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Cody JW wrote:On this subject, I was wondering what you thought of using half inch tubular webbing for handline,I have some and have used it before.You can carry 50 feet of it alot more compact than rope.I think the strength on it is around 1200 lbs.
NZcaver wrote:You're a smart guy - look up the specs.
Figure out the MBS/MSWL for your particular nylon cordelette setup (single/double, knots, wet cord, etc), and decide for yourself. Am I missing something?
knudeNoggin wrote:There is several things to comment on in this issue. Perhaps Bob Thrun will
contribute some remarks about discriminating between rates of force upon
such things as rope -- I know that he often challenges the common notions
of "shock load" as more myth than substance.
knudeNoggin wrote:1) Thanks for the URLink to that paradigm image of a cordellete.
Now, please note that is it sub-optimal, and really there should be but
ONE KNOT --viz., the "powerpoint"-- in the structure, not two; the two
free ends should be left free (or tied off with an Overhand stopper snug
to the powerpoint) on the clip-in (sort arms) side of the powerpoint
-- there is no reason to join the ends in some anchor leg! (This freedom
leaves the cord available for non-cordelette uses; it yields uniformly
strong anchor legs.)
knudeNoggin wrote:The clip-in eyes likely if anything make for a weaker
structure if there are three of them spreading the load on the 'biner than
just two; two eyes are way more strength than your body can handle
(and are double the single anchor leg, of course).
knudeNoggin wrote:2) 5mm "spectra" , "strength" : mostly in the situations encountered where
cordelettes are used one is concerned about an impact load; static material
such as HMPE (Dyneema, Spectra) or aramid (Kevlar, Technora) fibres will
increase the peak impact force. Thus, whatever equal or greater tensile
strength they might show which looks so good to marketers of a product
are less good in practice. Moreover, knots weaken these materials more
than they do for nylon.
knudeNoggin wrote:3) As has been presented in John Long's substantially revised, 2nd edition
of Climbing Anchors , the unequal legs of a cordelette make for unequal
load distribution (barring some clever anticipation of the effect by adjusting
each arm's tension at the tying).
It should be pretty easy to see that it doesn't
take much of an angle shift with static material such as HMPE cord to have
just one leg loaded.
knudeNoggin wrote:4) As for demanding that a single anchor leg sustain maximum expected load,
that too might be overdoing it: surely one must expect that the other two
legs are not worthless --i.e., they will require some significant force to fail-- ,
and as the expected loading is dynamic (what else?), it will be diminished by
the failing of those other arms; so, the maximum impact force to the overall
structure will be reduced before it hits an isolated leg (when loaded in the
expected angle to the cordelette).
ek wrote:knudeNoggin wrote:... Perhaps Bob Thrun will
contribute some remarks about discriminating between rates of force upon
such things as rope -- I know that he often challenges the common notions
of "shock load" as more myth than substance.
OK...but so what? What effect does that have on this issue?
An overhand knot tied to establish the power point / master point would still be considered to reduce the cord's strength by up to half, wouldn't it?
knudeNoggin wrote:1) Thanks for the URLink to that paradigm image of a cordellete.
Now, please note that is it sub-optimal, and really there should be but
ONE KNOT --viz., the "powerpoint"-- in the structure, not two; ...
This is irrelevant to my question--it does not affect the strength of the cordelette as per my calculations. However, this is a useful thing to consider and discuss; thank you for bringing it up.
The way you're saying we should tie cordelettes is perfectly acceptable, but not demonstrably superior. Typically one's protection will be sufficiently far apart that there will be little advantage to having the excess cord available. The excess cord ...
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