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mucci
Trad climber
The pitch of Bagalaar above you
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May 10, 2010 - 08:16pm PT
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^^^
This is the knott I was referring to, knott a in line.
So the argument for a "Flat" 8 is mute. Nobody uses it in climbing. It has always seemed dangerous to have opposing force applied to a knott.
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bluering
Trad climber
Santa Clara, Ca.
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May 10, 2010 - 08:19pm PT
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His experiences are probably vastly larger than the small number of places that you climb.
What does that have to do with knot strength or tendency to fail? The location makes a diff?
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scuffy b
climber
Where only the cracks are dry
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May 10, 2010 - 08:24pm PT
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I have seen the flat-figure-8 used to join two ropes for a rappel.
First reaction, shock. When I pointed out the flaws with the knot, I was
informed that I had supposedly recommended it at an earlier date.
A mistake, which fortunately was not tested. We switched to the good old
EDK (flat overhand) for our descent.
In fact, when I learned the knot, the first thing I was told is that the
flat 8 is no good. There's no way I would have recommended it, ever.
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Chiloe
Trad climber
Lee, NH
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May 10, 2010 - 08:27pm PT
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There might be confusion with the names but some people definitely have used the "flat 8," and I've seen them (wrongly) claim in writing that it was safer than a flat overhand or EDK. A flat 8 was the cause of a Zion fatality a few years back.
IFO use the EDK or flat overhand most of the time, including ropes of somewhat different diameters (like an 8.8 and a 10, wouldn't try it with a 6 and a 10). The tests I've seen say that's fine.
I don't know what "most" climbers use but the EDK does seem pretty common.
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Paul_in_Van
Trad climber
Near Squampton
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May 10, 2010 - 08:41pm PT
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My system is a 7 mil trail line and a single lead line (9.4 to 10.5+, whatever dia doesn't really matter).
I use an well dressed EDK (or overhand knot for those that are sensitive) with long tails (2' typically) and rap both strands with a reverso.
The slippage on the thin line can be an issue, so I monitor the potential slippage and as an additional precaution have a 80m trail line which matches to a 70m lead line with allowance for stretch and some slippage.
I might play with the double loop EDK as it sounds like it doesn't exhibit knot roll, but my tails are long enough that they can handle any rolls that might happen (and the test data shows that the force required to roll gets higher with each roll to the point that the rope fails at the knot directly rather than rolling off the end of the tails). I seem to recall that this took two or three rolls (is this Tom M's data? I haven't checked the link above to be sure.
End of the line here is that overhand 8 (force required to roll gets lower with each roll) is a horrible idea and if you are going to rap a single strand you better have a bulletproof safety system in place.
P
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bluering
Trad climber
Santa Clara, Ca.
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May 10, 2010 - 08:47pm PT
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What's the diff between a 'flat 8' and a Flemish 8 follow through???
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tradmanclimbs
Ice climber
Pomfert VT
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May 10, 2010 - 10:01pm PT
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I don't get all this talk about EDKs rolling. use it lots but never seen it roll. I do dress it properly.
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climbingcook
Trad climber
sf
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May 10, 2010 - 10:18pm PT
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What's the diff between a 'flat 8' and a Flemish 8 follow through???
flemish bend, flat 8. The flemish bend is a sane way to join two ropes to rappel, the flat 8 isn't.
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Chiloe
Trad climber
Lee, NH
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May 10, 2010 - 10:30pm PT
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I don't get all this talk about EDKs rolling.
Most people use "rolling" to refer to the way the EDK starts to fail in static pull tests -- it has to invert first (at something over 1,000 pounds). Unless the tails were tied short, it then has to invert again, and again to reach the ends. Not sure whether static tests have followed that all the way through an 18" set of tails (what I usually tie).
I used "roll" to mean something different in another thread, the simple fact that an EDK pulled over an edge tends to "roll" so the knot sticks up and the smoother side slips over the edge. That's a good feature in most rap setups but maybe a dangerous one if it gives the knot a chance to slide through a biner or large-opening rap ring.
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bmacd
climber
Relic Hominid
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May 10, 2010 - 10:50pm PT
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bluering
Trad climber
Santa Clara, Ca.
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May 10, 2010 - 11:17pm PT
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Thanks climbingcook, I agree....
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High Fructose Corn Spirit
Gym climber
Full Silos of Iowa
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May 10, 2010 - 11:22pm PT
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Nice to see the two different forms of figure 8 being talked about. And distinguished by way of language.
Back in the day, when I was trying to get straight on the phenomenon of inversion of knots (esp in overhand and figure 8), I called the two figure 8 types homo and hetero, short for homogonal (same side) form and heterogonal (different side) form I think, my own terms, to help me distinguish them in thought and practice.
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Delhi Dog
Trad climber
Good Question...
