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strength of cams reslung with cord?
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james_va


Nov 7, 2008, 8:18 PM
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strength of cams reslung with cord?
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Hi Folks,

I've traditionally replaced the webbing with cord on my cams as the webbing has aged.

Currently, I've got a single loop of 5.5mm Spectra cord on each, which I've read loses strength massively when knotted. So I'm planning to replace this with a double loop of 6mm perlon. This may be a squeeze on my Black Diamond cams, but I think it'll go through.

I once read someone say (speculate?) that cord in general, being thinner than the original webbing on a cam, might apply pressure on a thin enough band to pull through the metal.

My questions:

1) With a single strand of, say, 6mm or 7mm cord (rated to 1700/2600lbs, or 772/1181kg, respectively) would the metal loop be the first point of failure in theory?

2) Moving to a double loop of 6mm (my actual plan), same question?

3) More a request for opinions as I'd presume nobody has tested this, but with the Camalots specifically, does squeezing the double 6mm cord through the loop meaningfully alter the vector forces applied to the loop under load, for better or worse? (Versus a single strand that fits very loosely.)

Many thanks for any thoughts or info on this topic,

-James


esoteric1


Nov 7, 2008, 9:27 PM
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Re: [james_va] strength of cams reslung with cord? [In reply to]
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i double mine up, with chord, youve got an instant extendo on there.


evanwish


Nov 9, 2008, 12:07 PM
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Re: [esoteric1] strength of cams reslung with cord? [In reply to]
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just wondering, would trippling them work? three extension lengths..

maybe not since no company does it..


coolcat83


Nov 9, 2008, 12:44 PM
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Re: [evanwish] strength of cams reslung with cord? [In reply to]
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i've heard (on these forums.... that certain places that resling will give you a triple if you want (yates? i'm too lazy to look it up). i'm not sure i see the usefulness though. at that point you have extra bulk and weight on every cam that you may not use all the time. just sling for the length(or double for two lengths, i happen to like the double) if you really need longer your probably going to want a runner or double sling on it anyway imo. unless your aim is to climb without extra slings?


evanwish


Nov 9, 2008, 12:57 PM
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Re: [coolcat83] strength of cams reslung with cord? [In reply to]
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just wondering, i guess it could reduce the extra slings and carabiners you take with you..

i almost always extend the doubled slings when i use those cams..


coolcat83


Nov 9, 2008, 3:22 PM
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Re: [evanwish] strength of cams reslung with cord? [In reply to]
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evanwish wrote:
just wondering, i guess it could reduce the extra slings and carabiners you take with you..

i almost always extend the doubled slings when i use those cams..

i have some flex cams with the extenable slings and almost always extend them too, if/when i resling them or use cord I'll probably have the smallest length about as much as the extended sling now and then the extended will be even longer, at least for the small cams, larger ones would hang low, so I'd probably still go with a runner on those.


evanwish


Nov 9, 2008, 6:53 PM
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Re: [coolcat83] strength of cams reslung with cord? [In reply to]
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coolcat83 wrote:
evanwish wrote:
just wondering, i guess it could reduce the extra slings and carabiners you take with you..

i almost always extend the doubled slings when i use those cams..

i have some flex cams with the extenable slings and almost always extend them too, if/when i resling them or use cord I'll probably have the smallest length about as much as the extended sling now and then the extended will be even longer, at least for the small cams, larger ones would hang low, so I'd probably still go with a runner on those.

yeah i've tried starting off the climb with them already extended (or at least the ones i think i might need for the crux) but it doesn't work that great cause they just hang way too low.. doesn't work

you can, however, make sure the biner is clipped a from the side with the sewn part of the sling, so you can drop the other chord quicker.. maybe i'll post a pic for clearity {sorry}


coolcat83


Nov 9, 2008, 7:18 PM
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Re: [evanwish] strength of cams reslung with cord? [In reply to]
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evanwish wrote:
coolcat83 wrote:
evanwish wrote:
just wondering, i guess it could reduce the extra slings and carabiners you take with you..

i almost always extend the doubled slings when i use those cams..

i have some flex cams with the extenable slings and almost always extend them too, if/when i resling them or use cord I'll probably have the smallest length about as much as the extended sling now and then the extended will be even longer, at least for the small cams, larger ones would hang low, so I'd probably still go with a runner on those.

yeah i've tried starting off the climb with them already extended (or at least the ones i think i might need for the crux) but it doesn't work that great cause they just hang way too low.. doesn't work

you can, however, make sure the biner is clipped a from the side with the sewn part of the sling, so you can drop the other chord quicker.. maybe i'll post a pic for clearity {sorry}

well if you know you'll need it extended for a crux you could always have it extended but use a rubber band to hold the sling shorter, by this i mean, take the extended sling fold it on it's self and put a small rubber band around it, just tight enough to hold it in place, when you place the piece, pull the sling (you could even do this when clipping the rope) and it will slip out of the band and be extended, no unclipping needed, clip the rope if you have no already and there you go. did that make sense or should i post pictures?


