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mcclung
Jun 24, 2004, 6:50 PM
Post #26 of 34
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In reply to: Michael, apologies, you're right.
Thank you for being willing to admit when you're wrong, that takes a lot of character.
Don't get discouraged with the physics. I routinely think about problems the wrong way. Physics is counterintuitive for most everyone. Try teaching it sometime and you'll get a sense of how ingrained our wrong ideas are.
If you're every in Tucson we'll have to go climbing.
Michael
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oldsalt
Jun 24, 2004, 7:55 PM
Post #27 of 34
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I have been studying this subject and I have tried to sort through the language to picture this:
A wall has 6 bolts spaced 10 feet apart, so bolt #1 is at 10', #2 at 20', etc.
A fall while clipping the 3rd bolt would mean 10' of runout and a 20' fall on 30' of rope + the dynamic elongation of the rope. The elongation would be about 30% (according to Blue Water documentation) or 9'. This would give you an initial 20' fall, but the elongation would all end up on the sharp end. This now gives you 39' of rope draped over bolt #2 (20' above the deck). Your tie-in would be 1' above the deck - pull up your feet, please.
The fall factor is 29'/39' = 0.74 if the formula length(fall)/length(rope) includes elongation. If not, ff = 20'/30' = 0.67.
A fall while clipping the 5th bolt would mean 10' of runout and 20' fall on 50' of rope + the dynamic elongation of the rope. Now you have an initial fall of 20' + 30% of 50' = 20' + 15' = 35' or 65 feet of rope draped over bolt #4.
The fall factor is now 35'/65' = 0.54, or ff = 20'/50' = 0.40 without including elongation.
Which way is the fall factor calculated, with or without elongation? The numerous references that I have found are not explicit about this.
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tedc
Jun 24, 2004, 9:32 PM
Post #28 of 34
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In reply to: Which way is the fall factor calculated, with or without elongation? The numerous references that I have found are not explicit about this.
Fall Factor=Length of fall divided by rope out (when you fall, NOT after you fall )(If it was length after fall then fall factor would depend of exaclyl what rope you were using :? )
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oldsalt
Jun 24, 2004, 9:51 PM
Post #29 of 34
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Thanks, Ted.
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coomer
Jun 25, 2004, 1:21 AM
Post #30 of 34
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In reply to: That is what the rope is made for, longer falls, short falls have a harder impact causing more stress to the core of the rope. Short falls give more of a jerk that is why you want a longer fall 10/20+ft. We're not talking about 200ft falls. J
I saw someone else (hell maybe it was you) say almost the same thing in a different thread. You couldn't be more wrong...
There is so much mis-dis-information and completely laughable crap being posted on this thread it's scary.
FALL FACTOR is really the only worthwhile parameter to discuss in terms of forces on a rope
Force on a rope- and correlated damage, depends on FALL FACTOR only- which is length of fall divided by the total length of rope out- yes, it's been stated above, but needs re-stating obviously for some folks. Absolute fall distance means NOTHING without knowing how much rope is out. Your statement above is just plain WRONG.
UIAA drop tests are just an extreme case (if you're taking multiple factor 1.8 falls on your rope- you should climb something else). In reality, climbers *rarely* take falls over FF = 1
Guidelines- let your rope REST between hard falls (high fall factor). Retire yuor rope to secondary usage after a really hard fall (fall factor > 1.5) rope is cheap- your life may not be (really depends on how one values one's own life). Otherwise, retire your rope when the sheath begins to show significant wear (core shots are a big sign to retire your rope). See point one when considering sport climbing. Taking repeated falls without letting your rope rest- or switching ends is going to put much more stress on the life of your cord. Don't take high factor falls (especially close to the ground... ouch)!
