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thelawgoddess

screamers for ice climbing

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maybe you noticed bd doesn't make screamers? there is a reason for it. i tend to trust their research, since they proved placing screws (in good ice) downward is not the correct way to go (10 degrees up is). metolius had simolar test results and both companies do not manufacture them.

 

So BD and Metolius must not trust devices like gri-gris and reverso's since they don't make anything that performs the same function....Metolius must think all ice screws are bunk because they don't make any. It seems to me that i see alot more recalls from BD than I have from petzl/charlet moser. I wonder who has better testing? I am a huge fan of BD but if Charlet moser is still making them they are ok with me. I have used screamers and fallin on them and never have the the pieces pulled. I would really like to see some test results though. But saying they are unsafe because of company doesn't manufacture them isn't a great argument.

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It seems to me that i see alot more recalls from BD than I have from petzl/charlet moser.

shocked.gifyellaf.gif

 

i got my new collection of yates screamers today. they are sure pretty. grin.gif

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wallstein, i think you are a bit confuzed. metolius is not manufacturing any ice gear, so why would they produce screws? on the other hand they produce a ton of rock gear. now bd is located in the usa not europe, hence their policy od recalls. there were several cm tools that the heads loosened up. as the matter of fact a friend of my took a 30ft whipper when a head of pulsar completly come out. cm/petzel make very good product. they are from europe hence they don't to have to worry about liability lawsuits by trigger happy lawyers.

to me gadgets like screamers are just a gimmick. in this case they are heavy, bulky and at least their function is not 100%proven. enough said.

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considering the data that doolittle has brought us and the lack of ANY data (or solid physics, for that matter...) glaaskow has brought us, it seems like this issue is dead. Anyone have ANY data (or solid physics, and no, that crap above and in the other thread is just that: crap) to support this screamers = increased load? FYI: I wrote BD and asked them if they had any data and the person responing said something like "I haven't done any testing like that" and wouldn't comment any further. Yeah, they might seem like gimicks, but that's differnt than saying they increase loading.

 

Also, the industrial applications of screamer-like devices should be considered. Engineers don't (usually) just do shit because it seems cool.

 

Again, anyone have data or would like to put forward a solid argument against screamers?

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Well, forces are measure in Newtons(or pounds)

 

F=m*a

a=(v2-v1)/t^2

 

In any fall, the change in velocity over the interval of time (t) that the fall is being held by the gear is the same(maximum velocity ==> 0), so that will remain a constant, delta V.

 

The goal of a dynamic rope system is to minimize F.

Since mass m is fixed as the mass of the climber, acceleration a must be decreased. Since delta v is also a constant, time t must be maximized.

 

Time t is at it's minimum in a fall held by a static rope.

Time t is increased by use of a dynamic rope.

The use of a screamer in conjunction with a dynamic rope will serve to increase time t yet again by yeilding at a rated load.

 

If the impact force for a rope is rated to 8-12kN, and the activation focre for a screamer is >2kN, this means that the rope will not fully elongated prior to or during "screaming". Time t will increase during screaming, without the rope stretching. The force applied to the pro will remain at the activation force (approx 2 kN) while climber velocity approaches zero without the rope continuing to stretch. If the screamer completely activates, the rope will elongate, but the climber velocity will be closer to zero, and force applied to the gear will (hopefully) be less than the holding strength of said pro.

 

Blah, blah, blah, but I'd still like to see some test results. Consider the above to be a grant application, and I destroy all the screws and screamers you'd like.

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Say, Doolittle, that is a pretty good try at a "klenke post." thumbs_up.gif

 

Here's what I would say about the physics involved:

Looking at it in terms of the conservation of energy, a climber falling on the rope develops an increasing kinetic energy based on the vertical distance already fallen (1/2mv~2 = mgh). A screamer is a device designed to dissipate this energy by way of the ripping of the sewn segments. That is, it takes energy (or force if you want to look at it that way) to rip a seam. Since energy can be neither created nor destroyed, any energy used to rip the seams will not later be imparted to the protection above the screamer.

 

In a problem such as this, the energy balance and force balance equations both need to be used to obtain a solution. In this way, you can describe the problem/solution in terms of energy or force. Doolittle's force approach is confusing (in its writing style) but legitimate.

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the screw doesn't 'absorb energy'. The work done on the screw is zero. Energy is aborbed only in the climber's body, the knot cinching up, the rope as it stretches, etc. Now if the screw pulls partially, then some work is done on it. bigdrink.gif

 

Screamer activates at 500lbs? Which is roughly 2kN. Which is far less than the max impact force of a rope. So while the rope stretches, the screamer activates, so there will not be a shock load, nor does the screamer absorb whatever energy the ropes didn't.

