International Guild of Knot Tyers Forum

General => Practical Knots => Topic started by: knot rigger on May 10, 2015, 09:01:58 PM

Title: Figure 8 Loop
Post by: knot rigger 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
Title: Re: Figure 8 Loop
Post by: roo 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.
Title: Re: Figure 8 Loop
Post by: xarax 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 ! 
Title: Re: Figure 8 Loop
Post by: Z 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.
Title: Re: Figure 8 Loop
Post by: Dan_Lehman 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*
====
Title: Re: Figure 8 Loop
Post by: xarax 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 ! )
Title: Re: Figure 8 Loop
Post by: Dan_Lehman 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*
====
Title: Re: Figure 8 Loop
Post by: knot rigger 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
Title: Re: Figure 8 Loop
Post by: xarax 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 ).
Title: Re: Figure 8 Loop
Post by: roo 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.
Title: Re: Figure 8 Loop
Post by: agent_smith 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
Title: Re: Figure 8 Loop
Post by: knot rigger 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 :)

Title: Re: Figure 8 Loop
Post by: Dan_Lehman 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 (http://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*
====
Title: Re: Figure 8 Loop
Post by: xarax 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...
Title: Re: Figure 8 Loop
Post by: Dan_Lehman 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*
====
Title: Re: Figure 8 Loop
Post by: alpineer on May 15, 2015, 06:04:10 PM
Suspect water acting as a lubricant in those capsizing cases?
Title: Re: Figure 8 Loop
Post by: Dan_Lehman on May 15, 2015, 06:27:58 PM
Suspect water acting as a lubricant in those capsizing cases?
That helps, how?  And the yachting lines ... ?
(And all the other marine testimony of "sailors" ?!)

I'm thinking it might have something to do with surface
friction ("frictive" --my contribution to language-- vs. slick)
and thus a draw of opening the turNip rather than
sliding against ... and tightening w/less opening pull?!
AND --purely my surmise--, seeing one trawler (or was
it an apparent owner's pair?) with tail-outside bowlines
(aka "Cowboy", "Left-handed") and thinking that they
had deliberately so tied as a defence against capsizing
(so, work into the thinking the position of tensioned
side of the collar bight).   !?

I will anticipate others' having my suspicion that the lines
were particularly stiff, and that the stiffness essentially
made for looseness, which gave vulnerability to capsize:
no, these thick lines are rather flexible, in many cases.

Another idea : friction around a piling which resulted
in biased tension on the eye legs !?  Eh, that seems
a bit of a desperate grasp for a reason ... .


--dl*
====
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 06:41:47 PM
I expect that X. et al. can all express having no such experience w/"bowlines"!

  Are you living up to the mountains ?  :) Have you seen marine ropes, immersed into salt ?  :)
  Capsized bowline ? Never ! I mean, real bowlines, real mooring lines, real boats, real sailors - and real sea !  :)
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 06:48:07 PM
   Suspect water acting as a lubricant in those capsizing cases ?

   On the contrary, water, acting as lubricant, may prevent capsize - because, perhaps, the segments of the rope are offered the chance to rearrange themselves into the nub, fill the gaps, and absorb the more evenly distributed forces more efficiently ? ?
   That would be an interesting experiment : See if a bowline tied on a wet line ( or, a wet line tied as a bowline... :) ) capsizes earlier or not.
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 07:00:34 PM
  <material> <so-knotted>

  You are a material-fundamentalist !  :)
  <Knot> formed on <this-material>, is the correct description.
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 07:08:42 PM
   I would like to repeat something that I believe may be interesting : What about modifying the fig. 8 loop or bend, to make it easier to untie ?

... 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
Title: Re: Figure 8 Loop
Post by: Dan_Lehman on May 15, 2015, 07:55:57 PM
I cannot find the quote quickly, but somewhere Knot_Rigger
remarked --and posted URL to image of...-- that the S.Part
of the fig.8 eyeknot in the "strong form" would pull under
its twin and so achieve a tight turn ... .  Well, this might be
behavior dependent upon both dressing & setting and material.

I, too, can see this.  But is it inevitable, and is it --although
*apparent* in a highly loaded knot-- achieved without some
benefit --i.e., might there be some offloading of force in
the process of the S.Part pushing (against a well-set twin
part)?!  --that the S.Part had to press hard against its twin
in order to run fairly straight, and so ends up stronger in
this than where it runs straight more "unopposed" ?!

It does suggest that in material that is resistant to being
set as I muse could be beneficial for the "strong form"
the benefit of this form cannot be achieved readily (i.e.,
it might take devices to set the knot well enough, as
manual strength vis-a-vis expected forces is just too low).
(There is another factor : elastic, compressible material
should do things that static or firm material won't!)

I attach two views of a newspaper photo of a fellow doing
training rescue work in which one can see two fig.8 eyeknots
--in red & gold ropes.  Note how UNloaded one of the twin
strands is in the red rope; I believe that this is the twin
of the "strong form", and so we see how the S.Part gets
"into" making a tight turn, missing bearing against this
twin for offloading, the twin too loose in the setting.
And note the gold/yellow knot : it, too, is amply loose
--one can see through gaps in its parts--, maybe because
it's a stout, stiff rope, and not given special effort in its
setting (but even so, it might be one that, with higher
loads --those that only can show a strength difference--,
see the S.Part bypassing the "bear-against" aspect of my
conjecture.

I, too, like Knot_Rigger remarks, had viewed the knot as
showing a milder (if any difference) curvature with the
"weak" (inner twin) strand (which bears into parts that
turn around it, and pulls away from its twin (which will
show its lack of tension by sort of standing aloof in a loaded
knot)), and so wondered at Chisnall's assertion.  Looking
with Chisnall's result as an assumption, I arrived at my
conjuecture of this "bearing against" curvature leading
to the tight, around-eye-legs U-turn.  (But, also, one can
see a *brief* harder curve in the "weak form" S.Part
where it first is deflected around parts; but this might
quickly straighten w/o much consequence.)
AND . . . this conjecture led directly to my "building"
the "Lehman8" (vanity made me choose this moniker
over "bowlinEight" of my word-fusion formation).  I used
the 8 as a base, and then deliberately looked at how the
returning eyeleg could go into this and give the "padding"
("bearing against") benefit conjectured to benefit the
fig.8, and worked that around with a finish that has
some of the easy-to-loosen collar of the bowlilne.
A side benefit is that it seems to be a pretty slack-secure
knot, to boot.

X., I have anticipated your --sent whilst I'm keystroking--
thought:
Quote
I would like to repeat something that I believe may be interesting :
What about modifying the fig. 8 loop or bend, to make it easier to untie ?
Exactly my design goal (I was "designing" actually, rather
than just "fiddling" "what if..." variations (often productive
on its own)!) for the Lehman8 (not an end-2-ender).

Per X.'s & my discussion of the Lehman8, I attach two
(previously posted somewhere) images of this, with the smaller
2nd one showing the "easy untying" collar aspect's reverse
side, i.p.; YMMV on how very tight this might become, though
(needing a marlinespike for the "easy untying" aspect?
--but, nb, that IS easier than knots in which the spike is only
a hope, with no obvious point of insertion and use : here,
it would be at the colloar, to pry it around/off binding S.Part
to "padding" part, which I think would not require so much
stretching of material but just getting tightly pressed parts
to move against each other.  I recall one knot-forum person
admitting to having used this as a climbing tie-in, generally
liking it.

