Author Topic: Figure 8 Loop  (Read 14743 times)

knot rigger

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Figure 8 Loop
« on: May 10, 2015, 09:01:58 PM »
Is there a "right" and a "wrong" way to tie the figure 8 loop knot?

Dr. Dave Merchant, in Life on a Line asserts that there is. [1] but doesn't cite any other sources.

Bruce Smith & Allen Padgett in OnRope assert the opposite, that there is no difference in the the two forms of the fig. 8 loop. [2]

According to Dan Lehman, Rob Chisnall agrees with Merchant in Ontario Rock Climbing Association Ref. Manual (I haven't been able to find this source yet, perhaps DL will be kind enough to scan & post the relevant pages to this thread)

Smith & Padget cite Neil Montgomery's Single Rope Technique [3] as well as "destructive testing" and "Ashley".  I haven't seen anything on the topic in ABOK.  Montgomery states there is a 10% difference between the "weak" and "strong" form of the fig. 8 loop.

Montgomery cites G. R. Borwick's "Mountaineering Ropes" article in a 1974 issue of Off Belay.  I haven't yet seen this article in Off Belay, but I did find an article from G.R. Borwick entitled "Mountaineering Ropes" in the 1973 British "Alpine Journal" [4]  Borwick bases his conclusions of break testing he conducted.

Helmut Microys also cites Borwick in his 1977 "Climbing Ropes" article in the American Alpine Club journal [5]  Microys also cites H. Prohaska's arcticle "Die Festigkeit des Bandknotens im Kernmaterial"  in the May 1976 issue of Der
Bergsteiger
.  I haven't been able to find this article.

The website OnRope1.com asserts that there is no difference between the two versions [6]

I'm bringing this up to the group to get your collective thoughts on the issue.

[1] http://tinyurl.com/fig8LOAL
[2] http://tinyurl.com/fig8OnRope
[3] http://tinyurl.com/fig8SRT
[4] http://tinyurl.com/fig8AJ
[5] http://tinyurl.com/fig8AAC
[6] http://onrope1.com/Myth6.htm
« Last Edit: May 10, 2015, 09:24:13 PM by knot rigger »

roo

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Re: Figure 8 Loop
« Reply #1 on: May 10, 2015, 10:38:45 PM »
Is there a "right" and a "wrong" way to tie the figure 8 loop knot?
I suspect that if such a minor change in form really produced a difference that mattered to the safety of the user, the knot would have been pulled from life support applications quite some time ago.

If the rope is sized to safely handle an accidental overhand knot, even the wildest strength variations thus far measured in figure eight loop will be no problem.
« Last Edit: May 13, 2015, 12:05:47 AM by roo »
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xarax

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Re: Figure 8 Loop
« Reply #2 on: May 10, 2015, 11:32:26 PM »
   The only explanation I can think of about the sad fact that so many people were so much wrong, is that they were just copying each other  :) - so, after some time, each and very one of them would had copied each and every one else, and would start to believe in what he is saying ! A vicious circle of self-reproducing myths...
   I wonder, is it sooo much difficult to just take two short pieces of rope of different colour, just tie and dress a fig.8 loop, and just SEE, with your own eyes, how many distinct forms this knot can have ? Of course, nobody had ever TESTED all those forms - but, to even THINK that you should test them before you compare them, you should first enumerate them... and if you still believe that they are one or two, as everybody else says  :), why you would do what you should also believe everybody else would had done already ?  :)
   Step 1 : How many distinct forms does the fig.8 loop has ? NOT the fig.8 knot as tied and dressed by a I-copy-you, you-copy-me series of people, but the fig.8 knot per se !
   Step 2 : Which of them differ significantly, to make us suspect/conjecture that their structures may also behave significantly differently ?
   Step 3 : Is it interesting to actually MEASURE the behaviour of some, at least, of those forms, and if yes, of which ?
   Step 4 ( which separates the men from the boys... :) ) : TESTS - NUMBERS - END of the era of mythology !  :) :)

   What will an ignorant human ( one who, because he will never imagine that birds may be more clever than he believes, he will never attempt to change the words he tries to make them repeat ) or, for that matter, a knowledgeable parrot ( one who, because it will never imagine that humans may be more dumb than it believes, it will never attempt to change the words it tries to repeat ) ? He / it will start singing the same old song, again and again : " If there was any difference, then they would had found it already...etc, etc." The same happens with new knots, with new tying methods, with new conceptions about knotting. However, it does not happen with anything else !  :) Nobody will ever claim that " If this medicine or medical treatment or medical conception was any good, it would had been known, implemented and utilized already..." If there were no research and development, we would had remained some very few and very happy cave dwellers... :)  I suspect that this would had a minor change in the form of the thoughts of many people, and it may even have been easier and safer for them, but, unfortunately for them, things EVOLVE ! 
« Last Edit: May 10, 2015, 11:36:53 PM by xarax »
This is not a knot.

