Author Topic: Knot Testing  (Read 41034 times)

Fairlead

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Re: Knot Testing
« Reply #15 on: January 17, 2007, 04:55:26 PM »
Sorry Paul, I missed out the uses that I would put this knot to in the end of lines used in industrial roping (as we call it here.
First - by inserting a nylon hard eye and clipping in a Karibiner, or inserting a clip hook eye in the noose - to attach, hoist and lower tools, equipment etc.
Second - by clipping a Karibiner into the noose and pulling it up tight (also tape or seize the working end to the standing part) and use it instead of an eye splice or bowline - for use at the end of a safety line.  This is the reason I would like you to consider this in your tests, because I am convinced it is stronger than both the bowline and the eye splices (especially in braided ropes).

Gordon

PaulKruse

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Re: Knot Testing
« Reply #16 on: January 17, 2007, 05:57:23 PM »
Gordon:

Thanks for the picture.  I love that knot, but I don't think I've ever seen that knot used in any rigging.

Where do you think it would be useful for the rigging of scaffolding or fall protection?

Paul Kruse

Dan_Lehman

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Re: Knot Testing
« Reply #17 on: January 17, 2007, 06:23:57 PM »
You have both miss-read what I wrote - I referred to a Double Overhand NOOSE not a Loop.
Or not quite:  having recently read Wright & Magowan's 1928 article in Alpine Journal,
I glide by "noose" meaning "fixed-eye knot" too easily!  (They remark at the unseemliness
of the word, themselves, but go along with then traditional use.)

Yes, it develops friction.  In one test of 8mm low-elongation kernmantle rope,
the knot fared well; the break came not around the roughly 10mm dia 'biner,
but at the turn of the loaded end of the Strangle around the noose SPart
--IN THE NOOSE SPart!
cf www.caves.org/section/vertical/nh/46/doitie.html
It was also tested in arborist rope by Paolo Bavaresco, and IIRC, he found
it to be in the 70% range there.

This suggests to me that reorienting the Dbl.Oh. into a Fisherman's Bend
(Anchor H.), where the loaded line will make a fuller turn around the 'biner,
and contact the noose SPart after other parts contact it, and I think better
distribute its force around the line, should be stronger (and more easy to
untie).  This is obviously a better structure as the noosed object becomes
wider relative to the line, and one has more of a choke-hitch profile/angle.

Not that strength should be much concern in the range of choices here,
with such significant safety factors--your body will break long before
that 3/4" rope does.  I'm more concerned about running the round rope
over the hard edges of iron.  A 2-loop fixed eye knot will split to force
to 1/4 on each of four eye legs, and that seems good.

Hmmm, Paul, you say that it's soft-laid rope:  what commercial fishermen
do with much of there laid rope is tuck the end through it, when finishing
various knots (becket hitches, fisherman knots, 2 HHs); you might try
this with your laid line.

--dl*
====

postscript:

There is further advice on using the Dble.Oh., in cocktails--FWIW :

When you get all the way around [the lemon], cut the loop across so that it is now a flat strip,
then slice along the strip to make it into two strips about one-quarter of an inch / half a centimeter wide.
You can adjust the width for personal preference. Then tie the strip into a knot. I use a kind of
double overhand knot - I make a simple overhand or thumb knot (over the end and pull it through)
then pull it through once more.


(He doesn't say if it makes it stronger.  --slow-sip testing, anyone?  (I'll stick to tea, thank you.))
« Last Edit: January 17, 2007, 06:46:51 PM by Dan_Lehman »

KC

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Re: Knot Testing
« Reply #18 on: January 17, 2007, 06:52:00 PM »
i'd think flat rope/webbing should be around that beam as best.  Then 2 multipliers of leverging on a bend are minimized.  Stiffness(resiftance to bend) allows something to be leveraged, then the length of the bent dimension as other multiplier of load.  Flat rope/webbing generally has less resistnace to bend and being flat about Zer0 dimension on the bent axis.  Or perhaps a metal chain; i believe there is also stuff for linking to bolt holes.  Also, the knot drawn up tight at center mast on beam base would leverage it greatly, some teepee/ point would be more relaxed/ less leveraged.  This leveraged form shown would raise line tension, of line drawn around thsoe sharp corners.  Even if you could get by on a static pull; dynamic impact would be even more risky on corners; than static or slow draw tests would illustrate i think.  Perhaps even large spliced eye would be better choked; so that 2 legs would carry force around beam at 1/2 load; amd relieve leveraging some?  But i think best to use specialized system of attachmeant to beam/ made exactly for this use, then connect rope to it. At least a leather overwrap would soften corners.

