Question on Ropes

[mattp]

quote:

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Originally posted by Gordonb:

I don't think it was the breaking strength tha ehmmic was worried about. It was the streach/recovery time of a thin rope vs a thick rope...

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I still think you guys are getting too technical. Interesting question, perhaps, but even though there is some question about how the characteristics of the rope may have contributed to one recent accident, I read the "Accidents" journal just about every year and it seems to me that the modern ropes are well tested and pretty damn amazing and that the dymanic characteristics of the rope are not much of an issue. If you are worried about stretch/recovery time, go for double ropes. But the stretch/recovery thing is way down my list of reasons for liking that system. I think about sharp edges or the possibility of an ice tool cutting the rope (I believe it never has or almost never has happened with double ropes), I like the reduction in rope drag with double ropes, and I like being able to reach up with one rope and clip a piece over my head while I have a tight belay on the piece below. I like having two ropes for rapelling. It is a good system and it just happens to eliminate your concern about the stretch/recovery time issue as well (at least as far as being caught on the second piece in your chain is concerned).

 

[ 10-24-2002, 02:17 PM: Message edited by: mattp ]

[fern]

I think the answer to the question of 'how long is the recovery time of the rope after it's been stretched?' is something on the order of tens of minutes or more. Clyde Soles said something about this in the depths of the Death at the Coulee thread.

[Gordonb]

There has been some discussion of the recovery time, but no real numbers. Full recovery time is in the many minutes time frame, but in the seconds (or fractions of) during a fall, how much recovery is done between pulled pieces of pro?

[haireball]

you can't begin to generate the numbers you guys are asking for unless you can measure the force generated as the failing piece failed. in the fall that Ehmic describes, that force would have been insignificant (the piece was at her waist, creating a fall-factor of virtually zero, so the most force generated would have been 1 x her body mass at nearly 0 velocity, or a tad over 1/2 kn) so the rope would not have any great loading to recover from. what are you worried about? unless you're regularly taking factor 1+ falls, in which case, you need to work on your leading/protecting skills...

safe leading is all about minimizing the fall-factor and making sound placements. most any modern climbing rope will be virtually impossible to break unless you CUT it.

[chriss]

Don't dwell on this to long. There are more factors to this than can be calculated.

 

You're assuming the rope is at its maximum stretch when the piece pulls and then doesn't have time to recover when it loads the next piece.

But since you don't know how much force it took to pull the first piece or how you are falling in relation to the next piece (straight down to it? maybe it's off to the side a bit?) or how the belay is going react when loaded heavier or ....

The list goes on.

 

And the time of 10 minutes was for full recovery and can again vary widely.

 

But what do I know.

chris

[fern]

I don't think it would be hard to calculate/measure at all. But I don't think you would learn anything interesting. Also ropes may be hard to break, but biners are not.

[mattp]

quote:

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Originally posted by fern:

ropes may be hard to break, but biners are not.

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Yes, I have broken a 'biner. But here again, Mr. Haireball is right here: if you are taking those kinds of falls (falls that generate forces sufficient to break carabiners), you are probably doing something wrong. It is true that serious aid climbs require one to risk big falls with complex rope and protection scenarios where weird things can happen, but most accidents where equipment fails are accidents where it was somehow used incorrectly. Focus not on the dimension of your rope or the strength of your 'biners, but on placing good protection and avoiding leader falls on anything less than unquestionnable pro with a fall-zone free of things that might hurt you.

[SEF]

from mattp:

quote:

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Focus not on the dimension of your rope or the strength of your 'biners, but on placing good protection and avoiding leader falls on anything less than unquestionnable pro with a fall-zone free of things that might hurt you.

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I wholeheartedly concur on this. The real trick, though, is in consistent execution.

[neversummer]

So here's a question then...

Would you be better of running out a climb on a bomber piece of pro, then possibly falling a long way onto it, or putting in a questionable piece after the "bomber piece" then falling and having the questionable piece pull, fully streching the rope and loading up for a huge impact on your "bomber" piece? Would the second scenario increase the chance of complete failure in the system?

