Discussion Topic |
|
This thread has been locked |
dirtineye
Trad climber
the south
|
|
|
Jan 19, 2007 - 12:25pm PT
|
How much wottle
Would a Wootler wot
If a Wootler would wot wottles?
|
|
GOclimb
Trad climber
Boston, MA
|
|
|
Jan 19, 2007 - 03:28pm PT
|
Regarding this anchor, which I'm calling the two crossed-x slings:
Tito said:
>> I’ve used it [ed. two sliding x's with limiter knots to form a
>> three piece anchor] on many occasion and with the quad as per
>> Largo’s book it seems like a perfectly reasonably anchor, am I
>> missing something?
> a majority of force goes to the shorter leg? because it
What do you mean by shorter leg? There is the same length of webbing on both sides. In general, with crossed-x situations, because the biners act as (approximate) pulleys, the force is the same on a long arm as on a short arm. Look at it this, way - if the force started to get higher on the short arm than it was on the long arm, the sling material would slip through the biner towards the short arm until those forces were equalized again. Does that make sense to you? It is, in fact, why you see relatively good equalization on what the testers called the "unequal" setups.
Tito goes on to say, in regards to the mooselette:
> from looking at that rigging, it doesn't seem like it can
> equalize well because of all the friction produced by so many
> strands of cord running across biners.
In practice, it seems to equalize better than most. So far as I can tell, this is because there is typically only one strand moving through the power point (the movement through the other biners is very small, and not binding). But as Wootles pointed out, seeing this with body-weight or two bodies-weight doesn't tell us much about what might happen from a hard fall. Only a test rig could do that.
{snipped the rest of Tito's analysis, which seemed to be based on a faulty premise}
> hooking up a portaledge
> to an anchor and being able to get a good night's sleep does
> not prove that an anchor is reliable for trad climbing. unless
> you have test results that show otherwise, one can only assume
> that anchor won't equalize very well. the more strands of cord
> running around biners, the harder it is for an anchor to
> equalize. the two sliding x's with limiter knots would appear
> to be superior.
I have no idea why you would assume that. Build one yourself, it's very easy. You can feel that the tension equalizes at least approximately on the strands, and you can feel that even under with body weight, the strands move freely - which is not always the case with the sliding-x, and you can see that there are rarely strands moving in opposite directions to each other, which always happens with the sliding-x.
GO
|
|
Crag Q
Trad climber
Louisville, Colorado
|
|
|
Jan 19, 2007 - 03:38pm PT
|
GOClimb, What route is that in the mosselette picture? It sure looks like Eldo, but I can't match it up in my mind with any route.
|
|
GOclimb
Trad climber
Boston, MA
|
|
|
Jan 19, 2007 - 03:48pm PT
|
Crag_q wrote: GOClimb, What route is that in the mosselette picture? It sure looks like Eldo, but I can't match it up in my mind with any route.
Bingo! Good eye! Yellow ridge, just before the short traverse under the roof around pitch, what, four, I think?
GO
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Jan 19, 2007 - 03:50pm PT
|
Thanks wootles and John, great to have this data out in public. I know that it is difficult to find the time to write a formal paper up for a journal, perhaps we can have a productive set of thoughts generated in this shared environment of the Forum...
...I'm between meetings now, but I will post some calculational thoughts I have regarding the results later...
|
|
wootles
climber
Gamma Quadrant
|
|
|
Jan 19, 2007 - 04:24pm PT
|
The climber formerly known as Wootles
;-)
|
|
Largo
Sport climber
Venice, Ca
|
|
|
Jan 19, 2007 - 04:29pm PT
|
I've actually got to go to a meeting now but if someone can scan all the test stuff from the book and post it here, perhaps something more can be wrung from it. I'd don't have a scanner here at my home office.
JL
|
|
GOclimb
Trad climber
Boston, MA
|
|
|
Jan 19, 2007 - 04:48pm PT
|
Jstan wrote: I must be missing something. We all realize no two anchors have the same strength and we count on our ability to estimate this strength. Why are we trying to equalize the load??
Because the person who built the cordelettes that would have tested like these ones in a hard fall...
... probably didn't realize that there was essentially no equalization going on - all of the force of the fall would hit one piece, and, if ripped out, then hit the other piece. Not good.
GO
|
|
jstan
climber
|
|
|
Jan 19, 2007 - 08:34pm PT
|
GOCLIMB:
Do I have it correctly. Your answer is " we are trying to equalize because in this data we failed"?
Just trying to understand. That is OK but does not address my question.
My question was this. If I think I have one piece good for 3000# and another good for 1000# - I should not try to equalize. I should try to put say 2000# on the strong one and 500# on the weak one. If I try to put 1500# on both - one will rip. If I don't equalize the total force the anchor system (the sum of the two) can be substantially increased. If done correctly the total force can be 4000# instead of the 3000# one gets after ripping the poor anchor.
Before you are done this is going to need some mechanical network analysis using stress/strain data for the kinds of nylon used.
|
|
Trusty Rusty
Social climber
Tahoe area
|
|
|
Jan 19, 2007 - 09:47pm PT
|
After jugging up to my picture perfect iron curtain of 69 equalized pins, Dorton calmly stated "minimum 3 & max 5 dude"
With a typ. 500 lb load, equalizing is a must and the "perfect figure eight" is appropriate for walls.
C/Jones. . .that "partner" was right when it comes to wall climbing. . .. but as far as free routes the "sliding W" is probably better.
|
|
john hansen
climber
|
|
|
Jan 19, 2007 - 10:12pm PT
|
This thought just came to me after reading these posts.