i'd like to see tests on a Running Bowline preceded by Marl vs. Half Hitch on a lengthwise pull on spar for rigging type applications of lowering spars; if that fits the scope.

i think the coiled storage of extra line and the available slip lends Double Overhand Noose some dynamic loading benefits; not easily/ or usually tested.
« Last Edit: January 17, 2007, 10:41:16 PM by KC »
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PaulKruse

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Re: Knot Testing
« Reply #19 on: January 18, 2007, 05:42:56 PM »
Gordon:

Thanks for the list.  You found one related to fall protection, so the knot is “in.”  We often used “captured carabineers.”  These have a roll pin you drive into them to capture a loop at one end of the carabineer.  The Double Overhand Loop would serve the same purpose.  Might be able to find some others, too; depending on how it tests out.  Maybe securing the end of a bock and tackle system.

Dan:

Thanks for the testing link.  Results look like what I expected, based upon my previous tests of other knots.  Failures are often started by a loop in the knot strangling the rope, and/or by effects of friction and heating.  Bowline and Alpine Butterfly are two similar examples.

You need not worry about this line failing over the edges of I-beams.  I’ve dropped as much as 5000 pounds onto a rope secured in this manner, with very little damage resulting to the rope.  It still had its full published minimum breaking strength afterwards.

Yes, we have tucked the rope back into itself.  But we have never tested it that way and have therefore never approved it for critical applications.  A Flemish Eye in a wire rope, tucked back into itself, will give you back most of the full strength of the rope.

KC:

Give me pictures of what you propose, or arrange to tie the samples and supply them for the test yourself.  If it fits within the scaffolding/fall protection scope of the test, I’ll include it.  We do sometimes use the running Bowline, so that would be a good control to test the DOL noose against.

They sell anchor straps just for fall protection applications.  We use them, too.  They normally have extra padding sewn into them to protect against sharp edges.  We use them in some applications, and they are out of scope for these tests.

If any of you major contributors to this thread live near Cape Canaveral, Florida, feel free to contact me.  My desk number is 321-861-5560.  I've got to deal with our Company security people to get anyone into the shop, but if we can make them  happy I'm not opposed to involving you directly in these tests.

Paul Kruse
« Last Edit: January 18, 2007, 05:47:01 PM by PaulKruse »

Fairlead

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Re: Knot Testing
« Reply #20 on: January 18, 2007, 06:41:25 PM »
Thank you Paul,
I look forward to the results.
Just as a rider to your comment on blocks and tackles - some yachtsmen here now use the Double Overhand Knot in the end of their sheets in preferrence to the Fig 8.

Gordon

KC

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Re: Knot Testing
« Reply #21 on: January 18, 2007, 08:59:30 PM »
Oh, the Marl vs. Overhand thing is for lifting/pulling loads inline/not perpendicular pulls, not rigging bod.  i assume rest is self explanatory?  And have own catalogs of gear candy stores to ponder(?).

i am incognito here; probably better known as TheTreeSpyder in Lakeland, Fl.

Here is my explanation of Bowline on Karabiner for personal support.  If rigging and tighten line set, bowline on krab not too bad; stays unleveraged.  But, body movement, long term unchecked position can leverage flow of force off the long axis of krab.  Ushering force along long axis leverges short axis (minimum).  Ushering force through short axis of device; leverages the long axis (device carries maximum force of load x distance; so less safe).  Then ther is gate pressures etc.  Best to think of krab as open hook, with fancy mousing, carry at back throat.  Snaps are self righting, not problematic with bowline, in fact cinching hitches might not self correct!  And be permanent, where krab allows taking off end to free.
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Dan_Lehman

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Re: Knot Testing
« Reply #22 on: January 18, 2007, 09:33:42 PM »
Gordon:

