The Zeppelin loop vs the F8 in pulls

Ron

Member
Location
Chattanooga
What an interesting test! I pulled an F8 against an F8 tied in PMI 9mm (I had formerly posted 10mm; it was in fact 9mm)EzBend to get a baseline and one of the F8s failed at 3465 lbs. I think that's a bit low, but....

This is the version of the Zeppelin loop I tested:



I then pulled a ZL (Zeppelin loop) against an F8 loop and the ZL failed at, 3601 lbs. I told you that F8 vs F8 seemed a bit low!

I repeated the test - new rope and knots of course, and guess what? The F8 failed at 3397 lbs!

I repeated the test a third time and the F8 failed at 3536 lbs!

So in summary:

1- F8 vs F8 - failure at 3465 lbs
2- F8 vs ZL - ZL failed at 3601 lbs
3- F8 vs ZL - F8 failed at 3397 lbs (notice how close that failure is to the F8 vs F8)
4- F8 vs ZL - F8 failed at 3536 lbs
 

moray

Member
Location
Maine
Nice work, Ron! That nice tight grouping in your results gives great confidence in your numbers.

It's also good news. Now we have a reliable and strong loop knot that is super easy to take apart even after a huge load. Now if I can only figure out how to tie it...

Did you notice any creeping of the ZL tail during the tests? I'll bet it was negligible.
 

Ron

Member
Location
Chattanooga
[ QUOTE ]
Nice work, Ron! That nice tight grouping in your results gives great confidence in your numbers.

It's also good news. Now we have a reliable and strong loop knot that is super easy to take apart even after a huge load. Now if I can only figure out how to tie it...

Did you notice any creeping of the ZL tail during the tests? I'll bet it was negligible.

[/ QUOTE ]
Thanks! It is good news.

I did watch for tail creep - very impressed - it was negiligible, if there was any at all. But I especially watched for tail creep as the loading increased - I could see none.

It is a bit difficult to figure out how to tie, but once you've got a method, it's not bad. I think I'll do a video showing how I tie it; don't know that it's the best way, but it is methodical and linked to how I tied the bend.

The only drawback to it I see so far is that it can't be tied in the 'middle' of the rope, i.e. the tail has to be reeved through the knot.
 
Hey, thanks Ron!
You tested two knots, but have shown us only one of them.
We must wonder what <u>your</u> Fig.8 eyeknot looks like.
(The unfortunate presumption is that "F8" says all one needs
to know -- just go look it up, um, here or there or ... .)

You also don't have a tested rope-strength, but assuming
(something to be noted --i.e., assumption) that it's
close to the manufacturer's rating, which as best I can see
in quick Googling (not caring to download PMI's pdf files)
is around 5_000# (likely conservative), these figures for the
Fig.8 are in line with what Dave Richards's testing got (for F8).
[ cf. [url="http://www.caves.org/section/vertical/nh/50/knotrope.html]"]http://www.caves.org/section/vertical/nh/50/knotrope.html[/url]][/url]

Quick figuring:
3_500 / 5_000 ~= 70%
3_600 / 5_000 ~= 72%

But I see in a 5/14 post you got much higher figures (3_900+),
and suggested a higher breaking strength for the rope, too !?
(Most of the visible-in-Google-results figures I saw were "5,000#"
with one "6,100" which I tried to track down but quit.)

[ QUOTE ]
Now we have a reliable and strong loop knot that is super easy to take apart even after a huge load.

[/ QUOTE ]
!? But there is already quite a set of Bowlines for that -- old technology,
complemented with various methods to secure the knot.

[ QUOTE ]
The only drawback to it I see so far is that it can't be tied in the 'middle' of the rope

[/ QUOTE ]
Hmmm, with some added complexity, there is a way to achieve this in
a Rosendahl's-Zeppelin-like structure; but it's likely that much of the
appeal is lost (these variations are bulkier), and maybe even in some
cases strength. Some of these variations can be said to be better
eye-knot equivalents to the end-2-end knot: both legs of the eye
assume the position of one of the tails in joining the main line, but
of course they do this in 2-diameters space not one, which has an
effect on the knot's balance.

