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bigga
May 27, 2004, 5:52 AM
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I just had a look at the ratings on small cams...
It looks like all the smaller cams have a rating of 7 or 8 KN. Under 10 anyway...
How could that be considered bomber if a factor 2 fall is rated at 25 KN?
I have a feeling I've missed something somewhere...
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curt
May 27, 2004, 5:58 AM
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In reply to: I just had a look at the ratings on small cams... It looks like all the smaller cams have a rating of 7 or 8 KN. Under 10 anyway... How could that be considered bomber if a factor 2 fall is rated at 25 KN? I have a feeling I've missed something somewhere...
Did you ever look at a rope's maximum impact force?
Curt
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hugepedro
May 27, 2004, 6:02 AM
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^^^ What he said. Plus, if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing.
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areyoumydude
May 27, 2004, 6:06 AM
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The impact force on most ropes range from 8.5 kn to 9.5 kn.
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bigga
May 27, 2004, 6:15 AM
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I see...
After you said that I had to retake falling 101 again. Had forgoten totally the different forces at different points in the climb and had somehow gotten the idea that a factor 2 fall is 25KN anywhere. Thanks for pushing me to the refreshers course...
although my mistake has given me a pretty big buffer in my calculations:)
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alpnclmbr1
May 27, 2004, 6:32 AM
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In reply to: The impact force on most ropes range from 8.5 kn to 9.5 kn.
This is the force felt by the falling climber. In a turnaround situation such as falling on a piece of gear can approach 16kn (1.6x Force)
As far as gear strengths. A 10kn piece will very very rarely fail in normal use.
Small cams are still not considered bomber.
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bigga
May 27, 2004, 6:39 AM
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Although it still doesn't make sence to me...
First of all the impact force given on the rope is not the maximum force it can withstand but rather the force the climber will feel in a 1.78 factor fall according to Ron Bessems at http://toad.stack.nl/~stilgar/calc.php
But as far as the the cam is concerned I still can't get it all strait. A factor 2 fall produces 12 KN of force on the rope. At any point where you thread the rope through protection the force is almost doubled since the rope is pulling on both sides of the biner which is why the UIAA requires Carabiners to hold 25KN.
So if on a 1.9 factor fall the rope feels 9KN, the protection you are falling on would feel about 15KN according to http://flash.lakeheadu.ca/~lurock/factor2.html.
Now I could be wrong here, but it looks to me that in this situation, you're rope is bomber, your biner is bomber, harness, sling... all bomber... but your cam is still not bomber..
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alpnclmbr1
May 27, 2004, 6:58 AM
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They could make cams twice as strong and they still would not be bomber and they would weigh twice as much.
The limiting factor is the placement, then the rock, then the cam itself. Cam do not break in normal use. I have never heard of an undamaged cam breaking in a fall situation.
Also, for the most part, you do not get a close to factor two fall in a turnaround scenario.
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bigga
May 27, 2004, 7:02 AM
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When you say placement, do you mean the quality of the crack you are placing the protection in? ie angle, tapering etc?
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alpnclmbr1
May 27, 2004, 7:04 AM
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The quality of where in the crack you put the cam, and what cam you used.
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crshbrn84
May 27, 2004, 7:04 AM
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even though i havent been climbing long, would the use of a screamer, be good when using a micro cam to help obsorb some of the shock from the initial fall?
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squish
May 27, 2004, 7:08 AM
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In reply to: even though i havent been climbing long, would the use of a screamer, be good when using a micro cam to help obsorb some of the shock from the initial fall?
Yes. This applies regardless of how long you've been climbing.
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hugepedro
May 27, 2004, 7:09 AM
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In reply to: Now I could be wrong here, but it looks to me that in this situation, you're rope is bomber, your biner is bomber, harness, sling... all bomber... but your cam is still not bomber..
Yeah, which is why I said:
"if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing."
Why would you ever take a fall approaching factor 2 on a single micro cam?
P.S. check out the kn rating on a #3 wired nut. 5kn.
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solo
May 27, 2004, 7:13 AM
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In reply to: It looks like all the smaller cams have a rating of 7 or 8 KN. Under 10 anyway... How could that be considered bomber if a factor 2 fall is rated at 25 KN?
In reply to: .... if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing.
Think of that once more. The only situation where factor 2 fall can occur is when you fall directly on the anchor. There's no way you can produce a factor 2 fall higher on the pitch after you placed some pro. So if you are facing f2 fall on a micro cam, you are either an A6 climber or have suicidal intentions. :wink:
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elron
May 27, 2004, 10:12 AM
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I feel rather stupid asking this question, since its probably something I should know... but... is the fall factor the only thing that influences the force produced in the fall? I mean to say, does a factor 2 fall of 4 feet produce the same impact force as a factor 2 fall of 25 feet? I can't see how this is possible, but whenever falls are discussed, the only contributing factor seems to be the fall factor. I was always under the impression that the fall factor was combined with other variables such as distance fallen and amount of energy absorbed by the rope to figure how much force is felt by the falling climber.
