Author Topic: Information  (Read 5028 times)

Richard

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Information
« on: December 13, 2015, 01:53:25 PM »
Greetings,
I am looking for an institute or company that tests knots/rope for strength. This is mainly in regard to rope rescue work.
Any info or direction is appreciated.
Thanks,
Richard

Dan_Lehman

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Re: Information
« Reply #1 on: December 14, 2015, 07:21:42 AM »
Quote
tests knots/rope for strength.
This is mainly in regard to rope rescue work.
Yes, many of us have wanted such facility, to do variously
worthwhile or just entertaining (in real value, whether
recognized or not!) experiments.  Alas, I have no answer
beyond musing that some universities and maybe some
rope makers hold some potential.

Still, your query raises questions in me as to your objective
--what do you have in mind, and why?
Because I have seen what IMO are too common misguided
efforts, in method and presumed significance (i.e., they don't
really reveal what is presumed to be revealed).  E.g., if you
carry out tests in specimens of new rope made by maker-M
according to test_procedure_TP and knots tied by so-&-so,
will the results really tell you anything about the knots that
are used in various reaLife situations in other materials,
tied by others, and loaded per actual usage and not some
steady-rate/constant-pull device?!  (I doubt it very much.)

There is a common belief that a *knot* --meaning the general
schema for forming a like-named structure in knotable media--
has attributes of strength,
in contrast to saying that the actual physical tokens of this
schema have such attributes (and differ per several factors).
Of course, we do see *knot* strengths given as ranges.
And all this helps us, how?

So, what do you have in mind?
What is your want/need?


--dl*
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agent_smith

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Re: Information
« Reply #2 on: December 24, 2015, 10:59:58 PM »
Hi Richard,

Merry Christmas (its the 25 Dec here in my home - Australia)!

I too am curious... I'll be 100% honest and up front (in the Christmas spirit) - knot strength is largely a myth and investigations into such normally yield nothing of value. Usually, knot testers who focus on strength alone end up arriving at what I call 'false positives'.

A classic example of this is #1410 (Offset overhand bend) also given the very unfortunate name 'Euro Death Knot'. Many testers of this particular structure declare it 'unsafe' on account of its low MBS and alleged instability.

And yet, in 9.0mm class human rated ropes, it remains stable up to loads exceeding 5kN (the jamming threshold is 3kN). One has to ask the question..."What is the nominal intended load of #1410?" The answer is; 1 person.

If we assume that it is a 1 person load - then logically we can also say the nominal load on #1410 will be 1kN. In most rigging configurations, #1410 will be used to join two ropes together so a longer usable abseil length can be obtained. Also, the joined ropes will be doubled through 'rap chains' or some other fixed anchorage (or around a tree where no artificial anchorage is pre-existing).

This means that #1410 will only in fact be subjected to 50% of the load (in a double rope configuration).

At these low loads, #1410 is perfectly satisfactory.
Note: #1410 has what we term an 'Offset' structure - making it particularly well suited to translating around 90 degree edges.

The take home message here is that strength alone is a poor criterion in which to judge a knot.

What matters most is:
[ ] security
[ ] stability
[ ] resistance to jamming
[ ] verifiability

Notice that 'strength' is missing from this list.

...

Now I will qualify my comments in the light of the relatively new 'TRACE' system from a Canadian company called 'CTOMS'. The TRACE system is designed around a 6.0mm cord/rope system - and is intended for 'lead climbing' applications. I believe that the 6.0 mm cord is from a Japanese company 'Teijin limited' and is supplied in the USA by Sterling (need to verify this).

CTOMS supply special belay devices that are designed to function with 6.0mm technora cord.

website: http://ctoms.ca/Mission-Essential-Equipment/Rope-Access-Equipment

Apparently US Navy SEALs use the TRACE system. Its use is in lead climbing, abseiling and rescue. With 6.0mm cord, there is a new paradigm - and it is super lightweight and compact to transport.

My point is that with the increasing use of super thin cordage (ie 6.0mm technora) - strength might play a role. CTOMS favour a sewn end termination (rather than a traditional hand tied termination knot - eg #1047 Figure 8 eye knot).

