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sixleggedinsect
Apr 6, 2006, 3:35 AM
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regarding an issue that came up in the sewn vs. tied runner thread, i just went out and pulled on some spectra knots. to make a long story short, overhand knots in 10mm wild country tech slings, as well as wider bluewater tech slings, were holding at least 900 pounds with no slippage, which was as far as i took the half-ass test.
given that double and triple fisherman knots woudl be even less likely to slip, i feel comfortable rapping on tech slings (like spectra/dyneema) tied with these knots.
details and pictures
it was all a little off-topic for the other thread, so if you have any comments, please post them here.
cheers,
anthony
edit: the URL code thing doesnt seem to be working consistently. if you want to see details, copy and paste http://electricant.net/beta/spectra/spectra_knots.htm into your browser.
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sixleggedinsect
Apr 9, 2006, 10:53 PM
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update. tried with even beefier cords. in a couple quick tests, spectra-based webbing was breaking before the knots slipped.
not quite what i thought would happen.
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jimdavis
Apr 10, 2006, 1:26 AM
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Have you tried testing a Ring Bend(water knot) or a Fig-8 Bend?
I bet the fig-8 bend would hold just fine....
Jim
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sixleggedinsect
Apr 10, 2006, 11:58 PM
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In reply to: Have you tried testing a Ring Bend(water knot) or a Fig-8 Bend? I bet the fig-8 bend would hold just fine....
when you ask if i've tried the water/ring, what specifically are you asking about? essentially, that is the knot i used most. the overhand loop is the same knot as the ring bend/water knot. i just used it in a single strand instead of a continuous loop (which would likely be almost twice as strong).
as for the fig8, for the first testing round, and some of the second round, i used a single strand of tech webbing tied on one side with a overhand loop, and on the other with a fig8 loop. i was breaking 7mm nylon without slippage, so it would appear to be fine in this context, as you hypothesize.
J-ung: i posted the link. although- this testing i did is far from conclusive. it suggests that knots in the spectra webbing are fine for a one-shot deal anchor. whether the knot creeps faster than nylon (making it more susceptible to failure in multiple-use anchors where climbers are not checking whether there is adequate tail showing) is to be figured out by someone with more, uh, specialized equipment than i have access to.
in my head, i imagined spectra webbing knots sliding through themselves and failing with the tail going into the knot at high loads. from my minimal testing, this does not appear to be realistic. the 'slipperiness' of these webbings may refer to a different context, becuase surely it is based on something.
cheers,
anthony
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j_ung
Jun 7, 2006, 1:35 PM
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j_ung moved this thread from Trad Climbing to The Lab.
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scrapedape
Jun 9, 2006, 2:20 PM
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In reply to: In reply to: Have you tried testing a Ring Bend(water knot) or a Fig-8 Bend? I bet the fig-8 bend would hold just fine.... when you ask if i've tried the water/ring, what specifically are you asking about? essentially, that is the knot i used most. the overhand loop is the same knot as the ring bend/water knot. i just used it in a single strand instead of a continuous loop (which would likely be almost twice as strong). as for the fig8, for the first testing round, and some of the second round, i used a single strand of tech webbing tied on one side with a overhand loop, and on the other with a fig8 loop. i was breaking 7mm nylon without slippage, so it would appear to be fine in this context, as you hypothesize. J-ung: i posted the link. although- this testing i did is far from conclusive. it suggests that knots in the spectra webbing are fine for a one-shot deal anchor. whether the knot creeps faster than nylon (making it more susceptible to failure in multiple-use anchors where climbers are not checking whether there is adequate tail showing) is to be figured out by someone with more, uh, specialized equipment than i have access to. in my head, i imagined spectra webbing knots sliding through themselves and failing with the tail going into the knot at high loads. from my minimal testing, this does not appear to be realistic. the 'slipperiness' of these webbings may refer to a different context, becuase surely it is based on something. cheers, anthony
Anthony,
the overhand on a bight is similar but not identical to the water knot. In the overhand on a bight, three of the strands are loaded - one on one side, and two on the other. In a water knot, there are only two strands loaded - one on each side. This may or may not make a difference in the overall strength, that may or may not be compensated for by the fact that the total load is being held by two strands when you're talking about a sling being tied in a loop.
You could test a water knot by joining two pieces of webbing with a water knot, then putting an overhand on a bight in the free end of each piece, and testing as you have done.
Very creative methodology that definitely provides at least a rough idea of strength. Thanks for posting.
-Don
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cracklover
Jun 9, 2006, 3:22 PM
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In reply to: the 'slipperiness' of these webbings may refer to a different context, becuase surely it is based on something. cheers, anthony
IME, it's based on how poorly they work as friction knots for ascending nylon ropes.
Also, it's based on the results of testing spectra-based cords to failure. They found that cords with spectra innards failed in a unique way when tied with a double-fisherman. The sheath would break at relatively low loads, and the slippery spectra innards would simply slip out - retracing the knots - leaving a nicely tied double-fisherman knot made of nothing but sheath, while the unbroken inner cord simply came untied! Add an extra loop, and you get a tripple fisherman, which apparantly added enough friction so that it didn't have this failure mode.