The knot in orange & B&W (an interesting seen-in-marine
setting hollow braid of PP (B) & polyester (W)) is merely a
"quick8" were it stopped before collaring the S.Part
--yes, just the pinch of the 8 on the tail's leg will hold(!)--;
that I doubted such brevity led me to put in a bowlinesque
collar (and stuff a 3rd diameter out through the S.Part's
U-turn.  Looking at it now, I muse about turning it around
the collar clockwise, and then taking it not as shown
but to run "twin" qua "padding" against the orange S.Part's
turn, and so back out twinning the S.Part.
Well, with setting just so, and ... , maybe ....
All of which suggests the practical silliness of such contrivances,
if they require Advanced Knot Setting courses and guesstimations
of ultimate forces effects on particular_material_M !!
BUT, it is not w/o merit, I submit, that in pursuit of learning
what affects knot "efficiency" and so on, that we are able
to build such nearly-alike (small differences to isolate things
that might affect ...) knots for testing, and see what matters
(and in what material_M it matters or not).


--dl*
====
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 08:39:27 PM
   I believe that the only answer to our problems, is this :
   http://www.alibaba.com/product-detail/20T-Pull-Back-Ram_984242477.html

   ( Nice, clear pictures ! )
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 08:50:54 PM
    Perhaps if one "plants"/"nails" the Tail End another time into some opening of the knot... and the sheer compressible bulk / volume of this segment prevents the nub from being too tightly clinched around itself ?
   I believe that climbers and rescue workers would be more easily persuaded to use a more easily untied knot which has something more than their beloved fig.8 bend or loop, than something less !
Title: Re: Figure 8 Loop
Post by: Dan_Lehman on May 15, 2015, 08:55:59 PM
This is how I see the world:
Upside-down, from DownUnder!   :D

Quote
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.
It might be relevant for the purpose of setting "high lines"
which will require high tension for staying closer to straight,
and if not needing *strength* of the knot for this, might need
preferable/easier untying of one vs. other versions.
Perhaps the "ease of untying" difference (is there...?) will
have (some) significance in other uses, too.

Quote
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).
There might be some seen difference in offset loading (aka "EDK")
between the forms, although there is now some advice to
avoid the offset fig.8 in favor of the simpler and more
widely used offset waterknot (overhand) already.

((
BTW/FYI : Clyde Soles introduced the name "offset overhand"
which I liked --esp. the "offset" adjective, which is spot on
(such knots are NOT "flat"!)--, but I opted to go for "water knot"
as the least confusing name (not liking "ring bend" as this
knot doesn't *bend* to a ring; I no longer support Ashley's
desire to hijack "bend" for "end-2-end", as history used it
otherwise --a point that C.L. Day made).

Similarly, as an essential aspect of webbing/tape IS its
"flat"ness, I do not like "flat" vs. "tubular" for tape types
but "solid" vice "flat" --again, to the point!)
))

Quote
A person can tie #1047 deliberately 'messy' - and it will still hold a falling climber.
NB : "messy" is a non-particular description!  One messy
orientation and another one might be quite different in effect?!
NB-2 : "properly dressed" is sometimes advised, but is there
EVER any given specification to what this is, actually?!
(All I've seen is the further verbal guidance to avoid parts
"crossing over" each other, which is subject to interpretation.)
This goes to X.'s point about authors not having real knowledge
(in the No Author is Wrong challenge), but just parroting what
they've heard elsewhere!

TO THE POINTS WE DEBATE ("strong"/inner vs. "weak"/outer versions):
NB-3 : TWO sources --viz., CMC (3rd; & 4th?) & Dave Richards-- have
thought to test "tied in the bight & "follow through" *versions* of the
fig.8 eyeknot !!!  I believe that Agent_Smith has remarked at this,
as have I --that the knots (presumed to have been "dressed & set"
to whatever believed ideal the particular knot tester had, AND that
it was specific enough...-- that the knots cannot care about their
tying method : they are the same entanglement receiving force.
THIS IS A FAR LESS DIFFERENT CIRCUMSTANCE THAN "STRONG/WEAK"!!
And yet it was tested !!

It just would NOT occur to me to do this,
UNLESS
I had done some in-the-field, practical, actual-factual empirical
research
that revealed that there was a difference in
orientation (or a statistically significant bias) of result obtained
from the different tying methods.  THEN, well, yes, test these
different *knots* !!  But neither CMC nor D.R. give such thinking;
they just indicate tying method, for which there is no evidence
of differing results (and general guidance that results should be =) !!
(I find this amazing, appalling.  Mostly, also, w/o remark or critique.)

Quote
... a 'dressed' form of #1047 ... behaves more predictably under load
 and holds its form
... is in a vague way at least better specified
than the open-ended, who-knows-what, "messy" result.

Quote
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.
Whoa, this K.T. has made some small effort to learn this,
and --speaking of "thread"-- has introduced the technique
of sewing into test specimens colored threads to mark the
locations at pertinent points of interest.  (See attached!)
I think that I've seen clearly enough that it is the INNER
yarns/strand(s) of a part in a bend that by compression
break, and not the outer, presumed-more-stretched parts,
which was a commonly voiced theory (i.e., outer breakage).
One might see this in following the twist of laid rope where
one of three strands breaks, others stretch out intact, and
see that it leads to concave side of curve at rupture,
not the convex/outer side.

I'll attach two (elsewhere here previously posted?) pics
of such thread-marked tested knots --the ruptured one,
and the survivor eyeknot showing where the marked
spots were (likely) at point of rupture.  (I'm thinking
that these qualify me for a Nobel Prize in Knotting.)   8)


Quote
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.
But only if the testing comes with specifics of geometry
and so on, not merely --and as is common-- knot names
and test data, a not showing the pre-loaded geometry,
and the near-rupture geometry, and so on.
(I feel a lock on the Nobel!)

Quote
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)
That is spelled 'L e h m a n 8' (and spells "Nobel") !   ::)

In the attached photos of tested knots (in Dyneema, 5/16" 12-strand),
a pink thread marked a point I thought likely for rupture, and a gold
thread led or trailed this, anticipating movement in tightening
--i.e., that the gold might move for rupture where the pink had been.
Some white threads are at entry points, to show how much
material is drawn out during tightening/compression (this is
quite INelastic cordage).
The reverse fig.9 eyeknot was chosen over the common
one with this thinking : common one might benefit, in usual
material/fibre
, from some gripping effect, but in HMPE
the material is too slick for this,
so go instead for a form that seems to give a broader curve.
Note that the break point looks to be rather well around
this curve, maybe beyond the U-turn point, where the S.Part
bears against entering eye legs!?

In these cases, it will take more scrutiny to conjecture about
concave/convex side of curve vis-a-vis break point.


--dl*
====
Title: Re: Figure 8 Loop
Post by: SS369 on May 15, 2015, 10:01:58 PM
I agree with agent_smith for practical purposes and that is how I would use the figure 8 loop - without unnecessary worry. I personally tie in with a simple-locked bowline, but that's diverting.