Traditional ways of 'tying-in' might lower the MBS of the 6.0mm technora cord to a level that is considered outside of acceptable operational safety limits. I am still investigating this - and Dan Lehman should be able to shed more light on 6.0mm cord used in lead climbing applications (in terms of sewn terminations Versus a knotted termination).

This might be a useful application of Bowlines that have 3 rope diameters inside the 'nipping loop' (rather than only 2 as we see in common Bowlines ( eg #1010 Bowline only has 2 rope diameters captured inside the nipping turn).

I also would like to know more about your background and why you think knot strength is important...

Mark G
« Last Edit: December 24, 2015, 11:05:07 PM by agent_smith »

agent_smith

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Re: Information
« Reply #3 on: December 29, 2015, 11:30:46 PM »
I remain curious about the value of testing the qualities/merits of a knot based on pure MBS/break testing alone.

However, as I alluded to in my previous pot, it may turn out that strength has a role to play as we transition to thinner and thinner cords/ropes.
NOTE: I am specifically referring to human rated ropes used for fall-arrest (or fall-protection) applications (eg lead climbing / mountaineering / vertical rescue, caving, canyoning, rope access work, etc etc).

CTOMS have broken the paradigm with their 6.0mm diameter 'technora' cord based roping system.

CTOMS advocate a sewn termination rather than a 'tie-in' knot.

By the way, I am hoping to get my hands on the 'Quickie' belay device and 6.0mm cord and take it for a 'test drive'.

Falling on 6.0mm cord will be an enlightening experience...

I think Bowlines with 3 rope diameters inside the nipping loop could be of interest - and support the theory that increasing the radius of the first curve of the SPart as it enters the core/nub of the knot - will increase the MBS of the knot.

There hasn't been much testing to prove/dis-prove this theory (are there papers out there that have examined this theory?).

Mark

knot rigger

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Re: Information
« Reply #4 on: January 05, 2016, 09:00:15 AM »
Richard

There is a fall protection training and sales company that does offer third-party destructive testing.

https://www.gravitec.com/testing/

There destructive testing rig is quite impressive.  I've been through a couple of their training courses, and for fun, they let us bring some items to be broken.  It was fun.  I had a few splices I made tested and we also broke some UV degraded anchor slings.  They primarily use the rig to test fall protection equipment, as a third party testing service for manufactures of the equipment. 

I'm sure their rig could be used to test breaking efficiencies of rope and knots.  It would just be matter of time and money.

Mark:

The CTOMS system seems quite interesting.  I was at first quite alarmed to see any mention of technora and lead climbing, as technora is well known to have very little elasticity.  I see from the website that the rope in question is nylon core with technora cover.  So at least there is some nylon in there.  Given the small diameter, I would guess that the (technora) cover is designed to take more of the load than traditional kernmantle.  Otherwise why haven't we seen 6mm man rated nylon ropes before?  Perhaps it's the high efficiency sewn termination (approaching 100% efficiency I imagine), in which case the design factor would be greatly reduced by adding any knots into the line, perhaps to the point of it being unsafe for human load.

My intuition is that such a system is a limited niche product for specialized tactical teams, where the tight design factors are more of an acceptable risk, and the limitations and iflexibility of a "don't knot this rope" rope can be overcome with training and specific mission design.

cheers
andy

agent_smith

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Re: Information
« Reply #5 on: January 10, 2016, 11:27:10 PM »
Its would seem that Richard has vanished...

Quote
Otherwise why haven't we seen 6mm man rated nylon ropes before?  Perhaps it's the high efficiency sewn termination (approaching 100% efficiency I imagine), in which case the design factor would be greatly reduced by adding any knots into the line, perhaps to the point of it being unsafe for human load.

The reason you haven't seen 6.0mm cord in mainstream use for lead climbing is because its a paradigm shift and also because it has outrun national 'Standards' (eg EN/ANSI/ISO, etc). The CTOMS 'TRACE' system uses belay devices and cordage that doesn't fit within any national standards framework. Therefore, some people will automatically reject the product for fear of consequences...