Great to see some playing around with the test device &amp; knots!

*kN*

ps: And I should contribute a knots-testing continuation to this old
thread http://www.treebuzz.com/forum/showf...ing&amp;Number=185695&amp;page=10&amp;fpart=6
about knotting in super slick &amp; strong HMPE 12-strand rope.
By Brion's initiative, New England Ropes did some testing of five
eye knots in 5/16" urethane-coated Dyneema SK-75 (13_000# !).
With about 60' of line I was able to prepare five specimens which
had identical eyeknots at each end, per specimen (i.e., 5 knots).
(Choosing just which five was kinda painful.)

In short: they tested a simple Overhand mid-line stopper knot to
break at about 31%; the eye knots I contributed broke from about
33%-42% -- not much, alas. All test specimens had knots at both
ends, so the results are of the weaker-of-two of the <u>same knot</u>,
tied as identically as I could, and set w/pulley. The main plus side
to them was that there was no slippage --all breaks. I marked the
knots with threads at exit points (to assess slippage) and at two
points in the mainline where I expected the break to occur. While
there was noticeable compression of the knot --and so of
course material moved out of it--, there was negligible intake
of the tail. (photos before/after testing by me)

(So, I would've never doubted that Rosendahl's Zeppelin bend
or esp. similar, interlocked-Overhands (Butterfly, Ashley's) knots
would slip in normal cordage; unlikely I think even in the HMPE,
but that stuff is a strange animal.)
 
It should be noted that strength attributes attach properly
<u>to particular shaping of particular cordage</u>,
and assuming these tested-in-PMI-EZbend-rope values
to indicate results in arborist cordage is reaching too far.

Where are end-2-end knots most leaned into in arboriculture?

(E.g., in rockclimbing, common uses are:
- tying a short bits ends together to make a sling (tape &amp; cord);
- tying a climbing line to another, or to a thinner, "haul" line
for rappelling (low-force application) )


As for a TIB (Tiable Inthe Bight) eyeknot with properties similar
to Rosendahl's knot, there's a nice Butterfly-like one that should
give equally good results.

*kN*
 

Ron

Member
Location
Chattanooga
[ QUOTE ]
Hey, thanks Ron!
You tested two knots, but have shown us only one of them.
We must wonder what <u>your</u> Fig.8 eyeknot looks like.
(The unfortunate presumption is that "F8" says all one needs
to know -- just go look it up, um, here or there or ... .)

[/ QUOTE ]
The F8s were F8s. They were properly tied, dressed, and lightly set. The lays of the F8 were parallel and not crossing. I used both forms of the F8, i.e. the strand bearing the force on one F8 was on top or the outside, and on the other two on the inside.

Dr. Merchant, author of Life on a Line says there may be as much as 5% difference in strength between the two variations. Bruce Smith of On Rope, personally tested this idea and found no significant difference in the two variations.

[ QUOTE ]
...You also don't have a tested rope-strength, but assuming (something to be noted --i.e., assumption) that it's close to the manufacturer's rating, which as best I can see in quick Googling (not caring to download PMI's pdf files) is around 5_000# (likely conservative), these figures for the Fig.8 are in line with what Dave Richards's testing got (for F8)...

[/ QUOTE ]
I don't have a way of testing rope strength due pull length and lack of proper terminating fixtures. But the purpose was not to compare the strength of the knot to the new, unused rope strength, but to compare the ZL to a commonly used F8 knot.

A second, and equal purpose was to measure breaking point of the ZL by pulling it against an F8 loop knot which I had hoped would serve as a stronger terminating knot. That was my work-around for not having proper end termination fixtures. However, I was surprised (pleasantly) to discover the ZL broke the F8 two out of three pulls.

Much is known about the F8's strength and if the ZL was comparable then we have a valid comparison.