I think that there are tests out there that have been done, measured and video captured that show the parts orientations well enough and the motion of the knot during destructive testing. Thermal imagery included that indicates where the destructive heat is generated and most likely the cause of the rupture. I think so at least.

Watch the video. https://www.youtube.com/watch?v=s3fHYGY3YTo (https://www.youtube.com/watch?v=s3fHYGY3YTo)

SS
Title: Re: Figure 8 Loop
Post by: roo on May 15, 2015, 10:28:37 PM
Thermal imagery included that indicates where the destructive heat is generated and most likely the cause of the rupture. I think so at least.
I think some strain energy gets converted to heat and since strain is proportional to stress, this can be used to give an approximate indication of where high stress areas are, and thus where rupture is most likely.

But other effects can mask this.  There may be friction-generated heat, and some parts of the knot may lose heat faster just due to geometry.

edit to add related link:  http://www.researchgate.net/publication/252707600_Correlation_of_infrared_thermographic_patterns_and_acoustic_emission_signals_with_tensile_deformation_and_fracture_processes

It's interesting to see the high stress areas from the rope surface become more uniformly distributed as the rope travels away from the knot. 
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 10:46:34 PM
From DownUnder :
Right and wrong Figure-of-8 knot
http://www.ropelab.com.au/right-and-wrong-figure-of-8-knot/
Title: Re: Figure 8 Loop
Post by: SS369 on May 15, 2015, 10:49:31 PM
Thermal imagery included that indicates where the destructive heat is generated and most likely the cause of the rupture. I think so at least.
I think strain energy gets converted to heat and since strain is proportional to stress, this can be used to give an approximate indication of where high stress areas are, and thus where rupture is most likely.

But other effects can mask this.  There may be friction-generated heat, and some parts of the knot may lose heat faster just due to geometry.

Yeah, I know friction can be included along with pressure, both contributing to the demise of this and other knots. But, I think in this case, this Fig. 8 loop test video, it shows clearly enough with enough data, with this particular dressing, what and where the demise is going to take place. If you were to zoom in close enough...

Of course the rest of the surrounding knot parts (geometry) will carry away/absorb the heat, though I don't really see what that statement proves here. Maybe it slows the flow too much?
This was a slow pull test, but I am of the opinion that a fast pull test or drop test would have very similar results, just faster.

I am of the opinion that if you were to stop the pull test just short of the projected rupture point, it would take a Herculean effort to untie this. As well, the rope would be ruined there.

Regardless, the video shows a well enough completed test.

SS
Title: Re: Figure 8 Loop
Post by: roo on May 15, 2015, 10:51:29 PM
I think some strain energy gets converted to heat and since strain is proportional to stress, this can be used to give an approximate indication of where high stress areas are, and thus where rupture is most likely.

But other effects can mask this.  There may be friction-generated heat, and some parts of the knot may lose heat faster just due to geometry.

edit to add related link:  http://www.researchgate.net/publication/252707600_Correlation_of_infrared_thermographic_patterns_and_acoustic_emission_signals_with_tensile_deformation_and_fracture_processes

Slightly off topic, but this is an interesting related experiment:

http://demo.physics.uiuc.edu/LectDemo/scripts/demo_descript.idc?DemoID=1193

However, they left off the really fun part.  Once the rubber band is stretched and the heat dissipates, let it shrink back again and it really feels cold against your skin.
Title: Re: Figure 8 Loop
Post by: xarax on May 15, 2015, 11:29:44 PM
Slightly off topic, but this is an interesting related experiment:
http://demo.physics.uiuc.edu/LectDemo/scripts/demo_descript.idc?DemoID=1193
However, they left off the really fun part.  Once the rubber band is stretched and the heat dissipates, let it shrink back again and it really feels cold against your skin.

   Nice experiment ! Very interesting ! Thanks for the reference.
Title: Re: Figure 8 Loop
Post by: knot rigger on May 16, 2015, 05:48:28 AM
Quote
From DownUnder :
Right and wrong Figure-of-8 knot
http://www.ropelab.com.au/right-and-wrong-figure-of-8-knot/

A shame I have to pay to read this,  Xarax, anychance you have the text of this article without me having to become a member of this site?

Quote
Watch the video. https://www.youtube.com/watch?v=s3fHYGY3YTo

SS, fantastic video,  thanks for posting it.  It's very interesting.  I especially take note of which "weak" or "strong" form they happened to have tied!

Quote
Quote
A person can tie #1047 deliberately 'messy' - and it will still hold a falling climber.
NB : "messy" is a non-particular description!  One messy
orientation and another one might be quite different in effect?!

Dan, I knew exactly what A_S meant by "messy" dressing of the knot.  And I completely agree with his point: that while a messy dressed fi 8 may be weaker, and may be more prone to jamming after a fall... It's still adequate to the task at hand, and there is no reason to fear a "messy" knot would not hold a climber's fall.  All things considered, I personally dress all my fig 8 loops as well as I know how before they are loaded, but if I inspected one that was "messy" I may not fix it right away, depending on the circumstances.

Quote
Knot_Rigger, per you questions, the HSE report (one of a few?) is:
www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf‎

I got a 404 error when I tried that link

Quote
Quote from: knot rigger on May 15, 2015, 05:48:38 AM
Agent_Smith:
I wholeheartedly agree with everything you say in your post.
You are are ready to parrot him, then!

What he says makes sense, and to agree with what makes sense isn't "parroting" IMO.  (btw It's off topic but I don't care for the EDK myself, but I come from things more from a rope's access viewpoint than a sport climbing point of view)

Quote
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?!

Dubious?  really?  I was just pointing out how in my line of work, am indeed concerned with efficiencies of knots.  What about that do you think is "entirely dubious"  or what about this statement of fact (it is a fact that I do load calculations involving efficiencies of knots) should "we all" find dubious.

The point I was driving at was accuracy.  If you hadn't have truncated my quote, the point would (perhaps) been more clear.

here is the full quote:

Quote
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.

you go on to ask:

Quote
Tell us, how do you do this clever calculation of yours?...

I will be brief, as this is off topic of the thread:  Suppose in the course of inspecting some show rigging, we find a problem with a 400 lbs speaker system.  (perhaps there is a side loaded shackle that we need to fix)  Due to the details of the situation, we determine the best way to proceed is to temporarily lift the speaker with rope.  What we have on hand is 11mm Kernmantle with a breaking strength of 6000 lbs.  Given the nature of the load, the industry 'best practice' for lifting with fibrous rope would be to use a 10 to 1 design factor.  A 10:1 DF with a 75% efficient termination would give us a safe working load of 450 lbs.  A 10:1 DF with a 65% efficient termination would give us a SWL of only 390 lbs.  Less than the given load we need to lift.

This example may seem contrived to you, but I assure you that I have made these sorts of "on the fly" safe working load determinations many times.  You may think that a mere 60 lb difference between knot efficiencies isn't that much and doesn't matter that much in real life, and in a way it doesn't.  The healthy safety margin is a buffer against human error, the necessity of estimation, errors of information, and unforeseen loading events.  And that same safety margin would let me sleep at night, even if the rigger who tied the figure 8 knot we used happend to tie the weaker form.  However, I would like to do my calculations as accurately as I can, and there lies my interest in the question at hand.