Historically, it seems to be the military that are willing to adopt new technology/concepts. Once it has proven to be successful, 'civilians' then look at adopting the said technology/concepts.

My sources tell me that Navy SEALs are currently using the TRACE system...

...

Back to Richard:

I still hold the belief that pure MBS strength testing is largely a dead-end pursuit (unless you are specifically looking to probe structures within the knot. For me, this is sort of like 'accelerators' that physicists use to collide sub-atomic particles to probe their inner structures.

For example, I would support pure MBL break testing if it were specifically investigating the inner structure of a knot - like the effect if adding extra rope diameters inside a 'nipping structure' (nipping loop) of a Bowline.

The results of such testing could then be applied to specialist cords (eg 'TRACE' system technora cord etc) in order to boost its MBS.

In other words, at the moment, I see value in pure MBS break testing for ultra thin cords - and the benefits of such testing could translate to increased safety with those user groups that use thin cords.

One such 'user group' is high altitude mountaineers - where weight is absolutely crucial. Think the 'bottle-neck traverse' on K2. There is no way that any climber is going to pack haul 10mm or 11mm diameter cord to 'fix' in the 'death zone' - but, an ultra thin cord (eg 6.0mm) might work well. And mountaineers wont use sewn end terminations...they need to be able to tie a knot to form a 'termination' (ie to create an 'eye').

knot rigger

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Re: Information
« Reply #6 on: January 11, 2016, 01:08:07 PM »
Mark

The following is a quote from the ctoms website:

Quote
However if a knot is tied into TRACE? Systems rope, it will reduce the factor of safety below acceptable levels.

here is a link

http://ctoms.ca/Mission-Essential-Training_3/TRACE-Systems-Start-Here/

I think we've certainly drifted Richard's thread, but if Rope Rescue Richard is whom I suspect he is, he will probably be interested in our discussion. (if he returns)

I understand your point about thinner ropes outrunning standards.  I think though that the larger point about ultra thin line is that manufacturers are pushing the limits of material science (as they always do, and always should).  I can safely lift you on micro thin 3mm technora cord (if fact it's my profession) but I'm sure you wouldn't want to fall on it, or get it anywhere near sharp rock edges.  I can see how the military, or high altitude mountaineers need to shave design factor to allow for other factors, like weight.  In this instance, with the TRACE system, it seems that I was correct in guessing that one of the ways that they are able to shave down the design factor is to sacrifice the ability to tie knots.  As you note:
Quote
mountaineers wont use sewn end terminations...they need to be able to tie a knot

Also, the lead climbing belay device (dmm pivot) is only rated for such thin lines in twin or 1/2 rope use... so the benefits of such tiny rope is offset by needing twice as much of it :(

Regarding MBS testing and knots.  You say that it's a "dead end" but in the next line you site how it can be useful in evaluating different knots relative to each other.  You also see the benefit in MBS testing of "ultra thin cords".

Both of your musings on interesting possible uses hone in on what MBS of knots is useful for: defining safety factor.  I believe that your dismissal of the merit of investigation of knot efficiency through break testing is a result of the paradigm by which you approach using ropes and knots (ie: rockclimbing).   The most desirable or important qualities of a knot vary greatly with application.  I agree with you that security, stability, resistance to jamming and verifiability are important (and sometimes overlooked) qualities of a good knot.  These four qualities are the most important when looking through the lens of a climber.  Another knot user may not need to value these qualities as highly, and may value strength higher than other qualities.

I think sailors would be interested in knowing how strong their knotted ropes are.  And certainly arborists need to know how much weight they can safely hold with their knotted rope.   Industrial riggers would need to know how much weaker a rope becomes when knotted.

I'll give you an example from my own industry.  When flying a performer, it's desirable to use the smallest safe line to lift them.  I need to know how much a knot will weaken a thin line so that I can use the smallest (knotted) line that is strong enough for the task.  In this instance the strength of a knot is more important than other factors, such as resistance to jamming.  The know will be essentially a permanent termination, I don't care much if it jams.

cheers
andy

agent_smith

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Re: Information
« Reply #7 on: January 12, 2016, 12:29:45 AM »
A quick few points...

