What's the deal with half ropes?

dave custer wrote:

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...

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

Not a thing.

Dave K wrote:

I bought these for some easy alpine routes in Europe where I led short pitches and then belayed my 2 kids simultaneously.

Same brand, model, and diameter. They came in two colors like any half/twin set.

I used them as halfs. 

If I use them as twins, am I going to die?

Yes, ur gonna die!

When, where and how hopefully not for a very long time and likely not related to climbing on this or any other cord.

:)

Cherokee Nunes wrote:

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.

No disrespect taken. It’s not something I would do, ever. Reminds me of a Monty Python scene. Get the wrong color (was it blue or red?) and go flying through the air...

When mountaineering any fall you take is going to be on terrain that is far from vertical, so it is likely that your impact force/speed when will be much lower than when rock climbing (i.e. you'll be sliding along snow, or bouncing down rock). Therefore, cut resistance is MUCH more important than the ropes ability to take the force of a full leader fall multiple times. A skinny single rope can have a thinner sheath than a half rope of similar diameter, because the single rope has to have a thicker core in order to be able to take the force of multiple huge falls that are just not going to happen in a mountaineering environment. 

Ackley The Improved wrote:

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

Not a thing.

Isn't it? To take it to the extreme, would you agree that falling on a static line will mean higher force on gear than a dynamic rope?

Ackley The Improved wrote:

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

Not a thing.

Very curious about why this might not be a thing. Theory and data suggest otherwise, regarding both rope behavior and belay device behavior.

^Curious as well what Ackley meant 

Edit:  maybe a qualifier of “a Significant Thing” would be better ?    To avoid hair splitting.  

Tom Owain wrote:

Isn't it? To take it to the extreme, would you agree that falling on a static line will mean higher force on gear than a dynamic rope?

I think that's a false comparison. The subject is a single dynamic rope vs. a half dynamic rope. In your example, we could just as well substitute a steel cable for the static rope. But, that's not what we're talking about, either.

Unfortunately, manufacturers don't generally tell us the dynamic impact for one half rope tested with an 80kg mass. They use a 55kg mass to get a larger statistical sample. So, we have no direct comparison with a "single" rope. I wish they would give us those figures. Based on the published figures I see for triple rated ropes, (and given a static belay) I suspect the dynamic impact for a half rope with an 80kg mass is similar to a single rope. It may be a bit less, but I don't think it's a "rubber band" like so many believe.

wivanoff wrote:

I think that's a false comparison. The subject is a single dynamic rope vs. a half dynamic rope. In your example, we could just as well substitute a steel cable for the static rope. But, that's not what we're talking about, either.

Unfortunately, manufacturers don't generally tell us the dynamic impact for one half rope tested with an 80kg mass. They use a 55kg mass to get a larger statistical sample. So, we have no direct comparison with a "single" rope. I wish they would give us those figures. Based on the published figures I see for triple rated ropes, (and given a static belay) I suspect the dynamic impact for a half rope with an 80kg mass is similar to a single rope. It may be a bit less, but I don't think it's a "rubber band" like so many believe.

Petzl actually published some test results about the exact scenario you're describing: one strand of a half rope taking the UIAA fall with 80kg.

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=VOLTA-9-2-mm

The peak forces are similar (8.5-9.2 kN), but, alarmingly, the ropes only held 2 or 3 UIAA falls before breaking.

Alex Fischer wrote:

Petzl actually published some test results about the exact scenario you're describing: one strand of a half rope taking the UIAA fall with 80kg.

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=VOLTA-9-2-mm

The peak forces are similar (8.5-9.2 kN), but, alarmingly, the ropes only held 2 or 3 UIAA falls before breaking.

Is that really alarming? The UIAA test falls are very severe and difficult to duplicate in the field. Most falls are much lower fall factor. And, in DRT, we often clip the same rope to several pieces in a row. So, in that situation, the load is absolutely going to come one only strand.

I think what's more alarming is thin ropes cut easily over an edge compared with thicker ropes. That makes me wonder about a half rope with a thick sheath vs a triple rated rope with a thin sheath.

Anyway, here's a comparison and some comments from Will Gadd https://willgadd.com/single-and-half-rope-impact-forces-data/ 

"Half ropes likely do not offer significantly lower impact forces than single ropes in high fall-factor falls where one strand is clipped as is common."

A few things to consider:

In using ropes like Steve House in those sort of situations, you are juggling a ton of factors - weight, odds of falling, angle of fall, risk of rope stretch (much higher with 1/2 rope falls vs. single), getting to your goal in enough light, fatigue from dragging more rope/friction and getting through tough sections at altitude, using a single half rope for a short bit as a half length with doubled half rope of a single half rope, just to start....

If you don't have all these things in your conscious decision making, I would recommend you stick with single ropes for your own safety and your partner(s).