[ QUOTE ]
...Quick figuring:
3_500 / 5_000 ~= 70%
3_600 / 5_000 ~= 72%

[/ QUOTE ]
According to PMI's catalog, 9mm EzBend has a MBS of 4720 lbs. So the percentage of knot strength to new, unused rope strength would be:
3_500 / 4720 ~= 74%
3_600 / 4720 ~= 76%

[ QUOTE ]
...But I see in a 5/14 post you got much higher figures (3_900+), and suggested a higher breaking strength for the rope, too !?

[/ QUOTE ]
The rope in that thread (5/14) was 10mm. This rope was 9mm. I stated 10mm in the OP of this thread, but that was because I was use to testing the 10mm and mistated the size. I have corrected that in the OP.

[ QUOTE ]
(Most of the visible-in-Google-results figures I saw were "5,000#" with one "6,100" which I tried to track down but quit.)

[/ QUOTE ]
PMI lists 9mm EzBend at 4720 lbs and 10mm EzBend at 6070 lbs.

[ QUOTE ]
[ QUOTE ]
Now we have a reliable and strong loop knot that is super easy to take apart even after a huge load.

[/ QUOTE ]
!? But there is already quite a set of Bowlines for that -- old technology, complemented with various methods to secure the knot.

[/ QUOTE ]
The ZL is stronger or as strong as an F8 and can be untied much easier. The ZL is stronger and just as secure, if not more so, than most bowlines and it's just as easy to untie.

[ QUOTE ]
[ QUOTE ]
The only drawback to it I see so far is that it can't be tied in the 'middle' of the rope

[/ QUOTE ]
Hmmm, with some added complexity, there is a way to achieve this in a Rosendahl's-Zeppelin-like structure; but it's likely that much of the appeal is lost (these variations are bulkier), and maybe even in some cases strength. Some of these variations can be said to be better eye-knot equivalents to the end-2-end knot: both legs of the eye
assume the position of one of the tails in joining the main line, but of course they do this in 2-diameters space not one, which has an effect on the knot's balance.

[/ QUOTE ]
I was referring to the form I tested. My philosophy would be to use the ZL where practical and if a midline knot was needful, I'd have to bite the bullet and tie another knot, knowing it would be more difficult to untie than a ZL.

I made no implication that the ZL would behave precisely in arborist rope the way it did in EzBend. However, when I did my 450 lb load test in both EzBend (10 mm) and Velocity (11mm), they both held securely and untied equally easy.

I had a small surplus of 9mm PMI rope that I felt would be more worthwhile to test than some kind of small cordage. I did not have any surplus arborist rope.
 
[ QUOTE ]
The F8s were F8s. They were properly tied, dressed, and lightly set. The lays of the F8 were parallel and not crossing. I used both forms of the F8, i.e. the strand bearing the force on one F8 was on top or the outside, and on the other two on the inside.

Dr. Merchant, author of Life on a Line says there may be as much as 5% difference in strength between the two variations. Bruce Smith of On Rope, personally tested this idea and found no significant difference in the two variations.

[/ QUOTE ]
Thanks, that's a help. Seeing the knots under stress is even better;
but your results (revised vis-a-vis likely tensile (odd that on-line info
I was seeing for 10mm)) put things where we'd expect them.

As for Bruce Smith and his Knot Myth re the Fig.8 (eye knot, though
equally re end-2-end), he clearly does NOT address Merchant's point
-- he sets up the supposed inside/outside in an impossible form
(as though traced in 2 dimensions, nearly). Lyon Equipment's results
however, though brief, lend credence to the "doesn't matter" conclusion.
Merchant himself has a slightly different form, harder to dress; he seems
to choose this primarily for easier untying. (In some other place than
the Myth Busters --where his presentation is just plain stupid-- I recall
him claiming breaks at the entry point, which suggests that the details
beyond cannot be so important, regardless. But I don't trust folks in
their knot observations so much, esp. with the nonsense published
about certain things --and Bruce's dismissal of the American Death
Triangle contains too much nonsense to ignore.)

[ QUOTE ]
The ZL is stronger and just as secure, if not more so, than most bowlines and it's just as easy to untie.