1. CTOMS obviously are going to declare 'no knots' in the TRACE system - that sort of goes without saying. It is sewn terminations only.

2. As cords/ropes get thinner and thinner with each passing year - equipment has to keep up. In the case of the TRACE system (ie 6.0mm diameter technora based cord) - there is a special belay device designed specifically for use with 6.0mm cord - its called the 'Quickie'. (there is both a belay device and a rope grab device).

3. The DMM Pivot is just one of many belay devices on the world market. I actually own and use the 'Pivot' myself. It goes without saying that the 'Pivot' is not designed for - and not intended for use with a single strand of 6.0mm diameter cord. Although...it could be used on a snow slope (but not a vertical ice cliff). Gloved hands would be essential - although of course in snow environments, the belayer would be wearing gloves anyway! There are other belay devices that would possibly function satisfactorily with 6.0mm cord - provided some precautions were taken - and this would be on snow slopes only. Anything vertical and you should use the proper 'Quickie' belay device.

4. I re-assert (for the record) that pure MBS break testing would be of value with ultra-thin cordage (eg the TRACE 6.0mm technora based cord). In regular 11mm class ropes - pure MBS break testing is largely meaningless and often leads to incorrect conclusions about knots. However, well thought out break testing can be useful if used in a well directed and targeted manner. For example, break testing could help to probe the inner structure of a knot - rather like linear accelerators are used to smash sub-atomic particles to probe their inner structure. What I am against is pure MBS break testing as a means to declare one knot superior to the other merely on account of its higher MBS yield.

5. I repeat again that pure MBS break testing has value on ultra-thin cordage. As rope manufacturers push the technical boundaries toward thinner and thinner human rated ropes - the effect of hand tied knots will become significant. In relation to CTOMS in Canada, my view is that they are not 'knot heads' like the people here in the iGKT. They probably are ignorant of some of the advances knot heads have made in this forum - and the newer knot structures that have been discovered. It would be interesting for CTOMS to conduct some further MBS break testing of some of the newer eye knot discoveries - such as the Alan Lee inspired / Xarax created Bowline variants with 3 rope diameters captured within the 'nipping structure' (ie nipping loop).
One must understand that CTOMS testers only focused their attention on the traditional tie-in knots (like #1047 F8 eye knot).

...

And in relation to our vanished original poster (Richard) I think he would be interested in this discussion and indeed it has stayed relevant to his original enquiries.

Mark

knot rigger

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Re: Information
« Reply #8 on: January 13, 2016, 12:01:32 PM »
Hi Mark

Quote
In regular 11mm class ropes - pure MBS break testing is largely meaningless and often leads to incorrect conclusions about knots

I wonder if you could take a moment to educate me about what incorrect conclusions about knots MBS testing could (or has) lead to.

I contend that knot choice in all cordage (not limited to 11mm kernmantle) if done without considering knot efficiency, and based solely on security, stability, jam-resistance, and verifiability, could lead to incorrect conclusions about knots!  Take for example, a theoretical knot that has a low efficiency, but very good S,S,Jr&V.  By your criteria, this knot would be excellent, but without further analysis of design factor (which requires knowledge of MBS efficiency) a failure may occur under load, despite the knot passing your S,S,Jr&V criteria.

You limit your assertion to "11mm class ropes" which I understand.  And in fact I agree with you, the typical 'canon' of climbing knots, when used in climbing rope, for one person loads all have adequate efficiencies for the designed task.  However, this statement is predicated on the fact that the 'canon' of climbing knots all have adequate, known efficiencies, and it's somewhat disingenuous to state that MBS is meaningless.  I'll give you an example of a non-climbing-canonical knot that has excellent security, stability, jam-resistance, and verifiability: the Zeppelin Bend.  Would you climb with it?  Do you know it's MBS efficiency in Kernmantle?  (or any other line?  I'm curious)

I'm glad that you qualify your "pure MBS break testing is largely meaningless" statement to 11mm class ropes (for one man climbing loads)  To state that "pure MBS break testing is largely meaningless" for all cordage would be negligent hyperbole, and could certainly lead to incorrect conclusions about knots!

