/ first clip with double ropes?

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argybargy - on 13 Aug 2012
I am using double ropes on ice and trad climbs. I go by the book in that I clip one rope into each piece as I climb, alternating colours.

I have some climbing partners who insist in cliping both ropes into the first piece of protection. They say it reduces the fall load on a single rope in case of a fall. Then after this continue as normal cliping alternate rope colours. I understand that this would reduce the fall factor but should we really be cliping doubles as if they were twins on this first piece?

Bulls Crack - on 13 Aug 2012
In reply to argybargy:

Rather depends where the route goes? If it wanders about having both clipped in at the start could be a real pain and the alternate thing is only really if the routes straight up as well. I've always clipped according to circumstance.
jezb1 - on 13 Aug 2012
In reply to argybargy: They're half ropes, so only clip one rope per 'draw.
argybargy - on 13 Aug 2012
In reply to jezb1: Yes, they are half ropes, and that's exactly what I do. Have you heard of other climbers, like my mates saying that you should clip both in the first draw? What problems could this cause? Maybe more rope drag? What do you think of their reasoning of less stress on one rope with a fall on the first draw?
jonny taylor on 13 Aug 2012
In reply to argybargy:
You should not do this, and I don't think you'll find anybody experienced who would tell you otherwise.

"What problems could this cause"
Potentially rope drag, defeating a main purpose of using doubles in the first place, but the most important thing is that if you have two ropes running through some but not all of the same pieces of gear then in the case of a fall you have the potential for the ropes to slide against each other under heavy load. This could genuinely generate enough heat to start melting ropes, not something you want to be involved in at all. [With twins both ropes run through EVERY piece so the same logic doesn't apply]

"less stress on one rope"
The rope is not the bit you need to worry about. (Incidentally it will probably put a *greater* peak load on your protection, which *is* something you should be slightly concerned about).

I have never come across any mention of this concept of clipping both through the first draw before. I can't really even see what the supposed logic behind it could be. Most potential arguments that could be applied to the first piece of protection would also apply to all the other pieces.
Skyfall - on 13 Aug 2012
In reply to argybargy:

As said, not re commended. Importantly it will increase the impact force on the 1st piece of gear if you do fall off. Also potential issues re rope drag, opposing forces, friction etc. Half ropes are designed for single clipping.
deepsoup - on 13 Aug 2012
In reply to argybargy:

No, imo. At best it seems a bit pointless, at worst really quite a bad idea, depending on circumstances and wotnot.

> I understand that this would reduce the fall factor but should we really be cliping doubles as if they were twins on this first piece?

Reduce the fall factor? How so?
jezb1 - on 13 Aug 2012
In reply to argybargy: No I've never heard anyone doing this before.

The problems have been highlighted above. At best it increases rope drag, at worst you've got two ropes rubbing in a fall creating heat etc....
BoulderyDave - on 13 Aug 2012
In reply to argybargy: Most half ropes are also certified as twins (check your manufacturers website). The only advantage of double clipping the first pro is it will reduce rope stretch. The disadvantage is that it will increase overall rope drag and may hasten the wear on the rope.

Having watched other people do it, I did a bit of digging around and found out the above
Cake - on 13 Aug 2012
In reply to argybargy:
If you want to you could get two different pieces of gear in at the same place and clip them seperately, although I also don't see why. As someone above put it, using two ropes is great when the route is not in a straight line, so they probably want to be seperate.
Luke Brooks - on 14 Aug 2012
In reply to argybargy:
>I go by the book in that I clip one rope into each piece as I climb, alternating colours.

Not sure which 'book' you are reading. You don't necessarily clip alternate ropes, it depends on where the route goes. Each rope should end up taking as straight a line as possible.

> I understand that this would reduce the fall factor but should we really be cliping doubles as if they were twins on this first piece?

It actually increases the load on the gear if you do this - much more of an issue than limiting the force on the rope.