It seems that most , if not all, of the systems use 'static' materials.
What if you had a cordellet with dynamic qualities? Like a bungee cord that would stretch to help distribute the wieght to three or more anchors, if not'exactly..' equal, at least with less shock loads.
I know the first question would be "How do you haul the bags or jumar from it ?" It would have to have just enough stretch to make it work. Help me out here....The difference between gold line and modern ropes is amazing. Im sure they have the technology.
|
|
cintune
climber
Penn's Woods
|
|
|
Jan 19, 2007 - 10:22pm PT
|
"What if you had a cordellet with dynamic qualities?"
Yates makes an 8mm "dynamic prussik" cord that sounds like what you're suggesting. Having none of the expertise of the main contributors here, I have no idea how it would work in an anchor, but it's out there.
And there's always screamers.
|
|
climbingjones
Trad climber
grass valley,ca
|
|
|
Topic Author's Reply - Jan 19, 2007 - 10:26pm PT
|
I agree Trusty, walls and free climbs are totally different. What I like most is carrying a roll of duct tape to "back up" anything sketchy. I prefer a triple xyz config. Maybe I should carry some silly putty too. 69 pins though? Good thing he was carrying the gear, eh? Thats alot of slings too. Did he incorporate his underwear into that deal? Cracking a St. Pauly Girl here. You?
|
|
john hansen
climber
|
|
|
Jan 19, 2007 - 10:30pm PT
|
The screamer (unless I am thinking of the wrong product, or they have upgraded it ) relies on stitching ripping out to soften the impact. A bungee cordellet would load gradually without maximum static force's. The more stretch the more it would equalize.
|
|
wootles
climber
Gamma Quadrant
|
|
|
Jan 19, 2007 - 10:56pm PT
|
Dynamic cord won't equalize any better than steel cable. No matter what the materials are, given identical setups, the load ratios will always be the same. Dynamic cord will, however, lower the overall peak force which probably isn't a bad thing.
8mm dynamic prussik cord is nothing more than a hunk of 8mm half or twin rope. You probably won't see much more load reduction with a dynamic 8mm vs a standard 8 or 7mm accessory cord anyway. We're talking relatively short pieces of cord here. Also the tensile strength of dynamic cord/rope is generally less than the equivalent size static due to the internal structure, not that strength would be an issue.
|
|
TGT
Social climber
So Cal
|
|
|
Jan 19, 2007 - 11:10pm PT
|
My firmly braced feet are guaranteed to equalize.
And the rope burned flesh on my backside insures that there will be no shock loading.
|
|
tito
climber
|
|
|
Jan 19, 2007 - 11:16pm PT
|
What do you mean by shorter leg? There is the same length of webbing on both sides..
well, yes, but the big/main sliding x in the picture looks like nylon cord, which has some dynamic properties to it. the second, smaller sliding X looks like an 8mm dyneema sling, which doesn't have much stretch. since the right hand leg of the rigging will stretch less, it will feel more force. maybe i slightly overstated the differences in the amount of force going to each leg, and the real distribution of forces lies somewhere between a setup with equal leg lengths and one with unequal leg lengths.
In general, with crossed-x situations, because the biners act as (approximate) pulleys, the force is the same on a long arm as on a short arm. Look at it this, way - if the force started to get higher on the short arm than it was on the long arm, the sling material would slip through the biner towards the short arm until those forces were equalized again.
in a hypothetical frictionless environment that would be true. but that is not the case when friction is taken into account. as the biner slides across the cord in an effort to equalize the forces, friction fights against the biner. as a result, the biner only succeeds in getting 2/3 of the way to perfect equalization. the same phenomenon occurs when a climber hangs on a top rope. the belayer only has to pull with 2/3 of the force that the hanging climber exerts on the anchor. the friction from the rope running through the anchor point helps the belayer hold the climber up. good when belaying, but bad when trying to distribute forces equally to all the pieces of an anchor.
the more times cord or webbing runs over a biner in a rigging, the more friction prevents the system from equalizing.
But as Wootles pointed out, seeing this with body-weight or two bodies-weight doesn't tell us much about what might happen from a hard fall. Only a test rig could do that.
agreed.
|
|
Trusty Rusty
Social climber
Tahoe area
|
|
|
Jan 19, 2007 - 11:21pm PT
|
Clean Livin CJ. . . . J. Hanson is on to something big . .. .. Flexible American Spirit Summer Porn Squash, vagina stretched ear to ear. . something like a mother who leads 5-4 .. .Chemical Brothers Remix.
|
|
climbingjones
Trad climber
grass valley,ca
|
|
|
Topic Author's Reply - Jan 19, 2007 - 11:31pm PT
|
Dude yeah. A stretchy vagina equalizes everything. Or nothing. Not sure which. But who cares? Maybe this belongs on the "Men and women are different" thread. But whatever. My mother cant lead 5.4 though, she is to into worrying about my goat porn habit. I told her to get a life. But maybe I should just get a goat. Do they eat summer porn squash? Cause I have alot. Maybe enough to equalize an anchor. But only if I use the sliding Dub-ya. No screamers though, there will be plenty of screaming when you see the anchor that I build on top of that ice formation on Sunday.
|
|
john hansen
climber
|
|
|
Jan 19, 2007 - 11:37pm PT
|
With a twenty foot countinous piece of this stuff you you could make a two foot cordelette figure eight anchor could stretch to four or five feet it might be safer .Maybe this could even be applied to extreme free climbing or speed ascents with 'short roping'.
|
|
|
SuperTopo on the Web
|
Let us know!