I actually agree and applaud your analysis of knots by S,S,JR & V... I just think strength should be included, not dismissed.  If you want to try and say "maybe a figure 8 tye in isn't the best just because it's stronger than a bowline"  then say that! And I agree with that!  But don't say strength doesn't matter!  If it really didn't matter, why don't you tie in with ABOK #1009 (i know your answer, it jams, but i'm sure you see my point)

BTW, regarding the "quickie descender" I misunderstood it to be solely a descender, which lead to my assumption that the Pivot was the belay device they use for lead climbing.  I double checked, and discovered that the "quickie" desender is designed for "belaying a leader" according to the website.

cheers
andy


Dan_Lehman

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Re: Information
« Reply #9 on: January 13, 2016, 11:43:12 PM »
I wonder if you could take a moment to educate me about what incorrect conclusions about knots MBS testing could (or has) lead to.

I contend that knot choice in all cordage (not limited to 11mm kernmantle) if done without considering knot efficiency, and based solely on security, stability, jam-resistance, and verifiability, could lead to incorrect conclusions about knots!  Take for example, a theoretical knot that has a low efficiency, but very good S,S,Jr&V.  By your criteria, this knot would be excellent, but without further analysis of design factor (which requires knowledge of MBS efficiency) a failure may occur under load, despite the knot passing your S,S,Jr&V criteria.
A fair question (which I might try to address),
but turnabout is fair play, as they say, and to
you then comes the return, What actual case
can you cite where knot efficiency (aka "strength")
has made a difference?


To your question, a weak answer is that one can see
debates about which knot --for various purposes--
is "better" and answers seeming to point simply to
some indication of differences in break strength
(as measured in a particular --perhaps though not
well known-- way on a test device in some kind of
rope (though not necessarily that of user's interest)).

And the general case Agent_Smith has argued against
has been that of Abseil-Ropes-Joining knots used by
rockclimbers (and perhaps SAR folks, and some others
of similar applications, but with different rope --canyoneers?);
in such normal uses with usual cordage of the application
there is no approach to forces that will test strength
(arguably in some knot cases because instability will
cheat such a test --give sooner failure!).


Quote
However, this statement is predicated on the fact that the 'canon' of climbing knots all have adequate, known efficiencies, and it's somewhat disingenuous to state that MBS is meaningless.  I'll give you an example of a non-climbing-canonical knot that has excellent security, stability, jam-resistance, and verifiability: the Zeppelin Bend.  Would you climb with it?  Do you know it's MBS efficiency in Kernmantle?  (or any other line?  I'm curious)
Actually, I'll challenge the bit about "known efficiencies"
on two grounds:
1) it's arguable what is actually known, in that testing
is done somewhere and in some materials (usually new)
and knots are tied in a dressing & setting (& orientation)
that is typically NOT known (a simple case : the *traced*
fig.8 eye & end-2-end knots offer either of two twin
ends that might be the S.Part, yet seldom is the one used
explicitly indicated (one can sometimes infer which ... by
the shape of the loaded knot, if one knows how))
and
2) the loading done by a slow-pull test device is not the
sort of loading that will come by actual usage --more sudden
loading.

Now, there has been lots of testing and lots more usage
--i.e., knots loaded dynamically in practice-- and we can
say that the safety margin sure looks real by such experience.

(I think I lost a train of thought re above two points ...)
But I also will say that in general, it's hard to conceive of
ANY knot being weak enough to cause concern in the
above application, really.  But perhaps a tie-in (eye) knot
can be weak over time : i.e., repeated falls on some inferior
knot in the region of tying in (that end of the line) will see
degradation of rope strength at that region sooner than if
another knot had been used.  (There have been strength
tests done of cut-off ends of climbing ropes that show a
weakening there that exceeds weakened states mid-rope.)

And re the zeppelin bend, I don't think that one should
question its strength (there are some tests here and there
of a casual sort), though one might question its security
when slack and rubbed along rock.  (Rockclimbers only see
end-2-end knots in abseiling and in forming round slings,
yes?)