Check this out for more info on double rope technique: http://www.ukclimbing.com/articles/page.php?id=2737

mike kann - on 14 Aug 2012
In reply to argybargy: 1/ it does not reduce the fall factor. Fall factor is not related to the number of ropes you clip.
2/ if you mean't it reduces the force on each strand, then, yes, it shares the load, whatever that load may be.
3/ if you meant it reduces the load on the first anchor, no this is not correct - clipping doubles as twins dramatically INCREASES impact force, thereby making the first piece MORE likely to fail, and increasing the probability of landing on the belay.

In summary, tell them they're talking shite. Clip alternately with double ropes. Also they will most likely tell you that single ropes put more impact force on your runners. This is also incorrect - UIAA ratings are very very misleading, and in reality you will get loads that are much of a muchness. In the end, the only time you should be clipping ropes twinned is if you are using twin ropes, or are very sure that the protection is strong. Even then it will give you a harsher landing.
Al Randall on 14 Aug 2012
In reply to argybargy: This is wrong and has the potential to create a situation where one rope ends up rubbing against the other. This argument was wrongly used to advise against clipping half ropes together at all but as long as you stick to one system it won't happen. I thought that the real reason for not doing this was that two 9mm ropes together were two broad for krabs at that time. With modern ropes and krabs I think it would be OK. The most important thing is to stick with the system you set off with and don't mix the two.

Al
mike kann - on 14 Aug 2012
In reply to Al Randall: Impact force is the reason not to do it. It's just unnecessary - end of. There's loads info on here - its been discussed loads of times. There is just no good reason to double clip half ropes, unless maybe you're on a bolted route and you do it from beginning to end. Even then I'd rather take a single and a pull cord for abseiling as it's less of a cluster***k...
Al Randall on 14 Aug 2012
In reply to mike kann: Why are you telling me, I know and in affect said as much.

Al
mike kann - on 14 Aug 2012
In reply to Al Randall: "I thought that the real reason for not doing this was that two 9mm ropes together were two broad for krabs at that time. With modern ropes and krabs I think it would be OK."

Maybe I misunderstood?
Al Randall on 14 Aug 2012
In reply to mike kann: Perhaps I didn't put it very well. Yes it's impact forces but years ago some people said that it was to avoid the ropes rubbing together which is patently untrue as that is what you do with twins. It was also said that the width of the combined ropes put strain on the krabs because they were not designed to take two 9mm ropes side by side. Back then many krabs narrowed very dramatically so this seemed a reasonable argument. I also went on to say that you should stick with what you start out with so I felt as though I was being lectured but I'm sure you did not mean it that way.

Al
mike kann - on 14 Aug 2012
In reply to Al Randall: Not lecturing... just felt that saying anything to do with double clipping is OK might be misleading... it's not really ok, unless you're on twins or have strong anchors, but not because of what you cited... Speaking from an engineering point of view, I'm very dubious about the claims that the broadness of the rope would snap krabs, even when the ropes were wider - it was only a 1mm either way...
mariopulquerio - on 14 Aug 2012
In reply to argybargy:

I know very experience climbers that clip both ropes in the first protection while multi-pitching. The reason for this is that if you fall off after the first clip and have only one rope clipped, it can be very difficult for the belayer to hold the rope due to the high impact factor that you have on this type of situation (i.e. close to the belay). If you clip both ropes it becames much easier for the belayer to hold a fall on the first protection.

I have never fallen on the first clip while multi-pitching, so I really cannot tell if this is true or not. Does anyone experienced a hard fall on the first protection (while multi-pitching) with only one rope clipped? What was the reaction of the belayer?
pdone on 14 Aug 2012
In reply to mariopulquerio: With the usual belay device the rope will slip through it once the rope pulls with a force greater than about 2.5kN; this limits the force on the belayer to about 2.5kN. If there are two ropes taking the fall equally then the greatest force the belayer could experience will now be doubled to about 5kN; two ropes are each pulling with a force of 2.5kN. The force on the falling leader will also be doubled.

