Author Topic: Can we prepare some simple knot tests in our kitchen?  (Read 2710 times)

xarax

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Can we prepare some simple knot tests in our kitchen?
« on: February 16, 2011, 05:29:52 PM »
  I have decided that I "know" of many practical knots I have not evaluated yet, in a systematic way. My knot toolbox is loaded to the gills, and I feel I have to dispense with excessive weight...So, I plan to do some simple knot strength "tests", in my laboratory, the kitchen, hoping that some knots would be stronger than the others, and offer me the excuse to push the "delete" button.
   Many people use pulley systems, blocks and tackles, to achieve the heavy loadings required for destructive knot tests. Is there a reason for it ? Would nt a hydraulic or electric car jack be a simpler solution ? To be able to handle up to 11 mm climbing ropes, a car jack would only have to be able to lift 2.5 tons, right ?
   I think the most simple test is to organize "knot match races", where two bends, for example, are tied in line. Puling the one free Standing end of the one bend and the one from the other, we will see which bend breaks first, during a series of, say, 10 "races". We can complete such a championship and short things out rather easily, I think. Because we do not have to measure the breaking force, just to see which bend was broken first most of the ( 10 ) races.
   Any advice about this (naive ?) plan would be much appreciated.
This is not a knot.

Dan_Lehman

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Re: Can we prepare some simple knot tests in our kitchen?
« Reply #1 on: February 16, 2011, 08:59:57 PM »
If you Search among these threads,
you'll find that Derek has tried using a car jack,
and one immediate & should be obvious problem
is its lack of distance/stroke --climbing ropes, among
many others, even, will require a fairly long span of
extension to break, esp. in a test plan that entails
two knots & some kind of anchorage.

Another problem with A-vs-B testing is the lack of information
it provides, unless perhaps one tests some 10 specimens per
case?  Consider a 4:1 result : seems pretty lopsided, but in
fact the strengths might be close, and the next case could
make things 4:2, or by some chance a similar other-tester's
repeat of it would be 3:2.  E.g., Lyon Equip. did testing
(quick-search : this might be the URL for the PDF of it:
www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf )
in which they tested A-v-B, A-v-A, B-v-B, and in some
cases the highest value was of the loser (well, the break
force value is accorded to the broken knot) of A-v-B !
There is a "Knot Wars" site with (monthly?) mock battles
of this sort though with knots getting individual break data
and then that being compared; they don't seem to have been
so wise in evaluation.

But how to get any sense of calibration & absolute measure?

Quote
... hoping that some knots would be stronger than the others,
 and offer me the excuse to push the "delete" button.

To my mind, that is a poor evaluation criterion for knots
--or poor, in isolation.
Moreover, the testing should be tailored to practical circumstances
(unless your purpose, your business/need, is for some particular
knot-testing competition), and typical slow-pull testing is not a
great model of that.  In some testing of sewn slings of either
nylon or HMPE, joined with a "girth hitch", one tester found that
in (nearly?) all cases, the nylon broke on slow-pull, whereas in
many the HMPE broke in drop tests (but all held at least one
severe (UIAA) drop).  So, which material here is "stronger"?


Now, getting a way to mark cordage and learn where and thus
maybe how/why breaks occur, might be something more doable
(conceivably, it, too, will differ per circumstance).  Unfortunately,
using marking pens is itself considered a risk on the material (and
some testing done recently for climbing cordage shows this) --but
perhaps some minor marking can be effective for research and not
sufficiently abundant to be significant in strength.

--dl*
====

Dan_Lehman

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Re: Can we prepare some simple knot tests in our kitchen?
« Reply #2 on: February 16, 2011, 09:19:10 PM »
Here's a recently found (to me) anecdotal remark about the importance
of knot strength:


from [ forums.sbo.SailboatOwners.com/showthread.php?t=100760 ]

Quote
It makes no difference if you splice or knot your dock lines.
Sure, well done splices are stronger than a bowline. Some
think they look better, too. But I think the strength of
modern nylon docklines is the key factor here. I think a
lot of other nasty things are going to happen to your boat
before the working load of a dockline, in good condition,
is exceeded-- because of knot rather than a splice in the line.