Another thing to consider with those 1/2 rope falls tolerating 2-3 falls before catastrophic failure is they are testing brand new ropes. It may be less falls tolerated with used ropes, ropes nicked up/thinned out due to use, ropes iced up due to conditions, older ropes, ropes wet from conditions, sharper edges they are pulled taut over during a fall. The 2-3 falls is under ideal "lab" situations with brand new ropes.

Twin ropes are different in that they are NOT designed to be clipped separately like half ropes using double rope technique. Hence, they are lighter, skinnier, and tolerate less force before failure. Clip twin ropes (infinity symbol) together when leading. You getting awfully close to the edge with using twins for leading as a single rope...and they stretch even more than half ropes.

One can more safely belay up followers on half or twin ropes, because such falls are much lower in force. Still, they will stretch more. Though, stretching thinner ropes over sharper edges is less well tolerated than with fatter ropes. Think force/area in your mental calculations.

It's not meant to sound demeaning, but if you are stretching beyond the limits of equipment design, you have to accept them risks of doing so...so get up to speed on the physics and material science before going outside the parameters of intended design or you may wind up being part of accident analysis that leads to others learning from your mistakes.

Sorry about the missing word.

Summary of what could be climbing’s golden rule:  Be very deliberate in what you do and why

Good post Leo Paik.

Leo Paik wrote:

Twin ropes are different in that they are designed to be clipped separately like half ropes using double rope technique. 

I think you need to fix that sentence

What's the deal with half ropes?

Yup, half ropes aren't any stretchier in a hard fall. The fact more rope may go thru a belay or rappel device on a thinner rope just means your belay method isn't consistent between rope diameters. Get a different device etc.

If we wanted rubberband like ropes, we could go back to twisted Goldline. If we wanted more rope to slip thru the belay we could go back to hip belays.

Dave K wrote:

I bought these for some easy alpine routes in Europe where I led short pitches and then belayed my 2 kids simultaneously.

Same brand, model, and diameter. They came in two colors like any half/twin set.

I used them as halfs. 

If I use them as twins, am I going to die?

They appear to be the same rope but only the green one is labeled twin. Might want to ask Sterling why that is. It is unlikely they made two identically sized/named ropes with different specs. It may be that dual certification was done after initial production and one did not get marked as such. As far as using half ropes in the twin configuration, it will result in a higher impact force during a fall, which could be critical IF the fall is close to testing limits. On moderate terrain this is unlikely. 

Greg R wrote:

They appear to be the same rope but only the green one is labeled twin. Might want to ask Sterling why that is. It is unlikely they made two identically sized/named ropes with different specs. It may be that dual certification was done after initial production and one did not get marked as such. As far as using half ropes in the twin configuration, it will result in a higher impact force during a fall, which could be critical IF the fall is close to testing limits. On moderate terrain this is unlikely. 

https://www.mountainproject.com/forum/topic/120292281/sterling-duetto-84-dual-rated-or-only-half-rope#ForumMessage-120321352

Dave, you wrote: "Yup, half ropes aren't any stretchier in a hard fall."

If I understand you are saying that a single half rope is not stretchier than a single rope, that has not been my experience. If you happen to load only one rope of a double rope pair in a fall, which is NOT recommended, my experience is that you go a good bit further. Also, the general recommendation is to retire that rope even after a single lead fall in that situation. That can be problematic if you are on a multi-pitch climb.

UIAA tests for a half rope (one of a pair of doubles) is for a 1.7 factor fall with 55kg. It must survive 5 falls to pass. With a single rope, it is a 1.7 factor fall with 80kg. It must survive 5 falls to pass. To reiterate, these brand new single half ropes are tested to survive 5 55kg falls, which is estimated to be equivalent to a single factor 2 fall with an 80kg mass. That is how they earn those UIAA "1/2" or "1" labels on the ropes.

Leo Paik wrote:

Dave, you wrote: "Yup, half ropes aren't any stretchier in a hard fall."

If I understand you are saying that a single half rope is not stretchier than a single rope, that has not been my experience. If you happen to load only one rope of a double rope pair in a fall, which is NOT recommended, my experience is that you go a good bit further. Also, the general recommendation is to retire that rope even after a single lead fall in that situation. That can be problematic if you are on a multi-pitch climb.

UIAA tests for a half rope (one of a pair of doubles) is for a 1.7 factor fall with 55kg. It must survive 5 falls to pass. With a single rope, it is a 1.7 factor fall with 80kg. It must survive 5 falls to pass. To reiterate, these brand new single half ropes are tested to survive 5 55kg falls, which is estimated to be equivalent to a single factor 2 fall with an 80kg mass. That is how they earn those UIAA "1/2" or "1" labels on the ropes.

If you are clipping alternately using double rope technique you fall on one rope (with some exceptions). The link prior showed impact force with an 80k load on the half ropes tested as similar to single ropes. Unless you know the figures for your particular rope, you don't know what the impact force is.  Retiring a half rope after one fall is silly.