Author Topic: F-8 inline  (Read 4603 times)

zoranz

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F-8 inline
« on: February 15, 2013, 04:20:54 PM »
Hi all!
Question:  If you want to tie F-8 inline, which way is better?

Thx in adv,
zoranz

knot4u

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Re: F-8 inline
« Reply #1 on: February 15, 2013, 04:52:26 PM »
Hi and welcome!

Better for what? What is the application?

Both ways will generally be secure. However, if I am applying a load on the loop and don't want a jam, then I would not tie a Fig 8. I would tie a Span, Butterfly, or maybe a Fig 9. Without your app, I'm guessing what you want.

Dan_Lehman

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Re: F-8 inline
« Reply #2 on: February 15, 2013, 09:41:19 PM »
Hi all!
Question:  If you want to tie F-8 inline, which way is better?

Thx in adv,
zoranz

Hello, Zoranz!

The pair of images that you present are not so
obviously at odds with each other --mainly, in
that the upper one (colored) is ambiguous.
(One can suggest that at least there is a difference
in which eye leg lies left/right, but there is ambiguity
about how the collars --the turns of the eye legs--
are oriented.)

The orientation of the collars might affect the
security (also strength --but we should argue
that this is a practically meaningless attribute!)
of the knot when loaded end-2-end (and is, thus,
essentially a square/reef knot), or also otherwise?

Beyond this knot (in various orientations), there are
some other "directional"/"inline" fig.8s worth looking
at, though most of these are a little less efficient
in material consumption --this is a pretty simple knot!
(I'll post some images.)


Cheers,
--dl*
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X1

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Re: F-8 inline
« Reply #3 on: February 15, 2013, 09:50:08 PM »
  F -8 was the name of a fighter airplane of the fifties... :)
  http://en.wikipedia.org/wiki/F-8_Crusader
  However, the question about the "better" form of this fig.8 midline / TIB loop is very interesting. 
  This loop can be dressed in 4 forms, not only 2. ( See the attached pictures.)  In a tight enough knot, the three encircled and nipped segments ( the two legs of the bight and the "lower" standing part ) will be forced to settle in a "dense" configuration, in a position where they will touch each other. ( So, they will not remain "in a row", as shown at the fourth picture above ).
   I think that the second leg of the bight ( the leg which is not a direct continuation of the "higher" standing part and the fig.8 knot ) is not constricted hard enough-  and this happens in all the 4 forms of this loop. If the "lower" standing part is not loaded, or if it is not loaded sufficiently enough, this leg may slip. Therefore, in the case of the unloaded "lower" standing part, I guess that the "best" of those 4 forms would be the one where the second leg of the bight would slip less - but I can not predict which this would be.

P.S. 2013-18-2
As noticed by DL, there is yet another possible form, resembling the A2. So,(  for the time being :)), we have 5 possible different dressing of this loop, where the collars are not crossed very much with each other, and the lines follow fluid, "natural" paths into the knot s nub.  See :  http://igkt.net/sm/index.php?topic=4269.msg26580#msg26580
« Last Edit: February 18, 2013, 03:12:37 PM by X1 »

Dan_Lehman

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Re: F-8 inline
« Reply #4 on: February 17, 2013, 07:21:03 AM »
Here are some promised images of alternatives
to the commonly shown (only known) "directional
/inline fig.8 eye knot"
.  Down this path --i.p., using
the slip-knot / overhand noose as a starting base--
are many such knots, the main advantage to some
of them is ease of untying; some are not all so
*directional*, too, which could be a safeguard
(i.e., they will behave okay loaded by the eye
in any direction).


--dl*
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X1

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Re: F-8 inline
« Reply #5 on: February 17, 2013, 05:20:51 PM »
  In any fixed midline loop, the continuations of both ends will make one, at least, U turn, before they will reach the bight of the loop - either this U turn would be located deep into the core of the knot s nub, surrounded by the other segments of the knot, or not. I do not see any well-defined property that the "directional" loops have, and the "non-directional" loops do not. The "natural" orientation of the legs of the bight, when the ends of the loop are loaded but the loop itself is not, is only a transient characteristic. When the loop, too, will be loaded, it will be forced to align itself with the direction of the pull - and if this direction is parallel to the line, it will become "directional". So, I do not see why the simplest overhand-based loop (shown at the attached picture ) is not "directional" - and why one has to entangle the ends into much more complex and difficult to remember how-to -ie loops, like the loops presented at the previous post.
« Last Edit: February 17, 2013, 05:22:24 PM by X1 »

Dan_Lehman

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Re: F-8 inline
« Reply #6 on: February 17, 2013, 05:54:23 PM »
  This loop can be dressed in 4 forms, not only 2. ( See the attached pictures.)
The dressing shown are not uniform, and there are more
than four, by this measure.  I.p., the eye bight of the top
image should be rotated 180deg (top leg away, lower leg
coming towards viewer) and resemble the 2nd image
--the difference being which of the collars the right-side
end flows into.  (In fact, one can see in "in-the-wild" images
of fig.8 eye knots (not "inline") dressings that fall out of
symmetry like the top one; this might be induced in part
by torsion in working with the eye bight.