Z

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Re: Figure 8 Loop
« Reply #3 on: May 11, 2015, 05:56:22 AM »
Is there a "right" and a "wrong" way to tie the figure 8 loop knot?
I suspect that if such a minor change in form really produced a difference that mattered to the safety of the user, the knot would have been pulled from life support applications quite some time ago.

That's a good point. How about we say one might be a bit more right than the other? I could see the logic in that, but saying one way is "wrong" gets back to Roo's point.
« Last Edit: May 11, 2015, 06:24:07 AM by Z »
If you're reading this, it's too late.

Dan_Lehman

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Re: Figure 8 Loop
« Reply #4 on: May 12, 2015, 06:23:01 AM »
   The only explanation I can think of about the sad fact that so many people were so much wrong,
What do you mean by "so much"?
(There are categories/levels of consideration here;
and I think enough "wrongness" to distribute to more
than one of them!  Firstly, yes, you answer this in part:
they are sadly wrong about orientations.)

As Roo suggests, had experience --or some good testing--
shown there to be significant advantage to one or the
other orientation (or, more narrowly : had there been some
orientation that was bad!), this should've surfaced
into practice & advice somewhere along the way, by now.
(To this point, Roo can recall that --although not a matter
quite of life-critical applications-- the infamous highwayman's
hitch
has seen a great deal of promulgation in knots books,
and despite some considerable effort on his part, retained
one advocate of its use.  And I recall that even after the
offset figure 8 end-2-end knot (aka "EDK-8",
where the "EDK" is the offset water (overhand) knot)
had been linked to a death of a rappelling climber in Zion
Park USA (one of a pair of Brits), and had been shown
by Tom to be less stable/secure than the simpler offset
water knot
, some climbing / guide organization continued
recommending it for abseil use.  (Well, also one fellow then
busy with canyoneering, who had personally seen the ropes
used by the Brits, and called them "cables" for their stiffness;
he later I think removed the recommendation, just to be
more on the safe side.)

Quote
is that they were just copying each other
Although, in the case of Bruce Smith, he stopped copying
himself! ! :)

Quote
I wonder, is it sooo much difficult to just take two short pieces of rope of different colour,
just tie and dress a fig.8 loop, and just SEE, with your own eyes,
how many distinct forms this knot can have ?
Evidently so.  Among the anecdotal hearsays is that the
AMGA(?) tested some batch of these eyeknots tied both
in some "correct" (read, at least : "neatly dressed, with
no parts crossing...") and incorrect versions, and the
strongest (beware equating this with "best"/'right")
was among the incorrect --though we must note that
this strongest knot must have had some definite form
at rupture, not adequately described by saying what
it was not!

Quote
Of course, nobody had ever TESTED all those forms
Lyon Equipment, doing contract work for the UK's HSE,
did test some version of my "strong/weak form" and
concluded that for the fig.8 it didn't matter, for the
overhand the strong form was stronger, and for the
fig.9 the weak form was stronger.  Now, even with
their presumed awareness and correctness of getting
the forms right, there remains a question in my mind
about how the knots were set --my idea that the fig.8
benefits from setting by tightening via the tail(s) so as
to set a curved tail/twin against which the S.Part will bear.

Presumably/allegedly, Dave Merchant also did testing,
hence his claim; and he did so with awareness of the
forms, unlike Smith.  I'm very curious to see what
it is that Montgomery shows/describes (I'm hoping
for a good image and clear words).


--dl*
====

xarax

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Re: Figure 8 Loop
« Reply #5 on: May 12, 2015, 07:10:23 AM »
What do you mean by "so much"?

  When there are 18 different dressings, and you say there are 2, you are "so much" wrong ! ( 900% wrong... :) )
  When you had not examined where the area of maximum tension, and the area of maximum pressure, and the area of maximum friction are, so you do not know how this thing "works" as a friction mechanism, you are "so much" wrong !
  When you do not know where this thing breaks under maximum tension, when it breaks there and when it breaks somewhere else, you are "so much" wrong !
  When you had not tried to modify this thing, adding or subtracting a tuck of the last part /Tail End, for example, through this or that opening, in order to facilitate its untying easiness after heavy and repeated loading, you are "so much" wrong !

   We do not have the experiments we should had had, we do not have the theoretical explanation / prediction of the results of those experiments we could had , and you are wondering what I mean by "so much" ? The fact that "nobody is killed" if we continue to do this or that, means that we should continue doing them, and not even try to analyse and understand how they work, why they work, and try to see how we could possibly improve them ? A "bad" dressing is only a dressing which kills people ? Any dressing which does not, is "good" and OK and that s it ? Are we still in the Middle ages or something, and nobody has informed me about that ?

( "Some" testing sounds to me like "some" pregnancy !  :) You either test, and are pregnant, or not ! )
« Last Edit: May 12, 2015, 07:14:43 AM by xarax »
This is not a knot.

Dan_Lehman

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Re: Figure 8 Loop
« Reply #6 on: May 12, 2015, 07:45:53 AM »
Beware the inaccuracies stated here!

