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A couple of cordelette questions from a NOOB.

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A couple of cordelette questions from a NOOB.

Postby TimB » Wed Jul 18, 2012 5:43 pm

A couple of (dumb?) questions on cordelettes;

1) What cord diameter and material of construction do you folks prefer? I have seen everything from 5mm on up to 7mm; nylon or?
2) What length cord? 15 feet, 20, ??
3) Knots: just use a double fisherman's or??
4) Should cords be made from static line or can you use a dynamic line?

Thanks for the input!
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Re: A couple of cordelette questions from a NOOB.

Postby Fletch » Wed Jul 18, 2012 6:56 pm

EB, Dow, Kane or somebody else may correct me, but these are my novice answers:

1) depends if it dubs as a prussik. 7mm works great when the rope could be wet (glacier) and 6mm works better for drier applications - also depends on what size rope you're climbing on. But 6-7mm is what I use for mountaineering (i.e. not rock) applications.
2) no idea here. probably depends on the application. both would probably work fine.
3) double fishermans with cord and water knot with webbing. unless you're in a hurry - then there are all sorts of quick euro-death-knot-type of knots to use...
4) static. i think the sheath starts to screw with the knot on a dynamic one, but again, could be wrong.
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Re: A couple of cordelette questions from a NOOB.

Postby mfox79 » Wed Jul 18, 2012 7:02 pm

For my trad rack I have always used 6mm static cord. I believe it is around 20ft long. but I could be wrong. I have not untied it and its arounnd three years old
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Re: A couple of cordelette questions from a NOOB.

Postby TimB » Wed Jul 18, 2012 7:37 pm

Fletch, and fox:
Thank you.
I have some static(accessory cord) of 6mm dia, so I am set there, sounds like. I was just thinking(wondering) why we use static cord for anchors instead of dynamic, due to shock loading and such? However,Fletch; you answered that question, looks like.

Thanks again.
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Re: A couple of cordelette questions from a NOOB.

Postby mattyj » Wed Jul 18, 2012 8:02 pm

TimB wrote:1) What cord diameter and material of construction do you folks prefer? I have seen everything from 5mm on up to 7mm; nylon or?

The two standards are typically 7mm nylon or 5-6mm spectra/dyneema/technora cord. I used to use spectra for its low bulk but switched to nylon for several reasons. First being that although static, it has more stretch than spectra; drop testing has shown that a factor 1 fall on spectra-type cord produces forces > 20kn, which will kill you and also overload other anchor components such as biners and bolt hangers. Second being strength reduction due to repeated flexing; see this summary and the original report. PMI 6mm nylon is rated at 6.8kn; this means that a cordalette strand with a knot in it will only be approx. 6.8+(6.8*2/3)=11.3kn, which for me personally, is not strong enough to justify using it in an anchor.

2) What length cord? 15 feet, 20, ??

Typical length is 20 feet.
3) Knots: just use a double fisherman's or??

If using spectra-type cord, the recommendation is a triple fisherman's.
4) Should cords be made from static line or can you use a dynamic line?

I don't know of any reason not to use dynamic line, and I've wondered about using dynamic line to reduce anchor loads if you fall while at the belay, but then your cord is bulkier and weighs more - and I've never seen dynamic line sold by the foot.

If you're new to this, I would highly recommend reading up on the testing John Long et al did before the release of his latest climbing anchors book, which called into question how well a cordalette actually equalizes and how bad extension really is - and let to the adoption of alternative schemes like the equalette. I'm not saying that cordalettes are bad or that I never use them, but a lot of people are still blindly placing cordalettes for all their anchors based on assumptions that have since been proven inaccurate.
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Re: A couple of cordelette questions from a NOOB.

Postby TimB » Wed Jul 18, 2012 8:10 pm

mattyj,
Very helpful and just the sort of info I am seeking.
I will look up Long's study on that subject. I have been reading Lubben's book on anchor construction and going out on the side of the road and practicing placing pro and building anchors on any suitable rock that is within arms length reach. Get some funny looks from folks around here when you do that, btw. :lol:
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Re: A couple of cordelette questions from a NOOB.