evanwish


Nov 9, 2008, 7:34 PM
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Re: [coolcat83] strength of cams reslung with cord? [In reply to]
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coolcat83 wrote:
evanwish wrote:
coolcat83 wrote:
evanwish wrote:
just wondering, i guess it could reduce the extra slings and carabiners you take with you..

i almost always extend the doubled slings when i use those cams..

i have some flex cams with the extenable slings and almost always extend them too, if/when i resling them or use cord I'll probably have the smallest length about as much as the extended sling now and then the extended will be even longer, at least for the small cams, larger ones would hang low, so I'd probably still go with a runner on those.

yeah i've tried starting off the climb with them already extended (or at least the ones i think i might need for the crux) but it doesn't work that great cause they just hang way too low.. doesn't work

you can, however, make sure the biner is clipped a from the side with the sewn part of the sling, so you can drop the other chord quicker.. maybe i'll post a pic for clearity {sorry}

well if you know you'll need it extended for a crux you could always have it extended but use a rubber band to hold the sling shorter, by this i mean, take the extended sling fold it on it's self and put a small rubber band around it, just tight enough to hold it in place, when you place the piece, pull the sling (you could even do this when clipping the rope) and it will slip out of the band and be extended, no unclipping if you havneeded, clip the rope e no already and there you go. did that make sense or should i post pictures?

wow i'm not even going to deny it, i NEVER thought of that! very good idea... and its so simple too..

maybe cause i usually don't use those cams unless i've already used the camalot of that size..


coolcat83


Nov 9, 2008, 7:47 PM
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Re: [evanwish] strength of cams reslung with cord? [In reply to]
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evanwish wrote:
coolcat83 wrote:
evanwish wrote:
coolcat83 wrote:
evanwish wrote:
just wondering, i guess it could reduce the extra slings and carabiners you take with you..

i almost always extend the doubled slings when i use those cams..

i have some flex cams with the extenable slings and almost always extend them too, if/when i resling them or use cord I'll probably have the smallest length about as much as the extended sling now and then the extended will be even longer, at least for the small cams, larger ones would hang low, so I'd probably still go with a runner on those.

yeah i've tried starting off the climb with them already extended (or at least the ones i think i might need for the crux) but it doesn't work that great cause they just hang way too low.. doesn't work

you can, however, make sure the biner is clipped a from the side with the sewn part of the sling, so you can drop the other chord quicker.. maybe i'll post a pic for clearity {sorry}

well if you know you'll need it extended for a crux you could always have it extended but use a rubber band to hold the sling shorter, by this i mean, take the extended sling fold it on it's self and put a small rubber band around it, just tight enough to hold it in place, when you place the piece, pull the sling (you could even do this when clipping the rope) and it will slip out of the band and be extended, no unclipping if you havneeded, clip the rope e no already and there you go. did that make sense or should i post pictures?

wow i'm not even going to deny it, i NEVER thought of that! very good idea... and its so simple too..

maybe cause i usually don't use those cams unless i've already used the camalot of that size..

i did it once with a triple sling when i wanted to carry it but it got hung up on things when worn over the shoulder. so i did that then just pulled to extend(almost like a tissue box fold with slings:P), as long as the biners are on the ends you don't loose the band, or you can tie part of the band to the sling so it stays put then feed the folded part through it. just play with it. so if you place that camalot but want it slung but fast, put the sling on it, and band the sling super short then clip the whole cam/sling thing together, yes it will be lower by the height of the biner and maybe a little sling, but slam it in clip the rope pull and it's extended. practice on ground with the bands and gear just to get it set so you don't have it release when you don't want it to.


(This post was edited by coolcat83 on Nov 9, 2008, 7:50 PM)


jay2817


Nov 9, 2008, 7:51 PM
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Re: [james_va] strength of cams reslung with cord? [In reply to]
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Where does the information that Spectra looses strength when knotted come from? Spectra is slippery, and requires a TRIPLE fisherman's knot. It should hold about 4000 lbs.

6mm perlon is not nearly as strong, and is not recommended for stringing protection. For information and details, check:
http://www.xmission.com/~tmoyer/testing/High_Strength_Cord.pdf

6 mm nylon is NOT strong enough for the task you propose. Remember, all cord looses about 30% of strength when knotted. The 6mm cord would only hold 1200 lbs. That's just not strong enough to hold a significant fall.


shoo


Nov 9, 2008, 8:59 PM
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Re: [james_va] strength of cams reslung with cord? [In reply to]
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Back to the topic.

