Author Topic: Braided and kernmantle ropes : Pros and cons  (Read 10280 times)

xarax

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Braided and kernmantle ropes : Pros and cons
« on: June 17, 2011, 12:29:59 PM »
   Beside the specific chemical composition of the fibres a synthetic rope is made of, the way/pattern those fibres are woven into it plays a major role in its knotting characteristics.
   I have seen that the (single or double) braided ropes have a more flexible cross section, which is good for a practical knot, because the contact areas between the rope strands, inside the knot s nub, are greater. However, this flexibility results in some difficulty of tying the knot in the first place, and then dressing it in the proper, final pre-loaded form. A knot that has not been dressed as it should, runs the danger to be prone to slippage more, and have a lower maximum strength, than a properly dressed one. On the other hand, kernmantle ropes are slippery and less flexible, but tend to follow smoother paths inside the knot, are easier handled during the forming and dressing phases of the knotting procedure, and "remember" this dressed form during the loading phase.
   One other thing that I do not know, is the consequences those differences have in the knot strength. We have a vague idea that the wider a first curve of the standing part is, the higher the maximum strength of the knot will be. However, is this true, in the same degree, with a knotted braided rope, as it is with a knotted kernmantle rope ?
   A rope is not one single fibre, it is a weaved structure of many fibres. How do the different patterns those fibres are woven into the rope, effect the practical knots we tie on/with them ?
    
  
« Last Edit: June 17, 2011, 03:11:36 PM by xarax »
This is not a knot.

TheTreeSpyder

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Re: Braided and kernmantle ropes : Pros and cons
« Reply #1 on: June 22, 2011, 01:32:10 AM »
Because a tighter line will resist bending more, it can be leveraged more against the potential/rated tensile strength of the rope device's capacity.  A tight rope can help keep grit from working inside fibers and degrading them; there are trade offs!

Webbing will leverage deformity less on bend, than rope.  But, rope can be tied in a knot with less deformity!  Round over flat is a choice in itself.

i think that in working lines a Double Bowline is stronger because it takes a longer distance, to make the same deformity on the side of a single loaded leg's first deformity; as opposed to the other side of 2 legs of support (each leg carrying half the loading of the Standing) of the produced fixed eye.

To me, a rope is a flexible pipeline that can carry physical force (in tension direction only) in that line.  Some line carrys it's force on the outside around a core, some carry the force protected in the core, some use both sheath + core.

Dan_Lehman

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Re: Braided and kernmantle ropes : Pros and cons
« Reply #2 on: June 22, 2011, 03:54:36 AM »
 ???

. . .  wait a minute, "TheTreeSpyder" ... :

what year is this?  Am I dreaming?  Am I 21 again?!


 :D

TheTreeSpyder

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Re: Braided and kernmantle ropes : Pros and cons
« Reply #3 on: June 22, 2011, 11:21:11 AM »
Wellllllllll,

If it is a dream; it is probably a nightmare!
Heck; i even polluted a thread you started already;
  or something like that.


Bob Thrun

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Re: Braided and kernmantle ropes : Pros and cons
« Reply #4 on: June 22, 2011, 06:27:01 PM »
   However, this flexibility results in some difficulty of tying the knot in the first place, and then dressing it in the proper, final pre-loaded form.
Huh? Flexible ropes are easier to tie.
Quote
On the other hand, kernmantle ropes are slippery and less flexible,...
I have not noticed that kernmantle ropes are any more or less slippery than other ropes.  Slipperiness depends on the fibers used to make the rope.  Kernmantle ropes can be made stiff or flexible.  All the single and double braid ropes I have seen were flexible.

xarax

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Re: Braided and kernmantle ropes : Pros and cons
« Reply #5 on: June 22, 2011, 06:58:18 PM »
   However, this flexibility results in some difficulty of tying the knot in the first place, and then dressing it in the proper, final pre-loaded form.
   Huh? Flexible ropes are easier to tie.