GO
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tim
Jun 9, 2006, 3:38 PM
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It's great to see some hard evidence -- I am one of the people who has always thought that concerns about spectra knot slippage were more than a little overblown. The biggest concern in my mind was running out of biners and having to rap directly off a sling -- the low melting point concerned me.
I used Vectran cord as a prusik for literally years, and have sometimes resorted to using a wrapped spectra sling as an autoblock (I don't try to set any speed records on rappel, and so far, I've never managed to glaze one).
The only previous test of this sort that I recall seeing was Tom Moyer and Chris Harmston (or was it the Sterling guys?), in a paper titled 'Comparative Testing of High Strength Cord', which can be found here:
http://www.xmission.com/~tmoyer/testing/ (a GREAT resource!)
Their test convinced me that, for a dedicated prusik or (traditional) cordelette, nylon is the best choice (it proved to be the most resilient of the fibers). I junked my Vectran prusiks for Perlon cord, and switched to using an Alpine Equalizer for the cordelette (no fig-8 knot). But I've always been curious just how much weight a Spectra sling can take before a knot in it starts to slip.
Thank you for posting your data!
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dirtineye
Jun 9, 2006, 4:21 PM
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I've had a BD red and white cross striped specttra two foot runner for my rappell backup auto block for 4 years now.
IT's fine.
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cracklover
Jun 9, 2006, 5:01 PM
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In reply to: I've had a BD red and white cross striped specttra two foot runner for my rappell backup auto block for 4 years now. IT's fine.
I'm sure it is. Doesn't have to hold much on that side of the rap device. Try using that to prussik up a thin single line. Actually, please don't try it - it doesn't work!
GO
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sixleggedinsect
Jun 9, 2006, 6:20 PM
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funny. months of sittin' around, and suddenly: thread traffic!
In reply to: the overhand on a bight is similar but not identical to the water knot. In the overhand on a bight, three of the strands are loaded - one on one side, and two on the other. In a water knot, there are only two strands loaded - one on each side. This may or may not make a difference in the overall strength, that may or may not be compensated for by the fact that the total load is being held by two strands when you're talking about a sling being tied in a loop.
yeah. this hadnt occured to me earlier, and it was brought to my attention after i posted the same link on rec.climbing. im sure ill have a chance to pull on some more cord this summer, and i suspect there will be similar results. i'll just have to see.
re: other posters and the hypothesis that the slippery reputation of the tech fibers is based on their poor performance as friction knot slings-- i haven't gotten around to really 'testing' this, perse, but i have used a number of spectra slings (all of mine have nylon in 'em too, though) as friction knots and haven't seen anything that would make me doubt them.
of course, this may not apply to the really high-spectra-proportion slings which have less nylon on the outside. im looking forward to trying a couple out soon, just for my own edification.
the vectran/spectra/etc cords are generally fine for friction knots because they generally have a nylon sheath. they are too stiff for my liking for a dedicated prussik sling, but they work.
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tim
Jun 9, 2006, 6:46 PM
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In reply to: In reply to: I've had a BD red and white cross striped specttra two foot runner for my rappell backup auto block for 4 years now. IT's fine. I'm sure it is. Doesn't have to hold much on that side of the rap device. Try using that to prussik up a thin single line. Actually, please don't try it - it doesn't work!
No rational person would try a prusik with a spectra sling. A klemheist, on the other hand...
Well, here's some pictures. The line is an 8mm half rope. The weight is about 100lbs, give or take a bit. I stood on it briefly, but the S-hook started to bend before the klemheist slipped.
http://flaver.com/spectra/dsc_0001.jpg
http://flaver.com/spectra/dsc_0002.jpg
http://flaver.com/spectra/dsc_0003.jpg
Not suggesting it, just showing that it can be done and seems to work OK.
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cracklover
Jun 9, 2006, 6:57 PM
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In reply to: In reply to: In reply to: I've had a BD red and white cross striped specttra two foot runner for my rappell backup auto block for 4 years now. IT's fine. I'm sure it is. Doesn't have to hold much on that side of the rap device. Try using that to prussik up a thin single line. Actually, please don't try it - it doesn't work! No rational person would try a prusik with a spectra sling. A klemheist, on the other hand... Well, here's some pictures. The line is an 8mm half rope. The weight is about 100lbs, give or take a bit. I stood on it briefly, but the S-hook started to bend before the klemheist slipped. http://flaver.com/spectra/dsc_0001.jpg Not suggesting it, just showing that it can be done and seems to work OK.
Yup, IME, the fairly wide spectra slings with a lot of nylon in 'em in that configuration - straight across the sling, work pretty well. I've played with a lot of friction knots on a bunch of different types of runners. The new ones, especially the thin ones without a lot of nylon in 'em really suck at holding friction. By the way - check out the Hedden knot - it's a Kleimheist in reverse, and it has more holding power per wrap than a Kliemheist. Here's a link to pic of one.
GO
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gunkiemike
Jun 17, 2006, 11:02 AM
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My experience is that a 4-turn Klemheist knot in a Mammut 8mm spectra sling holds just fine (my 160 lb mass) on a 10.5 mm rope. I didn't expect it to - there's virtually no exposed nylon, and we all KNOW that Spectra is slippery - but I think the webbing's smaller size makes up for it.
My bottom line - I can use ANY cord/web I carry for a friction knot.
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