However it is probably true that it is easier to hold two ropes than one especially if the one rope is thin but it does mean the forces will probably be increased.
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Neil Williams - on 14 Aug 2012
In reply to mariopulquerio:

"I know very experience climbers that clip both ropes in the first protection while multi-pitching. The reason for this is that if you fall off after the first clip and have only one rope clipped, it can be very difficult for the belayer to hold the rope due to the high impact factor that you have on this type of situation (i.e. close to the belay). If you clip both ropes it becames much easier for the belayer to hold a fall on the first protection."

I don't have direct experience of this situation, but this sounds like a slight twisting of the idea that you should either clip the belay when setting off or put in some protection very low down to avoid a factor 2. That seems pretty solid (a factor 1 is vastly easier to catch than a factor 2), but I'm less convinced about the both ropes bit. Surely the non-clipped rope will just be slack and therefore irrelevant, rather than causing a problem as such?

Neil
argybargy - on 18 Aug 2012
In reply to mariopulquerio: After discussing this with my climbing friends this is also their arguement. That is, it would be easier to catch a fall if both ropes are clipped. But like you say I don't have experience of this either.

They were also saying that in clipping both ropes they are trying to avoid stressing one rope in the case of a fall. From the other comments here, I see that forces are increased to the protection. So really we shouldn't be clipping two ropes into one runner.

Jonny2vests - on 18 Aug 2012
In reply to jonny taylor:
> (In reply to argybargy)
> You should not do this, and I don't think you'll find anybody experienced who would tell you otherwise.
>
> "What problems could this cause"
> Potentially rope drag, defeating a main purpose of using doubles in the first place, but the most important thing is that if you have two ropes running through some but not all of the same pieces of gear then in the case of a fall you have the potential for the ropes to slide against each other under heavy load. This could genuinely generate enough heat to start melting ropes, not something you want to be involved in at all. [With twins both ropes run through EVERY piece so the same logic doesn't apply]

I agree with the general points people are making, but if I may make one small point, starting with both clipped then diverging does not really create much rope to rope friction. Starting diverged, then double clipping is much worse in that respect.
jezb1 - on 18 Aug 2012
In reply to jonny2vests:
> (In reply to jonny taylor)
> [...]
>
> I agree with the general points people are making, but if I may make one small point, starting with both clipped then diverging does not really create much rope to rope friction. Starting diverged, then double clipping is much worse in that respect.

That depends entirely on where the first runner is surely?
Howard J - on 18 Aug 2012
In reply to mariopulquerio:
> (In reply to argybargy)
>
> I know very experience climbers that clip both ropes in the first protection while multi-pitching. The reason for this is that if you fall off after the first clip and have only one rope clipped, it can be very difficult for the belayer to hold the rope due to the high impact factor that you have on this type of situation (i.e. close to the belay). If you clip both ropes it becames much easier for the belayer to hold a fall on the first protection.
>

That argument would suggest that it is very difficult to hold falls when climbing with just a single rope, which is clearly wrong.
Trevor Langhorne on 18 Aug 2012
Too many years ago I remember the leaflet that came with my new Edelrid rope showing clipping in various scenarios. When clipping two ropes into the same runner it suggested using two quickdraws, one for each rope. The reason for this was stated as being to minimise leverage on the crab gate.

When one rope is clipped into a crab the rope rests right in the corner of the crab, next to the back bar as intended by the manufacturer (many crabs have a slight groove in the angle to ensure this happens - this is very obvious on DMM and WC crabs as shown on their website). By clipping a second rope into the same crab the intended rope location is already used so it must rest closer to the gate thus transferring more of the load away from the back bar (the strong bit) towards the nose and gate of the crab (the weak bit). In theory this weakens the crab and under extreme cirumstances (severe fall and rope vibration causing gate to flutter) the crab might fail. Whether this would ever happen in reality is a mystery to me but I see little point in clipping both ropes into the first point of protection as a matter of course. If you wish to clip both ropes into the same piece (i.e. the hard bit is just above the stance) then Edelrid suggested using a locking HMS type crab as these are designed to take the load in the middle of the crab between the back bar and gate.

As always you pay your money and make your choice.
JJL - on 18 Aug 2012
In reply to argybargy:
> What problems could this cause?

Doubles the force on the first piece of pro in the event of a fall.