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Topic Author's Reply - May 11, 2010 - 12:35am PT
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Here ya go fatty
KNOTS
Flat 8
Flemish Bend/ Figure Eight Bend
Flemish Bend/Figure 8 with stopper knotts
Kleimhist/AutoBlock (Friction Knott)
**^^The picture stands corrected by this statment;
"The "Autoblock" is essentially the same knot as the Klemheist, except that in the last step you simply clip both tails together with a carabiner, rather than feeding one through the other."
Prusik
How to tie both
http://www.chockstone.org/techtips/prusik.htm
Single Rope set up used "correctly" from Petzl
And once again this link
http://web3.bdel.com/scene/beta/qc_kp_archive.php#123008
Cheers,
DD
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rgold
Trad climber
Poughkeepsie, NY
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May 11, 2010 - 12:42am PT
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I'd like to reiterate something mentioned by Ken M a while back, which is that it is extremely unlikely that a prussik above will catch a rappeller who goes off the end of the rope, and in fact there is a very good chance that a prussik above will not work in any emergency situation in which the rappeller is conscious, because the rappeller has to release the prussik in order for it to grab and this is beyond counter-intuitive.
The tests referred to were done by cavers, not guides, but made it clear that even when very experienced rappellers knew exactly what was going to happen and prepared themselves to act appropriately, they were still frequently unable to release their grip on the overhead prussik in time for it to grab. The test set-up had the rappellers using a short rope for their device but the prussik was on a long continuous rope. When they rappelled off the end of the short rope, their grip on the prussik kept it from locking at all on the long rope and they had to be stopped before the ground with an independent upper belay.
The only thing that will keep a rappeller from going off the ends of a rope are knots in the ends, which in some cases can cause a serious hang-up problem, especially if it is windy and the ropes are blowing sideways. Each situation has to be evaluated on its own merits in deciding whether or not to knot the ends, but under no circumstances should anyone trust this task to a prussik in either position; at least that's my opinion.
Discussions of rappel backups almost never seem to consider the position a party will be in with an unconscious rappeller hanging, say half way down an overhanging rappel, frozen in place by an activated prussik backup. I think rappel backups should only be used, if at all, by the first person down. Everyone else should get a fireman's belay from below, which eliminates for the rest of the party the very difficult and dangerous rescue scenario of trying to get an unconscious rappeller down before he or she succumbs to suspension trauma.
As for EDK's I like the name and the knot. Anything that concentrates the mind on the potential for death when rappelling is a good thing, I think. I absolutely hate tag lines, but as a dyed-in-the wool double rope user for many years now, I no longer have any occasion to use them. For those that do, perhaps it is mentioning that there is a "right" way to tie the EDK with ropes of different diameters; hopefully the picture below is self-explanatory. (Note: ends are short for pictorial convenience, the real knot should have forearm-length ends.)
Those wanting a a bit of extra security (on ropes of the same or different diameters might consider adding another overhand for extra roll protection, as in
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Doug Robinson
Trad climber
Santa Cruz
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May 11, 2010 - 12:47am PT
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ec --
Strength isn't the issue in a prusik. I like stronger cord for its other uses. I can use my prusik to tie off small knobs, where it's strong enough to be pro. Or use it as a runner. Not specialized gear, it comes in handy for lots of stuff.
Low melting point isn't an issue either. I don't do ripping fast raps cuz it's too hard on the rest of the system, like overheating your rope with the rap device. Of all your gear, be gentle with your rope!
And haste is more likely to shock load the anchor -- who needs that?
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Delhi Dog
Trad climber
Good Question...
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Topic Author's Reply - May 11, 2010 - 12:49am PT
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Thanks for the addition of the EDK.
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Mighty Hiker
climber
Vancouver, B.C.
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May 11, 2010 - 01:04am PT
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Regarding DD's and rgold's photos:
 I've never seen or heard of anyone using a flat figure 8 for rappelling, and can't imagine doing so. Scary!
I don't like the look of the EDK, but can accept it might at times be a practical solution.
The Flemish bend looks much the best, although DD's second example (long tails) looks healthier to me. It's the one I most commonly use, both because the figure 8 is such a standard and foolproof knot, and because it works to join ropes from 6 - 11 mm.
Glad we no longer use the double or triple fisherperson's, as they can be a pain to untie. But they work, although not so well with ropes of significantly different diameter.
The EDK/reepschnur/blocking knot & carabiner system seems an unnecessarily complicated solution to a simple problem. A last resort, not a first.
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Ken M
Mountain climber
Los Angeles, Ca
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May 11, 2010 - 02:19am PT
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"His experiences are probably vastly larger than the small number of places that you climb."
What does that have to do with knot strength or tendency to fail? The location makes a diff?
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Bluering, if you read his original post, to which I was responding, he doubted the veracity of the tester's statement, based upon his experience.
If one's experience location is limited, it will neccessarily give a bias, and a false "sense" of what people are widely doing.
Clear?
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Delhi Dog
Trad climber
Good Question...
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Topic Author's Reply - May 11, 2010 - 08:07am PT
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"I've never seen or heard of anyone using a flat figure 8 for rappelling, and can't imagine doing so. Scary!"
Yep, could not image using that knot either.
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