There is some evidence that what you say is true. According to the BD C4 Camalot instructions:

"Clipping directly into the wire loop with a carabiner can reduce the strength of the unit by up to 2 kN (450 lbf)."
http://www.bdel.com/...Cam%20Info%20Tag.pdf

Presumably, this is due to the fact that carabiners are thinner than the sling. Whether that is directly due to the carabiner pulling through the wire or indirectly through a change in angle where the wire attached to the stem, no clue.

I would assume that a thin cord would do the same if not worse, but have no evidence to back this up.


(This post was edited by shoo on Nov 9, 2008, 9:00 PM)


austin.timm


Nov 9, 2008, 9:27 PM
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Re: [shoo] strength of cams reslung with cord? [In reply to]
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shoo wrote:
Back to the topic.

There is some evidence that what you say is true. According to the BD C4 Camalot instructions:

"Clipping directly into the wire loop with a carabiner can reduce the strength of the unit by up to 2 kN (450 lbf)."
http://www.bdel.com/...Cam%20Info%20Tag.pdf

Presumably, this is due to the fact that carabiners are thinner than the sling. Whether that is directly due to the carabiner pulling through the wire or indirectly through a change in angle where the wire attached to the stem, no clue.

I would assume that a thin cord would do the same if not worse, but have no evidence to back this up.

I may very well be wrong but I believe that the OP is referring to the wire loop on the 2nd gen camalot with the single thumb stem not the new C4 with the thumb loop... In which case it is not necessarily ''more dangerous'' to clip directly into the metal loop.


krosbakken


Nov 9, 2008, 9:29 PM
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Re: [evanwish] strength of cams reslung with cord? [In reply to]
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evanwish wrote:
just wondering, would trippling them work? three extension lengths..

maybe not since no company does it..


I bought some metolius cams that had the webbing doubled, they are rad I love it. But metolius stopped doing it.

The doubles are sweet but triple sounds to messy.


shoo


Nov 10, 2008, 5:10 AM
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Re: [austin.timm] strength of cams reslung with cord? [In reply to]
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austin.timm wrote:
I may very well be wrong but I believe that the OP is referring to the wire loop on the 2nd gen camalot with the single thumb stem not the new C4 with the thumb loop... In which case it is not necessarily ''more dangerous'' to clip directly into the metal loop.

You're absolutely right. I reread the OP. Carry on.


dingus


Nov 10, 2008, 5:32 AM
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Re: [jay2817] strength of cams reslung with cord? [In reply to]
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jay2817 wrote:
Where does the information that Spectra looses strength when knotted come from?

jay2817 wrote:
Remember, all cord looses about 30% of strength when knotted.

Um..... maybe he got it from YOU?

DMT


james_va


Nov 10, 2008, 4:53 PM
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Re: [dingus] strength of cams reslung with cord? [In reply to]
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Hi Guys,

Thanks to all who have responded. Jay, thanks for the link -- I was actually thinking of the document you cite re: the loss of strength when knotted.

http://www.xmission.com/...gh_Strength_Cord.pdf

Page 3: "Knot efficiencies for a figure-eight knot ranged from 40% on the Gemini to 92% on the Nylon."

Also, see attached for a screenshot from the study that shows the fall-off in strength of nearly all the Spectra-type cords when knotted w/triple fisherman knots.

[As a tangent, the study notes that Spectra shows a fall-off in strength after being flexed (per the second attachment), whereas perlon doesn't.]

Actually, though, my concern is less about the strength of knotted Spectra than about the narrow force band a single strand of 5.5mm cord applies to the cam handle -- as mentioned about the carabiners and Camalots (I do have the older-school Camalots with the small metal rings, along with a bunch of other cams).

I was hoping that two bands of 6mm cord would be enough to dissipate the force such that it wouldn't be an issue.

Given that strengths are given for single strands, I was also hoping that with a double-looped 6mm cord -- which would have four strands connecting 'biner to cam -- the weight would be acceptably spread out.

So, two follow-up questions:

1-Would it be spread out enough for whichever cams are most vulnerable to pull-through? Any hard data to cite? [I understand that hard evidence is a long shot.]

2-How strong would 6mm that's always doubled (i.e., never extended) be?

Many thanks for the input and conversation.

-James
Attachments: Picture 1.png (34.5 KB)
  Picture 2.png (46.6 KB)


james_va


Nov 10, 2008, 7:43 PM
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Just to share some add'l info I found after looking into using tied webbing:

http://www.fishproducts.com/tech/webbing.html

Takeaways:

-in general (at least with webbing), loop strength may be ~10% less than twice the single-strand strength (assuming a single loop). Loops are tested over 10mm pins to simulate carabiners.

-webbing may (or may not) be OK to self-resling cams with, depending on how you choose to interpret the responses... (and I believe it may have been a single 9/16" supertape runner that came on my original cams)

Although his responses are now more than a decade old, thanks to Chris for the insights on the linked posts above.


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