Kevin
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taualum23
May 27, 2004, 12:33 PM
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Kevin,
Of course you are right, that the physics of falling are much more complex than any number (fall factor, for example) can make up for. Fall factor, velocity of climber, mass of climber, the impact forces of the rope, and how much rope is out all have to do with how much ACUAL force is put on the pro. If this poster, for example, is taking a factor 2 onto a micro-cam, his anchor is a micro-cam. I try not to do this.
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overzealous
May 27, 2004, 12:44 PM
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In reply to: I feel rather stupid asking this question, since its probably something I should know... but... is the fall factor the only thing that influences the force produced in the fall? I mean to say, does a factor 2 fall of 4 feet produce the same impact force as a factor 2 fall of 25 feet? I can't see how this is possible, but whenever falls are discussed, the only contributing factor seems to be the fall factor. I was always under the impression that the fall factor was combined with other variables such as distance fallen and amount of energy absorbed by the rope to figure how much force is felt by the falling climber.
Yes and no. (Someone more experienced correct me if I'm mistaken). The fall factor is an approximation of the force felt in a fall. All other factors being equal a 10 foot factor 2 fall generates the same impact force as a 50 foot factor 2. In the real world, all things are almost never equal :)
Things besides the fall factor that will effect the impact force felt include:
- friction in the system
- energy absorbed by settling of the protection, knot tightening, beley slippage, etc...
- Use your imagination... I'm sure you can think of plenty more "others"
This leads me to a question... at what point do "other factors" become more of a consideration than the fall factor. If I take a hypothetical factor two on 2 feet of rope (say a slip at the belay) should the two feet of rope be cut and discarded, or is there simply not enough force generated over this drop distance to be an issue?
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peroxide
May 27, 2004, 12:57 PM
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Fall factor etc explained.
Kevin. You are not alone.
First some definitions:
Fall Factor: Length of Fall / Lenght of Rope to Last anchor
Max Impact Force: max force felt by climber through rope
A fall factor of 2 means a fall onto belay. 20 foot fall, 10 feet of rope to belay, that is factor 2 and sucks.
The cool thing about climbing ropes though is that they are dynamic so they absorb this energy. To understand as simply as possible, they absorb energy per foot of rope.
So a fall of 10 feet above the belay or 30 feet are both factor 2 falls (20 ft fall/ 10 feet rope = 2 = (60 ft fall / 30 feet rop)) but the longer fall also has 3 times the amount of rope out to absorb the fall. So in essence the climber will feel physically similar forces on their body (yes there is accelaration etc but these details arent important at this level).
So to sum up...more rope...more energy absorption.
Now the energy back to the biner is a different story.
You take max impact force (set for each and every rope made) X fall factor X 0.84 (some energy is lost to friction around the biner) to get a decent estimate on the biner.
So assume a rope has a max impact of 10 kN. The following chart shows what the pro feels. Try it at home.
Fall factor * 0.84 * Max Impact Force of Rope = Force on biner
Rope out****distance from last piece*****fall factor******kN on pro
30___________5___________0.33___________2.8
30___________10___________0.67___________5.6
30___________20___________1.33___________11.2
30___________30___________2.00___________16.8
Manufacturers most likely build into the rating at least 20% for error (in other words a 10 kN rated nut probably is probably safe upto 12 kN of force if not higher).
In a bomber placement (good rock, cam contact, etc) cams rarely fail. The only examples are very tiny micro cams that people have daisy chain falled (factor 2) onto which means no dynamic anything...
Rock on
P :!:
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cantbuymefriends
May 27, 2004, 1:00 PM
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In reply to: This leads me to a question... at what point do "other factors" become more of a consideration than the fall factor. If I take a hypothetical factor two on 2 feet of rope (say a slip at the belay) should the two feet of rope be cut and discarded, or is there simply not enough force generated over this drop distance to be an issue?
Beal has a pretty good info page about "other factors" (ropedrag etc.), at http://www.impact-force.info/anglais/impact.html . Check especially p.2 "The theoretical fall factor" and p.3 "The actual fall factor".
Interesting to see that a lot of ropedrag will give you a higher actual fall factor. I thought it was the other way around...
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elron
May 27, 2004, 1:37 PM
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peroxide, etc... thanks for all the info. however... i'm still having trouble understanding how a 4 foot factor 2 fall can generate the same force as a 50 foot factor 2 fall. kN = force. F=ma. "m" is constant in the two cases. "a" (the acceleration from highest speed to 0) is dependent on several factors, the two biggest being initial velocity (before deceleration) and amount of time from start of deceleration to point of zero velocity. Maybe I'll grab a pen and paper later on and do some sample calculations to convince myself that this works. just seems a bit counter-intuitive. on a static rope the fall factor wouldn't even matter, i assume, since the rope doesn't stretch. so, what amount of rope stretch (elasticity) is required to go from the static rope scenario to the "fall-factor" scenario. at what point does rope stretch replace velocity as the key factor in determining the force felt by the climber?