One last point about my example.  The actual difference of 10% efficiencies in the knots would yield a 600lb difference in ultimate breaking strength.  The 600 lbs difference is larger than the 400 lbs load we're lifting!
Title: Re: Figure 8 Loop
Post by: xarax on May 16, 2015, 01:02:29 PM
the text of this article without me having to become a member of this site ?

  I do not have it either !  :)  It was just an effort to make out friend from DownUnder, agent smith, reply - I guess he knows the writer in person, and he can tell us more about the whole thing.
Title: Re: Figure 8 Loop
Post by: Mobius on May 16, 2015, 03:05:25 PM
the text of this article without me having to become a member of this site ?

  I do not have it either !  :)  It was just an effort to make out friend from DownUnder, agent smith, reply - I guess he knows the writer in person, and he can tell us more about the whole thing.

I live 'DownUnder' too, in Sydney :)

I have to say that the site looks really interesting and from reading their blurb it seems they do testing.
Title: Re: Figure 8 Loop
Post by: roo on May 16, 2015, 04:31:47 PM
Of course the rest of the surrounding knot parts (geometry) will carry away/absorb the heat, though I don't really see what that statement proves here.
I was thinking more along the lines of heat being lost to the surrounding airflow via convection and to space via radiant heat transfer.  In other words, the more exposed regions would lose heat faster, skewing the relative stress results to some degree.
Title: Re: Figure 8 Loop
Post by: Dan_Lehman on May 16, 2015, 06:03:21 PM
Quote
Knot_Rigger, per you questions, the HSE report (one of a few?) is:
www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf‎

I got a 404 error when I tried that link

And so did I, clicking on your copy of my URL!?!  ???
Well, I retrace my fetching steps (Google produced)
and again am using URL  into the PDF.

Here is the combination of "404" <> "working" URLs,
between which I've not been able to see any difference:
http://www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf‎<>
http://www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf
I copied above from my window's URLocator window,
in which I first got 404 from the left half (w/o extension of R),
then pasted in the R half which had just seen me INTO the PDF!?
HUH???  The '0' are indeed zeroes & all identical.
NOW --while typing this Reply--,
I copy-past tope URL from 'www' on, and ... "404".
I do the same with 2nd line, similarly, and ... AM IN!?!?!?
Holy double-vision, Batman,
what's going on here?
UPDATE :: By tediously using window Find and parts of
these URLs, I reach a non-matching point at 'p' of 'pdf' !?
I.e., URLs match up through final period but fail at an
apparently identical 'p'!?!?
MORE bizarre :: I just cut'n'pasted the offending 'pdf'
into Find window; all the OTHER "pdf"s --i.e., lower AND
uppercase-- were highlighted in yellow of multiple occurrences;
but, Next used in Find DID TOUCH THE UN-HIGHLIGHTED 'pdf'
of the offending/404 URL.  !?!?

(Google "hse Lyon Equipment knots test" and you should get
your own, if one of the (two identical (l00king!)) URLs above,
here, fails again.

... baffled ...  :o   :-[   :-\    ::)   :o
[edit : I just clicked on embedded --by system-- URLs above,
and again the 1st/upper one got "404", the 2nd apparently
identical one got me to the PDF.]
>>> now, putting both 'pdf', '.pdf', and fuller ending
of these URLs, I see ALL of them highlighted (by Find)
on this forum page, and Next to all, also (whereas before,
doing Next/Find in my post-compose window, I got the
odd yellow-highlighting EXCLUDING the offending URL's 'pdf',
but Next went to it, anyway.   :o   


Quote
Quote
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?!

Dubious?  really?  I was just pointing out how in my line of work, am indeed concerned with efficiencies of knots.  What about that do you think is "entirely dubious"  or what about this statement of fact (it is a fact that I do load calculations involving efficiencies of knots) should "we all" find dubious.

...  A 10:1 DF with a 75% efficient termination would give us a safe working load of 450 lbs.
A 10:1 DF with a 65% efficient termination would give us a SWL of only 390 lbs.  Less than the given load we need to lift.
Really, my point isn't obvious to you --and I gave it
in fuller terms than you quote?!?  You pick 65 & 75%,
and I questioned explicitly (a) how someonElse's figures
can be seen as relevant to your materials (and nature
of loading/forces), and (b) how you would you deal with
the 30%-points (51 vs. 81) difference in the CMC two
reference works!?
Ergo, ... "dubious"! (& QED  ;) )

You seem to imply --don't explicitly say-- that your different
(75/65%) figures attach to distinctly different terminations;
my point mainly was, in addition to taking that value at its
face, how you deal with the multiple values given for the
--nominally/apparently-- SAME termination!
(And, now with this URL mystery, how do we do ANYthing!)

--dl*
====
Title: Re: Figure 8 Loop
Post by: SS369 on May 16, 2015, 11:09:11 PM
Of course the rest of the surrounding knot parts (geometry) will carry away/absorb the heat, though I don't really see what that statement proves here.
I was thinking more along the lines of heat being lost to the surrounding airflow via convection and to space via radiant heat transfer.  In other words, the more exposed regions would lose heat faster, skewing the relative stress results to some degree.

I would think that instead of skewing the results, that would be part of the results. Even if you froze or chilled the rope, the thermal action would still be part of the equation.
The main point of providing the link was to be able to see the tightening action of the Fig. 8 (most people will never stress theirs that hard nor have a camera on it when it does, or see it when they take a whipper) and where the stress induced the disastrous result.

SS
Title: Re: Figure 8 Loop
Post by: agent_smith on May 17, 2015, 03:21:14 AM
After searching for Lehman Figure 8 and Nobel prize in the same sentence (never found the Nobel prize) I stumbled across this site:
http://www.elementrescue.com/Element_Rescue/Main_Blog/Entries/2014/8/2_The_Bowline..._Dont_call_it_a_comeback.html

Couldn't determine the author of the site - but I did find a Audie Murphy likeness (I wonder if he looks like Dan Lehman)?

Just to be clear - I wouldn't be posting in this forum if I didn't have an interest in all things knotting (although my primary interest is in the area of knots used in life support applications).

With regard to Richard Delaney and the 'Rope test lab' site - I am on facebook so I can post there - and I know Richard personally (I actually trained him as an instructor back in the 1990's). Richard is an enlightened man - very knowledgeable and passionate about climbing, rescue and anything that is captured under the general banner of technical roping. He has worked hard to put that facebook page together and make it work - and more power to him if he can generate some income from it (why not).

I will say that I don't agree with the term 'right' versus 'wrong' way to tie ABoK #1047 (Figure 8 connective eye knot). I would be more supportive of the term 'higher efficiency' versus 'lower relative efficiency'. Using terms such as 'right' and 'wrong' might lead to mass hysteria and needless concern that death is imminent if the lower efficiency form of #1047 is tied and relied upon.

If a trainee under my direct duty of care stood before me and tied the lower efficiency version of #1047, I would not cry foul and declare death to be imminent. And if the trainee paid zero attention to dressing (symmetry and form) and created a random 'messy' structure, I still wouldn't be concerned about imminent death - although I would argue a case for consistency and predictability/behaviour under  load. I support consistency when rescue teams tie knots - and I support the notion of attention to dressing because it makes the knot more predictable under load (it doesn't tend to alter into a distorted form under high loading - AND, it makes it easier to check and detect errors).

