What's the deal with half ropes?

So I've been looking into doing some mountaineering this season and I have noticed that some people use one half rope. Isn't that what you're not meant to do? Please explain why this is fine, thanks.

some half ropes are rated as singles as well, but yes...this is a calculated risk that some are ok taking. I'm not.

People will use one half rope for glacier travel and then double it up (halving the available rope) when leading more technical terrain.

I was looking into Steve House's ascent of Nanga Parbat and he used a single half rope and a tag line. I'm guessing his half rope was also rated as a single or is he just a little nuts?

https://www.petzl.com/US/en/Sport/What-would-be-the-results-of-tests-done-with-80-kg-on-one-strand-of-a-half-rope-?ProductName=RUMBA-8-mm

Bryce Dahlgren wrote:

I was looking into Steve House's ascent of Nanga Parbat and he used a single half rope and a tag line. I'm guessing his half rope was also rated as a single or is he just a little nuts?

Technically half ropes are designed to take the full force of a leader fall, however, they are typically significantly less durable than a single rope. You are trading safety margin for lower weight. I think to a large extent, the super skinny triple rated ropes have made this practice less appealing to those looking to shed weight.

Edited. Xam is right about the construction of a typical half rope vs a single rope.

Bryce Dahlgren wrote:

I was looking into Steve House's ascent of Nanga Parbat and he used a single half rope and a tag line. I'm guessing his half rope was also rated as a single or is he just a little nuts?

i think the latter. i don't know of any half ropes at 8.1mm that are also rated as a single. 

RGold has posted a number of times about half ropes and their pros ands cons.  Should be able to find it in an easy forum search.

You have to think about use cases. 2 pitches of 5.8 right in the middle of 2000 feet of snow and 4th class rock? Oh and a 10 mile, 5000 approach? I bet the weight of a half rope will be seductive, in the parking lot. Be willing to lead, when it comes down to it, and don't fall right?

Don’t confuse “rating” (and testing) with capability.   I often lead on a single half rope.
I pay special attention to edges, etc and I wouldn’t use them to “work a sport route”, but I have no doubt in its ability to hold any lead fall I’d ever take.   It may not pass the same number of FF 1.7 UIAA drops as a rated single, but I only need it to catch one.  

Bryce Dahlgren wrote:

Please explain why this is fine

It's fine because they aren't regularly falling on it. Gear choice is an optimization problem.

There are some examples of it being not "fine" as well. I think there was an injury/death on Matthes Crest a couple years ago, due to a half rope being severed in a fall.

Dylan Pike wrote:

Technically half ropes are designed to take the full force of a leader fall, however, they typically have thinner and less durable sheaths than a single rope. You are trading safety margin for lower weight. I think to a large extent, the super skinny triple rated ropes have made this practice less appealing to those looking to shed weight.

This is wrong.  Half ropes frequently have thicker sheaths, as a percentage of the total diameter, than lightweight singles.  The bulk of the tensile strength of a rope is carried in the core.  This has been discussed ad nauseam. 

One tangible data point is how hard it is for a pair of mammut genesis half ropes to wear out due to the very thick sheath.

Mark Pilate wrote:

It may not pass the same number of FF 1.7 UIAA drops as a rated single, but I only need it to catch one.  

I mean, not even. You could tie into both ends for the first half of the pitch, then untie one strand to finish. By the time you’re on a single strand, you’re already out of high FF territory. Of course, you’d need a no-hands rest to do this.

Disclaimer: I’ve never done this. Pulling a single rope through carabiners where both strands are clipped might be an issue. Dunno. Anybody try this?

Mark Pilate wrote:

Don’t confuse “rating” (and testing) with capability.   I often lead on a single half rope.

don't confuse capability with implied safety. just because something is "capable" of performing a task doesn't mean it is safe nor the best tool for the job. 

Ratings and testing (and certifications) exist specifically to help manage this gap...

curt86iroc wrote:

don't confuse capability with implied safety....

I assure you, I’m not confused.  ;)

“Safety” is a pretty gray area and tolerances are different for everyone.   I make no comment as to the “safety” of such tactics. 

