Author Topic: Figure-8 vs Figure-8-1/2  (Read 6594 times)

galilnoks

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Figure-8 vs Figure-8-1/2
« on: May 31, 2011, 12:51:37 AM »
The Figure-8 bend and end-loop are considered very secure and strong, but they are prone to jamming.  And the Figure-9 can jam even worse.  Discussions of this style of knot usually end here, with climbers declaring that they'd be happy with a jammed knot which saves a life.

I wonder whether something is being overlooked.  Although the Fig-9 jamming may be merely more of the Fig-8, the case may be different with the FIGURE-8-1/2 (which adds an extra half-turn before being passed through the loop -- see drawing).  

In fact, my experience with the Fig-8-1/2 has been very positive.  I think the Fig-8-1/2 has a distinct structure which improves the Fig-8.  For example, the Fig-8-1/2 is easier to tie without crossing lines; the entry curve has more support and seems stronger; and most importantly, it is much less jammable.  (The Fig-9-1/2 is similarly less jammable than the Fig-9).  

The changes made by the extra half-turn seem to be only beneficial, but the Fig-8-1/2 has been ignored (perhaps under the wrong assumption that it must be like the Fig-9).

Does anyone have experience or views regarding the Figure-8-1/2?
« Last Edit: May 31, 2011, 12:54:30 AM by galilnoks »

bowline

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Re: Figure-8 vs Figure-8-1/2
« Reply #1 on: May 31, 2011, 02:43:20 AM »
Gudday
I have a vague memory---- goes with the age thing--- that I have seen this called a Fig Nine knot. Not sure which book it was in , but assume it was American. Possibly superior security in slippery / stiff plastic type ropes.
Cheers
bowline

knot4u

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Re: Figure-8 vs Figure-8-1/2
« Reply #2 on: May 31, 2011, 04:31:06 AM »
Galilnoks, look closely at the Snare Noose (ABOK #1118).  It's based on a Figure 8.5, which you described.



Guess what?  I have not gotten it to jam.  Also, Ashley says it's easy to untie.
« Last Edit: May 31, 2011, 04:32:21 AM by knot4u »

Bob Thrun

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Re: Figure-8 vs Figure-8-1/2
« Reply #3 on: May 31, 2011, 05:34:24 AM »
This has been called a Figure-9 Knot.  I just grabbed the handiest book with a picture, Alpine Caving Techniques (2002).  The Lyon report has tests on both the Fifure-9 and Figure-10 loops.  I could easily find a reference from 30 or 40 years ago.

Dan_Lehman

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Re: Figure-8 vs Figure-8-1/2
« Reply #4 on: May 31, 2011, 05:50:43 AM »
Quote
Although the Fig-9 jamming may be merely more of the Fig-8, the case may be different with the FIGURE-8-1/2 (which adds an extra half-turn before being passed through the loop)

I must wonder what you call "Fig.9" given that you see your
"Fig.8 & 1/2" as different?!  (In fact, as Bob just notes, they
are the same --or should be : what is it YOU call "Fig.9"?)
Ditto for the "Fig.9 & 1/2" (for which we might expect to
find a "Fig.10" ).

The usual claim is that the fig.9 eyeknot is less prone
to jam than the fig.8.

Beyond the so-far published "fig.9" knot(s), there are two symmetric
forms of this topological entity, and one is well suited for an
eyeknot, and in normal cordage shouldn't jam.

--dl*
====

ps:  Good (or gud) to see that DownUnder is up!   ;)

galilnoks

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Re: Figure-8 vs Figure-8-1/2
« Reply #5 on: June 01, 2011, 06:38:15 PM »
Yes, there is some confusion in names.  I have seen "Figure-9" used to label both the addition of 1/2-turn and also of 1-turn to the Fig-8.  Since I believe the plus-1/2 turn, but not the plus-1, improves the Fig-8, published information may be relevant to my query only if the knot is not merely named but is described (and the descripton matches the knot actually used in the testing).  And yes, there are two versions of the plus-1 turn knot -- what I call the Fig-9, and the 'stevedore' version (see drawing), but my main interest is the distinct plus-1/2 turn, not either plus-1. (A stevedore-style plus-1/2 quickly converts into a plain plus-1/2).

