Knots for joining two ropes for life support

[DSMc]

... MBS yield testing is largely irrelevant and a meaningless exercise.
However, if MBS yield testing was done with a specific purpose in mind - for example to investigate the precise location from where fracture propagates - this would be meaningful.

How so?

 

[moss]

Wrong.
#1415 Double Fishermans (aka Grapevine) has an inter-penetrating geometry.
Each SPart penetrates into the opposite Double overhand strangle and load causes the 'strangles' to abut and crush inwards. Failure propagates from an SPart where it initially curves around the opposite SPart and its own tail segment. As to which SPart yields first, this is due to chaos theory and minuscule variations in tying. The fracture propagates from within the knot core and is yanked out. Also, most load testing machines inject force from one side - and it is thought that the break tends to occur on the side closest to the injection of force.
No one has really looked into this before - so there is no peer reviewed data to examine. It is an open question.


MBS yield testing is largely irrelevant and a meaningless exercise.
However, if MBS yield testing was done with a specific purpose in mind - for example to investigate the precise location from where fracture propagates - this would be meaningful.
Or, to investigate the effect of one additional turn to convert #1415 to a 'Triple Fishermans' - using #1415 as a 'control' - would help us test the theory of the first curve (or 'nip') being the likely source of fracture....

You’ve misunderstood my comment. I’m not referring to the cause, moment, or “anatomy” of the failure of a double fishernan’s. I’m talking about the observed tightening of the crossed coils during Richard’s test before the failure. In this case comparing the MBS of a triple vs. double fisherman’s would be interesting.
-AJ

 

[Brocky]

Welcome @agent_smith, thanks for bringing your extensive knot knowledge here! When I want to abuse my brain and get humbled with lack of knowledge I’ll visit the IGKT forum. It’s amazing how something so simple and commonplace can be so complicated as to how they work.

How so?

Post 70 might answer your question.

 

[agent_smith]

Thank you Brocky

For other readers absorbing the technical aspects of this thread, I should point out that I do in fact appreciate the work Richard Mumford has done.
However, from a pure research point of view, a lot of knot testers around the world fail to use a scientific 'control'. The omission of a 'control' appears to be commonplace - and it is hard to draw meaningful conclusions from such tests.

In the case of Richard Mumford's tests herein, what conclusions are we to draw? What exactly is being demonstrated and to what purpose?

Yes - we can see knots being pulled to their MBS yield point - and then 'bang' everything fails.
To a lay person, it all looks exciting and purposeful. But upon closer inspection, what is it that Richard is trying prove?

The pull-it-till-it-breaks mindset is all pervasive right across the entire roping industry.
If a control was used - and a specific targeted objective was made clear from the outset, the results might be more meaningful. For example, it is possible to use #1415 Double fishermans as a 'control' for a test of the #1415 derived 'Triple fishermans. If both end-to-end joining knots reached near identical MBS yields, we might be able to conclude that the extra turn does not boost the MBS yield. However, another test - slack shaking and cyclic loading might demonstrate that the 'Triple fishermans is more secure. Current theory posits that fracture propagates from the region of the first curve of the SPart. If this is correct, both #1415 and the #1415 derived Triple fishermans should have near identical MBS yields. The radius of the first curve playing a role in how force is dimensionally dispersed over the cross-section of the rope fibres.
You get unequal loading over the cross-section - with compression and expansion occurring. One theory posits that fracture propagates from the side that is under compression (and not expansion). Again, this needs to be proven in a round of rigorous tests using the 'scientific method'.

 

[moss]

....For example, it is possible to use #1415 Double fishermans as a 'control' for a test of the #1415 derived 'Triple fishermans. If both end-to-end joining knots reached near identical MBS yields, we might be able to conclude that the extra turn does not boost the MBS yield.

When Richard performs knot break tests he is providing valuable and interesting information about the basic characteristics of these knots. Climbing arborists and experienced rec climbers have accumulated a wealth of practical knowledge about the characteristics and behavior of knots, bends, hitches etc. that we use. Knowing that one knot breaks higher or lower than another adds to our knowledge base and is actually useful when making choices and considering all of the characteristics of a knot or bend used to join two lines.