I try to work out a sensible run for the ropes on the pitch and then clip accordingly. This may mean several pieces on one rope before using the other rope
Jonny2vests - on 18 Aug 2012
In reply to jezb1:
> (In reply to jonny2vests)
> [...]
>
> That depends entirely on where the first runner is surely?

Umm, not really.
Michael Gordon - on 18 Aug 2012
In reply to mike kann:
> Also they will most likely tell you that single ropes put more impact force on your runners. This is also incorrect - UIAA ratings are very very misleading, and in reality you will get loads that are much of a muchness.

Are you sure? I thought that singles generally stretch less than halfs which surely means (slightly) more force on the runners?

If I was climbing a route with marginal gear I'd much rather be climbing on halfs than a single.
jezb1 - on 18 Aug 2012
In reply to jonny2vests:
> (In reply to jezb1)
> [...]
>
> Umm, not really.

Well in my mind it does.

If the first runner is well off to one side and the route then cuts back to the other side your going to cause a big angle change in the rope line.

Anyway I'm out and it`s a moot point as it`s a silly thing to do regardless.
A Crook on 18 Aug 2012
In reply to argybargy:

Trying to remember back to a rope work workshop i did some years back with loads of newton meters and weights.

I memory serves correctly through experimental results ( not UIAA standard more to illustrate a point )The following was found. (much to the surprise of all).

Stretchy rope ; less load on gear and belayer longer distance moved

Less Stretchy ; bigger load on gear and belayer shorter distance fell

remember the gear take as a rule of thumb twice the load experienced by the climber or the belayer minus some due to friction and slippage.

So personally I use stretchy ropes (doubles) on all multi pitch routes. And nice fat singles when I go cragging.

And if the gear is so crucial it must not blow and its a wee bit iffy stick a screamer on it. and use a bouncy rope.
Jonny2vests - on 18 Aug 2012
In reply to jezb1:
> (In reply to jonny2vests)
> [...]
>
> Well in my mind it does.
>
> If the first runner is well off to one side and the route then cuts back to the other side your going to cause a big angle change in the rope line.
>
> Anyway I'm out and it`s a moot point as it`s a silly thing to do regardless.

But why would that be an issue. Rope to rope friction is negligible, no worse than rope to rock. Runner extension sounds like more of an issue there, you're scenario is hardly typical.
Al Randall on 18 Aug 2012
In reply to jonny2vests:
> (In reply to jezb1)
> [...]
>
Rope to rope friction is negligible, no worse than rope to rock.

Not sure I agree with that statement. Rope to rope friction could be high, one rope still the other moving fast and loaded with weight. Nylon against nylon is not the same as nylon against rock.

Al
Alex Slipchuk on 18 Aug 2012
In reply to argybargy: don't mean to but in! This post seems very long for a simple answer. The reason to clip only one rope for the OP's situation is that it.'s the stretch on the rope that reduces the load on the system. Clipping two ropes reduces the stretch, thus increase the load on the first and runner. Ensuring this runner doesn't fail is crucial to protecting the belayer. Simples! (Ps you'll probably find a lot of skinny winter ropes have a lot of stretch, this helps to reduce the load on ice placements). Apologies if this has been covered in the 30 OP so posts previously :)
Trevor Langhorne on 18 Aug 2012
In reply to The Big Man:

Not sure about using double rope increases the force by reducing the stretch. My rudimentary grasp of physics tells me that two shock absorbers (rope, springs or rubber bands) in parallel will share the force applied to them 50:50 (assuming two ropes of same dynamic qualities)so the overall force on the anchor remains the same. Yes each rope will stretch half as much but the total stretch is the same hence the force on the anchor is the same as with only a half rope clipped but the stretch is reduced which might be beneficial when climbing above a nasty landing.
Erstwhile on 18 Aug 2012
In reply to argybargy:

> cliping both ropes into the first piece of protection.

You are right. Bad idea. However, I admit to doing the same occassionally.
Draw your own conclusions.
Martin W on 18 Aug 2012
In reply to Trevor Langhorne:

> Yes each rope will stretch half as much but...