Quote
  In a tight enough knot, the three encircled and nipped segments
 ( the two legs of the bight and the "lower" standing part )
 will be forced to settle in a "dense" configuration, in a position where
 they will touch each other. ( So, they will not remain "in a row",
 as shown at the fourth picture above ).
And the turn of the eye bight's (mere) two, twin parts
won't lie in a plane containing the axis of tension
--but the fig.8 knots are often illustrated in this way.

More to the point, practically, is that one should be able
to position the *tail* (where the eye alone is loaded in
opposition to the intended end) AND THEN set it into
place by tightening the knot (where, were it loose, that
tail could conceivably be pulled out of that position).


NB : It is most interesting to read test data presented
in the CMC Rope Rescue Manual (3rd ed.) (<c>1998, p.56)
shows this "inline fig.8" to be weaker than a (normal)
fig.8
when through-loaded
!?  Granted, through-loading
gets one a sort of bulked-up square/reef knot, but the offset
loading of a fig.8 isn't typically regarded as strong
--and it known to be dangerous for security (but by this
data, clearly it was amply secure, and strong!).  The
respective figures are : 59% & 65% ; the butterfly
(in a dressing which we don't know --nb!) was 69%.


Quote
   I think that the second leg of the bight ( the leg which is not a direct
continuation of the "higher" standing part and the fig.8 knot ) is not
constricted hard enough-  and this happens in all the 4 forms of this loop.
If the "lower" standing part is not loaded, or if it is not loaded sufficiently
enough, this leg may slip.
Rather, with the same observations, I would suspect
the eye leg would possibly pull out --consider that
loading it delivers 50% to this part, loading the ends
puts 100% on the connected end, though that is
mitigated by going around the collar; but this loaded
end also might help mitigate the other end's turn
& nip, too.


--dl*
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Dan_Lehman

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Re: F-8 inline
« Reply #7 on: February 17, 2013, 06:05:30 PM »
  In any fixed midline loop, the continuations of both ends will make one, at least, U turn,
before they will reach the bight of the loop -  ...
Ahhh, so now you have me refuting this "any" with musings
of directional eye knots that are built from making some kind
of frictional knotting around a non-U-turning SPart !  But I'll
leave this as an exercise for the imagination, unlikely of any
practical value.
 ;)

Quote
I do not see any well-defined property that the "directional" loops have,
and the "non-directional" loops do not.
/ /
So, I do not see why the simplest overhand-based loop (shown at the attached picture ) is not "directional"
Look at loading them opposite to their obviously intended
direction of loading --THAT will show the property.
The overhand eye knot --probably the most common one--
can be loaded in "any" direction ; not so, "directional" knots.
Though it might be a worthwhile attribute that such knots
can endure such unintended loading.  (E.g., there is some
mid-line eye knot corresponding to Ashley's #1408 which
is non-jamming on one directional loading, not so much the
opposite, but as good as the butterfly in that.  Still I don't
regard this as a directional knot, though I would try to orient
it favorably by such consideration.)


--dl*
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X1

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Re: F-8 inline
« Reply #8 on: February 17, 2013, 06:51:04 PM »
  The dressing shown are not uniform, and there are more than four, by this measure.
 I.p., the eye bight of the top image should be rotated 180deg and resemble the 2nd image-the difference being which of the collars the right-sideend flows into.

   They are uniform, and they are unique, in the sense that the lines do not cross each other, they follow smooth, "natural" paths.
   One can start from those 4 basic forms, and twist the two legs of the bight clock-wise or counter-clockwise, in order to generate more dressings. However, in all those dressings, the lines at the collars will twist around each other, and the knot will be much more ugly, without being much more secure or strong. If we wish fluid, "natural" lines, these are the only "fluid", stable forms.
   There are three lines that go through the nipping loop : the two legs of the bight and the continuation of the "lower" standing end. In a tight knot, they will settle in a position where they will be adjacent to each other. I have tried all the combinations of lines and positions, and I have seen that those 4 dressings are unique in that they are the only ones where the two collars do not cross each other.
« Last Edit: February 17, 2013, 06:55:42 PM by X1 »

X1

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Re: F-8 inline
« Reply #9 on: February 17, 2013, 07:53:22 PM »
Look at loading them opposite to their obviously intended direction of loading --THAT will show the property.
 
