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Trentw
May 15, 2007, 5:21 AM
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Apart from increasing the impact force, is there any other reason why I shouldn't use a set of double ropes as twins?
My understanding has always been No. My climbing partner become very concerned with using doubles as twins. His reasons being that the ropes weren't designed to do that, and they may run at different speeds through the runners, thus causing excessive friction and heat, thus causing rope failure. My understanding is this is only a concern when going from a double system to a twin system DURING one pitch - which is a big no no, because of the stated rope failure potential.
So here I am to clarify some points for him, and if necessary go to rope manufacturers to verify my understanding. He just won't climb with doubles as twins, until shown otherwise.
I have a few other points of clarification in regards to this issue. My understanding is that the only thing that makes a rope a "twin rope" is that it has been TESTED as a twin rope. The only other thing different with an individual twin rope is that it is thinner and may have a smaller impact force. It has no other special characteristics that differentiate it from other dynamic climbing ropes. Can anyone confirm or correct that?
I have read that using doubles as twins can double the impact force. I doubt this a lot; yes, increase the impact force, but not by double. My question is "how much then?". Apart from doing a lot of mathematics I can look at the new Beal Joker rope system. It has been tested as a twin, double, and single.
Impact force as a single rope 8,2 kN
Impact force as a twin rope 9,5 kN
Thus only a 16% increase on the impact force, which is far from double.
Now unless someone can tell me that the Beal Joker has some super special properties, it is fair to say that any rope used as a twin system will act in a SIMILAR way, thus far from being double the impact force.
Can anyone do the mathematical calculations to show what the increase in impact force will be, and/or has anyone done anymore testing on double/single ropes being used as twins, in regards to impact forces?
Cheers,
Trent
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papounet
May 15, 2007, 8:11 AM
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Trentw wrote: My understanding is this is only a concern when going from a double system to a twin system DURING one pitch - which is a big no no, because of the stated rope failure potential.
Yes indeed.
You can use double as twins. (as french guides are prone to do when leading wth 2 seconds)
If during a pitch, you split them as double, you do NOT put them together again; but nothing prevent you form having 2 slings and biners on one piece of pro.
Trentw wrote: I have read that using doubles as twins can double the impact force. I doubt this a lot; yes, increase the impact force, but not by double. My question is "how much then?". Apart from doing a lot of mathematics I can look at the new Beal Joker rope system. It has been tested as a twin, double, and single. Impact force as a single rope 8,2 kN Impact force as a twin rope 9,5 kN Thus only a 16% increase on the impact force, which is far from double.
I believe you have read using doubled singles would double the maximum force.
The test are not done with the same value, out of my head the test weight (or is is mass ?) is 80kg in single, 80kg on twins and 55kg on the single strand of a double and the maximum force is 12kN for single and twins vs. 8kN for double
http://www.uiaa.ch/...N892DynamicRopes.pdf
Why UIAA choose different setup is because they considered that never a single stand of a double had to catch the full load, once the first strand became streched the second strand would come into play.
BUT be aware that the impact force reported is the one measured on the first fall not the last one before failure.
I am tempted to believe that this value could be noticeably higher for the Joker used as a single.
but Beal says otherwise on their page http://www.bealplanet.com/...istiques&lang=us
A absurdly high (>20) ff 1,78 fall rating on the joker used in double and twins on the other hand garantees in my eyes a soft catch again and again.
The formula you are looking for is the Young modulus spring equation.you can compute how the theoritical rope would behave in double setup with 80kg. I do not have the time right now. i remeber I did it before to alleviate someone concerns (very similar to your partner). bear in mind that real ropes do not behave exactly like spring.
the best explanation is at http://www.bealplanet.com/...rce_choc&lang=us
Beal did a very interesting thing. They used the mathematical model developped by the Italian Alpin club from real tests on drop tower and real rock condition to illustrate the force on the last runner in various situations with various ropes.http://www.bealplanet.com/...ur_chute&lang=us
Low force are not only confortable for both belayer and faller; they are safer when as the protection will withstand less of a load.
to put it in a simple manner, if a double rope can withstand 110kg (as in 2*55kg) on two strands, it can surely withstand 80kg on 2 strands. so in a way a double is 37% "stronger" than a twin. yet not so "strong" that it doubles the force felt by either humans or protection.
This applies to any double.