--dl*
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knot rigger

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Re: Information
« Reply #10 on: January 14, 2016, 06:23:37 AM »
Quote
A fair question (which I might try to address),
but turnabout is fair play, as they say, and to
you then comes the return, What actual case
can you cite where knot efficiency (aka "strength")
has made a difference?


Good question Dan.  Here is a link to give a good example.  It's from Harry Donovan's Entertainment Rigging

http://tinyurl.com/z75qlh7

Quote
a weak answer is that one can see
debates about which knot --for various purposes--
is "better" and answers seeming to point simply to
some indication of differences in break strength

Certainly to base an evaluation of any knot based solely on breaking strength is unwise, a point that I believe You, I, and Mark can agree.

Quote
And the general case Agent_Smith has argued against
has been that of Abseil-Ropes-Joining knots used by
rockclimbers  ... in such normal uses with usual cordage of the application
there is no approach to forces that will test strength

Are you saying that Mark argues that "pure MBS break testing is largely meaningless" due to his defense of his use of the EDK!  I would hope that his motivation for dismissing knot strength as relevant to rock climbers (and other knot users) is based on more than him wanting to defend the practice of putting one's life in the hands of a weak and unstable knot. (btw, I do understand why the EDK is used for what it's used for)

Quote
Actually, I'll challenge the bit about "known efficiencies"
on two grounds:
1) it's arguable what is actually known, in that testing
is done somewhere and in some materials (usually new)
and knots are tied in a dressing & setting (& orientation)
that is typically NOT known
2) the loading done by a slow-pull test device is not the
sort of loading that will come by actual usage --more sudden
loading.

Your argument that MBS for one knot in one material, in one condition, may not translate to the same knot in other materials, in other conditions is valid.  And certainly slow pull to rupture testing does not completely accurately model possible 'real life' failure modes.  However, I reject that the imperfections in the method of testing mean that the findings of the testing are useless.  In the absence of perfect information, decisions must be made on the best available information.  I base my understanding of common knot efficiencies (and corresponding design analysis) on as many published sources as I can find; when they are all largely in agreement, I feel safe in my conclusions.  To mitigate the possible effects of "knot book parotting" I try and seek out testing from a wide variety of agencies, and I won't clutter this thread by listing all of them right now.

Quote
But I also will say that in general, it's hard to conceive of
ANY knot being weak enough to cause concern in the
above application, really.

certainly not :)  It's conceivable for a knot to be so weak as to cause concern ... it's just inconceivable that anyone would use such a weak knot!   

Quote
And re the zeppelin bend, I don't think that one should
question its strength (there are some tests here and there
of a casual sort), though one might question its security
when slack and rubbed along rock.  (Rockclimbers only see
end-2-end knots in abseiling and in forming round slings,
yes?)

I think that the zeppelin bend isn't a rockclimbing knot mainly through it not being used and popularized, rather than through failings of S,S,Jr&V or MBS.  Climbers trust the knots they know, and the knots they know were the ones they we're taught. 

cheers
andy

knot rigger

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Re: Information
« Reply #11 on: January 14, 2016, 06:01:54 PM »
Mark

I've just reacquainted myself with your excellent Knots Study Guide and I have my answer to:

Quote
the Zeppelin Bend.  Would you climb with it?

I would still consider the zeppelin bend 'non-climbing-canonical' but simply through ignorance of the zeppelin's merit. 

Your study guide is excellent, and I support the notion that you should publish a propper knot book for climbers (and the rest of us).  I've certainly paid good money for books of lesser caliber and utility than your study guide.

Cheers
Andy

Dan_Lehman

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Re: Information
« Reply #12 on: January 14, 2016, 10:04:29 PM »
I've just reacquainted myself with your excellent Knots Study Guide and I have my answer to:
Quote
the Zeppelin Bend.  Would you climb with it?
I would still consider the zeppelin bend 'non-climbing-canonical' but simply through ignorance of the zeppelin's merit. 
Let's start with WHERE/WHEN you would consider
using this knot!