If you stop in half the distance (actually it's not half, but we'll let that ride) then the force causing you to decelerate is greater. Think of braking to a stop in a car from 30mph: the Highway Code says the minimum stopping distance from 30mph in good conditions is 23 metres. You can bet that you'd notice that. Now think of coming to rest from 30mph in 50 metres - much more comfortable because the deceleration, and thus the force, is less.
Jonny2vests - on 18 Aug 2012
In reply to Al Randall:

No, rope to rope friction will only be high if you did the opposite. Maybe you'll just have to trust me Al.
Alex Slipchuk on 19 Aug 2012
In reply to Trevor Langhorne: try stretching an elastic band. Then using another, double up. Compare the lack of shock absorbing (less stretch for an equal force applied) on yourself (runner)
john arran - on 19 Aug 2012
In reply to jonny2vests:

You're right that rope friction would be much more likely if you start split and then clip together and fall, but it's certainly not hard to imagine a situation in which the opposite would be the case too, particularly if the first piece was a little to one side of the line, so one rope would be stationary in the first krab, under a small sideways tension, while the other would be hurtling through it at high speed during the fall, under increasing sideways tension at the same point.

How likely this would be in practice is difficult to say, probably not very, but why accept even a small risk of buggering your ropes when you could very easily either just clip one, or clip each to a different quickdraw or krab?
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Al Randall on 19 Aug 2012
In reply to jonny2vests: Not sure what the opposite is that you are referring to. All I said was that rope to rope friction is worse than rope to rock. You can't disagree with that surely? The only other thing I have said is that you should continue as you start off, either both clipped all the way or clipped separately all the way. You should not mix and match. Why should I trust you? What makes your opinion any more valid than mine?

Al
Jonny2vests - on 19 Aug 2012
In reply to Al Randall:
> (In reply to jonny2vests) Not sure what the opposite is that you are referring to. All I said was that rope to rope friction is worse than rope to rock. You can't disagree with that surely?

Yes yes yes, but is it significantly so? I don't think so.

> What makes your opinion any more valid than mine?

Because mine is right! :-)

Jonny2vests - on 19 Aug 2012
In reply to john arran:

John, I clip both separately and I'm not advocating anything else, its just that some were saying masses of heat and friction gets generated either way you do it when actually one scenario (start separate, then clip together) is much worse than another (start together, then go seperate).
rgold - on 19 Aug 2012
A few comments on various points raised.

1. There are times when the leader might want to clip both ropes to a piece. The most usual situation is that the piece is needed as as directional to keep higher-up pieces from zippering. Also, if there are three in the party with two following simultaneously, directional pieces that keep the rope running to the seconds may have to be clipped with both ropes.

2. There is at least a potential concern about half ropes rubbing if they are both cipped to the same carabiner. The fact that twin ropes are clipped together does not disqualify this concern. The reason is that half ropes are used differently. You could fall on red without falling past the lower piece with blue clipped. In this case, blue is slack and red is running, and if they are both in the same carabiner lower down, there is some potential that one might burn the other. How likely this is in reality I do not know.

3. There is a difference between clipping two ropes to a single piece and clipping two ropes through the same carabiner. When I need two ropes in the same piece, I use separate carabiners for each rope, just in case there really is something to the rubbing scenario, and because I use small lightweight carabiners in which two ropes might create significant leverage. In clipping, I use different length slings so that the two rope-end biners can't collide and create mischief.

Clipping both half ropes to the same carabiner can have other unfortunate consequences. If the ropes separate either above or below the common carabiner, the resulting lateral forces at the common carabiner will rotate it into a cross-loaded position (unless there are rubber keepers) and will lift the carabiner, possibly thereby also lifting the associated nut.

4. Clipping both ropes to the first piece on a multipitch route in order to improve the belayer's grip is something I hadn't thought about. Some of the modern thin half ropes are going to be super hard to hang onto in a high fall-factor fall, because, as I argued in another thread, belay devices generally do not supply enough friction for such extreme events. The perceived need to clip both ropes to increase gripping ability is another piece of evidence for that argument. Of course, the real problem is inadequate belay devices, exacerbated by the fact that belayers often do not wear gloves.