The joker is a special case because it is burly enough even to be used a single, so it is largely exceding the safety values for double and twins usage. but is is not that burly that it can not be used as a twin
Beal Joker
Single rope – (UIAA – CE) - 1
Number of bobbins - 48
Weight / m - 53 g
Impact Force (with 80 kg) - 8.2 KN
Number of falls factor 1.77 (80 kg) - 5
Sheath Slippage - 0 mm
Extension during the first fall - 37%
Elongation with 80 kg Load - 8%
Resistance to a factor 1.77 fall over an edge of radius 0.75mm –No
Double rope – (UIAA – CE) - 1/2
Number of bobbins - 48
Weight / m - 53 g
Impact Force (with 55 kg/1 strand) - 6.0 KN
Number of falls factor 1.77 (55 kg/1 strand) - 20
Sheath Slippage - 0 mm
Extension during the first fall - 32%
Elongation with 80 kg Load - 8% / 1 strand
Resistance to a factor 1.77 fall over an edge of radius 0.75mm –Yes
Twin rope – (UIAA – CE) - oo
Number of bobbins - 48
Weight / m - 53 g
Impact Force (with 80 kg/2 strands) - 9.5 KN
Number of falls factor 1.77 (80 kg/2 strands) - >25
Sheath Slippage - 0 mm
Extension during the first fall - 29%
Elongation with 80 kg Load - 7% / 2 strands
Resistance to a factor 1.77 fall over an edge of radius 0.75mm –Yes
Trentw wrote: Now unless someone can tell me that the Beal Joker has some super special properties, it is fair to say that any rope used as a twin system will act in a SIMILAR way, thus far from being double the impact force.
I do say , yes any double rope used as a twin system will act in a SIMILAR way. but i may be wrong and I will check again
Trentw wrote: Can anyone do the mathematical calculations to show what the increase in impact force will be, and/or has anyone done anymore testing on double/single ropes being used as twins, in regards to impact forces? Cheers, Trent |
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papounet
May 15, 2007, 2:43 PM
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The Formula is
F= Mg *(1+ SQRT(1+K*(2*f/Mg)))
F = impact force in Newtons
M = falling mass in kg
g = gravitational acceleration = 9,81 ms-2
K = caracteristics of the rope
(Young’s Modulus X Section of the rope)
f = actual fall factor
Bealis kind enough to provide us with 3 force measurements for Joker rope
2 in laboratory and the Beal garanteed value. As well they say that even at thelast fall the rope does not exceed the standard maximum force
http://www.bealplanet.com/...de&lang=us#joker
Joker in single: 7,9 8,1 8,2
joker in double: 5,6 5,8 6
Joker in twin: 9,1 9,3 9,5
Modulus between 13000 and 19000 (they are 9 data points), which describe a rope between 6,8 and 8,1 kn in single strand with 80kn.
Now if we look at the formula again
F= Mg *(1+ SQRT(1+K*(2*f/Mg)))
with K between 13000 and 19000,
K*(2*f/Mg) is between 59 and 96
we can drop the +1 inside the sqrt
so F= Mg *(1+SQRT(K*(2*f/Mg)))
If instead of a single, we use double the rope, the modulus of the bundle is twice the modulus of the single rope
K' =2 K
F' = Mg* (1+SQRT(K'*(2*f/Mg)))
F' = Mg* (1 + SQRT(2*K*(2*f/Mg)))
F' = Mg* (1 + SQRT(2*K*(2*f/Mg)))
F ' = Mg* (1 + SQRT(2)*SQRT( K*(2*f/Mg)))
F'-F = Mg * (SQRT(2)-1 )
F' -F = 0,41
we could say
Doubling the rope adds between 41% of force
but remember we drop a +1 in a SQRT up
In fact, when plugging K values from 13000 to 19000 that MAY match a Joker kind of rope in the complete formula, we find that
Doubling the rope adds between 36 and 37 % of force
if we were to use a marginal rope that did between 11 and 12 kn,
Doubling the rope would add between 38 and 38,5 % of force
As a rule of thumb,
Doubling the rope = 40% more force
Why then, would the Joker be at 9,3k in twins and 8,1kn in single ?
The Joker is in single usage is far from a perfect spring: it is permanently being deformed during the elongation and ultimately breaks. the impact force in single use is much higher than the what the modulus computed from the double usage would predict. If the joker gives you 9,5 kn in double, it should give you on 7kn in single and not 8,1
On the other hand, the Joker used in a double mode, acts much more like a perfect spring.
