I know the obvious answer is "because they are" but I'm struggling to get my head around it.
A rope rated as a singe rope can be used as a sole rope to climb on, clipped to each protection point.
A half rope should be used as a pair, with rope drag being reduced by using one for left trending pro and one for right.
Given that if a fall takes place on half ropes, the chances are that only one rope will catch the fall at the next lowest clipped point, why isn't a half rope also usable as a single? Surely under the conditions that require a rope to be rated, there is no difference in loading between the two?
I'm sure there's an obvious answer to this, I just don't know it.
In reply to adamkitson: I believe it is just a durability/standards testing thing. Yes a half rope will catch a lead fall (in the incredibly unlikely event it doesn't you should be caught be the other rope on the next bit of gear), but it will catch fewer falls.
In terms of testing, a single rope might take around 10 of the standardized falls used by the UIAA etc (a bit under fall factor 2 with an 80kg mass?) before failing. By comparison, a half rope will only take a few falls before failing. Since it is difficult to compare small numbers meaningfully, they use a lower mass (55kg) and then the ropes survive a larger number of falls. It is then easier to compare a rope that survives say 12 falls to a rope that survives 14 falls at 55kg; both ropes might only catch 2 falls at 80kg and you would not see the difference in durability.
PS numbers are approximate for the sake of argument!
So they genuinely are a considerably weaker rope then? Should they be replaced if they take a fall?
Still, doesn't answer the point about why two are needed. If "half" rope simply means its thinner and weaker, surely it's still just a thinner and weaker single rope? Why do manufacturers say two are needed? From a safety view rather than a rope drag perspective.
Interesting about why they are called half ropes, although probably the same reason as "twin" ropes are also called half ropes, and trad type half ropes are also called "double" ropes. Such named because two are required.
So do people in general log the number of falls their ropes take and replace when the magic number is hit?
Also, do ropes, single or half, show serious signs of failing before they break? I ask, as a rope being able to take 11 falls..... I get through that number in one evening at the wall! Many of them decent falls from above the draws. Had my current sport rope over a year and it is still looking great! I get that a fall factor 2 is rarely put on a rope in practical climbing, but it must be cumulative!
In reply to adamkitson: To expand on Jim's answer (quoting from some UIAA documents):
The idea behind this [multiple-drop test standards] is rooted in the history of the UIAA Safety Commission: a reasonably high number of falls must be achieved, in order to be able to differentiate between two ropes (or between two different stages of wear in a given rope), in other words to provide a result that may approach a decent measurement of the rope’s performance. Indeed if, say, the resistance to a single fall ... were required as standard, it wouldn’t be possible to appreciate the difference between a rope which is just able to hold one fall (result : 1) and a rope which is just a little weaker (result : 0).
The same principle lies behind the classical DODERO test, in particular in the case of half-ropes: in the Plenary Session of the UIAA SAFCOMM held in Venice, 1979, Mr Lacoste of the Laboratoire de l’Armée, Toulouse, ... proposed a test for half-ropes based on 5 falls of a 55 kg mass: a long set of experiments had been carried out to find a multi-drop test which could, roughly, be considered as equivalent to 1 fall of an 80 kg mass. Resistance to this fall was indeed considered as the minimum requirement for a rope that could have been loaded by the fall of the leader on a single strand.
So what about the newer "triple rated" ropes?
Presumably if a 9.1mm rope is good enough to be rated as a "Single" the other ratings are pretty much obsolete?
Is there a situation where a 9.1mm "single rated" rope would NOT be acceptable as one of a pair of twin or half ropes?
or is this again just a matter of completing different testing / paperwork for the 3 different standards (e.g. the difference in sharp edge resistance of a Beal Joker when used as a single as opposed to a twin).
For someone like me who's weight fluctuates around the 58-60KG mark, a half-rope is *almost* a single rope. I have used it as such too.
I think the half ropes/single ropes terminology is confusing for beginners though. With singles getting thinner all the time, I imagine eventually we will just have 'twin ropes' and 'ropes'. Twins, as useful as they are, are quite a niche product in the UK and I haven't met many people regularly using them in fairness.
> Is there a situation where a 9.1mm "single rated" rope would NOT be acceptable as one of a pair of twin or half ropes?
In half-rope technique we are using the half-rope as a single rope i.e. that only one of the two strands is clipped into each piece of pro with one key different. The falls taken onto that single strand of rope are often shared by either alternate falls onto either of the two ropes or by falling sufficiently far where the secondary rope is engaged, therefore distributing the load between the two ropes. This justifies the lower strength rating of the half over a single.
A twin rope is tested to the same specification as a single when used as a pair. A single strand would not meet the requirements of the standard. By using two single ropes as a twin you have now the equivalent of four twin-rope strands catching the fall. As your weight is now distributed between four strands rather than two, the ropes will elongate less in a fall. The elongation is what would dissipate some of the energy and without this, the peak load onto the gear would increase. This increase in impact force could cause gear to fail or your back to fail. I believe the impact force isn't doubled but increases by about 40% or thereabouts by using a second single as a twin.
In summary, don't use singles as twins.
Disclaimer: not a mathematician of physicist. Could be wrong.