As mentioned in Item 3, the two ropes should be clipped to separate different-length quick draws. If the first piece is actually a part of the belay anchor, then the belayer can unclip one of the two ropes once the leader has placed further protection.

5. Unless I've missed something, the posts on the higher loads for two ropes clipped to the same piece are missing the critical physics point, which is that the energy absorbed by stretching the rope is proportional to the square of the stretch. This means that each of the two doubly-clipped strands will stretch approximately 70% of the singly-stretched strand (where 70% approximates 1/sqrt{2} ). Since strand tension is approximately proportional to the stretch, the two strand tensions add up to 140% of the single strand tension and so the anchor in the double-clipped case gets a load approximately 40% higher than if only one strand was involved.
Trevor Langhorne on 19 Aug 2012
In reply to argybargy:

48 posts, 48 different answers! Have emailed the manufacturers to ask for a definitive answer. Will post it when I get a reply.

mike kann - on 19 Aug 2012
In reply to Michael Gordon: Yep, I'm sure. UIAA tests are for different weights and therefore totally unrepresentative of forces transmitted. Halves are tested with a 50kg mass rather than 80, and when you load a half in the same way as a single you will obviously see much higher impact forces.
In reply to mike kann:
> (In reply to Michael Gordon) Yep, I'm sure. UIAA tests are for different weights and therefore totally unrepresentative of forces transmitted. Halves are tested with a 50kg mass rather than 80, and when you load a half in the same way as a single you will obviously see much higher impact forces.

Lower?


Chris
mike kann - on 19 Aug 2012
In reply to Trevor Langhorne:
> (In reply to The Big Man)
>
> Not sure about using double rope increases the force by reducing the stretch. My rudimentary grasp of physics tells me that two shock absorbers (rope, springs or rubber bands) in parallel will share the force applied to them 50:50 (assuming two ropes of same dynamic qualities)so the overall force on the anchor remains the same. Yes each rope will stretch half as much but the total stretch is the same hence the force on the anchor is the same as with only a half rope clipped but the stretch is reduced which might be beneficial when climbing above a nasty landing.

Yes - your physics is rudimentary ;) Think of the ropes as springs. If you put two springs in parallel and pull on them you will find it twice as difficult as you found it to extend one of them. The same applies to ropes and the force transmitted to the top piece. Another way to think of it is that force is a factor of energy and time. As each rope extends, it absorbs energy. The shorter the amount of time the rope is extending, the more energy is transmitted, and as two ropes will halve the time it takes for you to stop, more energy is dissipated at the anchor.

Also your analogy that thin rope is stretchy and thick rope isn't, is completely bogus. It entirely depends on the construction of the rope - you can get ropes which are more stretchy and thick than thin ropes. Look at rope stats if you want confirmation.
mike kann - on 19 Aug 2012
In reply to Chris Craggs: No, the weight of the climber remains the same whether you are using a half rope or single rope. You still have to stop the same amount of energy. UIAA tests are totally misleading in this respect as the test is representative of 2 ropes sharing the force rather than a single strand taking the total impact. If you look at for example triple rated ropes, you will see that for example the Beal Joker exhibits very similar impact forces in the single rope test to thicker single ropes, but also similar impact forces to half ropes in the half rope tests. http://bealplanet.com/sport/anglais/corde-joker.php
In reply to mike kann:

Sorry, I thought you meant a single rope vs one half rope, as in the OP.


Chris
mike kann - on 19 Aug 2012
In reply to Chris Craggs: I do though. If you load a half rope in the same way as a single rope, you will see a much higher impact value than stated on the UIAA test result. People have this idea that half ropes transmit less force - it's not necessarily the case. Yes if you clip the ropes to two pieces in parallel as the pieces share the load, but if you are clipped to one piece and the other rope shares none of the force you effectively have a single rope loading scenario, in which case you will see a very similar force result to a single rope. If you look at the Joker, you have direct values to compare. The worst scenario is twin clipping when the force transmited is much higher. Half rope loading represents a 5/8th 3/8ths split loading situation, so the UIAA value is much lower than you'd see loaded singly, which is represented by the single loading value.
In reply to mike kann:

I had always thought a large part of the point of 'halfs' was being thin and stretchy they were used on routes (e.g. ice?) where the gear was suspect, so as to reduce the peak force on said gear.