Now how do the test of double and twins relate to each other ?
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king_rat
May 15, 2007, 3:13 PM
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I have no idea what the answern, is but was just wondering why you would want to use doubles as a twin? Just curious
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dingus
May 15, 2007, 3:54 PM
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I have used 8.1 half ropes for more than a decade for alpine and ice climbing. These are considered 'skinny' half ropes. 8.8s feel like steel cables after using these things. But by contrast they are thick compared to real twins.
I treated them as twins maybe 95% of the time, taken falls, survived pelvis intact even!
The rope sawing thing I never bought into, never observed not even once, I have very little concern over this bugaboo. I think its bullshit, start to finish.
The compromise is if you start clipping the half ropes individually you should continue to do so, to minimize any rope sawing effect due to differing rope lengths and slack. I still say bullshit but its a harmless precaution I reckon.
I really have nothing more to say about it. I won't try the math (as I don't care). I don't feel the need to repeat others' experiences, let them speak for themselves.
All I can say is I'ved used half ropes as twins for many many years with no ill effects. Less in fact... less tangles, more speed, smoother belays.
Cheers
DMT
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mkro
May 15, 2007, 4:50 PM
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I have a set of Mammut Genesis 8.5 doubles. I probably lead 65% using the twin technique and 35% using the double technique. I spent a fair amount of time reading up on doubles & twins before buying these lines and I found the Mammut rope guide to be very helpful in regards to the application for doubles (halfs) versus twins. The Mammut rope guide indicates you can use either the twin or half/double technique with half/double ropes. Download the rope guide PDF file and check out the "Half (Double) Ropes" write-up on page 13 of the Mammut rope guide per the following link: [http://www.mammut.ch/mammut/downloads.asp]
I personally have no issue using halfs/doubles as twins. I can't imagine a fall generating excessive friction and heat, thus causing rope failure. Best, Mark
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papounet
May 15, 2007, 10:53 PM
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The formula for the fall factor leads to a very simple relation, which can be graphed.
Looking at actual values, I can't help think that the value of 55kg was the single strand of a double rope was not chosen randomly.
the numbers for ropes of good performance at the time the UIAA label was conceived could well have been very close to
6,2 kN with 55kg 1 strand (maximm allowed 8kN)
10 kN with 80 kg 2 strands (maximum allowed 12kN)
which would have fit one rope of modulus 16000.
in other words; 55kg is not a magic number, it is the number that one could have found by/
1. testing an acceptable double rope in twins mode with 80kg,
2. computing for a rope of half the modulus, the equivalent weight that would give as much %safety margin vs. the standard
3. validating with a few drop tests one strand of the twin, hops wou have a standard for double
In more than a way, testing 55kg on one strand and 80 kg on two strands are tests which are very close.
YET
If ropes were springs,
Doubling up the rope AND increasing the weight from 55kg to 80kg would increase the force by 69%
using Joker values, we find that 9,3/5,8=1,6 => 60% increase
A marginal double that passes with 8Kn on 50kg one strand would most probably not pass the twins test with 80 kg two strands as it would deliver 13,5 Kn
on the contrary a marginal twin delivering 12 kN on 80kg 2 strands would deliver 7,1 kN on 55kg one strand
the general consensus is that:
double can be used as double or twins, twins only as twins.
The maths show that (under some assumptions regarding stability of rope modulus).
some double would not be certified as twins
all twins would be certifiables as doubles
The onlw difference then is abrasion and sharp edge resistance, and of course wether or not can a leader guide 2 seconds one on each strand ,
The outcome: when choosing a double, choose one with force below 7,1kN. in the beal catalogue, no double go beyond 5,8 kN =>
As a point of comparison
Beal Ice twin 7,7mm, 7,3kN(average) would probably give something like 4,6 Kn if tested as a double
Beal Ice Line 8,1 mm 4,9kN (average), would probably give something like 7,9 kN if tested as a twin
(This post was edited by papounet on May 15, 2007, 11:17 PM)
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gavinshmavin
May 16, 2007, 2:18 PM
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king_rat wrote: I have no idea what the answern, is but was just wondering why you would want to use doubles as a twin? Just curious
I tend to do it a lot on longer routes I want/need two ropes for rapping, but the climbing doesn't wander enough to merit using the doubles "as doubles." Leading on two strands of 8.1 as twins is basically just as easy as leading on a single rope - easy to clip, falls feel about the same, etc. And it's simpler for the belayer.