Thanks for the list.  You found one related to fall protection, so the[Strangle Noose] is “in.”
We often used “captured carabineers.”
Please note my remarks about this knot, and pointers to improving it for both strength
(what you can check by testing!) & ease of untying:  vice the "strangle" common form,
use the "Fisherman's Bend"/"Anchor Bend" hitch form.  Let's not wait a hundred more
years or so of repeating the same things w/o looking around; now is a good chance
to test & see.  (You can find images of this Anchor-Hitch Noose (mis-)labled as a
Barrel Hitch or ... .  (I don't regard nooses as knots but as structures that
contain some knot--in this case, the Anchor hitch or, above, Strangle hitch.)
Here is a link directly to an image with 2- or 3-turn AHNoose:
www.mytreelessons.com/photogallery/Img36.gif
(And, yes, you might enjoy browsing KC's full site.)

Quote
Dan:

Thanks for the testing link.  ...  Failures are often started by a loop in the knot strangling the rope, and
Paul, another urging in the testing:  with needle & (colored) simple threads, make
markings in some knots so as to be able to, post-rupture, narrow down if not pinpoint
the place in the knot where they break.  There is much speculation about where (and
why--with some conjectures of one W. influencing speculation of the other W.!), but
little effort to see actually where it is.  That link to the Strangle-Noose testing had
images that pretty well show the point for it; for the Bowline, though, the knot is
going to blow apart (unless one can arrest the pull upon the first rupture of one
strand--which is how laid rope seems to go, in slow-pull, IIRC).  Another testing
tried to do this with high-speed cameras, and came to some conclusions for the
Fig.8 & Bwl loopknots, though for the latter they implied that the point ranged around.
Marking with e.g. a Sharpie raises concern about the effect of the ink (UIAA put out
warnings not to use ...), but I think that some simple threads sew in at , oh, 1"
intervals in the 3/4"dia rope would pretty much provide information as precise
as it really can be.
(I'm fresh from doing similar sewing for making determinations of the quantity
of material consumed in a series of knots--getting a total-length / dia. figure
for comparison.  Once I got the knack of threading the needle (do it by making
a narrow bight!), the task became less onerous.)

Quote
Yes, we have tucked the rope back into itself.  But we have never tested it that way
and have therefore never approved it for critical applications.
Upon a failure of this sort of quick-splice (witih but 2 tucks) in some logging activity,
there was testing done that showed that the tucking in 5/8" laid PP rope was quite
strong (the opp. attachment in device broke, not the splice, so we can only guess)
in slow-pull, but could slip out in shock loading.  Three tucks wasn't tried, but in
typical brain-closed conclusion, the common eye splice (per strand) was rec'd.
But here I'm only suggesting the single tuck be incorporated as a security
measure, though it might serve a little even in strengthening some structures
--i.p., doing so with a Clove Hitch vice half-hitches (2 tucks) or with a single HH
(maybe just 1 tuck) might get one the nice effective-loop distribution of the
load to all four legs of the Clove!

Quote
they sell anchor straps just for fall protection applications.  We use them, too.
...  We use them in some applications, and they are out of scope for these tests.
Ah, but in making attachment to whatever connection point these straps provide,
you might then be coming into the scope of Gordon's suggested (and my amended)
noose-hitch use (which is unlikely for direct attachment to the I-beam, but so too is
the Clove unlikely for attachment to a 'biner-like metal ring/clip) !

--dl*
====

KC

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Re: Knot Testing
« Reply #23 on: January 19, 2007, 03:28:59 AM »
i've argued and wondered; tossed back and forth with Dan; if crossing the Turns on Noose is same, better or worse; in static or dynamic tests.  And/or if Crossed Turns of Anchor to self to form Noose then, constitutes a different name.
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KC

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Re: Knot Testing
« Reply #24 on: January 28, 2007, 06:20:59 PM »
Another aspect of lifelines/ safety systems is elasticity.  Here we jsut get focussed on the pure strength/macho numbers factor.  This is opkay for static situations on the end of the line; but as we go to a dynamic/ fall situation we must then consdier dynamic properties of the support system.  The dynamics needed can be given by a seperate link in the system (like a stitch pack that shears so many stitches and holds on to the rest to give dampening to shock loading but still hold); or by the rope device itself.  This is where the elastic properties of rope come in to play.

