The Half Rope Puzzle

[JoshK]

[fleblebleb]

on the kind of ground that you are talking about I feel pretty safe doing this

 

My thoughts exactly.

[Cpt.Caveman]

i got the stratos 9 mil too. Good rope. Drop tested over sharp angles\edges. Read the edgeproof test. I think it's been known to be a better rope for this reason.

 

http://www.edelweiss-ropes.com/anglais/edgeproofed.html

 

Edelweiss “Edge proofed” ropes are tested to a factor 2 fall with the 80 kg massacross, not a rounded bar, but over a sharp edge only 0.75 mm radius. Traditional ropes fail this test but the Edelweiss “Edge proofed” ropes withstand it.

[COL._Von_Spanker]

Where in the greater seattle area can you get the edelweiss stratos?

[Cpt.Caveman]

http://www.promountainsports.com

 

[COL._Von_Spanker]

Of course. I shouldn't have even asked. Pricey but well worth it ay?

[mattp]

At nearly twice the price of any other 9mm, they are clearly TWICE as good. The rating for an edge over a hold is, as Cavey noted, unique. Also, they have a stiff handle to them, which I kind of like, and Edelweiss ropes are just plain good ropes anyway. But they ARE boingy.

[COL._Von_Spanker]

Is that a play on my wine rationale Mr Perkins? (or are they really twice as good). The way I see it is don't skimp on ropes.

[Cpt.Caveman]

I agree with Matt's comments. The best rope I own and the most durable. I chopped about 6 feet off mine by swingin my axe into it but otherwise no complaints. Cant complain about user error chopping a rope.

[mattp]

I DO think they are worth the price. But yes, a play on your words was attempted.

[COL._Von_Spanker]

You are quite the cunning linguist.

[fleblebleb]

Boingy?

 

You didn't drop back into wine-speak for a moment there did you?

[mattp]

No. The term is straight out of Edelweiss' technical manuals. You can do your own field test and duplicate their results if you try to jumar up one or if you rappel to the very end of the rope, let it slide through your braking device, and let go.

[COL._Von_Spanker]

I was schrund climbing toproped with 1 icefloss and I fell and it stretched roughly 5 feet. Boingy.

[Ross]

>good info Ross and Matt and Cpt. although Ross might have shared it a bit differently...

 

Talk about spray...

 

Tons of people, including me, thought this about doubles:

if you use them as doubles -- clipping even just the most recent two pieces alternately -- the second rope will share the load from a fall.

 

That's not true, except for falls past the anchor. Try it on paper or with a gumby doll and string or whatever. The backup rope would face exactly the same force or more as the first -- it doesn't "share" the load at all.

 

So I wanted to know how they could get away with being thinner when they're facing the same falls as singles.

 

Sure, it's good to have a backup. Sure, most rope failures come from being cut. That matters to us as climbers, and so do techniques that reduce drag and weight, but what I'm asking about is diameter and strength standards for singles vs halfs. The UIAA has an edge test, and while there's demand for it to be more popular, it isn't used in certification yet. Even the Edelweiss ropes mentioned above get their excellent cut resistance from superior fibers, not sheer thickness.

 

The question is, why is there a different standard in strength alone if they don't share the load from a fall? They really don't, when used as doubles, except in falls below the anchor.

 

The UIAA test was mysterious, too, using a factor 1.78 fall with only 55 kg. Did you know before this thread that a double CAN'T face that factor 1.78 fall, ever? I didn't. They're really simulating a factor 1.2 with 80Kg.

 

Now I see why: doubles -- used as doubles and clipped alternately even just twice in a row-- take the load alone for all falls except those below the anchor, which they share.

 

Other people posted info that, while true and obvious, totally missed the question ("thinner ropes weigh less", "thicker ropes are more durable", "half ropes reduce drag"), and while trying to understand how doubles are actually designed to work, I get called an "idiot," and "comprehension challenged."

 

I guess it's true: I came to the Boards for help with a climbing question.

 

Ross

[catbirdseat]

Isn't boingy good if you are ice climbing? The more energy the rope absorbs, the less that force is transmitted to your ice screw. Is that not so? Of course too much stretch and you might ground before being stopped in a fall.

[COL._Von_Spanker]

Boingy is good, less shock on the gear. It's just an observation about the different characteristics of half ropes as compared to singles.

[catbirdseat]

What are the reasons ice climbers favor twins?

1) two are better than one if you happen to hack one with an ice tool

2) They are more elastic

3) Lighter

 

Drag is not so much an issue on ice is it, otherwise they'd use doubles. Perhaps some do?

 

Are two twins springier than one 9.8 of the same strength? Or does it just depend on the brand?

[allthumbs]

why do skydivers carry two chutes?

[catbirdseat]

"Watch out for that math. If what you did was to determine that the cross sections add up to the same surface area, you have only determined just that: cross section add up to the same surface area. I would venture a guess that this does not correspond directly with stretch or with the dynamic characteristics of the system. "

 

I'm going way back in the thread here, but mattp brought up an interesting idea- at least for a nerd like me. That 9 mm is plenty strong enough and the only reason we climb with fatter ropes is for resistence to being cut over an edge. The Eidelweiss ropes improve their cut resistence by using aramid fibers in the core, which are tougher than nylon fibers. All fibers being equal, it is surface area (not cross section) which determines relative cut resistence. Surface area increases directly with of the diameter, whereas cross sectional area (i.e. strength and weight) increase as the square of the diameter. So you can see that you quickly get diminishing returns with increased diameter. I suppose that if you REALLY wanted a highly cut resistant rope (that was light) you'd climb with a flat rope (like webbing). Of course, that would be impractical because of problems with twisting, or would it? I wonder how a moderately oval section would behave in use?

[freeclimb9]

What are the reasons ice climbers favor twins?

Number one reason is that with two ropes you can make 50-70m rappels.

[catbirdseat]

Freeclimb, what I am trying to get at is why rock climbers don't use twins or doubles more often. Is it because they are more likely to climb as two rope teams of two and thus have the two ropes need for double rappels? Or is it because double rope rappels are not as critical on rock? (because they hang more and because anchors are more plentiful)

[mattp]

Ice climbers are more worried about kicking a rope with crampons or striking it with their tools, either while climbing or while falling, than climbers are. Thus, the redundancy of two ropes is more important to them. Also, rock pro tends to be much more secure than ice screws, and easier to evaluate with visual inspection. The additional stretch (cusion) added by thinner ropes is much less of an advantage rock climbing.

[icegirl]

this is very true, I've seen core shot with pick more than once. Who knows about kicking the rope, I'm sure it happens more than we think.

[freeclimb9]

why rock climbers don't use twins or doubles more often. Is it because they are more likely to climb as two rope teams of two and thus have the two ropes need for double rappels? Or is it because double rope rappels are not as critical on rock? (because they hang more and because anchors are more plentiful)

I generally use double lines when I plan to get more than 100' off the ground. I got into the habit while in Arizona where new routes had me wandering all over the place. Two ropes often can be equated with higher safety. However, I've also done long routes where, as a sort of statement, we only took one rope. As for why many rock-climbers don't use doubles, I think it's a question of simplicity; One rope is easier to manage.

BTW, I climb on Bluewater ropes exclusively. I bought an Edelweiss, and the fat picks of the sheath suck for handling compared to the finer ones of Bluewater.