 

My first instinct is to say the more pieces the better for both safety and for climbers piece of mind to not be 20 feet above your last piece. But it makes sense to me that if you take all the give out of the system, then load it up, you run a greater chance of pulling the bomber piece.

 

Pardon my newbieness if this has been discussed ad nasuem before or if the answer is "never place a questionable piece" (which from my standpoint seems impossible), but it seems like a good question to me.

[chelle]

I've been thinking about my rope since reading the thread on G. Kropp's accident and the discussion on how dynamic ropes react to a fall. And got to thinking about a fall I took last weekend (although not on my rope).

 

I have a Sterling 60m 9.6mm dynamic rope. I bought it because I wanted something lightweight and figure it is safe since I don't weigh that much. I weigh about 130 lbs. If I fall on my rope and a piece pulls and I fall another 10 feet to the next piece of gear, will I generate the static load forces people are talking about? Is this a "safe" rope to use cragging or should I get a 10mm rope for cragging?

 

The fall I took last weekend was on Classic Crack in Leavenworth just below the second buldge where the climb eases. Leading in the dark with shitty Tikka and didn't judge the size of the crack right. Put in a #1 cam, where I should have used a #2. The piece popped a second or two after I slipped out and weighted it (piece was at my waist). I then fell on a #3 cam which was maybe 5-6 feet below the 1st piece.

 

Thankfully noone got hurt, we all just laughed I swapped headlights so I could see better and finished off the climb.

 

Can any of you tech heads who like to (and can) calculate this stuff help me figure this out?

[mattp]

quote:

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Originally posted by ehmmic:

I've been thinking

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Not to be snide, but maybe you're thinking too much. You propose an interesting calculation, perhaps, but your rope is fine. Take a look at the last twenty years' worth of "Accidents in North American Mountaineering" and you will not find many (or any?) incidents where something like your 9.6 failed and a 10 would have held - or even an 11. Ropes almost always break because they are cut by something and pieces fail in normal free-climbing situations because the rock broke or the placement was poor.

[Gordonb]

Correct me if I am wrong, but I don't think it was the breaking strength tha ehmmic was worried about. It was the streach/recovery time of a thin rope vs a thick rope.

 

I have been pondering that question also. If your first piece pulls does the rope have enough recovery time so that it is still dynamic by the time it hits the next piece? Does anyone have the recovery time of a dynamic rope? Also what is the recovery strength? (after it stretches do you have to completely unload the system before it recovers?) Do any rope manufactures publish the modulus of elasticity and internal dampning numbers of their ropes?

[Greg_W]

This discussion about "recovery time", as gordonb puts it raises another question: Are you better off spacing your gear out a good bit? If you run it out, fall, and pop a piece won't the rope have more time to "recover"? Obviously this situation will lead to greater impact forces, as well. Which is better? Is there a happy medium? Probably.

[Lambone]

I haven't read all of these posts, so I may be repeating someone...but,

 

In theory a new 10 mil rope will typicaly be more "static" than a 9.6 mil rope right out oof the bag. That its they typicaly have a higher impact force rating. Although there is alot of variation between rope comanies and other variables.

 

If you fall and your first piece blows, yes the rope will be stretched, but it by know means be static.

[Gordonb]

I like neversummer's question. Rope dynamics will are very important in the optimum placement of pro.

 

I was a mechanical engineer in my previous carreer and my work consisted of breaking and analysing things like this. I understand the forces and dynamics of a fall, but I don't have a clear picture of the dynamics of the rope.

 

The rope is a spring and dampner in the system. The rate of spring and dampning create huge variables in the ammount of force placed on the load points. Without knowing the variables we are just guessing at where are load points should be placed.

 

This discussion is probably not much use in the real world, but I feel much more comfortable understanding the percise dynamics.

