/ Clipping both half ropes into one bit of gear...
Clipping both ropes doubles the stiffness of the system and so more force is required to stretch the ropes and this force is supported by your gear and is transferred to your body when you stop falling. Clipping alternately also has the advantage that your belayer can always watch you on one of the ropes.
Also, if you place a bit of high gear, you only need to pull up one rope to clip it, meaning should you fall with rope out before it's clipped, you've only got 2 x run out distance (+ rope stretch) from your last gear placement on the other rope.
> Also, if you place a bit of high gear, you only need to pull up one rope to clip it, meaning should you fall with rope out before it's clipped, you've only got 2 x run out distance (+ rope stretch) from your last gear placement on the other rope.
You could clip both, just one at a time!
This is also seen a lot on the "Odyssey" film (Pearson, Auer, Findlay, Ciavaldini), they are trad climbing with two ropes and nearly always clipping both into the gear. This went without comment on UKC as far as I could tell.
I nearly always clip alternately. I like the fact that slack is only being paid out on one rope as clip the other, if for no better reason! If length of fall is concern at any point I'll try to place two pieces of gear near the same point and a rope in each which significantly increases safety margin.
I'm not convinced about the significant danger of gear ripping argument, though. Its very rare in my experience that well placed gear well extende just 'rips'
It only doubles the stiffness if the tension in both ropes is equal or close to it, in reality for a variety of reasons one usually ends up significantly tighter than the other in this scenario.
There are some other down sides to it like the ropes rubbing together in the krab and a small increase in the bending load potentially applied to the krab but over all it's not something I'd lose any sleep over. Nor is it something I tend to do since it adds nothing and increases potential fall length while clipping (vs pulling up alternate ropes), something that can be important if pumped or on fragile rock close to the floor or a ledge.
just to throw more confusion and mystery into the mix, what would you do if your using ropes that are rated as both halfs and twins?
I dont use halfs or twins but just curious
Any chance they were using twins, not halves?
In answer to the question-
Taken from another forum;
"In response to a specific query about this, Mammmut had this to say...
"you had a question on your Mammut rope Phoenix 8mm and whether it can be used in twin and half rope technique in one single pitch. This is the case, you can always clip the two rope strands as twins, then split them as doubles, join again etc. This is exactly the advantage of half ropes compared to twin ropes where you always need to clip both ropes."
Hope this helps you,
best regards from Switzerland,
Productmanager Climbing Equipment
Mammut Sports Group AG, Birren 5, CH-5703 Seon"
"here's what Mammut has to say about the subject in our rope booklet: "...here you have the choice between twin rope technique, where both ropes run parallel through the protection and half rope technique, where the «left» and «right» ropes run separately through different protection points...". (incidentally that is available here, there's some good info buried within... http://www.mammut.ch/images/Ma... ) Speaking only for Mammut, we generally don't certify our ropes to more than one standard because there is a very real concern that people make assumptions about a rope based on the fact that it is marketed differently, that often don’t really hold true. As an example, our Serenity 8.9mm single rope was initially introduced with both single and half rope specs and many people assumed that it was “more durable” than a thinner half rope, when the reality is that it was far less durable than our thinner Genesis 8.5mm rope.
In general we would rather steer people into using their ropes in the manner that will result in the greatest degree of utility for most people, which is why we have shied away from dual certifications like this. It isn't right or wrong, but my sincere belief is that more people wind up with a rope that better suits their needs as a result. Hopefully that adds a bit of perspective, but please fire away if it raises still other questions."
> Clipping both ropes doubles the stiffness of the system......
Hardly, the impact force is only increased by about 10% to 20%. You can see this by either working through the standard model or by looking at ropes which are rated for single and twin use:-
Tendon Master single 8.7kN twin 9.6kN
Mammut Revelation single 8.7kN twin 10.1kN
Beal Joker single 8.2kN twin 9.3kN
Since in real like you will never get the lengths exactly the same it wouldn´t matter anyway.
