and durability of half ropes versus single rated ropes. This is something that is worth putting to rest. From just looking at the numbers, sometimes you'd be surprised of just how much sheath is on a rope. As manufacturers always give a percentage figure rather than the measured amount which can be misleading unless you do the math. Some examples mostly within the same brand to keep things as much alike as possible. I added some others that were suggested. 

Mammut Revelation 9.2mm single rated rope has a sheath of 36%. 9.2mm * .36 = 3.312mm thick sheath. 

Mammut Genesis 8.5 half ropes has a 45% sheath. 8.5mm * .45 = 3.825mm sheath thickness. So the Genesis 8.5mm has a slightly thicker sheath than a thin single rope. 

Mammut Infinity 9.5mm single rope has a 40% sheath. 9.5mm * .4 = 3.8mm sheath thickness. This is almost identical to the Genesis 8.5. 

Mammut Eternity 9.8mm single rope has a 38% sheath. 9.8mm * .38 = 3.724mm sheath thickness. Slightly less than the Genesis 8.5mm.

Mammut 10.1mm gym single rope has a 37% sheath. 10.1mm * .37 = 3.737mm sheath thickness. Slightly less than the Genesis 8.5mm. I found this surprising for a gym rope.

Mammut Galaxy 10mm single rope has a 36% sheath. 10mm * .36 = 3.6mm. Slightly less than the Genesis 8.5mm.

Mammut Gravity 10.2mm single rope has a 42% sheath. 10.2mm * .42 = 4.284mm. Thicker than Genesis 8.5mm, but were starting to get into fat rope territory.


Now let's compare to the two next smallest size half ropes they make:

Mammut Phoenix 8.0mm half ropes has a 42% sheath. 8.0mm * .42 = 3.36mm sheath thickness. It's obviously thinner than the Genesis 8.5mm, but only by less than half a millimeter. And still ever so slightly thicker than the sheath on the Revelation 9.2mm single rope. 

Mammut Twilight 7.5mm half ropes has a 35% sheath. 7.5mm * .35 = 2.625mm sheath thickness. Significantly thinner than the Genesis 8.5mm. 

It seems regarding the sheath that only the thinnest half ropes are significantly less durable. Go figure!   


Edit: Adding triple rated ropes for comparison.

Mammut Serenity 8.7mm triple rated rope has a 36% sheath. 8.7mm * .36 = 3.132mm sheath thickness. Slightly thinner than the Phoenix 8.0mm.

Beal Opera 8.5mm unicore triple rated rope has a 37% sheath. 8.5mm * .37 = 3.145mm sheath thickness. Slightly thinner than the Phoenix 8.0mm. 

Nick Drake · · Newcastle, WA · Joined Jan 2015 · Points: 483

If it'll hold a lead fall on one strand it'll hold a lead fall as a single. I've used my 8mm as a single on alpine routes before where sharp edges weren't a concern and chance of either partner falling *extremely low*. Cord diameter matters more when you're dealing with sharper edges. I don't have any problem using half ropes over 8.5 as singles on many routes, even if they aren't triple rated. However, yur gunna die.

anotherclimber · · Unknown Hometown · Joined Apr 2016 · Points: 70

Guy Keese,

I will have the last laugh when I get to the top of a wandering line with the least amount of effort. I discovered the single rope drag issue fairly early on when I started leading trad. Thank you for the encouragement.

coppolillo,

Funny we were on similar tracks with sheath thickness. I couldn't find the Edelrid Corbie rope on their web site. Did they replace it with another type? I'll add the Serenity and Opera sheath comparisons. Why do you say you don't want to lead significant portions of a route on a single half rope? A number of other people here seem to think this is ok. 



Nick Drake · · Newcastle, WA · Joined Jan 2015 · Points: 483
anotherclimber wrote:


coppolillo,

Funny we were on similar tracks with sheath thickness. I couldn't find the Edelrid Corbie rope on their web site. Did they replace it with another type? I'll add the Serenity and Opera sheath comparisons. Why do you say you don't want to lead significant portions of a route on a single half rope? A number of other people here seem to think this is ok. 