Just using the damage done at my marina during Hurricane
Isabel as an example, I had a 5,500 lb boat tied with 15
3-strand nylon 1/2 inch docklines. The boat was totaled.
The dock was totaled. All of the docklines, tied to pilings
with bowlines, survived. In looking around the destroyed
marina at all the other damaged boats, I never saw one
broken dockline ... .

[ and really given a concurrence, but couched otherwise ]

Although I usually agree with Warren Milberg,
I have seen dock lines go. In every case, though,
it was chafing, not the knot or splice giving way.


--dl*
====

xarax

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Re: Can we prepare some simple knot tests in our kitchen?
« Reply #3 on: February 17, 2011, 01:42:27 AM »
Thank you Dan Lehman.

...climbing ropes, among many others, will require a fairly long span of extension to break...

 I guess that this span would be a percentage of the initial length. So, we should keep the length of the un-tightened sample as short as possible. Why not 20-30 cm samples (distance between the two drums)?

uless one tests some 10 specimens per case

That is what I said. Like in sailing...10 races, and one should even consider the 6-4 result as a draw, I suppose.

But how to get any sense of calibration & absolute measure?

  Impossible, outside a well equipped laboratory of material sciences. I know very well the complexity of the task. No kitchen in the word can test ropes and knots in that sense  :). I prefer an amateur "game" than a pseudo-scientific "experiment".

To my mind, that is a poor evaluation criterion for knots--or poor, in isolation.

  You have to get rid of some dead weight, because your (mental) boat / knot toolbox is overloaded, and about to sink any minute. You should have to decide using one simple criterion, and this bras de fer is such. Can you propose anything else ? Just look around you : Is this excessive multiplicity of possible solutions not confronting the idea of "practicality" ? People do not want more knots, they want to learn some of them, that they will feel confident with, and I believe they are basically right. Too much information, about too many things, has been accumulated in our poor just-a-little-bigger-than-ape s brains...I can see from the posts in this forum, that most people are indifferent about "new" knots, to the point they are almost hostile towards them, but they care much about the "Best knot for..." and "How to..." threads. And they are supposed to be interested in knots more than the "average person...". I do not want people to feel lost in a vast ocean of knots, or believe that "anything goes", and just adopt the first thing it happens to come to their attention...IF we are lucky, and get some 8-2, or even higher differences, we would have an excuse, I repeat, an excuse to unload the boat a little bid, for the time being. Then, when we will understand more about knots, in a truly scientific way, we can re-evaluate our naive kitchen "experiments" .
   
the testing should be tailored to practical circumstances, and typical slow-pull testing is not a great model of that. 

It is the only possible thing one can do in his/her kitchen...I have not yet made ONE destructive test with a climbing rope with slow loading, I do not even dream to try dynamical loading ! We do not wish to escape from the one storm, of the excessive multiplicity of proposed knots, just to fall to the other, of the excessive multiplicity of proposed tests under excessive multiplicity of conditions, materials, loadings, temperatures, housewife moods, you name it... !  :) Simple, slow motion, linearly increasing elongation, it would be enough ! 

Now, getting a way to mark cordage and learn where and thus maybe how/why breaks occur, might be something more doable

   But the climbing ropes do have all those marks and patterns on their mantle...Are n t they enough ? And a (relatively) high speed camera is not such an expensive thing nowadays...
This is not a knot.

xarax

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Knot Wars !
« Reply #4 on: February 17, 2011, 02:31:33 AM »
   I have just learned about the "Knot Wars" series on fishing knots.(1) That is exactly the same idea I had for knots on climbing/rescue knots ! The only difference is the way they organize their championship there...I had in mind a different system, used in chess tournaments, the Swiss system... :) (2)
   Fishermen are practical people, and they love and enjoy their sport. They discovered this way to have some fun, to make some observations about knots under similar conditions. Of course, conditions in real life vary a lot. (That s why we call them "conditions", and not "invariants" !) Should this make us not do any test, ever ?  Fishermen entertain themselves with this game. Why knot tiers be different ?
   I would think of making this game even more amusing...Why not put some betting flavour in the recipe ?  :)

1. http://www.fishingclub.com/fishing/knot-wars.aspx
2. http://en.wikipedia.org/wiki/Swiss-system_tournament
« Last Edit: April 12, 2014, 02:40:27 PM by xarax »
This is not a knot.