IMO, I don't see a spot for it, except perhaps for an
ARJ knot (when we don't consider knots to have risk
of hanging up somehow).  (Just fiddled the knot with
diff.-dia. ropes and found a way or two to extend the
small-rope's knotting to give better security --which
looks good if one pulls down (retrieval) on the LARGE
("lead") rope, but I think that it is often recommended
to do opposite (esp. if the ARJ knot is used to have
stopper effect through the anchor to prevent being
pulled through, in anticipation of the smaller rope
feeding through the belay device faster --something
that I'd think could be anticipated with careful use
by occasionally abseiling while holding more tightly
the thinner rope so that in fact, deliberately, it's
the larger one that moves more (an idea I've not
seen suggested)).

And why is the question about THIS knot?  (The answer
is Because it's a fad knot for some knot luv'rs!)
--and not Ashley's bends #1452, #1425 e.g. (for
them, these "knot luv'rs" will prefer to offer the famous
"(Alpine) butterfly", which does have the benefit of at
least otherwise sort of occurring in the climber's knot set.

Where Roo advocated for a zeppelin appearance
--one infamously derided repeatedly as "false"--
was qua eye knot.


--dl*
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knot rigger

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Re: Information
« Reply #13 on: January 16, 2016, 11:16:21 AM »
Hi Mark

Quote
In regular 11mm class ropes - pure MBS break testing is largely meaningless and often leads to incorrect conclusions about knots

I wonder if you could take a moment to educate me about what incorrect conclusions about knots MBS testing could (or has) lead to.

Mark's post in another thread provides a clear example of the possibility of "incorrect conclusions about knots" based on MBS analysis without taking into account other factors of security, stability, jam-resistance and verifiability

http://igkt.net/sm/index.php?topic=5508.msg38090#msg38090

Dan:
Quote
And why is the question about THIS (Zeppelin Bend) knot?  (The answer
is Because it's a fad knot for some knot luv'rs!)

Are you accusing me of being a Fickle-Fad-Follower?  ;)

 The zeppelin came to mind simply because it has good S,S,Jr,&V, but limited data for MBS and it's not a common rock climbing knot. (of course then I see it in Marks own study guide)  I'm neither advocating or condemning its use for rock climbing (or any other activity).  Perhaps it came to mind due to it being "trendy"... but IMO it is superior to #1452, #1425, or the Butterfly Bend as it is far more jam resistant (in my experience) 

As far as it having an application for rock climbing, I see it's application as limited.  Perhaps in place of a double fisherman's in a "cordalette" self equalizing anchor is a good potential application.

cheers
andy

DerekSmith

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Re: Information
« Reply #14 on: January 16, 2016, 11:43:24 PM »

I'll give you an example from my own industry.  When flying a performer, it's desirable to use the smallest safe line to lift them.  I need to know how much a knot will weaken a thin line so that I can use the smallest (knotted) line that is strong enough for the task.  In this instance the strength of a knot is more important than other factors, such as resistance to jamming.  The know will be essentially a permanent termination, I don't care much if it jams.

cheers
andy

Andy, you fly folks on 3mm professionally.  I fly myself on 0.85mm Spectra as a hobby.

The Spectra is 100kg MBS and I am a lumping great 100kg.  The knots used are nothing more splendid than OH Loop knots.

Now granted, my kites are dual line, so I have a potential 200kg , but there is no guarantee that the load is going to be shared equally between the two lines.

How?

The answer is to make the cord stronger where it is knotted.

If we make a long rat tailed splice into a hollow braid, the cord gets stronger as it encompasses the rat tail.  By the time it has got to the eye, it is twice as strong as the line itself.

In my case, I put a sheath around the 0.85mm Spectra.  It has three properties, the first is that it allows me to actually tie a knot that will not slide away.  The second amazing property, is that it strengthens the line by allowing lateral transmission of load into the sheath.  And finally, it reduces the weakening loads in the knot by increasing the cord diameter by over a factor of x2 thus reducing the forces within the Spectra line.

The result is a stunningly strong simple knot - try it...  but don't fly too high !

Derek