[/ QUOTE ]
I await some testing of better bowlines, but improvement can only go
so far if the results you have hold for the particular material of interest
(one can see some variance in the Richards data, e.g.), and differences
at this level really don't have a practical effect.
But still a good point in favor of a bowline is that it can be tied <u>after</u>
the eye is sized, positioned -- no Overhand or Fig.8 to tie first.

[ QUOTE ]
My philosophy would be to use the ZL where practical and if a midline knot was needful, I'd have to bite the bullet and tie another knot, knowing it would be more difficult to untie than a ZL.

[/ QUOTE ]
A bowline, tied with a bight qua working end, would be easier to untie.
It's not such a good knot if the loading will come on the tail, though.
And, frankly, with the mainline bending/crunching around its 4 diameters,
I'm struggling to figure out why it would not be as strong or stronger.

[ QUOTE ]
I did not have any surplus arborist rope.

[/ QUOTE ]

Given your facility to run such tests, maybe you can bwcome a handy
collector of discarded/retired cordage for doing some quick'n'dirty
testing!

Cheers,
*kN*
 

Ron

Member
Location
Chattanooga
Just to be clear, Bruce is totally against the American Death Triangle (ADT) because of the heavy loading it puts on anchors. He and I talked FTF about this not long ago.

The F8 issue that Bruce refers to in his myth busters is that it makes no difference whether the load is applied to the inside or outside turn of the the knot. From his website:

[ 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.

[/ QUOTE ]

One doesn't even have to put an F8 under a lot of stress to see what Bruce is talking about. I just pulled each tail of an F8 in 8mm cord by hand and no matter which strand I pulled, that loop did in fact come to the inside of the knot.

Dr. Merchant's claim of 5%, not the 10% Bruce addresses, even if it's true, which I seriously doubt, it's an insignificant difference. If we put ourselves in a situation where a knot strength of 5% is significant, we're doing something incorrectly.

Well, 'my facility' is limited. It is the school's tensile machine and the few splices and knots I have pulled have been covered by my boss's instruction to become familiar with equipment in other disciplines in order to better cover one another in cases of absences. I'm electrical/electronic so learning a mechanical system is in complete compliance with the boss's request.

Unfortunately, this is not a continuous thing and it would become increasingly difficult to justify as 'learning'. But I have some other things in mind that may resolve the issues.

Unfortunately, knot pull tests need to be referenced to new, unused rope rather than used, retired arborist rope.
 
[ QUOTE ]
Just to be clear, Bruce is totally against the American Death Triangle (ADT) because of the heavy loading it puts on anchors. He and I talked FTF about this not long ago.

[/ QUOTE ]
Just to be clearer: the presentation on the OnRope1 site against the ADT
is seriously flawed. Consider first that the hypothetical ADT is with a 60deg
angle at the load end, which (1) is likely broader than most people will
be comfortable anyway (any anchor) and (2) it makes an equilateral
triangle which will have (think "equal") like loads at each corner (though
given significant friction at the anchor points there will be less than
equal tension in the ADT material between those points unlike between
legs from the power point, a slight force-mitigating factor for them.
The presentation starts with this point, roughly (and regarding the
full-force at <u>two</u> anchor points a doubling of the powerpoint's load),
but at the bottom it gets confused with the "120degree angleS" and
manages to DOUBLE force <u>on each of the anchors</u>!
("Assuming the ADT has three angles of 120degrees ...": wow, that is
really radical geometry --Guass &amp; Riemann are turning in their graves!)

THAT SAID --a point to the presentation--, I'm not trying to advocate
use of the ADT; just that in some quick'n'dirty joining of two closely
spaced bolts, it is far from the hyped Bad Thing some might fear.

[ QUOTE ]
[ 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.

[/ QUOTE ]

One doesn't even have to put an F8 under a lot of stress to see what Bruce is talking about. I just pulled each tail of an F8 in 8mm cord by hand and no matter which strand I pulled, that loop did in fact come to the inside of the knot.

