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forbin
May 5, 2004, 6:19 AM
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Today a guide friend of mine pointed out that double fisherman's have been proved unsafe for tech cord. He then told me that he doesn't trust the recommended triple either since he recently discovered that the kevlar can slide back through the nylon sheath. So he uses a euro death knot backed up with another euro death knot. Apparently a euro death knot can roll over in thin material, but if it is backed up, this can't happen. After reading a recent thread on material breaking strengths
http://www.rockclimbing.com/forums/viewtopic.php?t=59423
i'm not sure i'll be using tech cord for cordelettes anymore, but it's still useful for slinging hexes. What do you think?
alex
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strider
May 5, 2004, 7:54 AM
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But even if you sling your hexes with it, what knot are you going to use to tie the cord to the hexes?
I am curious about this since I use the tech cord as trad draws. I carry two shoulder length slings of tech cord, tripled up as trad draws, as my back-up prussiks. I hardly ever use them as draws because I usually have enough, but it never hurts to have 2 extra draws. I have mine tied with a double fisherman's and it seems to be sufficient. There is no rolling or anything like that and I have fallen on these. Nothing spectaculor but they did the job of stopping me. So far I think I will stick with the double fishermans since it has worked well so far. Maybe I will extend the tails or something...
-n
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mingleefu
May 5, 2004, 8:14 AM
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yes, the double fisherman's can still slip a little bit. It's minimal, by all reports, but it can happen.
so use the triple fisherman's. And leave no less than 1 inch in the tail of either end of the knot.
From your description, it sounds like the slings will have the EDK in there, and then also another EDK hanging off the side of the sling...
HEX
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\_/
looks a little clunky to me. use the triple fisherman's. Be sure to leave that 1+ inch tail on it, and dress it properly. you won't have any issues.
Note that the 1+ inch is the length of the CORE, not of the sheath of your cord.
should be studying...
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squish
May 5, 2004, 8:18 AM
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In reply to: so use the triple fisherman's.
IIRC, there is zero advantage to using a triple fisherman's knot rather than the standard double. I believe it's actually more slippery when triple.
Leave long tails and just check 'em once in a while.
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overzealous
May 5, 2004, 1:08 PM
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It depends on the material. For a material with sufficent friction against itself a double fishermen's can actually be more secure (since the outer and inner loops will grab but it's difficult to get the middle loop tight leaving slack in the system). With more slippery material (such as Spectra) this is not a problem and all three loops can be tightened under body weight.
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paulraphael
May 5, 2004, 5:06 PM
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Your friend's practice sounds very dangerous to me.
The EDK is a potentially weak knot. It's more than strong enough for rap loads, but pro needs to hold falls.
The normal failure mode of the edk is multiple knot inversion. Your friend's solution of backing up with another edk should solve that. But then the issue is how much of the strength of the cord does the knot preserve? Knots that bend the rope at tight radii at a high load point tend to be weak. My guess is that an edk would allow the cord to break at less than half its rated strength. double and tripple fisherman's knots preserve over 70%.
I wouldn't trust any unorthodox knots without seeing thorough tests done by someone who know's what they're doing (the UIAA, Black Diamond, etc.).
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dirtineye
May 6, 2004, 1:00 AM
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Why don;t you just send them to Yates and have em slung with sewn dyneema? I love my dyneema slung hexes.
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andypro
May 6, 2004, 2:08 AM
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In reply to: Why don;t you just send them to Yates and have em slung with sewn dyneema? I love my dyneema slung hexes.
:shock: :shock: They'll do that? How much did it cost you? (or do you ahve the WC dyneema slung hexes or soemthing...in that case, nevermind :P ) I just might have a look into this...Im sick of cord fraying and frying and all that crap on my hexes. :evil:
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forbin
May 6, 2004, 3:41 AM
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In reply to: I wouldn't trust any unorthodox knots without seeing thorough tests done by someone who know's what they're doing (the UIAA, Black Diamond, etc.).
Yeah, I agree, that's why I threw this out there to see if anyone knew of some science backing up or refuting the EDK (which, despite it's name, has never actually killed anyone to my knowledge).
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alpnclmbr1
May 6, 2004, 3:54 AM
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In reply to: In reply to: I wouldn't trust any unorthodox knots without seeing thorough tests done by someone who know's what they're doing (the UIAA, Black Diamond, etc.). Yeah, I agree, that's why I threw this out there to see if anyone knew of some science backing up or refuting the EDK (which, despite it's name, has never actually killed anyone to my knowledge).
http://www.xmission.com/...yer/testing/EDK.html
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dirtineye
May 6, 2004, 2:21 PM
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In reply to: In reply to: Why don;t you just send them to Yates and have em slung with sewn dyneema? I love my dyneema slung hexes. :shock: :shock: They'll do that? How much did it cost you? (or do you ahve the WC dyneema slung hexes or soemthing...in that case, nevermind :P ) I just might have a look into this...Im sick of cord fraying and frying and all that crap on my hexes. :evil:
I have not done this, but yates advertizes that they are the WC official reslinger, and al the sewn stuff I have ordered from yates has the ce sticker on it.
They have a wide variety of reslinging stuff on thier site, check it out.
When my dyneema slung rockcentrics ( or anything else I have) need mew slings, I'll go to Yates.