Is there a "right" and a "wrong" way to tie the figure 8 loop knot?
This is a biased question in a couple of ways:

1) it implies binaryness --of 1 and another 1--,
or at least of two endpoints in a continuum
(rather than more than this, either as *ends*
or as not-so-reasonably-called-*ends*);

2) It implies one test and result --one quality
for assessing value : i.p., strength-- when there
might be several (strength, or ease of untying, or ...);

Quote
Dr. Dave Merchant, in Life on a Line asserts that there is.
[1] but doesn't cite any other sources.
But he does claim --or is it just strongly imply-- that he
has done testing to support his claims.
(He might have been explaining more in some on-line forum,
IIRC?  I distinctly recall him somewhere saying that dynamic
loading would hurt some otherwise strong knots such as the
fig.9 eyeknot vs. having less difference to the overhand eyeknot.
AND HE GIVES CLEAR ILLUSTRATION OF HIS FORM,
which is in fact different than other forms.)

Quote
Bruce Smith & Allen Padgett in OnRope[2nd ed.] assert the opposite,
that there is no difference in the the two forms of the fig. 8 loop. [2]
Egadz, you're again going ambiguous :: please, people,
understand that there are TWO editions of On Rope;
in the 1st ed., the assertion echoes (we might suppose)
the claims of Montgomery!?
(Like knot_rigger, I don't know of Ashley even recognizing
different forms, let alone claiming that there's no difference!
His illustration of the TIB version gives no hint of S.Part &
tail distinction.)

Quote
According to Dan Lehman, Rob Chisnall agrees with Merchant in Ontario Rock Climbing Association Ref. Manual
(I haven't been able to find this source yet, perhaps DL will be kind enough to scan & post the relevant pages to this thread)
Perhaps, okay.
BUT NO NO NO :: Rob Chisnall clearly illustrates what
I call "the perfect form" (I think that Grog has this in
his on-line presentation, and with "strong form" loading),
and asserts the difference re that;
whereas Merchant introduces another form, for which
he claims advantage (and it's not clear exactly how he
considers his competition forms --IIRC, he makes some
remark about difficulty untying, rather than strength ...?!).
.:.  So, Chisnall & Merchant only agree in the assertion
that there is a difference between some versions; they
have different versions --there are more than two!-- of
the strength champion.

Quote
Smith & Padget cite Neil Montgomery's Single Rope Technique [3]
as well as "destructive testing" and "Ashley".  I haven't seen anything on
the topic in ABOK.  Montgomery states there is a 10% difference between
the "weak" and "strong" form of the fig. 8 loop.
One should beware using these labels, which are
ones I've used --and now take mostly as mere *names*
to denote a particular form, and less to connote some
relative strength.  And my versions of the knot do NOT
match the slop of common illustration, but follow from
Chisnall; they do not match Merchant, either.

Quote
Montgomery cites G. R. Borwick's "Mountaineering Ropes" article in a 1974 issue of Off Belay.  I haven't yet seen this article in Off Belay, but I did find an article from G.R. Borwick entitled "Mountaineering Ropes" in the 1973 British "Alpine Journal" [4]  Borwick bases his conclusions of break testing he conducted
.
Great find, thanks much !!!  :D   :D
Could a like-named article appearing in Off Belay
only a year later (nominally, by publication date)
be different?!  (My guess is that some arrangement
was made to permit the reprinting in Off Belay.)
((And, otherwise, do we think that there was any
earth-shattering revelation made in the year of
1973/4 that would change what was written for
Off Belay in '74?))

Quote
Helmut Microys also cites Borwick in his 1977 "Climbing Ropes" article in the American Alpine Club journal [5]  Microys also cites H. Prohaska's arcticle "Die Festigkeit des Bandknotens im Kernmaterial"  in the May 1976 issue of Der
Bergsteiger
.  I haven't been able to find this article.
Heinz, I will hope, is yet reachable via snailmail
if no other way.  (It's been a while since we've
exchanged correspondence --I'm way behind.)  :-\

Quote
The website OnRope1.com asserts that there is no difference between the two versions [6]
And Bruce's notion there of "two versions" should be
pointed out as not likely matching either Chisnall's or Merchant's
--but maybe the crudely illustrated who-knows-what-happens
of these other sources.

Quote
I'm bringing this up to the group to get your collective thoughts on the issue.

[1] http://tinyurl.com/fig8LOAL
[2] http://tinyurl.com/fig8OnRope
[3] http://tinyurl.com/fig8SRT
[4] http://tinyurl.com/fig8AJ
[5] http://tinyurl.com/fig8AAC
[6] http://onrope1.com/Myth6.htm
Good work!

--dl*
====
« Last Edit: May 12, 2015, 07:17:55 PM by Dan_Lehman »

knot rigger

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Re: Figure 8 Loop
« Reply #7 on: May 14, 2015, 09:37:34 AM »
Quote
I suspect that if such a minor change in form really produced a difference that mattered to the safety of the user, the knot would have been pulled from life support applications quite some time ago.