(On the question of names, I take it that those who call the plus-1/2 turn to the Fig-8, the 'Fig-9', also think we should call the addition of 1 turn, the 'figure-10', and the addition of 1-1/2 turns, the 'figure-11'.  I don't really care, but it seems to me (and to others) clearer to derive the names from the addition to '8' of the amount of extra turns.  The Fig-8's name is based on its shape; the Fig-9/10/11 series of names is not, and using whole numbers to count added 1/2-turns seems only to confuse what is happening. (See attached drawings--sorry I don't have loops for each.))

In any case, I've found the addition of 1/2 turn to the Fig-8 (what I am calling the Fig-8-1/2) to be less jammable than the Fig-8.  I think Fig-8-1/2 loop is as easy to tie (though retracing the bend quickly takes a little practice), and it seems more secure and stronger with the extra support.  I'm interested in views on these matters.

But my main interest is this:  the Fig-8-1/2 is a live improvement over the Fig-8 only if the reduction in jammability which I've noticed (via my body weight jumping in loops) also obtains when it is subjected to heavy loads (like those involved in catching a climber's fall).  If it is indeed less jammable under heavy loads, then climbers, among others, would have an improved alternative in this style of knot to the jammable Fig-8.  If the difference I've noticed does not persist under heavy loads, then there is no strongly persuasive improvement, at least so far forth...

KNOT4U:  ABOK #1118 is an interesting noose I'd overlooked--thanks (I like nooses).  Yes, there are structural similarities (and doubtless more that I cannot see), but #1118 is a sliding loop; the Fig-8 and Fig-8-1/2 are fixed loops (suitable for easily clipping in and out of biners).  Would a #1118 bend be a kind of grapevine?  The Fig-8 and Fig-8-1/2 bends have their characteristic and attractive (to me) retraced form.

Dan_Lehman

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Re: Figure-8 vs Figure-8-1/2
« Reply #6 on: June 01, 2011, 08:16:41 PM »
Yes, there is some confusion in names.

So, let's try to arrest that, here.   :)

Quote
I have seen "Figure-9" used to label both the addition of 1/2-turn and also of 1-turn to the Fig-8.

Really, where ?!
What I have seen is the sharing of the name "Stevedore" between
the asymmetric fig.9 and a. fig.10 --where "asymmetric" covers
the forms you have shown (except of course for the fig.8 ).

Quote
(On the question of names, I take it that those who call the plus-1/2 turn to the Fig-8, the 'Fig-9', also think we should call the addition of 1 turn, the 'figure-10', and the addition of 1-1/2 turns, the 'figure-11'.  I don't really care, but it seems to me (and to others) clearer to derive the names from the addition to '8' of the amount of extra turns.  The Fig-8's name is based on its shape; the Fig-9/10/11 series of names is not, and using whole numbers to count added 1/2-turns seems only to confuse what is happening. (See attached drawings--sorry I don't have loops for each.))

The nomenclature to adhere to takes the overhand as a base knot
(somewhat degenerate, in forms, but ...) and then grows by adding
a "half turn" for each subsequent member of the series; so, ...:
fig.8, fig.9, fig.10, fig.11, ... --from which it follows that all
odd, resp. even, members have the tail exiting the loop in the same
direction.  Somewhere else on this forum is a discussion of the issue
of What is a turn?] --and argument that 180deg is it,
which fits the popular naming of these knots (not yours).  It's surely
simpler to deal with whole numbers than halves.  In any case,
your issue really points more to *dressing* of the (half-)turns than
to their number.  Only in your "Stevedore" (yellow cord, not drawing)
do you show a common turning away from the loop and long reach
back to tuck through it; all others take part of their turning in the
reach back (but for the 8, which lacks dimension for this distinction).