To declare the lower efficiency #1047 as 'wrong' would (in my view) have to be justified against a whole host of other connective eye knot - eg the Bowline family of knots. This comes down to the issue of pure strength - whilst ignoring more important factors such as security and stability (and ease of untying after high loading event). The Bowline (secured form) is just as good - and better in my view - than a 'high efficiency' #1047.

Dan Lehman referred to Highlines - I always prefer to use a capstan-like hitch such as the so-called 'tensionless hitch' in highline rigging (ie for end terminations to anchors). If you really are going to put some outrageous loading on a highline system - what better 'knot/hitch' than the 'tensionless hitch'? Obviously its not a connective eye knot like the Bowline - but it is fit-for-purpose in such an application. If for some reason I couldn't employ a tensionless hitch - I would use a secured Bowline (not #1047) - because #1047 would more likely than not jam.

I know well enough about threading little bits of cotton thread tracers in ropes in preparation for break testing. I remember cursing Dan Lehman under my breathe years ago when he urged me to do this. I dont think my eyes could handle the strain anymore... But I agree that it is the proper method in knot testing.

And this type of research and discussion is a worthwhile exercise and it interests me - but it doesn't alarm me.

Pure research can lead to world changing breakthroughs - like studies of quantum physics led to the invention of the transistor which then opened the way for computers which then opened the way for the internet and me typing this post today :)

I dont know if the Lehman 8 is worthy of a Nobel prize though   ;D

Mark Gommers

Title: Re: Figure 8 Loop
Post by: roo on May 17, 2015, 07:21:30 AM
I was thinking more along the lines of heat being lost to the surrounding airflow via convection and to space via radiant heat transfer.  In other words, the more exposed regions would lose heat faster, skewing the relative stress results to some degree.

I would think that instead of skewing the results, that would be part of the results. Even if you froze or chilled the rope, the thermal action would still be part of the equation.
The main point of providing the link was to be able to see the tightening action of the Fig. 8 (most people will never stress theirs that hard nor have a camera on it when it does, or see it when they take a whipper) and where the stress induced the disastrous result.

SS
Hmm.  You may be thinking that those color maps are indicating more heat than what's actually being produced.   Those temperature variations are fairly mild (maybe around 10 degrees Celsius variation looking at the final chart of the video). 

To put a different angle on my previous comment, if you paused the test and let all those mild temperature variations dissipate, you'd get a very skewed result of it looking like all portions of the knot have equal stress, for example.
Title: Re: Figure 8 Loop
Post by: xarax on May 17, 2015, 08:52:31 AM
I support the notion of attention to dressing because it makes the knot more predictable under load

   I believe you should support the notion of attention to dressing, just because it requires ATTENTION, and attention is of paramount importance in your field... One should pay attention to anything he does - so he should also pay attention of how he ties the fig.8 bend or loop, or ANY bend or loop for that matter.

   However, there are more than TWO the possible symmetric forms one can dress the fig. loop, and until you do not pay attention to THAT simple fact, you are just parroting what it is parroted all those years by all those people - and I believe that this is NOT your style !

Pure research can lead to world changing breakthroughs

  It was always like that... so, somebody should tie and try, systematically, ALL the different symmetric forms of the fig.8 loop - which are MUCH more than TWO !  :) :)  NOT because some are weaker and some stronger, right or wrong, more or less efficient, etc, but simply, as you climbing people like to say, because they are there !  :) :) :)
Title: Re: Figure 8 Loop
Post by: agent_smith on May 17, 2015, 01:16:23 PM
Thank you for assuming that I am parroting a parrot Xarax. I would have preferred to parrot you instead of all the other parrots. A wise man once told me to never 'assume' - because it could make an Ass out of U and Me. So don't assume this parrot has parroted all the other parrots without first checking whether the parrot really was parroting the parrots.

Just parroting a bit more, this thread is receiving a lot of attention compared to other topics - I wonder why?

My point re 'dressing' was in fact used in a generic sense - in that it is desirable to achieve symmetry of form for the reasons I stated previously. I was not deliberately pointing toward any absolute dressing forms (weak Vs strong or whatever description you prefer) other to say that random tying without paying any attention to any particular dressing is not best practice and can cause issues.

Xarax, may I suggest that you join the rope test lab Facebook page and then pay the small subscription fee so you can provide commentary on their test results. Then you could report back here...

Title: Re: Figure 8 Loop
Post by: knot rigger on May 17, 2015, 10:17:21 PM
Quote
With regard to Richard Delaney and the 'Rope test lab' site - I am on facebook so I can post there - and I know Richard personally (I actually trained him as an instructor back in the 1990's). Richard is an enlightened man - very knowledgeable and passionate about climbing, rescue and anything that is captured under the general banner of technical roping. He has worked hard to put that facebook page together and make it work - and more power to him if he can generate some income from it (why not).

I have joined Mr. Delany's RopeLab website.  A_S, you convinced me, although I don't think that was your explicit intent.  I figure it's worth $60 to support the work of someone whose passions I share.  Also A_S, let me congratulate and thank you for your paper about the Bowline [ http://tinyurl.com/mkkcwbp ] which I have found very interesting and usefull.  Thanks as well for the link to element rescue site.  I've emailed Mr. Delany asking permission to share the whole of his article about the figure 8 knot with this thread.  In the mean time, I will attempt to summarize.

First, I like one way that he refers to the difference between the forms: by the path of the standing end; so we have an "inside" version, and an "outside" version.  I find these two terms superior because they don't have any implied judgment attached, they just describe the topology of the knot.
Second, his article is mainly about how easy it is to untie the knot after heavy loading, not pulling to rupture.  But this is very interesting in what he finds, and one conclusion he proposes.  He found that the "inside" version (aka "weaker") was harder to untie after heavy loading.  He also saw that often (but not always) the "outside" form "flipped" (his term) such that the outside bend flipped to the inside position with applied tension.  He loads the knot on common 11mm static ropes used in the ropes access industry, and chose to test them up to, and exceeding the Safe Working Load of the rope. 
Lastly: He draws this conclusion (in the form of a hypothesis)

"Further tests may be also confirm that that figure-of-8 knots that are difficult to untie may have been loaded above 5kN and thus above the SWL of the rope.  If this is the case then the figure-of-8 knot is certainly a good choice for anchoring ropes in tech rescue and rope access work."

I find this an interesting thought, that the knot is both the anchorage, and the indicator of potential abuse.

Ok then, Dan Lehman, thanks for clearing up the link to the HSE report.  I'm no wizzard with computers, and have no idea what went wrong there, but thanks for re-posting.  It turns out I have seen this report, but I had forgotted or neglected the information about the inside/outside versions of the fig 8 knot.  To summarize for the thread (you had already, but I will too)  for the overhand loop, the outside version is stronger, for the fig 8 loop inside and outside are the same strength, and for the fig 9 loop, the inside version is stronger (all according to the HSE report).  It's off topic, but anyone who climbs or does rope access work should read section 7 of the report about "cowstails", and be VERY cautious about using sewn cowstails.

more from DL:
Quote
Really, my point isn't obvious to you --and I gave it
in fuller terms than you quote?!?  You pick 65 & 75%,
and I questioned explicitly (a) how someonElse's figures
can be seen as relevant to your materials (and nature
of loading/forces), and (b) how you would you deal with
the 30%-points (51 vs. 81) difference in the CMC two
reference works!?
Ergo, ... "dubious"! (& QED  ;) )

You seem to imply --don't explicitly say-- that your different
(75/65%) figures attach to distinctly different terminations;
my point mainly was, in addition to taking that value at its
face, how you deal with the multiple values given for the
--nominally/apparently-- SAME termination!