[/ QUOTE ]

Wow, now you're worrying me. It should be obvious that the knot as shown
by OnRope1's MythBuster image (an easy-to-illustrate but impossible to
realize image) is bogus. Starting from that, there's no telling what will
result, but --yes-- things could go as described. But that hardly addresses
the issue, where one should be tying the knot "properly dressed &amp; set" and
not in this easy-on-illustrators form.

Look at Wikipedia's contrasting images for the Fig.8 end-2-end knot:
[url="http://en.wikipedia.org/wiki/Flemish_bend"]http://en.wikipedia.org/wiki/Flemish_bend[/url][/url]
The one of red-2-blue rope at left is (from Grog's site?) like OnRope1's,
presumably thinking to make the structure conspicuous but sadly leaving
one to wonder how to dress it; the image on the right is correctly dressed
and shows the clear geometric difference between loading the inner vs.
outer (hard to find fitting descriptors) strands of the knot -- it is shown
loading what I think some other folks (Lyon Equip, e.g.) have referred to
as "on top". The loaded strands in this form bear into their parallel twins,
and might get some effective cushioning from this; to ensure that this
occurs well, the knot should be set by hauling hard <u>on the ends</u>;
and when loaded, this knot's body will assume a sort of 45deg tilt to the
axis of tension, as the loading to the extreme ends of the body compress
the body.

In contrast, were the ends as shown here taking the load, they would
pull away from their parallel twin strands, not into them, and into
the twin parts bending around them; the knot body remains more aligned
with the axis of tension; the unloaded, "on top" parts --here being tails--
will be seen to be untensioned
(one can observe this in many photos of loaded Fig.8 eyeknots, as it
seems more common to have the interior vs. exterior twin as mainline).

And this much can be seen, yes, quite easily in one's hands, loading 6mm
or so with manual force of upper body vs. foot, or however. I've done the
same with Merchant's form; but his version is trickier to dress.

[ QUOTE ]
Dr. Merchant's claim of 5%, not the 10% Bruce addresses, even if it's true, which I seriously doubt, it's an insignificant difference. If we put ourselves in a situation where a knot strength of 5% is significant, we're doing something incorrectly.

[/ QUOTE ]
Quite so, esp. as there is usually little to show exact geometry and not
always the material. Again, one can see some differences across materials
in the Richards data (12.5 "static", 10.5 dynamic, 7mm "accessory").
Not sure where your Merchant "5%" comes from; I'm reading "up to 10%"
in <u>LoaL</u> in the "Important Note on Direction" under "Figure-8".
And, again, I'll note that Merchant's symmetric form of the knot differs
from those show in the Wikipedia site. (His loaded part comes in as the
OnRope1 site presumes, but it then crosses to the "inside" -- a form
that will see various crossing points in practice, methinks. And his prime
interest seems to be to prevent jamming rather than bump strength.

The ca. 1985 publication O.R.C.A Safety Manual (Ontario Rockclimbers)
asserted 10% and showed the form referenced above of rightside image
of Wikipedia's. Lyon Equip. found some 6%pt.s diff. on similar versions
of the Overhand eyeknot, but not of the Fig.8; still, one can wonder at
whether different setting (the bias of pulling on tail(s) could have effect.

[ QUOTE ]
Unfortunately, knot pull tests need to be referenced to new, unused rope rather than used, retired arborist rope.

[/ QUOTE ]
Point taken, in part; but most users are tying knots in used rope,
and to the extent that one can be sure of some evenness of ageing
effects, it makes sense to see what esp. the general reduction of surface
slickness might contribute to knot strength.
Beyond just obtaining some supposed strength-efficiency value,
by marking the rope and close observation during the testing,
it might be possible to gain insights into how the knot is weakening
the rope, where the break comes. E.g., I've some broken ropes where
of 3 strands (laid rope) 2 remain intact, only the 3rd broken; in such
a case, there's some possibility to see where the broken strand was
and parted (my observations are that it's on the <u>inside</u> of a bend
where its compressed).

*kN*
 

Ron

Member
Location
Chattanooga
We don't need to be discussing the ADT in a thread about the ZL. The fact is, the ADT is dangerous, Bruce illustrates the forces at the anchors with a number of different angles and compares that to the V configuration. It is illogical to claim something like that is flawed because in your opinion, most people would be uncomfortable with a 60° angle. They should be uncomfortable on an ADT at any angle.