Roo: I agree that the (potential) slight difference in strength between a "weak" and "strong" fig. 8 knot does not really affect its use in life support applications (by trained experts with a proper design factor etc etc).  Perhaps the "weak" version is 65% efficient, rather than 75%; both are adequate for the task.  I do wonder what you mean by "pulled" from life support applications.  Is there some governing authority on knot use that could do such a thing as stop all the people that currently use the fig.8 loop from using it?  ;)

Quote
is that they were just copying each other

Xarax, it is posible that there is a bit of "knot book echo chamber effect" going on here, but....

Quote
so many people were so much wrong

I don't think that ANY of these authors are "wrong"  They all reported the facts as they knew them. Even on the point of contention, the different sources agree on more points than they disagree, and the disagreement is over a (relatively) small percentage.  Each of these authors I cited touch upon the figure 8 loop (briefly) within the larger context of the greater work they authored, be it caving, SRT, rope rescue, or strength of rope.  (ie they had bigger fish to fry)

It is interesting to me that we find this information about the fig 8 (potential) difference in strength in books and articles about fields where knots are used, but no book about knots mentions it (as far I yet know)

Also Xarax, I agree that the only way to (possibly) settle the matter would be destructive tests.  I hope to be able to do them (someday... sooner rather than later I hope)

Quote
How about we say one might be a bit more right than the other?

Z: I suppose "strong" and "stronger" versions of the figure 8 loop would be the most appropriate names, but perhaps a bit confusing.  I'll stick to Dan Lehman's "weaker" and "stronger" monikers for the time being I think.

Speaking of Mr. Lehman

Quote
AMGA

who's that?

Quote
Lyon Equipment, doing contract work for the UK's HSE,
did test some version of my "strong/weak form" and
concluded that for the fig.8 it didn't matter

I'd love to see a copy of this testing, should anyone know where to find it.

Quote
Egadz, you're again going ambiguous :: please, people,
understand that there are TWO editions of On Rope;

Sorry about that.  I'm not planning on buying the first edition just to find out what the differences are.  And I don't usually cite which edition of the ABOK I have (for instance) but I take your point.

Quote
BUT NO NO NO :: Rob Chisnall clearly illustrates what
I call "the perfect form"...
whereas Merchant introduces another form...

Ok, to summarize what you're saying (i think): Chisnall and Merchant both assert that there is a 10% difference depending on if the standing part follows the outside or the inside "parallel" (giving a larger or stronger bend) but they show the fig 8 loop dressed differently.  I've attached two pictures of two of the most common dressings of the the fig loop (thanks Xarax, I stole them from your postings) [1] this dressing is what I've learned through multiple professional trainings, and I would say it is the consensus opinion, in my field, of the "best" way to dress a fig 8 loop. [2] this dressing is very similar, and I consider it adequate, if not perfect, and it is what Merchant shows in his Life on a Line.  So DL, is [1] your "perfect" form?

I have no evidence to support this, but IMO, one of the great qualities of the fig 8 loop, is that it is still secure, strong, and reliable, even if you haven't dressed it "perfectly".  It had been my working assumption, that while different sources show different dressings, that these do not crucially affect knot strength and security.  And that different authors showing a dressing other than [1] we're wrong (IMO) but not seriously, a difference of better vs best.  Moreover, I had not considered the dressing of the knot as part of the question of the "weaker" vs the "stronger" forms.  The crucial difference between the "weaker" and "stronger" forms (as asserted by Merchant and others) is which path the standing part takes in the knot, and the hypothesis is that the standing part taking the "outside" path yields a more gradual first bend in the knot, and thus a stronger knot.

Of course how you dress the fir 8 may effect strength as well, I suppose that's up for discussion.

IMO the best way to dress the fig 8 is [1], and I find that a commonly held assertion in my field.

Quote
(I think that Grog has this in
his on-line presentation, and with "strong form" loading)

 Grog does indeed show this [1] dressing, with the "strong" form of loading here:

http://www.animatedknots.com/fig8follow/index.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com#Figure8Loop

Quote
Could a like-named article appearing in Off Belay
only a year later (nominally, by publication date)
be different?!

It's my working assumption that this is the same article, but I did order that issue of Off Belay just to be sure :)

Quote
Heinz, I will hope, is yet reachable via snailmail
if no other way.  (It's been a while since we've
exchanged correspondence --I'm way behind.)

I would be greatly interested in hearing Mr. Prohaska's views on the strong vs weak form of the figure 8 loop.  Perhaps you could ask him on my behalf, or Private message me a way to reach him.  Thank you :)

Quote
Quote
The website OnRope1.com asserts that there is no difference between the two versions [6]
And Bruce's notion there of "two versions" should be
pointed out as not likely matching either Chisnall's or Merchant's

I had assumed that OnRope1.com was connected to Bruce Smith, but wasn't certain. Here is what his website says on the topic:

Quote
Myth #6: A Figure 8 knot tied "backwards" is 10% weaker.