The simplest graphical/form-wise presentation of this series
centers a piece of line (or representation of) and brings either
end up around in an arc (like an outline of an apple, say)
to cross at the top-center and cross-opposite in passing back
out of this apple-perimeter closed arcs.  (So, a *pretzel* for
the overhand form.)  For either end, the crossing alternate
over-under-over ... as needed for the given knot.

In a less simple presentation, the crossings occur on the
apple-perimeter sides (with some central crossing at top).

Quote
Since I believe the plus-1/2 turn, but not the plus-1, improves the Fig-8, published information may be relevant to my query only if the knot is not merely named but is described (and the descripton matches the knot actually used in the testing).

Ah, yes, and this is a nearly constant fault of test reports
--one can have little confidence in the actual knot geometry
at issue (esp. as one becomes aware of how divorced provided
images can be from reality).

Quote
And yes, there are two versions of the plus-1 turn knot ...

You miss my point:  there are two versions of the fig.8 and
three of all *higher* such knots (see above).  To these,
you add the aspect of particular dressing : you *cascade* the
(half)turn(s) after the initial closing of the loop, wrapping back
towards the eye rather than away from it, having the
finishing tuck near at hand rather than a far reach (which far
reach you show, again, for the Stevedore stopper).

Quote
In any case, I've found the addition of 1/2 turn to the Fig-8 (what I am calling the Fig-8-1/2) to be less jammable than the Fig-8.  I think Fig-8-1/2 loop is as easy to tie (though retracing the bend quickly takes a little practice), and it seems more secure and stronger with the extra support.  I'm interested in views on these matters.

Your testing by bouncing body weight ( = ?) on presumably some
finer cord than rockclimbing rope (accessory cord) --what size?--
seems pretty good for getting an idea of this.  We should remark
that your image is ambiguous about the actual 3-dimensional
geometry of the knot (as are so many images of the fig.8s )
You do apparently distinguish between the ends (many don't!),
but still one is left to guess the way they curve & turn together
in surrounding the eye legs, and so on.

As for strength, given that there have been some quite strong
results for the fig.8 eyeknot of some (and likely various) forms,
going for "stronger" seems a dubious quest.  It shouldn't be
a *selling point*.  Now, resistance to jamming, yeah.


--dl*
====
« Last Edit: June 02, 2011, 06:54:51 PM by Dan_Lehman »

xarax

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Re: Figure-8 vs Figure-8-1/2
« Reply #7 on: June 01, 2011, 08:52:33 PM »
   Galinocks, how would you name, based upon your scheme, the symmetric 8 1/5 + 1/5 (both ends) stopper in the attached picture ?
This is not a knot.

Dan_Lehman

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Re: Figure-8 vs Figure-8-1/2
« Reply #8 on: June 02, 2011, 06:53:45 PM »
   Galinocks, how would you name, based upon your scheme, the symmetric 8 1/5 + 1/5 (both ends) stopper in the attached picture ?

Since this knot doesn't fit the series (of a turn and then immediate,
or after 1..N  SPart wraps, close of a loop w/tucked-out tail),
it has no such series-name.  Why do you not see this?

--dl*
====

xarax

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Re: Figure-8 vs Figure-8-1/2
« Reply #9 on: June 02, 2011, 08:35:03 PM »
Why do you not see this?

   Oh, possibly because I see a little further... :) When one does something, anything, with the one tail of a parent symmetric knot, it is only natural to do the same thing with the other, is nt it ?
This is not a knot.

Dan_Lehman

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Re: Figure-8 vs Figure-8-1/2
« Reply #10 on: June 02, 2011, 09:12:13 PM »
Why do you not see this?

   Oh, possibly because I see a little further... :) When one does something, anything, with the one tail of a parent symmetric knot, it is only natural to do the same thing with the other, is nt it ?

