rope drag and fall factor quandry?

[tvashtarkatena]

Well, no need for your further participation then, eh?

 

Sometimes its interesting to know how something works.

 

 

 

 

Edited October 25, 2011 by tvashtarkatena

[Rad]

I find this thread very interesting and appreciate links to the actual data. I have no problem being wrong and changing my views and practices in the face of evidence, and even if articles confirm my suspicions it's good to know the numbers. For example, it's striking that using a locking device increases the force on the last piece up to 70% in some cases.

 

So thank you for posting the "academic" findings.

[bstach]

Sure beats spraying about the "war on terror"

[stevetimetravlr]

Great thread. I've found that instead of slinging every piece that needs it, I have 4 or 5 draws that utilize a Revolver biner on the rope clipping end, and I use those instead. This minimizes the length of a fall if I were to take it versus a long sling, also minimizes the rope drag, and makes the whole system seem to run smoother. In the case of a fall, they reduce the overall friction of the system, which after reading this thread seems like a good idea. Also clipping the anchors with the Revolver draws makes belaying with a top rope a joy as you don't have to pull very hard to take up slack with the pulley biners doing their job. My 2 cents worth or maybe 1.

[luvshaker]

I have noticed the brand of rope, and age of the rope makes a significant difference in friction on the rock....also, double ropes=double the rock friction.

Right on revolvers! Used those on aid pitches with traverses on them. They do work great.

[tvashtarkatena]

Revolvers: its nice to have a couple of pulleys along for all kinds of reasons.

[layton]

For example, it's striking that using a locking device increases the force on the last piece up to 70% in some cases.

 

Missed that one? Why is this?

 

Also, I think this is more than just academic. If I've got some serious rope drag and am thinking of running it out above a shitty piece just because I'm now on easier terrain or the anchors are close - I'll put another piece in.

[tvashtarkatena]

F = MA.

 

Presumably, locking devices catch falls faster = greater deceleration of fall = higher fall factor on your last piece.

 

It's...academic, really.

 

Cheers.

 

 

 

Edited October 25, 2011 by tvashtarkatena

[Rad]

Mike, look at the graphs in the link to the Beal site and note the difference in forces generated on the last piece between the traditional belay (e.g ATC) vs locking device (e.g GriGri).

 

F = MA.

Presumably, locking devices catch falls faster = greater deceleration of fall = higher fall factor on your last piece.

 

Translation: force = mass times acceleration (positive or negative). Increasing the time it take to stop a moving object decreases the deceleration (change in velocity/time). Thus, doubling the deceleration time halves the acceleration term in the equation and cuts the force in half. This same principle is why the bumper of your car is designed to crumple and why you have an airbag to increase the stopping time of your head in an accident. This is also why more dynamic elements of your belay system (rope, belay device, friction, etc, etc) will decrease the forces transmitted to the climber, gear, rope, belayer.

 

[layton]

sorry i read it wrong, i thought you said a locking biner increased the fall factor!

 

one of the nice reasons to use a mammut smart device is that it "slips" a bit on the autolock, similar to an atc. also nice for rope soloing on it since falls are so harsh.

 

to add - munter hitches slip less than an ATC or reverso if you find yourself belaying with one.

[tradhead]

Regarding the increased impact forces associated with autolocking belay devices, this point was raised by the UIAA a few years ago. There was a study that they published (which I can't seem to locate in my very quick internet search) that came to the same conclusion as the Beal data.

 

The conclusion of the UIAA study was that autolocking devices should only be used for TR belaying and not lead belaying due to increased anchor loads. Obviously not a universally accepted theory from what I see at the crags these days.

[JosephH]

Now Revolvers and autoblockers aren't academic. After my first decent fall on a grigri I wrote them off for trad leading, though I did still use a modded one for roped soloing for a number of years until the Eddy came along.

 

I've used the Revolvers a couple of times and thought they definitely have a place at the party relative to drag. You can skip some drag-related slinging on bomb placements, but I still wouldn't skip slinging anything that needs to stay put.