Not suggesting you do, but people do use half ropes as you would a single, and a single as you would doubles. The first should involve considering the risks (safety of going faster and lighter vs the danger of your single strand of half rope cutting).
A lot of the skinnier singles are triple rated now days, and often doubles can be twin rated too.
As everyone said, half and single ropes have to meet different UIAA standards and go through different sets of tests. That's all there is to it really. More info on UIAA's website, though specifications and paperwork are not for free.
On a side note, for rock climbing I use a pair of 8.6 mm Cobra II Unicore half ropes. The new Beal Opera is only 8.5 mm and it's triple rated as single, half and twin. It was presented at Outdoor 2014... how does that sound...
I think psychologically I would struggle to regularly climb on an 8.5 mm rope used as single, but the fact that the technology to meet UIAA single/half/twin rope standards at 8.5 mm exists, is quite impressive imo. I think it's fairly obvious where the industry is going...
Many years ago I met a rep from Edelrid in an alpine hut. This was probably about 1978 or there abouts. He said that they could produce much thinner ropes even back then that were easily strong enough but were reluctant to do so because a) the physcological affect of using such thin ropes could stop them selling b) handling could be problematical.
I certainly find my "skinny" twins are more prone to getting in a tangle. As far as I can recall the issue with using doubles as twins was more to do with the design of the krabs and the width of two ropes which in those days tended to be 9mm and, it was rumoured, put a force on the krabs that they were not designed to take.
> were reluctant to do so because a) the physcological affect of using such thin ropes could stop them selling b) handling could be problematical.
and probably c) that thinner ropes, even if passing the standard tests in laboratory conditions, had less redundant strength to cope with rough and sharp rock and general wear in normal use.
> As far as I can recall the issue with using doubles as twins was more to do with the design of the krabs and the width of two ropes which in those days tended to be 9mm and, it was rumoured, put a force on the krabs that they were not designed to take.
In my 17 years in the Outdoor trade, I frequently asked karabiner manufacturers about using two ropes in a krab.
I never got a clear answer.
Krabs are usually tested between two 12mm bars in the main axis tensile test machine. ( I recall )
In reply to adamkitson: People generally don't log falls not their ropes. You will find they will however check for damage, which may require the rope to be retired. Or, the more frequent cause for retiring a rope is they become like plastic (instead of elastic), and therefore falling on them becomes uncomfortable because of the lack of stretch and they don't handle as well as they used to (become wiry and kinky).
Ropes don't just snap - not even old well used ones, unless of course they are damaged (not just some fluffing of the sheath).
A good climber knows their rope, and generally what condition it's in and how long it has to go before they'd consider buying a new one - this doesn't necessarily correspond with what's written on the packaging.
One of my half ropes (approx 6 years old) has a bit of fluffing on one end, it's been there for about 4 years. I check it every time I use the rope, it's not got any bigger, and is still very much on the surface. I've taken falls on this rope and will continue to use it.
My single rope however is completely shot and due replacement, I've used it recently at the wall, it has no nicks or fluffing etc but is becoming plasticy to handle and falls not so comfortable. I probably won't use it again, although it's by no means in a dangerous state, it's just not nice to use.
You generally know you need a new rope anyway when you start eyeing up other climbers ropes thinking; 'ooh that's a nice new slinky shiny rope'!
> In my 17 years in the Outdoor trade, I frequently asked karabiner manufacturers about using two ropes in a krab.
> I never got a clear answer.
Always thought the bigger problem was the reduced stretch, like if you put a bunch of rubber bands together they don't stretch as far as one on it's own. If you put two ropes together (that aren't designed as twins) then they'll not stretch as much and therefore wont absorb as much energy, increasing the load on your gear and increasing the chance it'll rip.
> If you put two ropes together (that aren't designed as twins) then they'll not stretch as much and therefore wont absorb as much energy
if they don't absorb the energy of the fall, they break! And it's already been established that non-compromised ropes don't break.
The energy of the fall comes from the potential energy released by the mass of the climber descending under the influence of gravity. For a given climber falling a given distance, the energy is the same. (It's true that skinnier ropes stretch more, so the total distance the climber descends will be greater, but the stretch should be relatively insignificant cf the fall distance, so you can effectively ignore its contribution to the energy of the fall. Although it is catered for in the classic fall arrest equation.)
The reason that less stretch is a bad thing is that the fall is arrested over a shorter distance and over less time. That's what makes the peak force higher, not some hand-wavy idea that the ropes absorb less energy. The energy is there to be absorbed: it's how the rope absorbs it that makes the difference.
> increasing the load on your gear and increasing the chance it'll rip.
Also increasing the load on the climber, increasing the risk they will be injured by the fall arrest itself. On routes with bolts for pro, this is arguably a more serious risk than the gear failing.
[I should perhaps explain that a pet hate of mine is the incorrect use of terms like "force" and "energy", which have specific meanings in discussions about physics. At least when people use "energy" in the context of crystal healing or whatever, you know that they're talking b*ll*cks from the outset so it doesn't really make any difference if they misuse a technical term. Stick "quantum" in there as well if you need further proof that they're selling expensive snake oil…]