How do someone's else figures apply to my materials and conditions?  They don't, but the information is applicable in that the materials and conditions are approximatly the same.  In other words, I have to make a judgement call.  I base my decisions on the best knowledge of knot efficiencies I can find, then employ a large design factor to (among other things) protect against inaccuracies in reported knot efficiency.

As far as the figure 8 bend goes, I would used the most conservative efficiency of the two from CMC (and/or the most conservative I can find from multiple sources)  Specifically to the fig 8 bend, I choose not to use this knot!  There are stronger bends for high load applications (double and triple fisherman) and more convenient to tie bends for low load applications (double sheet bend).  [the zeppelin bend may be better for both applications, and I use it, but I haven't yet seen good efficiency data on the knot, and avoid it for life critical applications]

To make a judgment call about any given knot efficiency, and how it affects what knot I use, I would employ these criteria: 
(1) compare as many published accounts as possible of knot efficiency
(2) consider failure states (does it slip, jam, break, etc)
(3) consider the application to determine what is the most important; security, strength, ease of tying, ease of untying
(4) consider that my work will be inspected by others, and for that reason I may choose a more widely know knot over a "superior" one

Title: Re: Figure 8 Loop
Post by: xarax on May 18, 2015, 07:17:18 PM
   Climbers are sooo poor knot tyers ! They know only a very small number of knots ( and they even naively believe that these knots are the only ones, and the best possible ones, suitable for them, simply because they do not know anything else...), they do not know ( and they do not want to learn ) how those knots "work", they do not know ( and they do not want to try to figure out ) how to improve them, and, last but not least, they just do not care about knots ! Fortunately, knots were tied, tried, studied, and improved by sailors. If the water on planet Earth was less or was frozen, perhaps we would have had more climbers and fewer sailors - but I am sure we would have had fewer and worse knots !  :)
   When a knot tyer watches this video with the fig.8 loop, the very first thing he notices, is the most obvious thing : the initial shape of the fig.8 loop is distorted very unevenly, to a degree it becomes unrecognizable. Then, the next thing he notices is that this outer "higher" collar seems to be almost unloaded, that it, almost redundant ! Evidently, it does not participate in the dissipation of the tensile forces as mush as the other segments of the nub - and when a structure does not utilizes some of its available elements, or a knot does not utilizes some of its segments, it is not an optimally designed mechanism : it uses more material than it needs, and it uses it in a non-optimal way.
   Therefore, it is reasonable for a knot tyer to think that this knot could perhaps be "abbreviated" ( Dan Lehman s term ) : it can become less convoluted, yet remain as secure as the fig.8 loop - and perhaps it may become even more secure ! We can not be sure about the role played by the much less loaded/utilized elements, as this outer "higher" collar - it may be positive, but it may also be detrimental, and contribute in a less favourable loading of the other elements, which carry the largest percentage of the burden induced by the tensile and compression forces inside the nub.
   And, just after that, a knot tyer will ask himself if an "abbreviation" of the fig.8 loop would improve it regarding its greater problem, the difficulty of untying it after heavy loading. Perhaps a smaller, less convoluted knot, which consumes less material, but which utilizes this material in a more even and efficient way throughout its nub, would be easier to untie.
   My understanding, judging from the conservative, to say the least, way climbers see knots, is that an "abbreviated" fig.8 loop would never persuade them that it is equally or even more effective. However, perhaps the opposite strategy may work : Leave the redundant elements there, in their almost decorative role, and add something more, which will improve the overall balance and achieve a more even distribution of the forces  inside the nub, so the knot will be distorted less, and will become more easy to untie. This was the meaning of my idea to "plant" / "nail" / retuck the Tail End through a properly chosen opening of the fig.8 loop, so the equilibrium of tension, compression and torsion inside the nub becomes more pronounced.
   To whom am I telling this ? To people that have never just think for just a minute about the number of different dressings a fig.8 loop may have ?  And they still believe in the TWO infamous "strong" and "weak" forms, TWO "more efficient" and "less efficient" dressings, etc... ? In short, in the ying and the yang ?  :) And they call me, the poor old sailor who dares to tell them that there are more stable and symmetric dressings of the fig.8 loop, a parrot ?  :)  :)

   It was always like this, even in the purest scientific fields, like physics. The new ideas were established, only after the previous generation of physicist had retired... Perhaps, in the future, some young climber, who will also happen to be a knot tyer, will tell himself : " Enough, with this sacred fig.8 loop ! Let us search for something else.."

   The parrrrotttt.   
Title: Re: Figure 8 Loop
Post by: xarax on May 18, 2015, 10:45:28 PM
   If any member thinks that the previous post is not fair to climbers attitude about knots, I would had wished and asked him to tell this me so, and PROVE it by refuting, word by word, sentence by sentence, what I have written there. However, judging from past  experience, I do not expect something like this to happen... Climbers, in particular, or people who believe they know better about the fig.8 loop, just because they "use" it more often than me, will just ignore it, and will never reply - as they did in all my previous posts and attempts, years now, to show the many different table and symmetric forms the fig.8 loop can have. The same had happened with my post about the alleged superiority, re. strength, of the fake, so called "Zeppelin loop" relatively to the secure  bowlines - no answer, ever... ( And I am not talking about a-symmetric dressings, which are numerous, and which, given the a-symmetric way a loop is loaded, perhaps they will be even more optimally dressed ).
Title: Re: Figure 8 Loop
Post by: SS369 on May 19, 2015, 12:04:15 AM
   If any member thinks that the previous post is not fair to climbers attitude about knots, I would had wished and asked him to tell this me so, and PROVE it by refuting, word by word, sentence by sentence, what I have written there. However, judging from past  experience, I do not expect something like this to happen... Climbers, in particular, or people who believe they know better about the fig.8 loop, just because they "use" it more often than me, will just ignore it, and will never reply - as they did in all my previous posts and attempts, years now, to show the many different table and symmetric forms the fig.8 loop can have. The same had happened with my post about the alleged superiority, re. strength, of the fake, so called "Zeppelin loop" relatively to the secure  bowlines - no answer, ever... ( And I am not talking about a-symmetric dressings, which are numerous, and which, given the a-symmetric way a loop is loaded, perhaps they will be even more optimally dressed ).

Climbers or sailors for that matter, do not have to refute anything, line by line or any way.. Some may care to as had happened with the men from Sailing anarchy with their testing, but refuting is not what all this is about. It is, imo, about sharing and learning and what we figure out.

I am a climber, I have sailed (not the ships of yesteryear) and use knots almost daily, besides tying my shoes. (They don't come undone during the day  ;) ). I also like to explore new things and I tie every offering here and elsewhere. I show the one's that have merit to me to others who climb and work, they decide whether it is for them or knot. When your life is dangling on a knotted rope, the climber/rescue tech or the sailor of yesteryear or today keeping his rigging working is the one who makes the decision.