As for the F8 loop being stronger when force is applied to the outside loop vs the inside loop I made a video to illustrate what Bruce was saying about the F8:

http://www.youtube.com/watch?v=vTVrVQwhy8A

Edit:
Shoot! I didn't tie the F8 in the video the way Dr. Merchant shows it. In addition to the load being applied to the top loop, he has the load strand positioned a bit differently. I don't know how that's going to set under load, so I'll have to try it that way also.

I think one valid observation here is that it seems that the 'proper' tying of an F8 is not as simple as we may assume it to be IF all this is true, AND IF we need the maximum strength from the F8. The question is, with so little difference between a purportedly properly tied F8 and one 'reversed' (as Dr. Merchant puts it), i.e. 10% does really matter?

Climbers have been using F8s for years and I've seen them tied various ways from sloppy to neat, etc. and I've yet to hear of a climbing accident because of how the F8 was tied.

Much ado over little perhaps?
 

moray

Member
Location
Maine
[ QUOTE ]

ps: And I should contribute a knots-testing continuation to this old
thread http://www.treebuzz.com/forum/showflat.p...=10&amp;fpart=6
about knotting in super slick &amp; strong HMPE 12-strand rope.

[/ QUOTE ]

KN, I wondered if we were ever going to hear back from you about that. Did you conclude anything from this? Where are the pics of your knots? Maybe you should reopen the original thread so we don't hijack this one...
 

caleb

Member
Location
Asheville, NC
This also may be unrelated but I've been using the zeppelin bend in webbing to make anchors around trees for the slack line in my yard. Pulled the line tight with an advantage and have proceeded to bounce the bejesus out of it with my body.
It works in webbing with vitually no creep whatsoever, FYI....
 

Ron

Member
Location
Chattanooga
Zeppelin in webbing - hadn't thought about that. Thanks for posting that!

A water knot can be difficult to untie; have you tried to untie a Zeppelin after it has been loaded like that?
 

SingleJack

Well-Known Member
Location
W MD
There have been several references to the F8 with respect to Dr. Merchant. In the interest of 'full disclosure' it should be noted (as an aside) that Dr. Merchant, in his <u>first edition</u> of Life On A Line, expressed a preference to the F9 over the F8:

[ QUOTE ]
The figure 9 should be the knot of choice in any full rescue loading where a figure 8 knot would normally be used. The figure 8 has a place as a general working knot, but there is no realistic reason for using it when the figure 9 is identical in operation and a lot stronger. - Dr. D. F. Merchant, Life On A Line, 2003.


[/ QUOTE ]

Having not received the <u>second edition</u>, yet, it will be interesting to know if this 'preference' is in the latest edition.
 

Ron

Member
Location
Chattanooga
He still says the same thing in the 2nd edition.

He states a strength range for the F9 (loop) from 70% - 85%, a rather wide range of 15%.

He states a strength range for the F8 (loop) from 65% - 75%. Of course one has to wonder if that's his version of the F8 loop. If it is, then that implies that what he calls a reversed F8 loop would only have a strength range of 55% - 65%, i.e. 10% less.

Also, while we're disclosing, on p 152 of the 2nd edition, he shows an inchworm set up using two Rescuescenders (or at least they look like Rescuescenders, and he does recommend the Rescuescender at another place in the book). I tried to set it up as shown and couldn't find any combination of screw link sizes (or carabiners) that would go through the hole in the cam at the same time. Wonder how he did that?

Also, very much to his credit, with regard to the F8 loop, Dr. Merchant states, "...data from the top ten manufacturers the strength varies from 59% to 88%.

And he says in bold, "Our advice is simple - you can't ever be sure how strong your knots are, but if you assume they're all only 50% then your rigging will be safe."
 
-- some quick remarks --

[ QUOTE ]
Much ado over little perhaps?