Truth: Absolutely incorrect. The second a load is applied to the 'outside' loop.  It will be forced to the inside of the course the lines take as they trace the knot. All efforts to keep the load line at a greater radius will only result in the load line taking the path of the lesser radius.

after which is shows an incredibly unhelpful depiction of a figure 8 loop dressed flat, with no tail visible (good grief!)  But what the text says is very interesting.  That when tied in the "strong" form, and loaded, the standing part slips under the tail part, and finds the tighter radius bend regardless.  I have seen this for myself as well! Both 'in the field' and in break testing, here is a link to a video of a break test:

http://tinyurl.com/ABKbreakingVideo

The figure 8, on the right, is tied in the "strong" form "perfectly" dressed, and you can see how the standing part behaves.

 Another observation I've made of the "perfectly" dressed [1] knot is that the "inside" path appears to take a wider bend than the outside path.  It's not much of a difference, but you can see it on Grog's depiction fairly well.  It's not apparent in Xarax's pictures [1] because I think the knot wasn't set as you would set a fig 8 loop (Xarax pics are clearly fig 8 bends).  This difference is slight, but by the "wider radius bend" theory, the "weaker" form should perform better!  Of course neither of the pictures show a heavily loaded 8 either, and I'm sure the behavior would change under extreme loading.

Ok, final thoughts (for today):
1) I can only really settle this issue of strength with break testing, which I'd like to do, but my break test rig is temporarily down :(
2) while the theory of why one form may be stronger than the other seems valid, I personally see inconsistencies in the application of the theory (ie does the "stronger" form really result in a wider radius bend in the standing part)
3) if there is a slight difference in strength, both forms are adequate and safe for life safety applications (when used appropriately by trained personnel of course)
4) despite that, it sure would be interesting (and possibly useful!) to know what the difference in strength is

xarax

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Re: Figure 8 Loop
« Reply #8 on: May 14, 2015, 10:26:42 AM »
Quote
so many people were so much wrong
I don't think that ANY of these authors are "wrong"  They all reported the facts as they knew them.

  When you do this, and only this, in knots ( just "report the facts as you know them"), you are wrong !  :)  :)
   You have to produce facts, to tie and try, and you have to investigate those new facts by yourself, and not just reproduce already established myths - because knots are so easy to tie and test by yourself. For example, you have to actually TIE ONE ( = 1 !) fig.8 bend or loop, and see how many variations it can have ! Ant try to imagine how differently those variations would "work", when they will be loaded.
  The "fact" that the fig.8 bend or loop can be dressed/loaded in two ways, in not a "fact" ! It is a plainly wrong, and I dare to say, stupid myth !

Even on the point of contention, the different sources agree on more points than they disagree

   You seem so relaxed by that  :) - on the contrary, THAT is what makes me worry !  :)
   If I have to read a source that agrees always with anything else written about the same thing, I read the Bible.

and the disagreement is over a (relatively) small percentage


   So, according to this argument, truth, in general, and science, in particular, is only about disagreements in big percentages !  :) :) :)
    You will be surprized to calculate the percentage our present theory of gravitation is improved relatively to the previous one  - but your smartphone works because of THAT "relatively small percentage" !   :)

no book about knots mentions it

   Wrong ! No book about knots in the past:) ( And, of course, in the past of this planet, and relatively to this planet...)
YOUR book will mention it ! You will tie and test ALL the possible dressings of the fig.8 loop and bend, and report your results to us. To not wait to learn about the already known facts - generate new ones ! Perform experiments ! 

thanks Xarax, I stole them from your postings
Xarax pics are clearly fig 8 bends

   You are welcome, but you did not "stole" anything ! ! ! You used pictures of knots to illustrate something you want to say about knots, which is something we all do, from time immemorial ! My pictures are public, and I believe that everybody knows that I am not selling them !  :) :) ( In particular, those pictures are so bad, that they could nt be sold, even if I had wished it !  :)
   No, they are not even pictures of bends, in the sense they do not show which is the Standing and whch the Tail End, and they are not loaded... They are just pictures illustrating the different dressings the NUB of a fig.8 bend or loop can have, if the segments follow slightly different paths. You will notice that in half of them the Standing and the Tail Ends are at the same "side" ( upper or lower side of the picture ), and in half of them at the opposite "side".
   My point is that all those people who you site, are NOT knot tyers ! They are just knot USERS, they are interested in the fig.8 knot and loop as a tool for their own purposes, for their own ropes, for their own loadings, etc. They are NOT interested in the great, beautiful fig. 8 bend and loop per se, as a knot ! They just don't give a s... about it, because, as you say, the ( believe...) they have a bigger fish to fry...
   To me, as a knot tyer, the biggest fish of all is this marvellous knot, the fig.8 bend and loop - I am not interested in this knot because it saves people, or because it entertains people, or because it makes some people richer and sad, and some people poorer and happy. I am interested in it because it is KNOT, NOT because of anything else ! ( And because it is so simple, conceptually, and so beautiful a knot ! ) 

P.S. I believe that, before you start to examine and test the fig.8 bend and loop - which is not so easy, because it has many variations / dressings ( even if we take account only the symmetric ones...) -, you should first finish your work on the Butterfly loop - and test it on thicker ropes ( 9 - 12.5 mm ).
« Last Edit: May 14, 2015, 10:36:55 AM by xarax »
This is not a knot.