Hson P wrote:

I mean, not even. You could tie into both ends for the first half of the pitch, then untie one strand to finish. By the time you’re on a single strand, you’re already out of high FF territory. Of course, you’d need a no-hands rest to do this.

Disclaimer: I’ve never done this. Pulling a single rope through carabiners where both strands are clipped might be an issue. Dunno. Anybody try this?

You want to go no-hands and have your belayer take you off belay in a high consequence situation (alpine climb, far from civilization) so that you can lead the first half of the pitch "safer"? No thank you. 

If the climbing is in that much need of fall protection, maybe better just to do that one pitch as two and do the doubling up of the half. Still seems less than ideal as you'll be moving slower with so many short pitches.

Long Ranger wrote:

You want to go no-hands and have your belayer take you off belay in a high consequence situation (alpine climb, far from civilization) so that you can lead the first half of the pitch "safer"? No thank you. 

If the climbing is in that much need of fall protection, maybe better just to do that one pitch as two and do the doubling up of the half. Still seems less than ideal as you'll be moving slower with so many short pitches.

You wouldn’t need to go off belay for this. The belayer just starts belaying on one strand and pulls the other one down to create more slack on the brake strand. You could even leave the brake strand threaded in the belay device. Obviously, you would need to figure out *which* strand to pull, maybe a bipattern would be best for this.

Edit: even better, put the second strand on a clove hitch on a locker attached to the climber’s belay loop. That way, they can just dump the clove to continue climbing. No stance required. 

Hson I wouldn't even consider that as a viable solution. The leader is half a rope out and is untying WHICH END, exactly? How is she supposed to know which strand the belayer is still gripping? The list of ways this could go wrong is extensive. Couple this with high mountain enviro, wind, out of sight, can't hear, etc.... (and we PLANNED it this way???). 

Don't be married to your solution, mate. Its not a great idea and I mean you no disrespect in saying so.

Many Interweb climbers have enquiring minds but it all comes down to Safety Margin with half ropes. Their margin is less because a second half rope is intended to be backing them up but they are perfectly capable of catching a severe fall....ie once or twice.

Super skinny single ropes can do this better (ie 5 times) but this assumes no offending sharp edges...

Fatty ropes even more (7-9) etc. That extra weight is extra margin of safety.

Keep in mind that no one has ever broken a climbing rope during actual use...but they often get cut and the skinner the more easily cut.

Your mileage may vary and any rope can be cut given a bad enough fall over a sharp enough edge.

You pay your money and you take your chances mitigated by your skills at avoiding sharp edges and nasty whips. Climb on a fatter rope if you wanna cover your mistakes a little more. 

If you want an Alpinist's fate of commonly dying young then take all kinds of silly risks for no good reason....

Hson P wrote:

You wouldn’t need to go off belay for this. The belayer just starts belaying on one strand and pulls the other one down to create more slack on the brake strand. You could even leave the brake strand threaded in the belay device. Obviously, you would need to figure out *which* strand to pull, maybe a bipattern would be best for this.

As CN said above, this sounds like a CF trying to figure out which strand to untie, which side to pull out of the device, etc. And meanwhile the second has to untie. I’ve never seen a bi-pattern half rope but if someone made one at 100 meters that would be awesome. Being able to do really long easy snow/ Ice pitches and rap 50m with no knots would be sweet. (Although naked A threads would suck).

Using a half/twin rope as a single rope is "fine" if you're wiling to understand and accept the associated risks, which include:

• Increased susceptibility to cutting, roughly proportional to cross-sectional area of the rope (for pendulum cuts; more complicated fall perpendicular to sharp edge). Some large percentage of the rope failure incidents involve the use of a half/twin as a single rope. My recollection is this number is about 30%, but the internet has that number somewhere, perhaps in German...
• Increased fall distance during fall arrest due to stretch--30% elongation is standard for normal, single rope use & double that could be exciting; even for the 2nd falling at the start of a 60 meter pitch increasing the normal 10% stretch by about a factor of 2 might lead to more excitement.
• Increased fall distance during fall arrest due to rope feeding in belay device, especially one that is not designed for skinny ropes.
• Increased likelihood of belayer losing control of the rope during fall arrest--an event that happens lots more often than the severing of ropes.

An advantage is reduced force on the gear during fall arrest...