[/ QUOTE ]
1) There is obervation &amp; consideration of knots for the sake of getting
a general idea of use, and that needn't delve into the nitty-gritty;
("Much ado over knotting" is one version of this. :eek:)

2) Then there is the close scrutiny so as to understand what's going on,
as a more academic interest; for this, one needs to know details and to
pay close attention, et cetera. -- and for gaining understanding,
not likely so much for making practical decisions. (We might concur in
Merchant's assertion that a Fig.9 eyeknot will usually be stronger than
a Fig.8 eyeknot, and ... prefer to use a bowline , or a Fig.8, sensibly
operating well within safe boundaries such that any strength differences
are irrelevant: they are equally amply strong.)

And we should be at least intellectually curious about how such ranges
of strengths come to be. Let me toss in that Moyer reported 92% for 5
tests and IIRC this also is 5 Weaker-of-Two (both ends of specimen)
testing, in his Sterling 7mm of his famous Hi-mod cordage paper.
He showed me some not-quite-unambiguous various configurations
of that. -- and also wondered about the figure. But he tested strength
of the rope, not merely took rated strength as the basis! (And both
AMGA &amp; CMC Rope Rescue Manual have the Overhand eyeknot as being
as strong as &gt;some&lt; Fig.8!?) Huh ?!

3) Did I conclude anything from the few tested knots in Dyneema SK-75?
Yeah --along with seeing Brion's video of a Dbl.Bowline eye collapsing(!)--,
that stuff is, ah, in the colloquial "not from around here, are ya?" !!
Man, all bets are off with that stuff.
And note that one might hear "Dyneema/Spectra" in cases where the
cordage has that <u>in the core but w/polyester sheath</u> (and I must
believe it's to this cordage that Merchant's way-too-understated-otherwise
claim of losing additional 10-30% is aimed), and is how such stuff comes
into rockclimbing/caving/SAR but for webbing; but even here, Moyer's
tests I think showed Fig.8 strengths of that cordage at around 40% (!).
MY stuff (like what Brion's videos showed) is pure, 12-strand material;
and unlike some older Spectra ("900"?), which contrary to "always white"
claims, is grey (Amsteel Blue is, yep, blue; urethane?), the tested Dyneema
from NERopes has an obvious blue coating on it (in obvious uneveness),
which stiffens it and maybe *slickens* it as well (as though it needs help!).
[Let me say that this "stiffening" is overcome easily --not like some
stiff ropes (PMI non-"EZ-bend" rope, e.g.)--; the 12-strand does bend.]

I chose knots for some various presumed attributes:
- some <u>twist</u> in the mainline, as load distributer, strength enhancer;
- Reverse Fig.9 for <u>broad initial bend</u> of mainline, again re strength;
- a Bowlinesque orientation of the Fig.8 to see about strength and also
ease of <u>untying</u>;
- my "Semi-Symmetric Fig.9" esp. re <u>untying</u>;
- and a "Quick8" esp. re <u>slippage</u>

After seeing the slippage from Brion's video, I concluded that, no matter
the twisting of the mainline, force would flow through to the u-turn.
I'd been happy to have figured how to make what I hoped was a reasonable
rope knot corresponding to the angling (tiny line) Bimini Twist:
in the BTwist, the mainline twists with end, and flows into the eye, w/o
any u-turn; the tail counterwraps this core twist; it's generally regarded
as 100% knot (but YMMV on how that's figured --100% of what (with
many rated strengths being way understated)). But in rope, this would be
comically big &amp; bulky. The end's counter-wrap (to the core twist) is in a
sense passive: it resists the untwisting within it of the core. There
are ways for use in rope to make the counter-wrap active -- i.e.,
loading pulls on this wrap, twisting the core tighter, as the core is trying
to untwist. So, there was a hope; it still takes some span to put in a few
twists -- "twists" are longer than "wraps". But given the slickness of HMPE,
I figure that it's pretty much all for nought: one just can't suck off much
load at all (like running rope through a block vs. over a limb -- big diff.,
but same u-turn angle, given diff.s in friction).
So, I kept in a potentially practical "twist" knot,
but for the Fig.9 (which I think some Oregon testing had claimed ~=50%,
but those folks were unresponsive or unknowing, alas, re knots), I opted
to load it in reverse, where one gets a pretty broad curve. Happens to have
been the "winner" --ONE testing of one specimen-- by a small margin.
(And, it appears that the break came oddly well into the knot, <u>after</u>
a u-turn (needs more scrutiny) !?)