   I bypass that "Huh" ...Mistied...
   No.  I was talking about "this" flexibility of the cross section. But ths applies in general, too. Flexible rope working ends are not easily driven into the knot s nub, and need more attention into their handling, so that the knot is dressed properly. Stiff ropes go into the structure almost by themselves during the tying phase, and tend to occupy the optimum place into the knot nub during the dressing phase. Flexible ropes do not "remember" the actions of our fingers long enough, and have to be carefully set and reset in each step.

I have not noticed that kernmantle ropes are any more or less slippery than other ropes.

    :) Well, I, for one , I have, and many other knot tyers have noticed the same thing, too. Old knots were abandoned and new knots are invented to adress this situation. You must be very young, so you have not met the old ropes, or very old, so you do not remember them !  :)
« Last Edit: June 22, 2011, 06:59:43 PM by xarax »
This is not a knot.

Dan_Lehman

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Re: Braided and kernmantle ropes : Pros and cons
« Reply #6 on: June 23, 2011, 06:47:56 PM »
Let's leave that different ropes can have different behaviors.

There are some kernmantle ropes (PMI's standard (No-Flex, my name) "pit rope", e.g.)
that really don't want to bend to even a 1-diameter radius; but there are some laid
ropes --hard laid-- with similar intractability (and forget about splicing them!).

But there are some more flexible kernmantle ropes (PMI's "EZ-Flex"), though
these tend still to be moderately firm & non-bending.

FYI, my evolving definition of "kernmantle" (and I favor "mantle" vice "mantel"
for its English (at least) significance) is {{a rope composed of an outer sheath
around a core that itself is a multiplicity of fibres or cords, not able to be used
qua single rope}}.  This contrasts with some definitions that I've seen in which
it appears that the relative novelty of climbing/caving/SAR ropes is only lately
being accommodated.  Granted, probably most of what is called "k." is in fact
meeting these narrow definitions, but it seems better to define the term in a way
that is more useful vis-a-vis rope construction.  If the core cannot stand by itself,
then ... "kernmantle".  (A "two-in-2" double braid thus doesn't qualify; and there
was one (Rocca?, Spanish?) rockclimbing rope that had a braided core, which
would make it non-k. by my definition; I don't loose sleep over this.

There are some rather big ropes made with quite soft lay that bend over
backwards with no complaint.

With a firm cross section, one has smaller contact patches (theoretically,
a round cross section would yield sequence-of-tangent-points, linear
contact areas, yes?); with compressive rope, the contact patches get
planar.  The so-called (by me) "reverse groundline hitch" is a common
commercial-fisherman's knot that depends on relatively flat (as thoug
compressed) cordage, which is even often used in adjacent pairs,
thereby exaggerating the width dimension vs. thickness, and getting
relatively large contact patches.

I will revisit my brief test of a mid-line eyeknot tied in 12-strand Spectra
--a very slick multifilament material, in a very smooth construction--
which surprised me by holding, for some small but pulley'd extra loading
of maybe 200#?  And then the same knot (approximated, we might
say, re pure geometry) in firmer cross-section kernmantle accessory
cord (6mm, nylon, not new, though hardly much used but for age),
seemed to not hold even in my manual loading (IIRC) !!  --which I see
as an effect of material firmness, with a result contrary to material
slickness.

And beyond flexibility is another factor, *springiness* !?  I found some
soft-laid but rather hard cross-sectionally 4mm? diameter polypropylene
cord to refuse to honor the EBDB's security, holding only briefly
before gently loosening all 'round (!!); yet the Janus bowline with
its sharper turns of the bight did not loosen so much --the bights
tried to open like scissor legs and the turNip resisted this easily,
and that was all (whereas in the EBDB all of the turns just
widened in diameter!).  --this was quite a surprise.  I still think think
that the EBDB is one of the most secure bowlines for many
ropes, but not for that cord.


--dl*
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