   I had asked for a "definition", not a "view "!  :)
  I can see that some eye-knots have a "natural" ( "obviously intended" ) inclination towards one end. ( However, this inclination is apparent only when/if the eye itself is not loaded ). If the first U turn is buried deep inside the knot s nub, the loop can not but "look" "directional" - but I do not see the effect that this might have on the strength of the knot ! The first U turn exists, either "inside" or "outside" the knot s nub, and that is the weakest point. It might "look" more safe if this U turn is not visible... but the tensile forces will penetrate the mantle of the knot, they will find it and they will load it in just the same way they would have loaded a visible U turn, at the end of the knot.
   One other posible solution is to tie a "bi-directional" double loop and use any single eye we wish, or both of them. This particular double loop is easier to tie than most "directional" single loops. ( See the attached pictures ).
« Last Edit: February 17, 2013, 07:56:44 PM by X1 »

Dan_Lehman

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Re: F-8 inline
« Reply #10 on: February 18, 2013, 05:52:34 AM »
  The dressing shown are not uniform, and there are more than four, by this measure.
 I.p., the eye bight of the top image should be rotated 180deg and resemble the 2nd image-the difference being which of the collars the right-sideend flows into.

   They are uniform, and ...
/ /
... those 4 dressings are unique in that they are the only ones
where the two collars do not cross each other.
You're missing the point : in all but the topmost dressing,
the left collar feeds into the lower eye leg --this is the sort
of "uniform" dressing I mean (which is often completely
missed for the fig.8 knots because they are presented
in the impossible "flat"/perfect-trace 2-dimensional image).


--dl*
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TMCD

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Re: F-8 inline
« Reply #11 on: February 18, 2013, 11:42:14 AM »
Ashley likes your bottom picture the best as do I but I wouldn't use either of those in line loops, I'd use something less likely to jam up. I would use ABOK 1150, awesome knot with the ability to take great strain and not even jam up.

X1

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Re: F-8 inline
« Reply #12 on: February 18, 2013, 03:01:45 PM »
the eye bight of the top image should be rotated 180deg (top leg away, lower leg coming towards viewer) and resemble the 2nd image
--the difference being which of the collars the right-side end flows into. 

  Correct ! Thank you Dan Lehman. The collars in this A3 form are not crossed any more than in the A2, so if the A2 is included in the set, this A3 should be included, too.
 
« Last Edit: February 18, 2013, 03:23:31 PM by X1 »

X1

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Re: F-8 inline
« Reply #13 on: February 18, 2013, 04:17:22 PM »
I would use ABOK 1150, awesome knot with the ability to take great strain and not even jam up.

   In all those TIB loops ( ABoK#1150 included ), the one leg of the eye is not entangled into the knot s nub as much as the other. It is secured only by a single U turn, a single collar - so if the "lower" standing end is loaded with much less or much more than 33% of the total load, this leg will run the danger to slip through the knot towards the one or the other direction. I would like a TIB loop where the continuatiions of both legs will follow a more convoluted path into the knot than a single U turn, be it at the end of the knot, or buried deep inside it. The simple, most-easy-to-tie-knot-in-the-Universe double line overhand knot, is much better in this respect ! I do not believe that it will jam too easily - double line knots do not jam as easily as single line knots.

Dan_Lehman

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Re: F-8 inline
« Reply #14 on: February 18, 2013, 06:35:46 PM »
... , I'd use something less likely to jam up. I would use ABOK 1150,
awesome knot with the ability to take great strain and not even jam up.
Note that you might want something that "jams up" in the
sense of being firmly set, resistant to loosening --though not
destined to become "welded" on use (agreed) !  What #1150
can do is to point out that by working with a bight one can
develop some familiar knots into mid-line knots, and beyond
the common bowline might be some more robust options
in terms of slack (& other) security.

There is an accepted SAR practice in which the bowline is used
qua mid-line eye knot --i.e., its tail is also loaded.  This occurs
in some use proximate to the end of the line (so it's not
overly difficult to tie the knot) to attach to a litter.

   In all those TIB loops ( ABoK#1150 included ), the one leg of the eye
is not entangled into the knot s nub as much as the other.   ...
I would like a TIB loop where the continuatiions of both legs will follow
a more convoluted path into the knot than a single U turn, be it at the
end of the knot, or buried deep inside it.
The simple, most-easy-to-tie-knot-in-the-Universe double line overhand knot,
is much better in this respect ! I do not believe that it will jam too easily
--double line knots do not jam as easily as single line knots.
One can involve the overhand component in many knots.
I believe I've elsewhere presented this mid-line eye knot
cognate to Ashley's #1408 (which I've felt is a sort of
symmetric butterfly), which I was happy to discover; it is
better that the "directional" aspect of it is appeased by loading
it such that the double-collar is around the eye's SPart.
The point of this is that whichever collar surrounds the
loaded end will be kept from tightening around the nub
by the tension on the SPart --holding the collar open--;
but the collar around an unloaded end can be draw tight
around the nub and be jammed (to some degree).  In
this #1408 cognate, both eye legs run to turn
around one side of the knot, with one collar put at the
remove of a turn which goes through the nipping center
--and so that collar should be less tensioned and less
prone to collapse (and should collar the unloaded end).


--dl*
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« Last Edit: February 18, 2013, 10:48:48 PM by Dan_Lehman »