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noeman
Nov 16, 2004, 6:44 PM
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When following on jumars, do you prefer a eight on a bite or butterfly and if it is the eight, why?
From my understanding the eight on a bite is 40% weaker.....maybe I am wrong please let me know.
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forkliftdaddy
Nov 16, 2004, 6:50 PM
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i prefer an eight or an overhand because they are easier for me to tie.
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iamthewallress
Nov 16, 2004, 6:53 PM
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If you're talking about back up knots...8 on a bight.
Fast to tie, hangs well, and you can fit many of them on the same biner. I've never used a butterfly, but it seems like it would not hang straight down like the 8. I don't know if a pile of these would rotate the biner.
Tie in biners break. And people who don't back up often enough have been known to deck or become injured on the way down when their jugs have detached, but figure eight tie in knots in healthy 10.5mm dynamic cord do not break after factor <1 falls. 40% stronger is 40% more than more than enough.
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t-dog
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Nov 16, 2004, 6:56 PM
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if you're talking about rebelays as you jug, to limit how far you would fall in the unlikely event that both your jugs came off the rope, I usually simply tie an overhand on a bight cause I'm too lazy to make a figure 8, and you have to remember that this is at best a Plan B, that you should never need to use.
If I misunderstood your question this probably won't make much sense :?
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noeman
Nov 16, 2004, 7:46 PM
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Yes, I was talking about a back up knot, and have jumared a lot, it was question of technique, I thank you all for your answers, just wanted to see some different perspectives. thanks again
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euroford
Nov 16, 2004, 8:19 PM
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i'm fine with just using an overhand on a bite.
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sarcat
Nov 16, 2004, 8:23 PM
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I was just at the ITRS symposium and a study presented tested the strenght of an 8 on a bite vs. the butterfly and several other knots. The direction of pull was from the two ends of the rope. The butterfly was significanly stronger than the 8 on a bite.
I'll bring in the paper tomorrow and post by how much.
Also noted was that at the end of the rope where forces are from one direction the 8 on a bite was only somewhat weaker than an 8 follow through.
However, if you are worried about the kind of knots that would break ropes in your system by force most likely you should be concerned with other issues.
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ricardol
Nov 16, 2004, 8:37 PM
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As far as back up knots ..
I use an eight on a bight as the first knot .. and then subsequent backups are done using an overhand on a bight..
as far as what knot i like to use to fix the line i'm jumaring .. i use a clove hitch -- backed up with an eight on a bight to some part of the anchor.
-- ricardo
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noeman
Nov 16, 2004, 8:51 PM
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However, if you are worried about the kind of knots that would break ropes in your system by force most likely you should be concerned with other issues.-sarcat
When I follow I understand it is back up so off the deck I will go 40 ft do my first back up, and then if the route has no ledges or sharp edges one more time around the half way point. If there is an overhang(rope slicer) or a ledge(bone breaker) I will jumar above it high enough where rope stretch will still be no issue and then do another knot. I understand the use of the back up and the dynamics, I was just curious if your jumars did pop and you went for that 80-100 ft ride which not would you feel more comfortable with....
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sarcat
Nov 16, 2004, 8:57 PM
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80-100'er huh?
My preference based on the strength of knots test reports I've read:
- in the middle of a rope = butterfly
- in the end of a rope = 8 follow through w/grapevine backup.
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chico
Nov 16, 2004, 9:02 PM
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For jugging fixed line? Tie a clove hitch and back that up with a eight on a bight. end of story. simple, clean, effective, badda-boom!
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iamthewallress
Nov 16, 2004, 9:06 PM
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In reply to: I was just curious if your jumars did pop and you went for that 80-100 ft ride which not would you feel more comfortable with....
Non-intuitive though it may be, your fall will be less than a factor 1 and the force that you generate should be well within the holding power of a good rope and any knot mentioned. If you put a biner in your lower jug your chances of coming off are even smaller anyway.
It's cross loading your biner, falling over an edge, or hitting something on the way down that you probably need to worry about more.
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mr.shortround
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Nov 16, 2004, 10:03 PM
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In reply to: Also noted was that at the end of the rope where forces are from one direction the 8 on a bite was only somewhat weaker than an 8 follow through.
Ummm.... that makes no sense. An 8 on a bite and an 8 follow through make the exact same knot. The way they are tied is different, but in the end they are the exact same. How could one be weaker????
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drector
Nov 16, 2004, 10:12 PM
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The butterfly is useful if you are going to be pulling on the knot OR pulling on the rope coming out of it. If you are backing-up jugging then each knot you tie will be a new high-point and that knot will only be loaded on the loop. This makes the figure-8 optimal since it is easy to tie and has plenty of strength when loaded on the loop.
If there is another climber jugging up after the knots are tied then the butterfly is best since there will be a few of those knots above him/her and they will be loaded in a way that the butterfly is designed for. The figure-8 is not optimal in that situation.
There is another version of the figure-8 that has better loading characteristics when tied mid-line. One of the rope strands exists the knot in a downward hanging direction. You'll have to look it up. It's a figure-8 variation.
Dave
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sarcat
Nov 16, 2004, 10:15 PM
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You are correct they make the same knot. The difference in the study was the direction of pull on the knot by the rope. An 8 on a bite suggests pull can be from both ends with the knot in the middle.
