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merganzer

twin ropes

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We are comparing two systems in which the rope runs exactly the same. We are not comparing singles to half ropes in which one is clipping alternately. All things being equal- that is routing over rock, sling lengths, etc. - the twin rope setup will have more drag. It is simple physics. You have a greater ratio of surface area to volume with twins. Period.

 

Although I haven't used twins myself (although I have used half ropes), a friend of mine has and says the drag is much worse than with singles.

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I think CBS is WAY over simplyfying it.

 

It has a lot to do with the angles which the rope travels between pro and around/over objects. The rope could be in such a position as to not even come into contact with the rock and yet still have a lot of rope drag. The difference in rope drag between a twin system and a single rope set up in the identical scenario is likely to be very little.

 

I totally agree with Rodchester on this one; CBS is way off in his thinking. The more a rope runs in a straight line, the less drag in the system. The more bends or corners it takes, the greater the friction. That's why you sling pro, dude. Don't they teach that shit to you Mounties? hellno3d.gif Scary if they don't; it's fundamental.

 

I almost cracked up when i read catturdeat's description of ropedrag...what an idiot! yelrotflmao.gif

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We are comparing two systems in which the rope runs exactly the same. We are not comparing singles to half ropes in which one is clipping alternately. All things being equal- that is routing over rock, sling lengths, etc. - the twin rope setup will have more drag. It is simple physics. You have a greater ratio of surface area to volume with twins. Period.

 

Although I haven't used twins myself (although I have used half ropes), a friend of mine has and says the drag is much worse than with singles.

 

First off, you may be correct....but CLEARLY the difference betwen the two would be sooooo small, that few would ever notice it.

 

Second off, in the real world the drag cuased by the placement of gear/slings as well as the nature of the route will dictate the rope drag to such a point that any difference caused by the type of system, twin versus single (which as we all know is already almost nothing in real world terms) would be dwarfed to the point that it isn't even relevant in an academic sense.

 

Not trying to be an ass here or anything CBS, but while your point may be correct in a physics sense, it is meaningless in application.

 

wave.gif

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You guys aren't conceptual thinkers, are you?

 

Why think 'conceptually' when we can address REALITY. A half-rope system allows us to reduce rope drag over a single rope system. Period.

 

And, no CBS, as engineers/designers, Rumr and I aren't really "conceptual thinkers". rolleyes.gif

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And, no CBS, as engineers/designers, Rumr and I aren't really "conceptual thinkers". rolleyes.gif

Being an engineer does not make you smart. Here's an example of a stupid engineer. wave.gif

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And, no CBS, as engineers/designers, Rumr and I aren't really "conceptual thinkers". rolleyes.gif

Being an engineer does not make you smart. Here's an example of a stupid engineer. wave.gif

 

Smart isn't the issue, dipshit, it was dealing with concepts. Pull your head out, and reattach your 'junior shitlicker' badge.

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I HAVE actually climbed on twin ropes and I don't ever recall thinking that they caused a bunch of extra rope drag as compared to a single. Catbird may be right about the increased surface area, but then again maybe not for a couple of reasons: First, we are not talking about the total outside surface area of the ropes, but that part that rubs on the rock or ‘biner it passes through. If one of the twins is a little tighter than the other, the drag may primarily be coming from one, smaller diameter rope, with less tangential surface area rubbing on the rock or ‘biner in question. Second, I don't know how the increased flexibility of thinner ropes adds to or decreases rope drag.

 

As long as we're speculating and calling guys idiots for speculating around here, I'll point out one point of speculation on the prior page that I disagree with: the idea that if an edge is going to cut one rope it will cut both twins. I believe that has been shown NOT to be the case. About fifteen years ago I remember reading that there had never been a case of a pair of twins being cut over an edge during a fall event.

 

Twins are not a bad way to go, and for belayers who may have difficulty feeding one rope while reeling in the other, the technique is more manageable.

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About fifteen years ago I remember reading that there had never been a case of a pair of twins being cut over an edge during a fall event.

But how do we know that in the past fifteen years there hasn't been a case of twins cutting? Geek_em8.gif

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But how do we know that in the past fifteen years there hasn't been a case of twins cutting? Geek_em8.gif

 

That would change nothing about my statement. I would be VERY surprised if, during the past fifteen years, it had been found that twins were cut anywhere near as often as a single line.

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Thumbs up for half ropes. thumbs_up.gif

 

Though a set of twins would be nice to have too, for waterfall and alpine ice.

Edited by Stephen_Ramsey

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You guys aren't conceptual thinkers, are you?

 

Why think 'conceptually' when we can address REALITY. A half-rope system allows us to reduce rope drag over a single rope system. Period.

 

And, no CBS, as engineers/designers, Rumr and I aren't really "conceptual thinkers". rolleyes.gif

 

Actually the relevant factor is the ratio of the diameter of the rope over the radius of the inside rope bearing curve of the biner. Smaller ropes or bigger biners reduce this. That's why using multiple biners on a top rope anchor makes it easier.

 

Duh. rolleyes.gif

 

Sanitation engineer?

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You guys aren't conceptual thinkers, are you?

 

Why think 'conceptually' when we can address REALITY. A half-rope system allows us to reduce rope drag over a single rope system. Period.

 

And, no CBS, as engineers/designers, Rumr and I aren't really "conceptual thinkers". rolleyes.gif

 

Actually the relevant factor is the ratio of the diameter of the rope over the radius of the inside rope bearing curve of the biner. Smaller ropes or bigger biners reduce this. That's why using multiple biners on a top rope anchor makes it easier.

 

Duh. rolleyes.gif

 

Sanitation engineer?

 

I think another factor is the weight of the line. With a single there is more weight hanging and so at each bend you have the potential to develop more friction. With two lines each one weighs less and so develops less. My experience is like Matts in that I havn't noticed any difference. Sounds like a boring weekend project climb this pitch single then again with twins, tie a scale on your line and check it out. Just dont fall with that thing.

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The drag difference between a single and double should be almost nothing. Friction for ropes or belts going around something (i.e. a biner) is only really a function of the types of surfaces involved.

 

The equation relating how much more tension is on the rope your trying to pull is

T2=T1*e^(mu*beta). Where T1 and T2 are rope tensions, mu the coefficient of friction between the surfaces and beta the angle of the direction change for the ropes. So assuming the sheaths are more or less the same and the skinny ropes don't actually kink, then it shouldn't make a bit of difference. The diameter of the biners, amount of surface contact etc doesn't really make a difference, same goes for friction over rock. So the idea is to minimize the number of turns the rope takes, and it's easiest done with 1/2 ropes clipping alternate pieces. For twins and singles it won't make a difference unless you manage to kink or the twins.

 

wave.gif

Sorry, had to be engi-nerd for a moment! I'm all better now. fruit.gif

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CBS and I have been looking at and discussing the differnces between a single and a twin system, not a double. If a said double anywhere I apologize.

 

wave.gif

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People vote with their wallets and twins tend to lose out since they are used less than often than either half ropes or singles, at least on rock.

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