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sawin
climber
So., CA.
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Apr 16, 2008 - 04:00pm PT
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saho this looks fairly nice except possibly 1?
Grey, Blue and Purple I can see being replaced by Air Voyagers
reducing load factor. Pink I can see being replaced by perlon
or equivalent. I've never used screamers?
I suppose it's possible to use Camelots, Hex's, Friends, Nuts,
Stoppers etc. very close to each other with per_se a very small
Micro catching a fall and not taking a 180 degree angle crossing
over the carbiner hence possibly further load reduction upon the
micro and other piece or pieces are occuring. However that pro
has a con being the rope drag.
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clustiere
Trad climber
berkeley ca
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Apr 16, 2008 - 04:30pm PT
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interesting idea. Great for desert aid routes like in the fishers ehh.
What about fabric burn??
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JohnRoe
Trad climber
State College, PA
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Apr 16, 2008 - 05:39pm PT
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Al wrote
"A lighter and simpler solution that I frequently employ is to leave off the figure 8 knot and create a SERE anchor. In MOST situations (where I have 3 decent pieces in), sharing the load more equally between all pieces greatly decreases the chance of any of the pieces pulling. This makes for a much stronger anchor and nullifies the benefit of a non-extending design.
Worst case scenario: Unexpectedly a piece pulls and the (3 pieces of pro) system extends roughly half of the length of the loop attached to the failed piece - typically around 1.2-1.5 feet. This suddenly lowers the power point and drops the falling climber an additional 1.2-1.5 feet plus another few inches of rope stretch. As this is a small portion of the typical fall distance and highly unlikely, I see omitting the Figure 8 as a safer (and faster)choice than the commonly advertised set-up in many situations."
The "worst case scenario" above is correct provided you set things up so that each cordelette loop from a piece of gear goes into *both* sides of the power point locker. If the three pieces are "left", "middle", and "right" that means you pull down the three loops and then put a half-twist into the loop from "left" to "right" (like when you make the sliding X).
If in a hurry one forgets or bungles this, the worst case scenario seems to be that one piece pulls and you end up hanging on a very long American Triangle on the other two, falling almost twice the length of the attached loop rather than half.
Sure you know this, just thought it might be good to mention...
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EB
Trad climber
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Apr 17, 2008 - 01:32am PT
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Thank you for the comments on the analysis of this anchor system. Comments from del cross and rgold were particularly insightful and have uncovered some errors. Rather than contribute to further confusion, I have decided to remove the math portion of my post. I will reenter a corrected version when I have it put together. I left the text portion in rather than delete the entire post because I think that part still presents a useful description of the anchor system.
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 17, 2008 - 08:58am PT
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"Al,
Where is your redundancy when you take the fig 8 out of the cordalette? How strong is your cordalette? Even though you have equalized your protection you have limited yourself to one piece in that if the cordalette (which is loaded 100%) fails you now are left with this equation
100%-100%=nothin' "
Let's not forget about this real issue. A rock could fall, or be pulled off by a falling climbing, and impact the belay, cutting the cordalette.
If it had an eight, there's hope.
No Eight, Sorry Charlie
Peace
Karl
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rgold
Trad climber
Poughkeepsie, NY
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Apr 17, 2008 - 02:04pm PT
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Eric,
Thanks for your efforts so far, which as we all know are done in your abundant spare time. Looking forward to the revised version.
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EB
Trad climber
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Apr 18, 2008 - 12:54am PT
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del cross:
I'd bet that your 7.5 feet is probably not too far off, especially if you let the angle between legs get smaller.
Once we have some more reliable equations, two questions I would like to answer are:
1) What is the comparison between max loads in each leg with and without the screamers (all other things being equal), and
2) How gracefully does the system degrade: that is, if you are above the maximum height allowed for complete screamer deployment, what does the max force in each leg go up to at the end of the fall when screamers have reverted to regular (static) slings.
With respect to (2), you have brought up something else that I think is very important: you suggested that not all legs will finish their screamer extension at the same time (almost certainly true for legs with different angles relative to the vertical). This leaves open the possibility that one or two legs will see a disproportionately higher force at the very end of the fall (for falls greater than a certain height). Any analysis needs to look as carefully at what happens after one or more screamers finish extending as during extension.
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TradIsGood
Chalkless climber
the Gunks end of the country
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Apr 18, 2008 - 12:59am PT
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This analysis screams for experimental evidence.