> Any chance they were using twins, not halves?
A lot may depend on your ropes? My new nasty Tendon half ropes are also rated as twin ropes, and therefore designed to be used as one. I guess older chunkier half ropes with skinny modern krabs (eg. Nano23's) may be an issue; but that's more an issue of mis-matched kit. I guess if you're worried about the force being put onto a bit of pro you could utilise a screamer?
As said already it can be difficult to change between clipping both or just one rope into gear. In norway I noticed the other pair on the trip having twisted ropes due to this. I could see this being dangerous if using passive pro which may risk being lifted out? The rope drag may also reduce the impact of rope stretch and therefore put even more force onto the loaded piece of pro.
> Hardly, the impact force is only increased by about 10% to 20%. You can see this by either working through the standard model or by looking at ropes which are rated for single and twin use:-
> Tendon Master single 8.7kN twin 9.6kN
He said stiffness, not impact force. The two are not the same (or even proportional).
> Clipping both ropes doubles the stiffness of the system and so more force is required to stretch the ropes and this force is supported by your gear and is transferred to your body when you stop falling.
I'm not sure that makes sense. What is the "stiffness of the system" and why would it double because two ropes are through a crab instead of each separately? I've fallen a few times on both ways and have never noticed a difference in the feeling of how the force is "transferred" to my body.
It works fine with all ropes, even chunky ones, mostly because it's nearly impossible to get the rope lengths and tensions equal so one always does the majority of the work.
Two fat ropes in a tiny krab isn't ideal since one ends up running well out from the spine, often over an area of reduced radius (modern forged krabs tend to feature thin bodies carrying radiused rope bearing areas) and imposing bending loads but in reality it'll cope fine unless you're doing something really out of the ordinary.
The main issue is it's basically pointless unless you're worried about decking on stretch or cutting a rope away from the part of the route where they run together.
Stiffness is the extent to which the rope resists stretching in response to an applied force. Stiffness depends on the elastic modulus of the rope (an intrinsic property), the cross sectional area (which is why the stiffness doubles), and the length of rope (why we deal with fall factors rather than fall lengths).
Intuitively it is obvious that if you have to stretch more rope fibres, then the force required to produce the same extension will be higher. Therefore, a higher stiffness will produce a higher peak impact force for the same fall. This is mitigated to some extent by the fact that the higher force will produce more stretch in the rope.
If ropes worked as a simple spring but they don´t.
The stiffness is the spring constant* of the rope two ropes loaded with the same force will extend half as much as one strand. If you are clipping alternately or left/right you are going to be caught on one or other rope mainly.
> I've fallen a few times on both ways and have never noticed a difference in the feeling of how the force is "transferred" to my body.
I don't suppose half of the things that get debated to death on here make much difference, but I guess if you fell onto a static rope it would rattle your spine a bit how little shock absorption one can get away with depends but the ropes are designed to be used in a certain way.
*assuming hookien behaviour as a rough approximation
...which is to say that all the correct approaches and all the physics fallacies are on full display, but I agree there is surely no need to duplicate all that again.
In the real world, it seems clear that there isn't going to be all that much difference in the total load to the gear, if for no other reason that the strands aren't going to be exactly the same length anyway.
A potential source of concern with todays tiny superlight carabiners is that clipping two strands may load the biner well away from the spine, in which case you can't expect to get the rated strength of the biner.
There can be problems with alternate clipping of both ropes and just one rope at a time. For example, if two ropes running in separated parallel lines are clipped to a single piece and then a fall occurs, the tension from the separated strands will lift the piece to which both strands have been clipped, possibly extracting it if it is a nut. (Yes, I've seen this happen...)
Personally, I never clip both strands of half ropes to the same biner. When the line goes straight up I just alternate. On the very rare occasions when I clip both strands to one piece, I usually do so with slings of different lengths, so that the fall is caught on only one of the strands.
I've never understood why people do this - what is the worry? That one rope on its own is going to snap?
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