Ropes do not *break* in the field (barring bizarre circumstances like pinched ropes increasing fall factor beyond FF = 2- it's happened). Ropes for the most part fail because they are loaded over an edge. So, stop worrying about how many falls you've taken. Fall smart- rest the rope, retire if the sheath is worn excessively or you feel mushy, or hard spots in the core, AND watch for sharp edges!
Cheers
Eric
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punk
Jun 25, 2004, 1:46 AM
Post #31 of 34
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it is funny how simple answer become a scene from "Revenge of the Nerds"
with I am smarter bull :roll: :roll:
So in short you can still use the rope for a while but keep an eye on the changing status of the rope, and like the old say…”when in doubt retire it out”. when you do so, destroy it as well, so no dirtbag will pick it up from the trashcan and hurt himself, and have the audacity to give you the hospital bill …well more bizarre stories then that happen but that is a different post altogether.
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beesty511
Jun 26, 2004, 10:50 AM
Post #32 of 34
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In reply to: Fall Factor=Length of fall divided by rope out (when you fall, NOT after you fall )
Just to be clear, fall factor uses the length of the rope out between the belayer and the climber at the moment of impact, but before the rope starts stretching. If the belayer yards in rope after the leader falls or backs up after the leader falls, the fall factor is different than if the belayer had done nothing because the amount of rope available to absorb the fall energy and/or the length of the fall can change by the time impact occurs.
In reply to: ]Force on a rope- and correlated damage, depends on FALL FACTOR only...
Damage to the rope is a real world effect, and the things that contribute to rope damage are not easy to quantify, and they certainly don't depend only on the theoretical fall factor. In falls out on the crag, in addition to fall factor, friction plays a big part in the damage caused to the rope because friction can effectively limit parts of the rope from contributing their full share of energy absorption, which will cause other sections of the rope to absorb more energy and therefore reach higher tensions than predicted by the theoretical fall factor. Even if you idealize the situation and eliminate friction from consideration, the tension in the rope also depends on the mass of the climber. A small child taking a factor 1 fall on a rope will stress it less than a large adult taking the same factor 1 fall.
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old_apple_juice
Jun 26, 2004, 3:28 PM
Post #33 of 34
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Registered: Apr 15, 2004
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So when Dean Potter is taking a bunch of 60 foot falls on tombstone, does he rest them, or bring multiple ropes or what???
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coomer
Jun 26, 2004, 8:39 PM
Post #34 of 34
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Registered: May 30, 2004
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In reply to: "beesty511 In reply to: ]Force on a rope- and correlated damage, depends on FALL FACTOR only... Damage to the rope is a real world effect, and the things that contribute to rope damage are not easy to quantify, and they certainly don't depend only on the theoretical fall factor. .
For a given climber (mass) FF is your best description of the overall impact on the rope (and damage). I gave pretty simple guidelines in helping people to determine when to retire a rope. Peak impact force on your rope is also something to consider when climbing routes with dicey protection- but we're (I'm) trying to keep it simple. Yes, there are a multitude of factors that dtermine overall damage. But you can judge how harsh a fall is on your rope by looking at the fall factor. If you take a high FF whipper- at least switch ends before going back up- and consider retiring the rope... I don't think I've ever taken a fall with FF > 1, I've only caught maybe one fall with FF > 1- but there were screamers employed and it was a dynamic catch on overhanging terrain, and no visible, or tactile damage to the rope- I continued to use it for quite some time.
Your best indication of the state of your rope is visual and tactile inspection- core shots- soft spots, burn marks, hard spots- all good indicators that you've damaged the rope- retire it. Otherwise, it's probably still good to go. Keep away from acids as the damage may not be immediately obvious from from subjecting it to Sulfuric acid fumes- but strength may be severely compromised.
All of this pseudo-physics inspired analysis is a waste of time.
And as I stated before, the vast majority of rope damage doesn't come from the force during a fall, but usually from sharp edges- pinching between pro and rock etc. Personally, I pay more attention to how my rope is routed, than how many falls I've taken on it.
Cheers
e
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