If we use an elastic rope on a 5:1; it will probably work agianst us; in that we have to stretch the rope as we pull the load, so have to pull extra distance.  But falling into an elasticy/dynamic line can save your organs and back from getting ripped up, so in this case the elasticity works for us!  Falling and being caught by a static/stiff line can be like being caught by cable; it'll catch ya; but probably very suddenly and sharply.  i look at the unforgiving strength hold of the tensile rating as the macho part of the rope, and the elastic dampening of the forgiveness but still hold as the feminine side!  Thus when all we do is talk about tensile strength and tensile strength preserved; i think we are missing a large portion of what is going on in a system.

This elasticty is like tensile strength is dependant on the materials and consturction of the manufacture.  Elasticity also depends on how much elastic line is in a system and the percentage of the rope capacity used.  So, being caught by a 1' line is harsher on your body(and equally/ oppositely the support) than falling into a 50'line; because the 50'line has more elastic length/rubberband to dampen your fall.  As a rule of thumb; if we fall into 10' of line it will produce a line tension 2x of falling into a 40' line(4x length gives 1/2 rope tension in dynamic events).  Or (in these nominal lengths and weights) we must drop the weight to 1/4th; to drop line tension in half; dropping load in half or doubling rope length gives about ~30% line tension drop, not 50%.  The other factor is how much of rope tensile rating is used.  So, the more shock on a given line, the more elasticity in response.  So, if we double a line over, we double the tensile (approximately) but the elasticity drops more; because each leg of the line now carries half the weight of the loading!  And this does not count towards extending the line length; for more elasticity.  But, if we go the other way, reduce line strength or double load line; we will get more elasticity; but also reduce our CtF(Cycles to Failure) of the line.  This more elusive elastic property is the first to fade out as a rope degrades do to exposures and useages.

In trees we use these factors to be aware of the dampening of body shockloading line; and/or a load shockloading a support in rigging.   The thumb rule numbers say that a 6' drop without much elasticity will save you; but rip out spleen.   Also/or in rigging; we can fail a wek support by shockloading too much, without elastic or other dampening of the force.  Statically a 1:1 will place 2x load on support; while a 2:1 will place 1.5x load on support, 3:1 1.33x on support etc. so a higher ratio is easeir to command and places less force on support.  But, if a load impacts, the 1:1 offers more elasticity/dampening of force and the higher ratios become less friendly/shock both ends of system more; inclucing the support.
« Last Edit: January 28, 2007, 10:57:25 PM by KC »
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PaulKruse

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Re: Knot Testing
« Reply #25 on: February 03, 2007, 05:54:01 AM »
Sorry for the delay in getting started on the testing.  Other contractors working in close proximity to us on the same project have recently had four falls, one fatal.  Sorry to say, he had decided not to tie off that day.  Two others were seriously hurt as a result of not tying off correctly.  The other was back to work as soon as he could re-rig new equipment, since any fall results in all your equipment being impounded for further investigation.  He was the only one of the four using the equipment correctly, and he had no injury.  So three of the four are either seriously hurt or dead, apparently as a result of someone not following his training.  All of this has pushed knot testing down a bit on the list of priorities in favor of spending more time just making sure that our people are not making similar errors.  (To be fair, it appears that one of the injured ones did tie off correctly and that his injuries were caused mostly by his buddy, who did not tie off correctly, falling on top of him and knocking him off the steel more than 400 feet in the air.)

But now I have time to return my attention to the subject of testing.  I greatly appreciate all the help you have all given me.  It will result in a much better test plan.

I have done some quick tests of the Double Overhand Noose.  It is a great knot and I’ve added it to our tool bag.  Much thanks for the idea of using it to tie a rope to a carabineer.  It is correct that you need to keep your loads correctly aligned when using a carabineer.  We normally used a captive carabineer for that purpose, but this does the same thing.  It eliminates the need to drive a roll pin into the carabineer, and therefore eliminates a possible FOD hazard when working in places were FOD is a serious concern.  (Foreign Object Debris, for those of you not working in the aerospace business.)

This note is getting too long.  I’ll post another one to address some of the fall protection issues you have raised above.  In fact, look for it in a new thread.

Paul Kruse