roo

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Re: Figure 8 Loop
« Reply #9 on: May 14, 2015, 03:21:44 PM »
Roo: I agree that the (potential) slight difference in strength between a "weak" and "strong" fig. 8 knot does not really affect its use in life support applications (by trained experts with a proper design factor etc etc).  Perhaps the "weak" version is 65% efficient, rather than 75%; both are adequate for the task.  I do wonder what you mean by "pulled" from life support applications.  Is there some governing authority on knot use that could do such a thing as stop all the people that currently use the fig.8 loop from using it?  ;)
There is no one authority, but a collection of authorities operating in different capacities (guides, instructors, authors, government agencies, etc).  For example, wouldn't you expect a responsible knot book author to mention that a slight form variation in a given knot causes it to become so amazingly weak that it caused death or injury in a life-support application?  The danger of such a situation caused by innocent error would preclude such a two-faced knot from ever seeing critical use.
« Last Edit: May 14, 2015, 03:25:52 PM by roo »
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agent_smith

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Re: Figure 8 Loop
« Reply #10 on: May 15, 2015, 03:14:35 AM »
This is how I see the world:

The notional concept a right Vs wrong (or strong Vs weak) method of tying a Figure 8 connective eye knot (#1047) is more likely than not, only for the realm of discussion and debate among knotting theoreticians.

There is no real-world practical application of the 'strong form' over the 'weak form' of #1047 within climbing or rescue contexts.

As I have pointed out many times before, strength is irrelevant in climbing/rescue applications.

The 'ideal' knot is one that is secure and stable and doesn't jam. Also (preferably) it can withstand loading from multiple directions (eg refer to 'wrap 3 pull 2' anchoring knot).

A person can tie #1047 deliberately 'messy' - and it will still hold a falling climber.

A person can tie #1047 deliberately 'dressed' - and it will still hold a falling climber.

If a climber tied the so-called 'weak' form of #1047, I would not cry with alarm and warn the user of imminent death. I would allow activities at height to proceed as planned with no alarm.

The only justification I can give a trainee climbing/rescue technician for tying a 'dressed' form of #1047 is the following:
1. To present a consistent form/structure for inspection - everyone ties the knot in the exact same way - checking is easier and therefore 'tying errors' can be more easily detected and corrected.
2. To ensure stability under load - the dressed form of #1047 behaves more predictably under load and holds its form ('messy' versions of #1047 tied with no regard to symmetry/form tend the behave unpredictably under load - distorting into contorted forms). Note: Although #1047 may have ended up distorted, it will still sustain load.

...

Knotting theorists have long tried to pinpoint with precision the locality of knot rupture but to date it has eluded them. This in my view might be a prime driver for the subject matter of this thread.

As for all of the knot book and vertical rescue authors of past and present - I tend to roll my eyes with a lot of what is printed - as a significant % is parroted / copied.

For example, the endless debate on the so-called 'EDK' end-to-end joining knot which I  find amusing :)  With the possible exception of Dave Drohan's report (http://www.bwrs.org.au/?q=research   at page 22) I have yet to see a well presented test report / paper that provides data for the amount of force required to get a specimen end-to-end joining knot to translate around a 90 degree edge. In my [limited] testing, ABoK #1410 (offset ring bend / offset water knot) is the only form that easily translates around a 90 degree edge with the lowest pulling force. In comparison, ABoK #1415 requires in excess of average human pulling strength to force the knot to translate. Literature all over the web tends to focus obsessively on breaking strength only - a ludicrous notion.

Many climbers focus only on their gymnastic ability to climb 'hard' routes. There is a perception that people who can climb very hard routes by definition also are knotting intellects and uber masters of knowledge and skill. In the mainstream, nothing could be further from the truth (there are some exceptions of course). Most climbers simply parrot what they've been taught or shown or what they might glimpse other climbers doing at the local cliff. For example, the endless debate about what is the 'best' knot to use to tie-in to a climbers harness (eg the endless Bowline Vs Figure 8 debate).

From a purely theoretical standpoint, narrowing down the precise nature of rope rupture in tensile pull-to-failure tests is interesting and helps us to learn more about the science of knotting. Altering the path of a curve/turn of rope within a knot might yield a few % points difference in strength - and this is exciting for theoreticians as it moves the science a notch forward.

For Joe average climber, the weak Vs strong form of the #1047 is irrelevant in my personal view. It matters more that the tie-in knot will remain secure and stable while in the act of climbing - and will not catastrophically fail in a fall event. Humble old #1410 is plenty strong enough even for a tandem abseil/rappel (ie 2 people co-existing on the same rope eg in a rescue situation. It is also secure and stable.