[chucK]

It seems to me that

The amount of ropestretch that the crummy above piece will use up before it blows is proportional to the amount of energy it will absorb that will now not hit the by the bomber below piece. So, it does not seem obvious that the crummy above piece is a bad idea. For example, if the crummy piece does not blow at all, then it has significantly reduced the force on the below piece.

 

Now, where the problem might be is that, even though ropestretch is used up at proportional rate of the energy absorption, I think it is well known that your dynamic system can withstand a lot more energy than a static system, thus losing ropestretch may be much more critical than absorbing energy.

 

This'll get you thinking next time you climb Lovin' Arms !

 

As Mattp said though, you won't have to worry about this question with a two-rope system (as long as you're alternating the clips).

 

[ 10-25-2002, 09:56 AM: Message edited by: chucK ]

[freeclimb9]

quote:

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Originally posted by Lambone:

In theory a new 10 mil rope will typicaly be more "static" than a 9.6 mil rope right out oof the bag. That its they typicaly have a higher impact force rating.

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No. Impact force of a rope is a reflection of the fiber type and weave more than diameter. For example, Bluewater's 11mm Enduro has an impact force of 8.5 kN which is less than the thinner 10mm Energizer at 8.7 kN.

With regard to determining the force of a fall, there are too many variables to do so by calculation. It's gotta be done empirically. Even then, the body tension of belayer and climber (faller?) will affect the force, and be tough to duplicate.

[chelle]

Thanks everyone. I'm not going to worry so much about the rope and just focus on gear placements so that the pieces are bomber. I've been pushing myself more lately and am taking more falls. This was my first fall where a piece blew and I didn't think twice about it until I read the discussion on the gear blowing out at the coulee.

 

Maybe I'll just use my double ropes for awhile...

Michelle

[chucK]

Michelle,

Like SEF said, the real trick is in the consistent execution. You can say that you will focus on more bomber placements now. That's a good thing, but you know that you will soon come to a spot where you want a piece and there is a placement there, but you're not totally convinced it will hold.

 

What do you do then?

 

You can focus on the gear placement being bomber as long as you can hang out at that stance but at some point you will have to decide whether that placement is worth it. Will it help or hurt me? That's the tought part. Goran and this discussion will just make it a little tougher now for some of us until someone figures this sh*t out.

[DavidW]

interesting questions and discussions all but I'm surprised no one has mentioned screamers or load limiiters or any of the numerous "exploding" quick draw products. Me being a relatively large individual (190#) I've often had my doubts about even well placed pieces of gear.... especially ice screws and brass nuts.

 

I am extremely reluctant to take falls on gear leads and don't recommend anyone make a habit of it, still I'm pretty certain the reason I'm here to join this discussion is that I used Yates load limiters.... on two occasions I've been stopped just above the ground pieces that I'm certain would have blown with a conventional quick draw approach.

 

Sure, they are goofy looking...... but really not very heavy or awkward. I tend to use them on EVERY ice screw, and sometimes have one or two on my rack for clipping rusty old bolts, skanky fixed gear or small stoppers.

[chucK]

That could spice up the discussion! If you had just ONE screamer, do you think it would be better to put it on the upper questionable piece or the lower bomber piece?

[DavidW]

I'd attach it to the questionable piece.... if there were gonna be several questionable pieces and I had only one screamer I'd try and decide which piece posed the greater threat of hitting something if it failed.

[mattp]

On the questionnable piece, of course. I don't remember the last time I fell and pulled a piece that I thought was "bomber" and I may never have done so.

[chucK]

So you guys don't buy the argument/fear that the stretched out rope will blow away the bomber piece (as apparently happened to Goran) since the rope is now static?

[Beck]

Lambone's comments about mm ropes/lower impact forces generally holds true, doesn't it? Thinner ropes less impact force, twins an even lower impact if clipped into one piece? This is just one small contributing factor to this whole topic, still it that might mean Ehmmic's rope choice is an OK one for her?