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dirtineye
May 6, 2004, 2:26 PM
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In reply to: In reply to: In reply to: I wouldn't trust any unorthodox knots without seeing thorough tests done by someone who know's what they're doing (the UIAA, Black Diamond, etc.). Yeah, I agree, that's why I threw this out there to see if anyone knew of some science backing up or refuting the EDK (which, despite it's name, has never actually killed anyone to my knowledge).
Personally, I like the flemish bend, aka rewoven or retraced figure 8 bend, but that knot from Edlrid's tests that is a "flat double fisherman's", is one I would consider and have tied enough to feel comfortable with IF I were worried about a knot getting stuck.
Please if you go to this link above, read what Moyer says about knots geting stuck vs rappel knot failure.
Non of this answer,s the question about a knot for tech cord, I thought I had seen the triple fisherman's recommened for that somewhere. Moyer has a link to high strength cord on teh page the above link takes you to though.
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paulraphael
May 6, 2004, 3:57 PM
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the manufacturers recommendations that i've seen all call for a tripple fisherman's on tech cord. i haven't heard any informed allegations or seen tests showing the knot slipping.
it's a MUCH stronger knot than the edk. remember that the whole point of the edk is to resist hanging up on flakes and cracks when you pull rappell ropes.
as an aside, the edk is more than strong enough for rappelling, but it's very important to tie it right. meaning, tightly, without crosed strands, and with 9" or longer tails. especially with different sized ropes. the edk's security is much more dependent on these details than other climbing knots.
this is probably old news to everyone, but i don't think it can be repeated enough. there's no redundancy at your rap knot, so it better be 100% good.
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jumaringjeff
May 6, 2004, 4:12 PM
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I used to use a cordelette that was made out of tech cord, but ever since I retired it and started using plain 'ol 7mm perlon for my cordelettes, I'll never go back.
As far as hex's, I currently have mine slung with spectra cord but I plan on slinging them with dyneema this summer.
Simple as that.
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csoles
May 6, 2004, 5:04 PM
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In reply to: As far as hex's, I currently have mine slung with spectra cord but I plan on slinging them with dyneema this summer.
What, praytell, do you think the difference is?
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sandstone
May 6, 2004, 7:19 PM
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I had Ragged Mountain in NH sew custom slings on my old TCU's. They did a great job, and their people were very friendly. At the time they said they could do most any kind of pro, except for Tricams (you'll have to get Yates to do those).
http://www.raggedmt.com/
Also, Ragged has a huge selection of hard to find webbing, cord, fabric, plastic and metal buckles, etc. If you're ever looking for something that you just can't seem to find, Ragged probably has it in stock.
This probably sounds like an advertisement, but it's not -- I'm just a satisfied customer.
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jumaringjeff
May 6, 2004, 7:31 PM
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In reply to: In reply to: As far as hex's, I currently have mine slung with spectra cord but I plan on slinging them with dyneema this summer. What, praytell, do you think the difference is?
well let's see....
1. dyneema is more supple than cord, reducing the effects of rope drag.
2. no need to worry about a knot (which is what the thread is about in the first place)
I could probably think of others, but those two reasons are enough for me. But hey, this is just my opinion. I'm sure others prefer cord on their hexes, and that's just fine.
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geezergecko
May 6, 2004, 9:10 PM
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In reply to: In reply to: In reply to: As far as hex's, I currently have mine slung with spectra cord but I plan on slinging them with dyneema this summer. What, praytell, do you think the difference is? well let's see.... 1. dyneema is more supple than cord, reducing the effects of rope drag. 2. no need to worry about a knot (which is what the thread is about in the first place) I could probably think of others, but those two reasons are enough for me. But hey, this is just my opinion. I'm sure others prefer cord on their hexes, and that's just fine.
There is dyneema cord and there is spectra cord.
There are also dyneema slings and spectra slings.
When you mention spectra, you are implying cord, and when you mention dyneema, you are implying slings, are you not?
As far as I know, dyneema and spectra are identical materials (or very very close). The different names are because of patents in Europe and the USA. The same applies for perlon (Europe) and nylon (USA). You say tohmahtoh and I say toemaetoe...
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jumaringjeff
May 6, 2004, 9:33 PM
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yes.
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rgold
May 7, 2004, 3:18 AM
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Getting back to knots in Tech Cord. Here are some things we actually know:
From Blue Water Technical Manual:
"We also recommend joining the ends of Titan cord slings with a triple fisherman's knot to minimize any chance of the knot slipping."
Tech Cord is Technora, and according to Tom Moyer's tests (five trials), Technora loops tied with a double fisherman's knot broke at an average of 3628 lbf (std. dev. 46 lbf). Loops tied with a triple fisherman's knot broke at an average of 4231 lbf (std.dev 190 lbf). No slipping in the triple fishman's, but
"For a double fisherman's knot, Gemini and Titan share an interesting failure mode. The sheath breaks at the knot and the slippery core unties, pulling through the sheath. When a triple fisherman's knot is tied, this doesn't happen. The strength gain for the triple fisherman's is not large, but it is enough to change the mechanism."
Based on these results, using an EDK instead of a triple fisherman's makes no sense. It is way less stable, and in 11mm rope (!) it breaks at half the values of the triple fisherman's knot in Technora. Unless someone can cite reliable test results to the contrary, the triple fisherman's is the way to go for Tech Cord.
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