 

Now let's look at this more closely. Climber, mass of 75kg, falls 10m. KE=PE=mgh=7357.5 J

Screamer activates at 2kN, Work W=f(delta h). Say the screamer, when activated, extends, 1/3m. Then W=666.666J. Which is only 9% of the energy of the falling climber. Might make a difference.

Ahh, semantics. bigdrink.gif

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The important thing is that more kinetic energy to be dissipated or absorbed by the tearing of the threads than released from potential energy by the resultant extension of the sling. This is in fact the case.

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hey paul your post doesnt say where the climber falls from ie fall factor. are you pretending that a 10m fall with a fall factor of 0.1 will generate the same forces as a fall factor of 1.0 hellno3d.gif if i was your prof i'd fail you!

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hey paul your post doesnt say where the climber falls from ie fall factor. are you pretending that a 10m fall with a fall factor of 0.1 will generate the same forces as a fall factor of 1.0
Uh, Dru - as long as gravity is the same, a 10m fall has exactly the same forces produced.

 

Fall factor describes how much rope is available to absorb the energy.

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hmmm, you guys should try that one again, you might be surprised....fall factor determines the force on the anchor boxing_smiley.gif

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hmmm, you guys should try that one again, you might be surprised....fall factor determines the force on the anchor boxing_smiley.gif

in a frictionless world like your sex life. but in the real world friction absorbs a lot of energy in falls and other things.

smileysex5.gifthe_finger.gifboxing_smiley.gifwave.gif

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ya and so does hitting a ledge, a belayer, or a toby henson crashmapazad with spikes on the way down cantfocus.gif

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hmmm, you guys should try that one again, you might be surprised....fall factor determines the force on the anchor boxing_smiley.gif
A screamer rips if the force on it is greater than the activation force. How much energy is dissipated by the screamer is constant, the force is irrelevant so long as it's greater than the activation force. Once the screamer is fully ripped, then we start getting interested in the true force. But that's not what we're talking about.

 

My previous example simply illustrated that a screamer has a non-negligible effect on reducing the force on pro, Mmmmkay? boxing_smiley.gif

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hey paul your post doesnt say where the climber falls from ie fall factor. are you pretending that a 10m fall with a fall factor of 0.1 will generate the same forces as a fall factor of 1.0
Uh, Dru - as long as gravity is the same, a 10m fall has exactly the same forces produced.

 

Fall factor describes how much rope is available to absorb the energy.

Sounds like you have a misconception. The impact force developed in a 10 m fall varies with the fall factor. IF is directly proportional to both your weight and the FF. Fall factor and not distance fallen determines whether impact force is sufficient to activate the screamer.

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But Impact Force also depends on the elastic modulus of the rope Geek_em8.gif ....not to mention friction of the rope through biners and the dynamics of the belay and and and....

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"...already stated this opinion of screamers in this thread , but he hasn't backed it up yet, despite a lot of evidence to the contrary."

 

 

Thanks to Doolittle for some of the only actual numbers here!

 

Lots of comments from this and the above quoted thread seem to back up what it sounds like lots of climbers already know from (mostly secondhand) experience - they do rip when they need to. And from posted observations, much of the time they demonstrate their effectiveness directly - they only rip part way . This means they dissapate the force of the fall to the point that there's no longer enough force to continue activating the screamer. Sounds like it works to me!!

 

cj001f mentions (without presenting backup) "Rigging for Rescue did some destructive testing on Yates screamers. During the drop the force was delayed, but once the screamer was fully-extended, the force went right back up to what it was w/o the screamer in place." Perhaps "destructive testing" is beyond the types of forces dealt with in regular climbing?

 

The long and short of it seems to be that they work in the field, and that's where it counts, for my money. Thanks for the info!! (Maybe it's time for physics class again after all...)

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cj001f mentions (without presenting backup) "Rigging for Rescue did some destructive testing on Yates screamers. During the drop the force was delayed, but once the screamer was fully-extended, the force went right back up to what it was w/o the screamer in place." Perhaps "destructive testing" is beyond the types of forces dealt with in regular climbing?

That was iain.

 

My comment about a 10m fall being the same was purely in regard to the force acting on the rope. It's the same. Hence my comment about FF affecting the energy absorbtion of the rope, and thereby the forces on the anchor. The angle of the climb matters as well Geek_em8.gif

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