I am sure that many who have read and will read the articles posted here will find some things interesting, even go so far as  to make their own test rigs and test them out. They don't have to do this or refute anything. And if they are hounded or condescended to, guess what, they leave. Or decide to lurk and not contribute anymore. I have seen this a few times.

No, I wouldn't support the statement that climbers are soooo poor knot tyers, they may not have the same zeal as others. Some tie very nice looking Fig. 8 loops or anchor knots or bowlines and bends. Best of breeds, who knows?
Some just want to climb. Not such a hard concept.

There are climbers and sailors who tie much , much more convoluted knots than what is offered here and they don't claim that another tyer is is a poor knotter because he is at a different level of understanding or interest.
We cannot force another to show interest they do not have.

I strongly suggest that we, the members of this forum, stick to knots with friendly, interesting discourse. Period.

SS
Title: Re: Figure 8 Loop
Post by: agent_smith on May 19, 2015, 12:38:47 AM
Quote
Climbers are sooo poor knot tyers ! They know only a very small number of knots

Now your parroting might have stepped over line.

Many climbers are very good at tying the knots they use on a routine basis. Jim Bridwell ('the Bird') was quoted as stating that he climbed all of his famous routes using less than 6 knots.

Many climbers would argue that knowing a small handful of knots very well is better than knowing hundreds of knots less well. In contrast, an IGKT member will want to intimately know hundreds of knots and hitches and the science behind them.

My main point here is that climbers are not knotting enthusiasts like the members of the IGKT forum. Climbers see knots as tools (like a screw driver). They dont really care how the screw-driver is designed  - they just want to know that it works.

You see, IGKT members are passionate about knots and knotting - thats why they are involved in this forum. You wont see many rock climbers in the IGKT forum - because they are more interested in being outside enjoying their sport - and challenging themselves in the vertical world.

You cant criticise them for (knowing and using only a select few knots) because they are simply wanting to participate in and enjoy their sport. They want to improve their climbing ability and push their personal limits. The harness they wear, the rope they use and the knots they tie are just means to an end. Most climbers are using either the Figure 8 eye knot or some secured Bowline derivative - all they care about is that it will not fail - it will save their life if they fall.

Xarax, in making such comments ("climbers are sooo poor knot tyers") you are judging others against your personal knotting values and morals. You have a different objective (and different type of passion) in mind than the average climber.

Not everyone will share your passion for knots and all things knotting - you cant force your set of values (about knots) on others.

...

Edited for enhanced clarity...
Title: Re: Figure 8 Loop
Post by: xarax on May 19, 2015, 01:26:18 AM
Climbers or sailors for that matter, do not have to refute anything, line by line or any way..

  Of course they "do not have to", if they are not interested in what I had said - but if they claim I had not been fair to them, they HAVE to explain why ! When one says that somebody is too damning in what he says, he has to prove it - otherwise he just ignores it.

...if they are hounded or condescended to, guess what, they leave.
   When you participate in an "open" Forum, where everybody tells his own thing, and for his own reasons, which do not always have a relation with the issues discussed, you run this danger, indeed. Personally, I were "hounded or condescended to" DOZENS of times, but my love for the knots themselves had kept me in - at least until I will be kicked out ... :)

   No, I wouldn't support the statement that climbers are soooo poor knot tyers 

   First, I was speaking generally, about the average climber, not the rare climber who happens to be a knot tyer, or vice versa. Second, I had elaborated a little on this statement : I said :
1. They know only a small number of knots. ( True or false ? )
2. They do not know ( and they do not want to learn ) how knots "work". ( True or false ? )
    I have followed many discussions on climbing sites, I have a few friends who are climbers, and I have never ever met one who tries to "see" a knot not only as a "tool" which has only to "do the job", but also as a structure, as a mechanism, in order to get some idea of how and why it "works" the way it "works". Some of them had tested some knots, that is true, but only very few knots, on a very limited number of samples, on a very limited variety of materials - and they had never tried to modify the knots they already know, and test those modifications, too, to explore some hidden potential. The only kind of knots where there have been some experimentation, is the climbing gripping hitches, but even thee there is no explanation of why some work better than the others... I had read only some hand-weaving arguments - not convincing at all, I should say.
   In particular, in their beloved, basic knot, the fig.8 loop, they still have not seen that there are many stable ways to dress it, not only two, as parroted again and again, and that some of them may be significantly better than the others, if not re. strength, at least re. easiness of untying. Also, I had never ever see any modification of the holy fig.8 loop. I said that :
   4. They do not know ( and they do not want to try to figure out) how to improve them. ( True or false ? )
   Why ? Will it punish us as heretics ? Is its form carved in stone, and can not be changed, ever ? WHO had proved that this is the One, and the Only, and "Best" super-duper loop in the Universe ? HOW had he did that ? Is the "argument" that, "because it does not kill the climber, it is OK" any sort of "proof" or "explanation" which one can discuss seriously ? So, any knot which does not kill the user, is OK, and we have to use this, and nothing else, the nest 4 billion years ?

   THOSE were the 4 lines / which one should first discuss, before he starts to claim that I was not fair with climbers... Of course, he can ignore my arguments, but then I can also ignore his whining about my unfair and/or too damning critique of the knotting abilities /interests of climbers.
   
Some just want to climb. Not such a hard concept.

...While when one just wants to know how things work, and how knots work, and how many different knots can exist that do the same thing with the minimum danger of slippage, with minimum amount of material, with minimum time required to tie and/or untie them, THEN it becames a HARD concept... :) :) :)

they don't claim that another tyer is is a poor knotter because he is at a different level of understanding or interest.

   Do me a favour, SS369. Suppose, just suppose that I believe I have some reasonable arguments, and that my opinion is not totally unfounded or biased, and I think that the answer in all those 4 questions above is "True". WHAT word should I use ? If "poor" is not the proper word ( it was the first word that came into my mind...), which is the word that describes thi s hypothetical, at least, situation fairly and squarely ? Please, tell me, and I will edit my previous text immediately.
   I do wish to provoke discussions, not bad feelings ! I do not consider myself a genuine/proper  :) knot tyer, because I do not test knots, so my argumenta are mostly of the hand-weaving, or line filling, kind... However, I just want to learn from other more experienced and knowledgeable people. Not such a hard concept.  :) :)
Title: Re: Figure 8 Loop
Post by: xarax on May 19, 2015, 01:59:59 AM
  Now your parroting might have stepped over line..

  Tell it to people who do not like the picture of my avatar !  :)

Many climbers are very good at tying the knots they use on a routine basis. Jim Bridwell ('the Bird') was quoted as stating that he climbed all of his famous routes using less than 6 knots...

   Is this an argument against my statement, that they know only a few knots ?  :)
   I can do ALL of my famous walking, using shoelaces tied with only ONE knot !  :) Am I a good knot tyer ?  :)
   It is amusing how people defend what they are doing - If somebody needs or uses 6 knots, and he is "very good at tying them", he is a GREAT knot tyer !  :) I use only ONE knot, and I tie it magnifically, so I suppose this makes me a Knot-semi-God or something...  :)

My main point here is that climbers are not knotting enthusiasts like the members of the IGKT forum. Climbers see knots as tools (like a screw driver). They dont really care how the screw-driver is designed  - they just want to know that it works....
   It is boring to me to quote, line by line, word by word, sentence by sentence, how many times I had said the same things, and I have repeated them in the text to which you supposedly reply. So, please, you do not have to parrot me, while, at the same time, you are trying to argue with what I say ! Because, if you do this, THEN, "your parroting might have stepped over line.." (sic)

You cant criticise them for wanting to participate in and enjoy their sport.