If someone posted news of a discovery of a new knot climbing tie-in knot that is:
[ ] easy to tie - ('easy' is based on an inexperienced climber attempting to tie the knot)
[ ] is secure
[ ] is stable
[ ] is easy to untie after high loading event (eg a 100 kg+ falling climber - who generates significant impact force)
... would be more interesting than pure theory about 'strong' Vs 'weak' form of #1047 (more interesting to me personally)

Mark Gommers
« Last Edit: May 15, 2015, 03:21:46 AM by agent_smith »

knot rigger

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Re: Figure 8 Loop
« Reply #11 on: May 15, 2015, 05:48:38 AM »
Agent_Smith:

I wholeheartedly agree with everything you say in your post.   I agree that the difference in "strong" vs "weak" form is mostly irrelivant, for most applications.  Where is guess I disagree, is that I do find the difference interesting, despite it's irrelevance.

I often need to calculate the safe working load of a system, and the difference would matter to me in this situation, but only so far as getting the calculation as close to accurate as possible.  All (well done) rigging load calculations carry a comfortable margin of error in the design factor.  (I'm sure A_S and others know what I mean by design factor, but for any who don't, it's the ratio of the ultimate breaking strength to the safe working load, and most rigging in my field would have at least a 5 to 1 design factor)

Thanks for chiming in A_S, it's good to keep things in perspective, and I certainly wouldn't want anyone reading what we've all  written and getting the erroneous impression that the fig 8 loop is somehow lacking. 

Quote
Quote from: knot rigger on May 14, 2015, 09:37:34 AM
no book about knots mentions it

   Wrong ! No book about knots in the past !  :)

Ok Xarax, you're quite philosophical there.  You crack me up :)


Dan_Lehman

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Re: Figure 8 Loop
« Reply #12 on: May 15, 2015, 08:13:10 AM »
Knot_Rigger, per you questions, the HSE report (one of a few?) is:
www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf‎
and
>> The American Mountain Guides Association (AMGA)
>> certifies guides in three different disciplines: Rock, Alpine, and Ski.


Agent_Smith:
I wholeheartedly agree with everything you say in your post.
You are are ready to parrot him, then!
(beware : "Here comes Xarax!" --if not me, sooner.    ;D  )

Quote
I agree that the difference in "strong" vs "weak" form is mostly irrelevant, for most applications.
Except that there are more things attached to the
forms denoted by these *labels* --to reiterate that
although I brought them in with thought of connotations
re strength, we should now be happy to read them as
mere labels distinguishing two (of more than two) versions.

There might be differences of significance in security,
of stability with *offset* ('a la "EDK") loading,,
and of more/less per end-2-end/eyeknot.  --of untying!?

Quote
Where is guess I disagree, is that I do find the difference interesting, despite it's irrelevance.
Or, of having this difference noted but ignored
re testing : would we note the difference between
what are regarded --without our deep philosophical
treatment-- as "different knots" and shrug off this,
in a like casual way?  How odd if so : if knots have
different names then we must test ... , but
if we find much difference within one named thing,
no need to bother, after all, it's *still* a <name> !?

Quote
I often need to calculate the safe working load of a system,
and the difference would matter to me in this situation,
We should all find this sort of statement entirely DUBIOUS :
what sort of basis do you have to play around with such
*numbers* as though they mean something?!

E.g., don't you yourself question this kind of thinking,
after you e.g. note such numbers-you-would-use huge
ranges as you did in ...
Quote
Quote
In the 4th edition of the CMC rope rescue field guide
(I just own the field guide, currently not the full text)
they state that the [strength] of the figure 8 bend is 51%,
and they state this 51% is much lower efficiency that in their
previous tests
(which I believe are widely cited by other sources).
Quote
Now you scare me : how can CMC come out with such
nonsense?!!!  I mean that in the sense that LOTS of
testing has put its strength well higher than 50% !!
--i.p., their own, as pub'd in their 3rd version : it gives
the fig.8 end-2-end knot (of some loading (they
use the easy-for-artist-but-impossible-for-rope image))
as 81% which is stronger than their grapevine!!
How do they explain this drastic revisionism?!?!?

This is soooo beyond the pale dramatic, ...shocking
that one cannot comprehend what is going on!!
This is THIRTY %-POINTS (51 vs 81) difference!!!

[[edit-add : Part of my alarm comes from a mistake I realized
 part of the way into this rant --and then I withheld some text ...--,
 in that what is really in my mind re "the fig.8" is the EYEknot,
 not the end-2-end knot.  It's the eyeknot that is so much
 used and tested; the end-2-ender is considerably less so.
 AND, we should expect that there might be significant
 difference, in that the end-2-end knot (presumably some
 symmetric form) must do wonderful things all-at-once
 for TWO S.Parts, whereas an eyeknot can *sacrifice*
 kind treatment of the eye-legs, since they need only
 reach 50% and together get full tension; so, the lone
 S.Part can be given special treatment, so to speak.
 I.p., I'm coming to think that part of the strength
 for the eyeknot comes from the eye-legs' parts
 turning --and somewhat gripping-- around the S.Part!? ]]


Tell us, how do you do this clever calculation of yours?
(Will you check dates of these pub.s, and maybe think
"hey, it's about due for the 5th ed. to emerge, and maybe
it will show another dramatic change!)  Why do you believe
that any particular testing applies to YOUR materials?
(That is something sadly missing from all the texts
above : that strength (etc.) applies to a *knot* and
not to material-M knotted with knot-K !)