And equally that could be complete tosh!

Chris
mike kann - on 19 Aug 2012
In reply to Chris Craggs: It is I'm afraid tosh ;) There is some truth to it but not as much as people think. I've been trying to pursuade DMM to do some definitive tests so we really know what's what but no results so far... thickness as I said above does not corolate to stretchiness. Case in point, Joker shows impact force of 8.2kN on a 9.1mm cord, whilst the top gun at 10.5 shows 7.4 kN. The stretch is totally defined by rope construction - the amount of twist in the core is responsible for reducing the impact, the more twist there is the lower the impact as it has more potential to stretch. Obviously the greater the diameter, the more space you have to put twists inm and so often you find bigger diameters have lower impact forces...
Simon Caldwell - on 19 Aug 2012
In reply to Chris Craggs:
And I always thought that as the maximum force came on one rope, due to stretch the other rope would now be starting to take force too, hence even if the first failed, the second would have much less force to absorb. Which is why I always try to alternate rather than slavishly keep one rope of left and one for right.

It is almost certain that I'm wrong :-)
mike kann - on 19 Aug 2012
In reply to Toreador: No, you're not. That is how they are meant to be used. My point is that if you run it out on a half rope, or in the OPs scenario, are climbing above the belay and only clipped to one rope, the impact force seen will be very similar to the impact force seen if you did the same on a single rope. If you twin clip a double rope, it will increase the force massively.
rgold - on 20 Aug 2012
In reply to mike kann:
> (In reply to Trevor Langhorne)
> [...]
>
> Think of the ropes as springs. If you put two springs in parallel and pull on them you will find it twice as difficult as you found it to extend one of them. The same applies to ropes and the force transmitted to the top piece...
>

If you are saying that the top piece gets double the load with two strands that it would have felt with one strand, then you are wrong. I explained a few posts above that the load on the top piece from two strands is about 40% higher (not 100% higher) than the load from a single strand stopping the same fall-factor fall.

>...Another way to think of it is that force is a factor of energy and time. As each rope extends, it absorbs energy. The shorter the amount of time the rope is extending, the more energy is transmitted.
>

No, the tension in a climbing rope (modeled as a spring) is a factor of the relative amount of stretch only, and the energy absorbed by the rope (integrate the tension) is proportional to the square of the relative amount of stretch. It doesn't matter how fast or slow the stretching is.



Jelly Mould Surfer on 20 Aug 2012
In reply to argybargy: I recently towed out a Skoda Octavia Estate, stuck up to it's axils in a field, out with a length of 25 year old 9mm. Although effectively only a static load - it shows you shouldn't have to worry about the rope being able to take the load.
jimtitt - on 20 Aug 2012
In reply to mike kann:
> (In reply to Toreador) No, you're not. That is how they are meant to be used. My point is that if you run it out on a half rope, or in the OPs scenario, are climbing above the belay and only clipped to one rope, the impact force seen will be very similar to the impact force seen if you did the same on a single rope. If you twin clip a double rope, it will increase the force massively.

Well according to the figures for the Beal Joker single strand against twin the force increases 15% which is hardly massive.
mike kann - on 20 Aug 2012
In reply to rgold: http://en.wikipedia.org/wiki/Impulse_(physics)

That depends on which theory you use to look at it. If you consider impulse, then yes, time is related to the force. Ok it may not be double - I was tired, but the sentiment is the same - put two springs in parallel and it's harder to extend rather than easier.
mike kann - on 20 Aug 2012
In reply to jimtitt: 15% could be the difference between it failing and it not though, especially if the placements not very good and you take into account pulley effect.
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rgold - on 20 Aug 2012
In reply to mike kann:
> (In reply to rgold)
>
> That depends on which theory you use to look at it. If you consider impulse, then yes, time is related to the force.
>

You never mentioned impulse. You said, "Another way to think of it is that force is a factor of energy and time. As each rope extends, it absorbs energy. The shorter the amount of time the rope is extending, the more energy is transmitted."