Postby Kahuna » Wed Jul 18, 2012 8:32 pm

No need to over complicate such a simple piece of gear.







Simpler answer... BUY ONE!

Sterling 7mm x 20' Cordelette=$10.95

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Re: A couple of cordelette questions from a NOOB.

Postby TimB » Wed Jul 18, 2012 8:39 pm

A5RP wrote:No need to over complicate such a simple piece of gear.







Simpler answer... BUY ONE!

Sterling 7mm x 20' Cordelette=$10.95

Image


Oh, yeah...good idea!
:oops: :lol:


btw, never heard of GearXpress. Looks like a good site.
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Re: A couple of cordelette questions from a NOOB.

Postby Kahuna » Wed Jul 18, 2012 9:46 pm

Gearxpress is a family owned Web dealer that originated in Ill. Great bunch of guys w/great service and deals!!!
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Re: A couple of cordelette questions from a NOOB.

Postby kylenicolls » Thu Jul 19, 2012 7:24 am

TimB wrote:PMI 6mm nylon is rated at 6.8kn; this means that a cordalette strand with a knot in it will only be approx. 6.8+(6.8*2/3)=11.3kn...


Is that some assumption that a strand with a knot in it retains only 2/3 of its load rating?

Thanks, Kyle.
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Re: A couple of cordelette questions from a NOOB.

Postby mtndonkey » Thu Jul 19, 2012 3:58 pm

Everything has been covered fairly well already, but I'd like to throw in another tying recommendation than what was previously stated. I really like using two overhand knots for several reason. They are much easier to untie after the anchor has been loaded, it is simple to tie (read hard to screw it up), and easy to adjust the length of the anchor. Many people use double fishermen's knots and tie them incorrectly, yet it looks right.
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Re: A couple of cordelette questions from a NOOB.

Postby mattyj » Thu Jul 19, 2012 5:17 pm

kylenicolls wrote:Is that some assumption that a strand with a knot in it retains only 2/3 of its load rating?


Yes. Although it varies a bit based on the knot tied and properties of the rope, 2/3 is a good approximation for the standard climbing knots when tied with nylon. Although in reality both strands are tied into the powerpoint figure 8, which probably means that each is only rated to 2/3 with the weak point being the powerpoint knot. 2*6.8*2/3=9kn (!).
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Re: A couple of cordelette questions from a NOOB.

Postby brenta » Thu Jul 19, 2012 7:26 pm

mattyj wrote:PMI 6mm nylon is rated at 6.8kn; this means that a cordalette strand with a knot in it will only be approx. 6.8+(6.8*2/3)=11.3kn, which for me personally, is not strong enough to justify using it in an anchor.

The PMI site quotes 7.5 kN for 6 mm nylon accessory cord. That makes some sense, because 7.2 kN is the minimum for CE certification and PMI claims its cord is certified.

Also, when a leg contains a knot, the rating of that leg is roughly twice the strength of the knotted cord, as you say in your later post, because the tension is the same in the two strands. (Ignoring friction, which could make things either better or worse.)

On the other hand, you have at least two legs, each worth about 10 kN. Then again, perfect equalization is a myth, and most of the load may be on one leg. However, loads in excess of 10 kN are very rare. Except that...

All in all, I prefer my cordelettes to be a little stronger, but I don't think those who use 6 mm cord are gonna die.
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Re: A couple of cordelette questions from a NOOB.

Postby mattyj » Thu Jul 19, 2012 7:39 pm

You're right. REI says 6.8, for some reason.
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Re: A couple of cordelette questions from a NOOB.

Postby brenta » Thu Jul 19, 2012 8:04 pm

I don't know how to explain the difference. It may be a different product. REI also carries pre-cut 6mm PMI cordelettes for which they list 7.5 kN.
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