As for UNtying, ... ha!! I think that it is possible to do this <u>with tools</u>,
but it's not happening by fingers, at least not w/o much effort (and I have
not wanted to untie knots whose at-break-load-geometry I want to
examine further). It was esp. surprising to see how the Semi-Symmetric
Fig.9 got tightened, where I thought forces would hold its tightening at bay.

*kN*
 

Ron

Member
Location
Chattanooga
[ QUOTE ]
...Also, while we're disclosing, on p 152 of the 2nd edition, he shows an inchworm set up using two Rescuescenders (or at least they look like Rescuescenders, and he does recommend the Rescuescender at another place in the book). I tried to set it up as shown and couldn't find any combination of screw link sizes (or carabiners) that would go through the hole in the cam at the same time. Wonder how he did that?...

[/ QUOTE ]

I just figured out how he did this; it's pretty obvious actually - you have to use long ovals! I didn't have any long ovals and no combinations of ovals or biners I had on hand would work.

So I ran over to On Rope 1 (I've been leaving the '1' off and it is part of the name. On Rope is the name of the book) and picked up two 6mm long ovals and they worked great. Now to try out the inchworm and another application that this would be well suited for - I think.
 

caleb

Member
Location
Asheville, NC
[ QUOTE ]
Zeppelin in webbing - hadn't thought about that. Thanks for posting that!

A water knot can be difficult to untie; have you tried to untie a Zeppelin after it has been loaded like that?

[/ QUOTE ]

Yep. I cut the last water knot I used in my slackline out because I didn't even want to try. The zeppelin takes a little finnagling, but it comes out.
 

Ron

Member
Location
Chattanooga
[ QUOTE ]
Yep. I cut the last water knot I used in my slackline out because I didn't even want to try. The zeppelin takes a little finnagling, but it comes out.

[/ QUOTE ]
That's really good news! Thanks again for posting this.
 
[ QUOTE ]
The only drawback to it I see so far is that it can't be tied in the 'middle' of the rope, i.e. the tail has to be reeved through the knot.

[/ QUOTE ]

I'm abashed to say that my response to this point, above, was
to a then-mused-way-to-do-this and I'd completely forgotten
about the arguably true Zeppelin eyeknot !!


Well, heck, there are so many knots ... (and a few more ways to
skin this cat, fyi).

I've got a photo (which I'll get around to later) of sketches of a set
of "zeppelin loop knots" including the one just recalled. But, here's
a tying method which should get you the knot verbally:

- begin tying the Z loop as you would normally do (I'm presuming
that you begin by tying an Overhand in the mainline and then
bring the tail back into this --after sizing the eye-- as though
it were a 2nd end joining the first),

- but at the point of just finishing/forming the Overhand
component in the mainline, do so with a bight (which in direct
words is "tie a Slip-knot"), and see yourself at this very point

- as tying the finishing/end's Overhand component <u>in reverse</u>
(and so you'll be pulling the Slip-knot's bight around and out and
it becomes the eye; you are left with but <u>one</u> tail, that of the
Slip-knot).

And in this way you have exactly the Zeppelin mechanics
-- that "69" / "bq"/"pd" orientation of opposing feeds into the
rope, the interlocked Overhands. Except that one side has twin
lines with half-force to the single mainline --a bit of imbalance
geometrically. And this knot is NOT so hard to tie; one just
needs some practised familiarization. (Maybe it becomes one
item for use of that 9mm rope you had left to test with?)

*kN*

ps: I hope you appreciate the sacrifice I made to post this:
I was sitting on a jackpot, bingo, 3-of-a-kind, "222" posts !
Now another 110 to go for that to happen again.
 

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