You could make the your first sentence true by replacing "force" by "impulse," but the second sentence, which is presumably deduced from the first sentence, remains false. Energy absorbtion (not "transmission") by a rope, if modeled as a spring, depends only on the maximum extension and hence on the maximum tension and not on the time it took to achieve that extension and so not on impulse.

If you are willing to leave the realm of "rudimentary physics," meaning abandoning the simplest rope model, then you might yet stand a chance of being correct. The following paper by Bedgogni and Manes, http://www.sciencedirect.com/science/article/pii/S1877705811007417, proposes a rope model that employs not only the strain but also the strain rate, bringing time and so, implicitly, the concept of impulse into play.

mike kann - on 20 Aug 2012
In reply to rgold: Hence why I said another way to think of it. I understand that you don't describe a spring action using impulse. They are separate models which bring you to a similar conclusion. And lets be fair here - the guys said his understanding of it was x which was not correct - I retorted with a smiley and pointed out what happens. Momentum and impulse are all to do with what we are talking about - I may not have explained it well and made mistakes but that was partly because I was mortally hungover...
The Biochemist on 21 Aug 2012
In reply to argybargy:

On a separate safety note, about two months ago, I was watching a friend go up the Left Unconquerable, and against my advice put both half ropes through the first bit of gear. I admit, the route is pretty straight up (however as my next point will demonstrate, that is irrelevant).

He then put in a piece on the right and a piece on the left and clipped as you would do half ropes, thus causing the left rope to have an angle at the first clip.

He then fell about a metre above those pieces of gear, and the angle of the left rope pulled the first piece out when it was loaded sideways!

Luckily his upper pieces held but has no one else come across this potential problem? Half ropes are designed to take a fall individually - so why on earth do it?
Al Randall on 21 Aug 2012
In reply to Alissabray: If I'm understanding you correctly that was more to do with the angle of the rope through the gear rather than the fact that both ropes were clipped into the first piece. The same would probably have happened if he had only clipped the one rope in the same way. Unless of course the right hand runner was preventing the first runner from laying naturally to the left. Hope that makes sense.

Al
In reply to Alissabray:
>
> On a separate safety note, about two months ago, I was watching a friend go up the Left Unconquerable, and against my advice put both half ropes through the first bit of gear. I admit, the route is pretty straight up (however as my next point will demonstrate, that is irrelevant).
>
> He then put in a piece on the right and a piece on the left and clipped as you would do half ropes, thus causing the left rope to have an angle at the first clip.
>
> He then fell about a metre above those pieces of gear, and the angle of the left rope pulled the first piece out when it was loaded sideways!
>
> Luckily his upper pieces held but has no one else come across this potential problem? Half ropes are designed to take a fall individually - so why on earth do it?

Sounds like maybe you were standing too far out from the rock?


Chris
Michael Gordon - on 21 Aug 2012
In reply to Al Randall:
> (In reply to Alissabray) If I'm understanding you correctly that was more to do with the angle of the rope through the gear rather than the fact that both ropes were clipped into the first piece.
>

Agreed. Perhaps the runner wasn't extended enough? (admittedly you often don't want to extend too much on the first bit of gear)
The Biochemist on 22 Aug 2012
In reply to Al Randall:

No no, The first bit was below the right piece, not the left, so I would have gone through the first bit with the right rope only.

And no Chris, I wasn't belaying I was just watching. The angle was created by the rope going vertically up to the first piece then pulled off to the left by the higher piece being so far left.
Al Randall on 22 Aug 2012
In reply to Alissabray:
> (In reply to Al Randall)
>
> No no, The first bit was below the right piece, not the left, so I would have gone through the first bit with the right rope only.
>
So would I but my reasoning is still valid.

Al

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