I see : you *centered* your perspective and let *play* work
from that ; you didn't see further, but about *half* the
distance in opposite directions.   :D

Ah, but you're on the wrong *scheme*, then : we're not here
with a structure with two *tails*, but one, which "works" the
knotting --the start's with the SPart!

 ;)

xarax

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Re: Figure-8 vs Figure-8-1/2
« Reply #11 on: June 02, 2011, 09:33:48 PM »
you didn't see further, but about *half* the distance in opposite directions.
 
   Due to my age, I am pardoned for not being short-sighted, I suppose, but not for being cross-eyed ! ( The exact opposite applies for you...)  :) I mean that the 8 1/5 + 1/5 knot is to 8 1/5 knot something more than the 8 1/5 knot to the 9 knot. It is natural, in a series where we had started moving from the 8 to the 8 1/5, to go from the 8 1/5 to the 8 1/5 + 1/5 first, before we jumb to the 9. Or, if you like, to move to the second dimension, too, as in the IQ test squares that measure other things, besides sight. My original question was not such a dull one, I believe.
« Last Edit: June 02, 2011, 09:37:51 PM by xarax »
This is not a knot.

knot4u

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Re: Figure-8 vs Figure-8-1/2
« Reply #12 on: June 03, 2011, 08:45:47 PM »
The Figure-8 bend and end-loop are considered very secure and strong, but they are prone to jamming.  And the Figure-9 can jam even worse.  Discussions of this style of knot usually end here, with climbers declaring that they'd be happy with a jammed knot which saves a life.

By the Figure 9, I'll assume you mean the Stevedore.  I have not found the Stevedore (what you call Figure 9) to be jam-prone.  Are you sure about your assertion?


knot4u

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Re: Figure-8 vs Figure-8-1/2
« Reply #13 on: June 03, 2011, 08:48:57 PM »
This has been called a Figure-9 Knot.  I just grabbed the handiest book with a picture, Alpine Caving Techniques (2002).  The Lyon report has tests on both the Fifure-9 and Figure-10 loops.  I could easily find a reference from 30 or 40 years ago.


The Figure 9 Loop on Wikipedia has a half turn more than the loop in your pic.  You may want to edit Wikipedia if you're motivated and confident.

http://en.wikipedia.org/wiki/Figure-of-nine_loop
« Last Edit: June 04, 2011, 06:10:44 PM by knot4u »

galilnoks

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Re: Figure-8 vs Figure-8-1/2
« Reply #14 on: June 03, 2011, 11:19:58 PM »
BOB THRUN: thanks for the picture of the 'Fig.9'; in addition to documenting the name, it shows how simple and smooth the "plus-1/2-turn" is (my bumbling drawings make it look very awkward...)
 
===QUOTE xarax: How would you name, based upon your scheme, the symmetric 8 1/5 + 1/5 (both ends) stopper in the attached picture ?
 
Ha! I've no idea -- maybe I'd weakly hazard that it's not really a Figure-8-knot-plus-turns, so there is no need to pay homage to the Fig-8 knot as a paradigm (on my thinking, why else use "Figure-" in the names for the 9-10-11?).  So call it what you will.  But there is(are) 8(s) cleverly twisted in there, it deserves some homage -- very good. (Makes a decorative loop, too.) It also poses a problem for the 9-10-11 scheme, right?
 
 
===QUOTE Dan_Lehman: ...Really, where ?!

For example, the Fig-8-plus-one-turn is called a "Figure of nine loop" at Wikipedia (http://en.wikipedia.org/wiki/Figure-of-nine_loop --see attachment).  A stevedore-style loop is pictured, but the description is not clearly so qualified:
   "It is tied as a figure-of-eight loop but with an extra turn
   before finishing the knot - hence its name." 
[It is possible that I've taken such descriptions to include both stevedore and non-stevedore versions of a Fig-8-plus-one-turn knot, ignoring the next sentence: "It may also be described as a stevedore's knot tied in the bight."]