(I'm HALF impressed that CMC admit to the difference;
but one must demand that they explain --okay, even
conjecture-- how this can be so :: they did their prior
data-making themselves, with 5 tests per, including
testing the rope (nice, that) --not some off-the-wall,
one-off fluke with a found-on-the-ground shoestring.
((Maybe the full 5th ed. carries more info?))
30 percentage-points; 63% as strong /158% stronger

{{edit-add : Just doing a quick conjecture that such dramatic
differences can result from mis-READING /-typing data (typos),
I looked at the absolute force values given for the end-2-end
knot of issue here : CMC (3rd) give "8,640 (38.73) ... 19% [lost]"
and above this, for the only other end-2-end (Grapevine)
"8,440 (37.83) ... 21%".  Goodness, what a comedy of like
numerals (esp. the metric values in parenthesis!).  Yes, one
can smell a typo/misreading occurring in presenting this,
which need occur in one case and be then in calculations
 of the other figures (metric & percent).  Surmising that maybe
'6' vice '8' is right for the fig.8, one ends up with an
"efficiency" (read : "strength") of 60%-ish, which still stands
at a noticeable remove from the dismal "51%" of 4th edition!

Btw, what other end-2-end knot values are given in 4th ed.?
}}


Quote
There are certainly stronger bends out there
Well, how do we know this?
Not per the 3rd ed..  And if we're willing to dismiss that,
then by what basis do we believe <what> ???!

(Btw, what does the 4th ed. say of the overhand loopknot?
--I'm just realizing (!! <=that's pretty dramatic in itself, egadz )
that CMC 3rd. has it as the strongest :: 85% !!)


--dl*
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« Last Edit: May 15, 2015, 08:04:22 PM by Dan_Lehman »

xarax

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Re: Figure 8 Loop
« Reply #13 on: May 15, 2015, 10:42:10 AM »
   There must be something in the philosophy ( or the lack of... :)  :) ) of the Anglo-Saxon world ( which I admire), which "something" is completely Alien to me !  :)
   I tie bowlines - the good, old, standard, common ones - for mooring of sailing boats, almost half a century now. Never did one of them slipped, or even run the danger of slipping, although the loads with which the lines were loaded were, sometimes, enormous. Hundreds of my friends do the same thing, and nobody ever told me that a bowline slipped. Yet I try to tie "secure" bowlines, and, beyond "tight hitches/nooses/binders", those are the only knots I tie. Am I sooo stupid ?
  There is a thing called "knowledge", which is NOT related, each and every time, with another thing called "application". ( And I am not going to judge the usefulness, for humanity, of this particular application called "climbing" here...  :) :) ). Why is this so hard to understand, I can not understand. And, regarding the thrive of  knowledge of the knots per se, ANY percentage, of anything, is interesting !
   I am sure that there are thousands of possible tangles/knots that "will not slip" and "will not kill" anybody, ever...  We are interested to find the simplest, more secure, more strong, more quick to tie, more easy to untie, more easy to inspect, more neat, more clever, more beautiful of them, even if they will NOT be "used" by any climber, ever - because we would be forced to move to another planet, and there are no mountains in spaceships, as far as I know...
« Last Edit: May 15, 2015, 10:47:18 AM by xarax »
This is not a knot.

Dan_Lehman

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Re: Figure 8 Loop
« Reply #14 on: May 15, 2015, 05:37:09 PM »
   I tie bowlines - the good, old, standard, common ones - for mooring of sailing boats,
almost half a century now. Never did one of them slipped, or even run the danger of slipping,
although the loads with which the lines were loaded were, sometimes, enormous.
Hundreds of my friends do the same thing, and nobody ever told me that a bowline slipped.
Yet I try to tie "secure" bowlines, and, ...
This goes straight to my point made above : we are in
a significant way wrong to attach "strength" and other
attributes to the *knot* (where "knot" means the
general schema that makes an entanglement of knottable
material --an ideal variously manifest in materials)
rather than to <material> <so-knotted> --with emphasis
on the material, put into the form of the schema.
"A bowline ..." just gets one off on the wrong foot;
"heavy mooring lines, knotted in bowlines" is direct.

(And I use this example because I have so often found
these lines with capsized bowlines, and I expect that
X. et al. can all express having no such experience w/"bowlines"!
(I also found some 3/4" ? laid PP rope out in Virginia
countryside with a cut-off such capsized knot, which probably
wasn't the result of some wayward mariner, but similar
behavior got in a different environment.  And in counter-
point, I've seen magazine images of yachting lines in
quite loose-collared bowlines which presumably (a)
represented not uncommon tying that didn't result in
capsizing!?  I don't have a good explanation, but my
observations cannot be denied!
  Now, in the relatively new material of kernmantle ropes,
there have been enough observations of bowlines coming
loose to warrant an investigation & exploration of the problem
and possible redress.  And, of course, with the devilishly
strong-static-slick most modern materials, especially HMPE
fibre, all bets are off!!!)


--dl*
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