WHO did that, WHEN ? Are you imagining you are talking to Savonarola ?  :) :)
http://en.wikipedia.org/wiki/Girolamo_Savonarola

Xarax, you are judging others against your personal knotting values and morals. You have a different objective in mind.

  I am judging others in comparison to something they do NOT do, either because they do not love it, as I do, or they are not interested in it, or because they simply do not need to do it ! They do NOT tie enough knots, they do not know how they work, they do not want to improve them. HOW on Earth ( UpOver or DownUnder this Earth ) have you IMAGINED that !@#$%^&*()_+ "against my personal values and morals" (sic) ?  Are knots "values" which are endowed with "morals ?  :) :) I do not play tennis, if somebody tells me that I am a poor tennist , he is  " judging me against his personal knotting values and morals " ?  :) :) :) Is tennis a "value" or a "moral" ?  :) :) I do not speak English, but I start to believe that we should start to talk to each other in LATIN, or something, because what you say is all Greek to me !

   Now your parroting might have stepped over line..

   I quote your fair statement about me again, so you will enjoy it a little longer !

   @ SS369 : Now you know how "we, the members of this forum, stick to knots with friendly, interesting discourse."
   Period.
Title: Re: Figure 8 Loop
Post by: xarax on May 19, 2015, 02:22:30 AM
    As I might had expected, I am already under the crossfire of two climbers, who, perhaps in their subconscious effort to prove that I am not mistaken in what I had said  :), they had not written A WORD, not even ONE single word, about the crux of the matter, explained in the 5 ( = five) paragraphs after the first, of my reply at :
    http://igkt.net/sm/index.php?topic=5313.msg35501#msg35501
    I have to suppose they had read only this first paragraph, or only the first sentence of this paragraph - because all those 5  next paragraphs were about the fig.8 loop, and only about the fig .8 loop, about which I am parroting, of course, and I do not know, but which they "use", so they know.
Title: Re: Figure 8 Loop
Post by: SS369 on May 19, 2015, 03:32:36 AM
    As I might had expected, I am already under the crossfire of two climbers, who, perhaps in their subconscious effort to prove that I am not mistaken in what I had said  :), they had not written A WORD, not even ONE single word, about the crux of the matter, explained in the 5 ( = five) paragraphs after the first, of my reply at :
    http://igkt.net/sm/index.php?topic=5313.msg35501#msg35501
    I have to suppose they had read only this first paragraph, or only the first sentence of this paragraph - because all those 5  next paragraphs were about the fig.8 loop, and only about the fig .8 loop, about which I am parroting, of course, and I do not know, but which they "use", so they know.

Perhaps if you had not expected what you perceived, it would not happen.

You are not in any crossfire. Something you wrote was disagreed with (Your opening remark) and the all consuming statements are not fair to the members who may not have your zeal. One cannot make another thirst for learning, especially by calling them out.
Ridicule is the worst education tool that I know.

Quote
    Do me a favour, SS369. Suppose, just suppose that I believe I have some reasonable arguments, and that my opinion is not totally unfounded or biased, and I think that the answer in all those 4 questions above is "True".

So what. They come here for some reason and should not be made to feel little. They may be budding tyers and want to learn from such masters.

As for your other Fig 8 layups, prove that they are better. Test them.

This is off topic nonsense and I care no more for it. So, if you'll take it private with whomever you want to, go for it.

SS
Title: Re: Figure 8 Loop
Post by: xarax on May 19, 2015, 04:33:44 AM
the all consuming statements are not fair to the members who

  I wrote my opinion about the majority of climbers, NOT about the members of this Forum ! If I will be censored for my opinion, fine ! I have been censored before, and I know... I said that climbers, IN GENERAL, are poor knot tyers, and I mean it, and nobody told me which more correct/proper word I should had used ! I know enough climbers, and I read enough posts in enough climbing Forums to have an opinion on this matter, I believe. Other members will have other opinions, but I do not claim that their opinions are not fair to me ! !
 
This is off topic nonsense

The ONLY on topic things were written by me, at Reply#43, of which the climber lobby picked up only the FIRST sentence ! And, of course, NOT A WORD, not even ONE, about anything else of the 5 next paragraphs of this post...
Title: Re: Figure 8 Loop
Post by: Dan_Lehman on May 20, 2015, 08:59:56 AM
   When a knot tyer watches this video with the fig.8 loop, the very first thing he notices, is the most obvious thing : the initial shape of the fig.8 loop is distorted very unevenly, to a degree it becomes unrecognizable. Then, the next thing he notices is that this outer "higher" collar seems to be almost unloaded, that it, almost redundant ! Evidently, it does not participate in the dissipation of the tensile forces as mush as the other segments of the nub - and when a structure does not utilizes some of its available elements, or a knot does not utilizes some of its segments, it is not an optimally designed mechanism : it uses more material than it needs, and it uses it in a non-optimal way.
X., I presume that you attached the image of the
near/at-rupture state of the knot?  Can you add the
one at the start --the "set"/start state?

Wow, what compression.  And I see (in the final) that
the S.Part's nip-grip of the eye legs likely has let less
of their forces return the favor (gripping, i.e.) to the
S.Part itself --an imbalance that grows, with tension.
One might wonder if the test specimen had been of
a frictive rope (and maybe of a less elastic one, too!)
would the same imbalance occur, or would perhaps
the eye legs get in some good grip on the S.Part so
that a different geometry obtained at later states?!

Thanks,
--dl*
====
Title: Re: Figure 8 Loop
Post by: xarax on May 20, 2015, 12:54:26 PM
I presume that you attached the image of the near/at-rupture state of the knot?  Can you add the one at the start --the "set"/start state ?

I had just "frozen" the video, used Shift + PrintScreen keys to capture the image, and then I had "paste-ed" it in Paint, and saved it as .jpeg.
Title: Re: Figure 8 Loop
Post by: Dan_Lehman on May 20, 2015, 05:56:52 PM
I presume that you attached the image of the near/at-rupture state of the knot?  Can you add the one at the start --the "set"/start state ?

I had just "frozen" the video, ...
Of these nexTwo pics,
the top one shows a "weak form" fig.8, clearly indicated
by the tensioned S.Part pulled (down) away from the now
idle upper twin part.
Whereas the bottom image I think shows the "strong
form", eye below and S,Part & tail (and it almost looks
to be a tightly bound trio of parts!?) above,
with the S.Part deeply pushed against and then even
past the thus-bulging-outwards (unloaded) twin part.

But neither of these shows a pre-loaded, hand-set
(I presume) knot state.  I'm curious re that vis-a-vis
how much anticipation of the latter bearing-against
force can be done in setting hard the tail, so to leave
not enough material to give way to the S.Part's
pressure (or not w/o a good *fight* that consumes
some force!).  !?

Thanks again,
--dl*
====