The ambiguous use of "Fig-9" (as Fig-8 plus 1/2-turn vs. 1-turn) is not uncommon in (infrequent) online climbing and caving discussions of improvements to Fig-8.  I remember seeing the name "Figure 8-1/2" with a drawing only once; "Figure 10" only a few of times.  Usually, "Figure 9" seems to be used ambiguously or sloppily. In "Caving Knots" (CSCA Technical Publication No 3. 2001--available on the web) a Figure-9 (Fig-8-plus 1/2 turn) is drawn, but the description reads: "A Figure of nine is similar to the Figure of eight but with an additional turn."
 
 
==QUOTE Dan_Lehman: It's surely simpler to deal with whole numbers than halves.

No, halves are quite simple here, surely within the grasp of any who can follow your explanation.  But maybe names with '1/2' in them are the problem: they sound weak or wishy-washy.  From a marketing point of view, I'd never have named my hoped-for solution to a jamming problem of a knot favored by rock climbers a pitiful 'Figure-eight-and-a-half'.  Even something like 'Stevedore1,2,3' sounds more attractive, or, for that, Figure9-10-11. (Would that the last was not functionally confusing.)
 
 
===QUOTE Dan_Lehman: The nomenclature to adhere to takes the overhand as a base knot
(somewhat degenerate, in forms, but ...) and then grows by adding a "half turn" for each subsequent member of the series; so, ...: fig.8, fig.9, fig.10, fig.11,...

Is the nomenclature "to adhere to" one that was in fact deployed in the naming history of these knots, or is the 'Fig.9-10-11' nomenclature a new convention?  Is this naming convention entrenched today in the knotting community or in this forum?

Aren't there many other knots which grow by adding half-turns (forming a 'series') that do not follow this nomenclature?  Any special reason why it should be followed here? 

Doesn't your explanation apply even if we decided to lump the half-turns for more functional names?  Would a name which more closely matches the way the knot is tied confuse people who understand your kind of description?

I can't help adding that your explanation of counting additional half-turns seems esoteric, no doubt of interest to knot-connoisseurs, but nonetheless ending up with names which are misleading to others. The "Fig-8-1/2, 9, 9-1/2" series of names is self-explanatory in a way the "Fig-9, 10, 11" series is not.  Functional descriptive phrases (used, say, in teaching how to tie it) like "Figure-8 plus 1/2 turn" transparently become names like "Figure-8-1/2".  But when a name like "Figure-10" is functionally described as "Figure-8 plus 1 turn", it invites responses such as "It doesn't look like a 10--," or "8 plus 1 doesn't equal 10 -- so why is it called a Fig-10? Because you are counting the number of extra half-turns and adding that to 8? And why do you do that?" "Well, you see..." That is, I suggest that the Fig-8 is named because of its distinctive shape, and is the paradigm; the others are in a sense merely modifications of the Fig-8 starting point; we want to flag the family resemblance by continuing to use "Figure-" as part of the name even though we are no longer referring directly to the shape of each modification; and hence they should be named in a way that makes the modifications to the paradigm functionally obvious (and doesn't require a knot-education to understand), and that is the turning amount needed to tie it (as already occurs in the wild: witness the wikipedia entry quoted above "...with an extra turn before finishing the knot - hence its name"). After all, these are practical knots, not merely mathematical shapes. At least IMHO at the moment.

However, I have admitted that it is largely a matter of indifference to me which names are used.  If the '9, 10, 11' names are entrenched at this forum, I'll switch accordingly (if y'all don't want to switch conversely!) -- at least until practices in the wild really mess things up. 
 
 
Well, since we're off discussing nomenclature, I gather no one yet has views about the jamming question.  (Yes, I use soft, flexible 5mm kernmantle for my jumping-in-loops jamming tests).  Any intuitions then?  Or other ideas about how best to respond to the Fig-8 jammability and still remain with that style of knot?  Or views on marketing prospects of Fig-9, given that it (now, and perhaps insurmountably) has a bad name from being confused with the very jammable Fig-10?