:-)
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 18, 2008 - 02:11am PT
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"Three fully ripped screamers absorb 1.8 kJ of energy. That much energy corresponds to a fall of 7.5 feet for a "standard" leader. That's not very far and I think suggests that screamers in the anchor are most effective for a relatively short fall. "
Seems to me that there are lots of factors weighing in that we don't have numbers for.
I took a 20+ footer on the Muir on a screamer and it didn't even fully deploy.
Peace
Karl
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TradIsGood
Chalkless climber
the Gunks end of the country
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Apr 18, 2008 - 11:53am PT
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navblk, The load is not doubled unless the protection is a "frictionless" pulley.
To see that most readily, imagine that the rope is knotted into the protection. Then the load is climber only, the line to belayer can be slack.
This was covered to some extent in Hartouni's post in the Fall Factor thread.
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TradIsGood
Chalkless climber
the Gunks end of the country
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Apr 18, 2008 - 01:20pm PT
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sawin, nav.
What I am pointing out is that friction reduces the force on the belayer side (unless you have a frictionless pulley). The force on the protection is the vector sum of the forces, but the two legs are not identical. The other obvious way to notice this is to see that the 100 pound belayer is lifted off the ground by the hanging 150 pound climber.
Empirical evidence - measurement of the actual performance of the legs, versus predicted would be a good idea.
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sawin
climber
So., CA.
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Apr 18, 2008 - 04:16pm PT
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delcross,
A 7/8" metal cable is very static, though I would hate to
fall 20' on it.
I'm looking at this of course with equipment in mind.
< Link >
Do you recommend the link above or the Muir Wall for
a 1'st grade V1?
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Ed Bannister
Mountain climber
Riverside, CA
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Apr 18, 2008 - 06:45pm PT
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Geez,
Russ was right, if the thing has three screamers, no deployment till 1800 lbs if the rig is equalized.
So, if you want the effect of a screamer, clip it to the cord, and, you then are hanging off a single piece and have no reedduunnddancy, geez.
take your pick,
the truth is if you only tie in with a cordellette, you are constantly dependant on a single piece of gear. If you are talking belay stance, generally a bad habit for anything besides a rope, at least in old timers terms, and the journal.
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sawin
climber
So., CA.
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Apr 18, 2008 - 08:33pm PT
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del cross,
Maybe with a CAT 977, D-8, D-9 or train pulling it or it pulling
a train with a crane.
Are you saying either climb asked about has that potential?
Iv'e been there and beyond free climbing and soloing.
Are you referring to apogee? What idea? Of course not and
that many years back when he allegedly stated what he did
I doubt he knew velocity of orbits.
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rgold
Trad climber
Poughkeepsie, NY
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Apr 18, 2008 - 11:06pm PT
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Navblk4 wrote:"Maybe this will answer your question:
http://www.myoan.net/climbart/climbforcecal.html"[/i]
Petzl has a fall calculator that is reliable---go to http://en.petzl.com/petzl/SportConseils?Activite=14&Conseil=56. I'd be extremely wary of others, especially if they don't tell you what formulas are being used. I think that sites whose language is imprecise or just poorly written, and sites that reveal fundamental misunderstandings of the physical principals involved should be considered suspect and not used. The MyOAN Rock Climbers (sic) Shock Force Calculator seems to be an example of such a suspect site, for more reasons than the failure to use an apostrophe when it is required.
Infelicitous or imprecise language: "the force of your shock is dependent on..." (Beyond repair, but worth a chuckle) and "The fall factor is the ratio of the distance you fall to the length of the rope." (Not "the length of the rope," but rather "the amount of rope from belayer to leader at the instant the leader falls.")
Misunderstanding basic principles (combined with amusing language): "Dynamic rope considerably decreases the shock a climber feels because it has the ability to stretch and absorb more of the force."
These just beg to be made fun of---I'm going to restrain myself. But with these telltale clues suggesting possible incompetence, note that in spite of the description of the fall factor (yes, faulty, but we know what they mean), when you enter "Length of rope"=10 meters and "Distance from last anchor"=5 meters, the Rock climbers Shock Force Calculator calculates the fall factor to be 1.5 instead of 1. Further experimentation reveals that the calculator is incapable of finding any fall factor to be less than one, apparently because it is performing the calculation
(Not the) Fall factor = 1 + (dist from anchor)/(length of rope)
This happens to get fall factors of 2 right, but nothing else of course.