TMCD

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Re: Can we prepare some simple knot tests in our kitchen?
« Reply #5 on: February 17, 2011, 01:05:05 PM »
I love this idea, but I suppose a proper test would be hard to achieve. I have seen proper testing of fishing knots being tested against each other...with a clear winner.  The testing was done to find out what fishing knot broke first, they used about six different but commonly known knots. The clear winner was the Palomar Knot, it beat the trilene, half blood, clinched knot etc.  They used six lb fishing line for each battery of test, it was quite interesting.

IF you could tie some of these bends in fishing line, THEN you could possibly discover a clear winner. But it would be extremely difficult to tie certain bends, knots, etc, in fishing line.

xarax

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Re: Can we prepare some simple knot tests in our kitchen?
« Reply #6 on: February 17, 2011, 01:52:55 PM »
    Thank you TMCD,
    But why ? Why it is would be hard to achieve it with other cord material, while it is relatively easy to do it with fishing line ? Is it only because of the harder=heavier  loading we need in case we use of other materials ? But this is only a scale problem, not a fundamental one. With a hydraulic jack / crane, we can easily break any climbing rope around 9-11 mm, I guess. I have no experience with destructive tests whatsoever, so I wonder if I am missing something here...
   My conjecture is that topology and geometry of knots is more important/critical than the material used. One can argue against this conjecture, and claim that results of "Knot War" type strength tests on pairs of knots that are tied and tested with one material, may be reversed when the same knots are tied with another. However, I am not aware of any experiment that supports this argument. And I suppose that this, if it will happen, it would be only in a very special and rear case, that does not disprove the general rule of my conjecture.
« Last Edit: February 17, 2011, 01:53:32 PM by xarax »
This is not a knot.

Dan_Lehman

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Re: Can we prepare some simple knot tests in our kitchen?
« Reply #7 on: February 17, 2011, 06:31:52 PM »
... I have seen proper testing of fishing knots being tested against each other...with a clear winner.  The testing was done to find out what fishing knot broke first, they used about six different but commonly known knots. The clear winner was the Palomar Knot, it beat the trilene, half blood, clinched knot etc.  They used six lb fishing line for each battery of test, it was quite interesting.

IF you could tie some of these bends in fishing line, THEN you could possibly discover a clear winner. But it would be extremely difficult to tie certain bends, knots, etc, in fishing line.

PLEASE do not misconstrue the results of one test done in such a
very limited set of circumstances as establishing some characteristic
of a **knot** !  At best (i.e., barring valid critiques of methods),
such a test shows only that some material(s) so knotted perform
as indicated.

You might refer to the Knot Wars and find that the Palomar was not
the winner (well, that seemed to be implied, but when I viewed a set
in 2009, I thought they only established the Round-Turn + Uni as
the contender for the prior champ, Palomar; looking in 2010's
set, though, I didn't see the competition between those two!?).

Looking over their table of test data, there seemed to be contradictions with
the accorded victories (or problems with method : e.g., if in 3 lines
A wins one by a large margin but B wins the other two, an average
can favor A, but would you?  --not if your line was either of the two
in which B won).  I wasn't paying close attention, but I think that there
is a slight change of lines used from year to year --not too surprising,
in that selling line is what the sponsor wants to do, and advertise new.

Also, I was quite impressed that, in 13-20?-pound test lines, these knots
--almost all are what I'd call "noose-hitches", btw, the *knotting* being
done around the structure's S.Part, not the swivel's ring-- are all in what
I'd call **spar hitch** sizing, NOT **ring hitch** : i.e., the hitched-to
object was relatively large vs. the line diameter --maybe 5 times !!!
So, bump your line from that thin 6/13/20# to 30/50/80# line,
and what will you then find?  (or narrow the ring --might small hooks
offer smaller diameters than those swivels?)

--dl*
====

ps:  I was able to stop/freeze-frame the videos in some cases
well enough to get a half-decent look at the highly loaded knots;
it seemed that in some cases the Uni had deformed.  I will note
that their tying of the Uni left it in the apparent form that tying
guidance shows pre-setting --which point is made because
in theory that anchor-/fisherman's-bend-like structure can transform
into a strangle form.