I'll see if I can bring in the test data criteria and post it tomorrow. They pulled on rope with an 8 on a bite and an 8 follow through. Maybe it was how they pulled on the rope by aplication of the knot?
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moondog
Nov 16, 2004, 10:22 PM
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hey, that's 8 on a BIGHT ya hoons!
Butterfly? Sure, if you need to catch a breath...
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climbhoser
Nov 16, 2004, 11:23 PM
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you said it, sarcat, the butterfly is stronger when pulled in TWO DIRECTIONS! However, this isn't how it would get pulled in the event asked about in this thread. In this case the figure eight on a bight is no doubt the strongest knot to tie. However, there are obvious problems with bulkiness, time it takes to tie, etc...
The butterfly is best used for glacier crossings where there's three or more people on a rope...for the middle people, the peeps on the end get the eight on a bight. Funny enough, the AMGA has actually taken the practice of recommending the 8 on a bight even for these situations because rarely is the impact force in a crevasse fall going to be as great as that in a rock climbing fall. It's also easier to tie while guiding clients ;)
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crotch
Nov 16, 2004, 11:27 PM
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I think the 8's you tied are examples of "inline figure-8", not "figure-8 on a bight".
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moondog
Nov 16, 2004, 11:40 PM
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yah, only the one on the left is a "false" inline 8...
Edit: whoops! I originally said the right one wasn't right, but it's the left one that isn't right...right? :oops:
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sarcat
Nov 16, 2004, 11:50 PM
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The middle and right knots are directional 8s. I never said they were 8s on a BIGHT. They are the SAME knot only directed opposed.
Didn't someone once say "the best knot is one YOU know how to tie correctly"?
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moondog
Nov 17, 2004, 12:20 AM
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In reply to: They are the SAME knot only directed opposed
The two knots pictured are clearly different. Note that the segment of rope between the two knots is captured in the right knot by the same bend that captures the bight (clip-in loop), whereas it is not similarly captured in the left knot. The right knot appears to be a correctly tied inline 8, but the left is not. Hope that makes sense...and pardon the pedantry...just in the mood I guess. :roll:
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knudenoggin
Nov 17, 2004, 12:43 AM
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In reply to: The middle and right knots are directional 8s. I never said they were 8s on a BIGHT. They are the SAME knot only directed opposed. Didn't someone once say "the best knot is one YOU know how to tie correctly"?
Actually, the middle & right knots although intended to be identical show that
dressing matters--they're a bit different: the line between them, note, runs
to the leftmost turn of the left (center) knot, but is the interior parallel turn
in the right knot (more clearly loading like a Square knot).
As for that "40% stronger" for the Butterfly, I don't buy it. As another noted,
if you fall on any of these tied-in-the-BIGHT (TIB) knots, you'll load them as
end loopknots (that they have relatively lonnnnnnnnnnnnng ends beyond is
irrelevant)--there'll be no loading of them qua *bends* unless by some
miracle (cat wrote w/Magic Marker on right spot the pissed to erase it :o)
the first-loaded eye breaks and you continue falling to the next: then, the
first loopknot would loaded qua bend.
Moreover, note that the Butterfly is asymmetric: ever see test data that
reflects this point (e.g., tested qua end-loop from each end)?
Finally re testing, yeah, by golly, CMC Rope Rescue Manual carries test data
for both the "Fig.8 on a Bight" AND "Fig.8 Follow-Through" (who would think
that the test device cared?), and got (drum rollll) a 1%pt. diff.--i.e., noise.
(More interestingly, they also got--as did Adam Fox's testing--allegedly high
strength from the Overhand loopknot (higher than for Fig.8!?), which I think
resulted from transposing the digits of test data, but given Fox's results,
hmmm, maybe not? Lyon's results were significantly less for Overhand.
And as these knots have two obvious ways to be loaded--which end, i.e.--,
I've tried to learn from Jim Frank of CMC how they were tied (no luck so
far).)!
In any case, the UIAA has long noted that ropes simply don't break at the
knot--not even in the sever UIAA drop test.
--*knudeNoggin*
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kai_da_klimba
Nov 22, 2004, 8:46 PM
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moondog is right about the two knots being different.
only the one on the right is a correctly tied in-line figure 8.
the clip-in loop formed by the knot and the end of the rope running in its direction need to go through the same bight of rope.
the correct way to tie the knot involves forming a loop, not just a bight, and passing it around the standing end of the rope.
For an excellent illustration of how to tie this useful little knot, see D. Fasulo's "Self Rescue" book by Falcon press.
Kai
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stymingersfink
Nov 26, 2004, 12:38 AM
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you talkin bout for use as a b/u while jugging? Why not use your gri-gri?
While juggin a haul line, you will not be able to tie b/u knots to carry with you. The haul bag will prevent this. Gri-gri or mini-traxion works great here.
While jugging the lead line to clean, one will be tied into the end of the rope. In conjunction with a gri-gri, one will be always connected to the rope if both jugs *WERE* to pop off, as well as being pre-threaded for lowerouts.
Being tied into the end of the rope is your back-up in case the locker your gri-gri is on becomes cross loaded and fails. Of course, since you will not be falling obscene distances while jugging a fixed rope, it is highly unlikely you will be able to generate the forces necessary to cause the biner to fail.
Would you agree, or am i just crazy?
To answer your real question however, butterflys all the way. Can be loaded in either direction, and is as strong as an 8, yet easier to untie after the knot has been shock loaded.
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