Kevin
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fitzontherocks
May 27, 2004, 2:05 PM
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I was curious about just what cam ratings actually meant. I found this on the Metolius site. Maybe it will shed some light.
Strength ratings are derived by holding a camming unit in a steel testing fixture and pulling on it until it breaks. This is the strength rating you see printed in the company literature or stamped on the cam. If a company wants a higher strength rating, they can simply use a beefier axle or stem(or whatever part failed in the test). However, in the real world, cams rarely fail by breaking. They almost always pull out. Having the strongest axle, stem or sling is totally irrelevant if that is not the point of failure in a real-world application. If a cam pulls out at 1000 lbf because the cams slipped or because the rock pulverized, what good is an axle with a 10,000 lbf breaking strength going to do? That is the difference between designing cams to work in a testing jig versus designing cams to work in the real world. Strength is the cam©ˆs ability to hold up to a particular standard in a controlled test. Holding power is a cam©ˆs ability to maintain its placement under a load (i.e. hold a fall) in a real-world placement.
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bigga
May 27, 2004, 2:10 PM
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Solo... excellent point.... :lol:
"Think of that for a minute" Gotta admit, the obvious never even crossed my mind.....
Still, even at less than factor 2, an 8KN , 9KN Cam is still pretty well below the outer limits of popping out on a serious fall which is fine if the people using it realise this. But since I've started asking around on this subject, quite a few people (and I'm not knocking them cause I'll put money that they are more experienced climbers than I am) have told me that the small cams are absolutely bomber, when even according to the specs engraved in them by the manufacturers, they are definitely not. Someone even told me he took a factor 2 on a small cam. Now as solo pointed out, he must iether be mistaken, or should be thanking G-d almighty for saving his as* after applying close to 24KN of force on his last piece of pro which was only designed to take about 8. At least according to the specs of the cam, it seems that all of you guys who have taken these serious falls on small cams and have had the cam hold, its not because its supposed, but probably because you placed the piece unbeleavably well, in the perfect shape and quality of rock, to allow your piece to perform ABOVE its specifications. I know that to most of you guys climbing traditional, this fact is probably not news to you, it caught me back abit since its news to me (and I dont trad), but if there is someone out there who doesn't know, be aware of the amount of protection you are placing... it could be dangerous to have a false sense of security about a piece.
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bigga
May 27, 2004, 2:23 PM
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And another thing... and correct me if I'm wrong.
People are saying that a factor 2 generates about 12KN on the rope which is correct. Now assume you are falling with a tension of 12KN in the rope. The biner feels almost TWICE that force.... since the rope is pulling on the biner both on the side of the climber and on the side of the belayer, and both sides pull with the force of the tension in the rope which is as we've said 12KN... In effect its not doubled but multiplied by 1.66 for reasons that I'm not 100% percent sure of. apparantly friction between the biner and the rope as was explained to me on another web site. Iether way a factor 2 fall places about 20KN of force on the anchor... not 12.... that is why there is such a huge difference in safety requerements between carabiners...Which are required to take 25KN if I'm not mistaken since they carry double the force.... and things like your rope and harness, all required to take 15 and less. So, nope, I still don't see how a small cam is bomber...
(I'm no expert, just trying to work it out with the numbers)
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dingus
May 27, 2004, 2:29 PM
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Fuck sake man, put a screamer on it and climb!
DMT
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tedc
May 27, 2004, 2:56 PM
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In reply to: peroxide, etc... thanks for all the info. however... i'm still having trouble understanding how a 4 foot factor 2 fall can generate the same force as a 50 foot factor 2 fall. Kevin
Your confusion is understandable. And you hit upon the key to your puzzlement with the word time. While the FF does essentially determine the max force felt by the system, a longer fall with an equal FF will apply force to the system for a longer time than a shorter fall. For a given FF, the forces will max out (at about the same value) as the climber comes to a stop at the bottom of the rope stretch but the whole time the rope is stretching the force will be building and the rope stretches for a longer period in a longer fall.
It an ideal case this time is not to important because if a cam will hold 10KN for .001 sec it should hold 10KN for .1 sec right? Maybe?
Other issues like how far does the belayer get pulled up are MUCH more dependant on the amount of time a certain force is applied.
How about a FF2 onto a poorly equalized (i.e. cordalette) 3 piece anchor. Forces applied for .001sec. (maybe a 3' FF2) may only be enough to rip the first crappy piece :shock: ; where forces applied for .1sec (maybe a 15' FF2) may be long enough to POP, POP, POP all three crappy pieces. Bye,Bye :cry:
So, are all Factor X? falls the same? NO.
But then again, didn't Sharma say "Climbing isn't about MATH." :?
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