Here's some from when I was looking at ropes. For sheath mass I just multiplied rope weight by the sheath %. Weights are rounded to the nearest tenth for a 60m rope based on manufacturer gr per meter. Triple rated ropes are indicated with **

Note how much more sheath you get with a lighter half/twin rated genesis than the triple rated Serenity:

Mammut Phoneix 8mm, 5.5lbs, 18gr sheath
Beal Pro Mtn 8.8mm, 6.2lbs, 21gr sheath
Mammut Genesis 8.5mm, 6.4lbs, 24gr sheath
**Beal Opera 8.5mm, 6.4lbs, 18gr sheath
Beal Cobra 8.6mm, 6.4lbs, 18gr sheath
**Mammut Serenity 8.7mm, 6.7lbs, 19gr sheath
**Sterling Nano 9mm, 6.9lbs, 14gr sheath
**Maxim AIrliner 9mm, 6.9lbs, 21gr sheath
**Beal Joker 91., 7lbs, 19gr sheath
**Bluewater Icon, 7.3lbs, 19gr sheath

Note that the weave of the fabric plays a large role too. While the Bluewater doesn't have a lot of sheath mass I have noticed much less "fuzzy abrasion" given similar use when comparing to a Joker or Nano. I have also been more impressed with the sheath life of the Mammut Genesis over the joker/nano.

jktinst · · Unknown Hometown · Joined Apr 2012 · Points: 55

One thing to keep in mind on pitches that have a single major zig-zag stretched over the whole pitch is that if you clip only one rope on the "zig" and the other on the "zag" to avoid friction, your doubles no longer function as back-ups to one another against cutting (except for a short section after switching from one to the other). I feel that this feature of doubles is one of their significant advantages.

For this reason, on pitches that have this configuration, I will occasionally clip the secondary rope on longer slings. It does add a bit more friction than if I didn't but nothing like what it would be with a single rope. Of course, if I did need to be arrested on the secondary rope when it's clipped to the longest slings, I'd still take a major tumble but again, not quite as major as in the alternative.

cyclestupor · · Woodland Park, Colorado · Joined Mar 2015 · Points: 93
anotherclimber wrote:

Mammut Revelation 9.2mm single rated rope has a sheath of 36%. 9.2mm * .36 = 3.312mm thick sheath. 

I'm pretty sure your math is wrong.  You can't just multiply diameter by sheath_mass_percentage to get sheath thickness.

I doubt it is possible to come up with a decent estimate of sheath thickness.  To estimate it you would need to know the density of the core vs. the sheath, and given that the sheath is woven, and the core is spun, the densities could be drastically different I would think.

However, if we assume that the core and sheath density are the same.  we could calculate the sheath thickness as follows...

sheath_thickness = diameter - sqrt((diameter*diameter) / (sheath_fraction + 1))

Though I may have made a mistake in my math the "+1" part seems wrong.  I'll double check it tonight.

rocknice2 · · Montreal, Quebec · Joined Nov 2006 · Points: 3,038

D= diameter of rope

R= radius of rope

Rc= radius of core

Rs= radius of sheath

%= percentage of sheath.  eg. 37% = 0.37

V= volume of total rope

Vc= volume of core

R=D/2

V=πR^2

Vc=V-(V*%)

Rc=√(Vc/π)

Rs=R-Rc

cyclestupor · · Woodland Park, Colorado · Joined Mar 2015 · Points: 93

I made several mistake in my math.   This looks better

Sheath_thickness = diameter * (1-sqrt(1-sheath_fraction)) * 0.5

rocknice2 · · Montreal, Quebec · Joined Nov 2006 · Points: 3,038
cyclestupor wrote:

I made several mistake in my math.   This looks better

Sheath_thickness = diameter * (1-sqrt(1-sheath_fraction)) * 0.5

5.97 = 10 * (1- ✓(1- 0.35)) * 0.5

I don't think that's correct

rocknice2 · · Montreal, Quebec · Joined Nov 2006 · Points: 3,038
rocknice2 wrote:

R=D/2

V=πR^2

Vc=V-(V*%)

Rc=√(Vc/π)

Rs=R-Rc

0.5 = 10/2

78.5 = π×0.5^2

51 = 78.5-(78.5*0.35)

4 = ✓(51/π)

1 = 5-4

10mm rope with 35% sheath

Sheath thickness = 1mm 

anotherclimber · · Unknown Hometown · Joined Apr 2016 · Points: 70

Ha! I knew someone would correct my math. LOL

You two are far ahead of me in that department. Are my basic calculations so far off to not even be close? Or to even compare against other ropes of the same manufacturer? Is Nick's approach of using weight a better way of doing this without needing to understand advanced mathematics?

Guideline #1: Don't be a jerk.

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