I haven't bothered to check the accuracy of the remaining shocking calculations; who could have any faith in those results given what has come before?
Del X wrote:"I've also read hints that systems with screamers might not behave quite the way that simple theory predicts."
As far as I know, the "simple theory" predicts that a single screamer will, in general, have little effect in reducing the maximum impact to its anchor, and experiments confirm this.
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Karl Baba
Trad climber
Yosemite, Ca
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Apr 18, 2008 - 11:49pm PT
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"no deployment till 1800 lbs if the rig is equalized. "
I thought having an equalized anchor was the goal. I idea of a scream0lette is for the screamer to deploy in a tough situation until equalization is reached. Then you have a system that is serene. The other equalization systems extend or aren't redundant (and don't absorb energy like a screamer system either.)
Peace
Karl
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Al_T.Tude
Trad climber
Monterey, CA
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Apr 19, 2008 - 04:55am PT
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John - Yes, when using a cordelette w/o figure 8 knot, a sliding x must be used as with a sling equalizing 2 pieces.
When I need greater extension to reach the pieces that I am equalizing I retie my 5.5mm spectra cord cordelette from a loop into a rabbit runner (a cord with a small loop at each end). I clip the two loops into the power point biner at the bottom and run the resulting loop up to one piece, down to the power point and back up to the next piece etc. This does not require the sliding x as the ends are captive.
Karl - My opinions about leaving the fig 8 off are based on 3 solid pieces and it being appropriate MOST of the time, not in all situations and not with the "crappy" placements that you postulate.
Gobie wrote "Where is your redundancy when you take the fig 8 out of the cordelette? How strong is your cordalette? Even though you have equalized your protection you have limited yourself to one piece in that if the cordalette (which is loaded 100%) fails you now are left with this equation
100%-100%=nothin'"
Good catch, Gobie. I missed that very significant benefit of the figure 8. We often do trust our lives to one element; one harness, one rope, one biner. However, it behooves us to avoid that when practicable. That alone makes a good case for putting the figure 8 knot into the cordelette.
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Moof
Big Wall climber
A cube at my soul sucking job in Oregon
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Apr 21, 2008 - 01:08am PT
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"Rope slippage is another issue. I've read that a tube style belay device will slip at 2-3 kN (Petzl's fall simulator assumes 2 kN). Is this realistic? If it is and if the rope isn't redirected through the power point, then in a factor 2 fall the force on the entire anchor is limited to 2-3 kN. So why bother with the questionable virtue of screamers in the anchor? Why not just wear a belay glove instead?"
Most common use for screamers is aid climbing, where a gri-gri is also commonly used. No slippage.
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TradIsGood
Chalkless climber
the Gunks end of the country
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Apr 21, 2008 - 07:31am PT
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Karl, in the screamolette, the only time you will have equalization is if/when all three screamers are actually tearing - assuming that they really work as advertised and tear at a fixed force regardless of extension. Once they have stopped, if the anchor holds, you are back into static analyis with slightly more perpendicular angles - i.e. at that point they have just become ropes of likely unequal length but similar stretch characteristics to each other.
(Of course, the more parallel legs should be more equalized.)
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sawin
climber
So., CA.
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Apr 21, 2008 - 12:39pm PT
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_c_
a_b
In the real working static ground world, the 3'rd middle leg
is usually not feasible to achieve and is not applied such
as with tilt up building construction. Assuming a+b = 300,
then c=300 and each leg carries 100. It's easier to acheive
2 leg balance.
However working above the ground with tons of mass over critical
objects a tri-pod or quad pod equalizing the load is of the
upmost necessity as crane charts read static weight hence a
shock load (caused by dynamic mass) of a max static load could
roll $100,000.00's and destroy $1,000,000.00's below. Of note
when I rigged these, equality between the legs of the load I
admit is not instantaneous though equals out over a very short
distance and in fractions of a second. I have rigged 100's if
not 1000's of these with 0 roll overs or a failed load.
The secret as mentioned is a power point for the screamers
to activate. Now that I have thought about this it should
not be to difficult to build a balanced screamer system.
Opinion:
I only have experience with Air Voyagers. Applying knowlege
of missed-distance at super-sonic mulitple mach speeds we know
the vibration from acelleration and also decelleration causes
tracking signal disturbance (same as gate flutter).
It appears the vertical screamer design is feasible for test
as the horizontal Air Voyager design allows more acceleration
and deceleration causing (gate flutter) as they are not a
constant brake as are the screamers.
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