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Trentw
May 17, 2007, 4:44 PM
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king_rat wrote: I have no idea what the answern, is but was just wondering why you would want to use doubles as a twin? Just curious
There are a few reasons. I guess if your not familar with these systems, it may not be obvious.
My main reason is actually in response to the biggest con of double ropes. Double ropes have a steep learning curve. If I'm climbing with someone that hasn't used doubles before, especially a begginer, I would rather climb with a simple system, like singles or twins. Even if I owned a single, I may prefer to use a twin system for all its other advantages; longer raps, redundency etc.
Have a search for the pros of twins, and cons of doubles. Lots of info out there that will explain it better then I can now.
Trent.
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billcoe_
Aug 8, 2007, 3:28 PM
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I just bought a set of the Metolius Monster Ropes, these things are the lightest ropes on the market 38gm/M. Lighter than any ice Floss or twin rope.
Yet they are rated, by the Uiaa, for both Twin and Double. To me, that means that they pass the criteria for impact and elongation blah blah blah no matter which way I want to use them.
If I choose to clip alternately/individually like a double, or clip both ropes to each biner like a twin, I just figured it was fine. Fact I'm counting on it.
I'm not exactly sure what papounet is saying?
Papounet ?
Link to Metolius http://www.metoliusclimbing.com/ropes_dynamic.htm
UIAA falls: twin 16, half 6
weight: 38 g/m
sheath slippage: 0
max. impact force: twin 8.5 kN, half 5.7 kN
elongation: twin 7%, half 8%
certification: UIAA, CE, EN 892
How could a rope get certified for this unless it was acceptable practice? Perhaps YOU specific rope is not certified, and thats your partners complaint?
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paulraphael
Aug 8, 2007, 3:51 PM
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gavinshmavin wrote: king_rat wrote: I have no idea what the answern, is but was just wondering why you would want to use doubles as a twin? Just curious I tend to do it a lot on longer routes I want/need two ropes for rapping, but the climbing doesn't wander enough to merit using the doubles "as doubles." Leading on two strands of 8.1 as twins is basically just as easy as leading on a single rope - easy to clip, falls feel about the same, etc. And it's simpler for the belayer.
Exactly. It's nice to have the option to use them as twins on straightforward pitches, half ropes on wandering ones, or even as single ropes on 4th class terrain or glaciers.
And in some situations you might choose twins over a single rope purely for redundancy/chop resistance (alpine climbing in a place with lots of nasty flakes or rockfall, etc.).
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greenketch
Aug 9, 2007, 5:44 AM
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Billcoe, I agree that the versitlity is great. I undersand that there is some challenge in the switch usage. One needs to be extra careful to determine at the start of the route which way you are going to go. If twin stay that way for the full pitch. the same with double. This has to do with the differant rope lengths out from double usage and then passing through the same biner in twin style clips. IN a fall the differing lengths can lead to friction damage as one rope slides against the other.
This is only what I have been told I have not pursued it with a manufacture or lab yet though.
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flint
Aug 9, 2007, 6:15 AM
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So, I am slightly confused, I am quite a nOOb on the doubles front. I have seen a few cases were a group was using doubles technique, but they ran both ropes through the same point (biner) on their jesus nut off of the belay.
I understand the idea of the ropes causing greater friction due to one passing or moving over the other, so my question is, was the above scenario incorrect, and if it was not, can a double set up be split from a twin at any point (but obviously never put back together)?
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reverse_dyno
Aug 9, 2007, 8:03 AM
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I have an easy answer. There are three certifications.
one for half ropes
one for twin ropes
one for single ropes
Only use the rope in a way that it was certified to be used. If a rope is certified only for use as a single, than use it only in that way. If a rope is only certified as a half rope, then do not use it as a twin rope.
There are plenty of ropes currently manufactured that are certified for both twin and half. If you want to use your ropes as both twin and half, buy a rope certified for both.
Ropes are certified for a reason. Why ignore the certifications and use a rope for something that it was not certified for? It seems to me that no manufacture would tell you that it is alright to use a rope in a way that it was never certified to be used. If they did so, and it failed for some reason in that mode, the user could sue the company for recommending an unsafe practice.
If your belayer can not handle half rope belay technique, you should not be climbing with them in a situation where you would use half ropes. Are long pitches, with sharp rocks a good place to have an unexperienced belayer? If you are too lazy to use half rope technique, why are you climbing?
As a point of information: In Switzerland people always use half ropes as twins and belay using the Munch hitch. So if you do so, your half ropes are not going to suddenly break and you fall to your death.
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tradmanclimbs
Aug 9, 2007, 11:12 AM
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Every half rope i have ever bought comes with a little booklet full of cute little drawings. They all show the half rope used as a twin to be just fine. RTFM Read the fucking manuel! Pisses me off royaly when some noob who doesn't know shit other than what they read on RC.com yells at you right in the middle of the crux Are those halfs or twins? You know you are't supposed to clip both of them if they are halfs, I read it on the internet.... STFU NoooooB and quit short ropeing me or I will solo the next scary traverse and leave your Nooob ass hung out to dry
(This post was edited by tradmanclimbs on Aug 9, 2007, 12:23 PM)
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skinner
Aug 9, 2007, 1:23 PM
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papounet wrote: The joker is a special case because it is burly enough even to be used a single, so it is largely exceding the safety values for double and twins usage. but is is not that burly that it can not be used as a twin
Huh?
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papounet
Aug 27, 2007, 5:28 AM
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billcoe_ wrote: I just bought a set of the Metolius Monster Ropes, these things are the lightest ropes on the market 38gm/M. Lighter than any ice Floss or twin rope. Yet they are rated, by the Uiaa, for both Twin and Double. To me, that means that they pass the criteria for impact and elongation blah blah blah no matter which way I want to use them. If I choose to clip alternately/individually like a double, or clip both ropes to each biner like a twin, I just figured it was fine. Fact I'm counting on it. I'm not exactly sure what papounet is saying? Papounet ? Link to Metolius http://www.metoliusclimbing.com/ropes_dynamic.htm UIAA falls: twin 16, half 6 weight: 38 g/m sheath slippage: 0 max. impact force: twin 8.5 kN, half 5.7 kN elongation: twin 7%, half 8% certification: UIAA, CE, EN 892 How could a rope get certified for this unless it was acceptable practice? Perhaps YOU specific rope is not certified, and thats your partners complaint?
Dear
just saw your post (I spend a month in Australia :-) )
It is possible that my posts were not the clearest. what should i try to explain ?
1/ using 2 strand of a specific rope instead of one strand => roughly 40% more force (imagine climbing with your doubled large single, how harsh would the arrest be)
2/ from a physics model, all twins would also certified as double but it is possible that some very strong doubles would not limit the force transmitted to the climber to a value acceptable for twins certification. Luckily, I could not find a double currently sold that would belong to that category.
As I prefer robustness ropes over weight (i climb 99% on rock routes), I prefer using doubles rather than twins in all cases except ice
3/ I am perfectly confident, as many people here, that you can use double together in twin technique or separately in double technique or in one pitch starting as twins (2 strands together) then switching to double (provided that one you have split the 2 strands, you do do put them together again in the same biner).
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papounet
Aug 27, 2007, 5:48 AM
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skinner wrote: papounet wrote: The joker is a special case because it is burly enough even to be used a single, so it is largely exceding the safety values for double and twins usage. but is is not that burly that it can not be used as a twin Huh?
the UIAA tests for double and twins are not identical.
When made comparable (by using 2 strands for both),
the twins test ask for a lower limit on the force transmitted to the climber. so all ropes certified for twins also meet the double requirements. but a theoritical double on the high end of the certification limit for doubles could be beyond the twins limit, hence
In the real world
The joker values are
Joker in single: 7,9 8,1 8,2
joker in double: 5,6 5,8 6
Joker in twin: 9,1 9,3 9,5
so the ratio of the beal garanteed value vs. the maximum value acceptable for cetification for UIAA are
single 8,2/12 = ,68
double 6/8 =,75
twin 9,5/12 = ,79
If the joker was more robust (burly) it would transmit a larger force to the climber. if it was garanteed for example 7,9 kn on the double test, it would probably deliver around 12,51kn on the twin tests
It would still certify as double, as single, but not as a twins.
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