I would like to see a two turn grapevine go up against a three turn, if the three turn breaks higher we'll have more to discuss ;-)
-AJ

 

[Mowerr]

Any test data I have seen shows the triple breaking higher.
When Richard posts test videos for us, it's usually because many of us have requested it and/or paid for him to do it. Before I came across his videos I never saw many if any tests, especially in the configurations he does for us. Yes sometimes we don't need the strongest knots but for some things like rigging apps we do.
Plus I don't think treestuff or any of the bigger companies that u can pay for breat tests don't give u the video but Instead you only get numbers and a picture.

 

[Chaplain242]

Thank you Brocky

For other readers absorbing the technical aspects of this thread, I should point out that I do in fact appreciate the work Richard Mumford has done.
However, from a pure research point of view, a lot of knot testers around the world fail to use a scientific 'control'. The omission of a 'control' appears to be commonplace - and it is hard to draw meaningful conclusions from such tests.

In the case of Richard Mumford's tests herein, what conclusions are we to draw? What exactly is being demonstrated and to what purpose?

Yes - we can see knots being pulled to their MBS yield point - and then 'bang' everything fails.
To a lay person, it all looks exciting and purposeful. But upon closer inspection, what is it that Richard is trying prove?

The pull-it-till-it-breaks mindset is all pervasive right across the entire roping industry.
If a control was used - and a specific targeted objective was made clear from the outset, the results might be more meaningful. For example, it is possible to use #1415 Double fishermans as a 'control' for a test of the #1415 derived 'Triple fishermans. If both end-to-end joining knots reached near identical MBS yields, we might be able to conclude that the extra turn does not boost the MBS yield. However, another test - slack shaking and cyclic loading might demonstrate that the 'Triple fishermans is more secure. Current theory posits that fracture propagates from the region of the first curve of the SPart. If this is correct, both #1415 and the #1415 derived Triple fishermans should have near identical MBS yields. The radius of the first curve playing a role in how force is dimensionally dispersed over the cross-section of the rope fibres.
You get unequal loading over the cross-section - with compression and expansion occurring. One theory posits that fracture propagates from the side that is under compression (and not expansion). Again, this needs to be proven in a round of rigorous tests using the 'scientific method'.

I believe that all the types of tests build a picture of the system to the observer, and agree that industry measures tend to have a kiss (keep it simple) approach to testing when it comes to regulation and comparison but I believe that occurs more to fulfill regulatory bureacracy, which in turn opposes the efforts to build working knowledge by the general user partially because the safety police will regulate more and apply greater spectrums of tests for compliance until the system defeats itself.

We see that on polystyrene cladding for structures, whereby no material passes the tests so everybody just says it passes to sell a product resulting in fires and significant loss of life.

It would be better for industry and consumer bodies to work together in association (in the absence of corruption) to achieve a system whereby engineering is used generally to develop products that are ideal to task, and open about product/method strengths, weaknessess. However many social factors seem to be at odds with achieving those goals (competitive advantage, financial viability, regulatory agency modus operandii etc) so maybe its best to keep the system whereby the consumer bodies don't take everything on blind faith and test products/methods and give feedback as required, and we work together the best that we can to understand what mechanical systems we are using with the funds and resources available....

 

[Richard Mumford-yoyoman]

I have said the break strength is the least important character, just difficult to get without special gear. Watching how it breaks, (rope and knot) is very valuable. Seeing how the core and cover interact. Anyone can test how easy a knot is to tie or verify. In fact test how well it stays together by putting it in the dryer for 5 mins. etc...

 

[agent_smith]

Knowing that one knot breaks higher or lower than another adds to our knowledge base and is actually useful when making choices and considering all of the characteristics of a knot or bend used to join two lines.

I disagree completely.

The MBS yield point of a knot does not tell you anything meaningful UNLESS you are specifically investigating a geometric change or assessing if the knot remains jam resistant right up to the point of failure. And you must use a 'control' - otherwise, your tests are invalid. I am unclear if readers of this thread actually know what a scientific 'control' is?
I would remind readers that #1410 (Offset overhand bend) is an example where 'pull-it-till-it-breaks' tells you nothing meaningful.

There is no load that an individual climber can generate that will reach the MBS yield point of a knot.
A climber cannot even approach the MBS yield point of a simple overhand knot (#46 / #514) or a simple overhand loop/eye knot (#1046). These knots will maximally jam (rather than just initial threshold jamming) - and so for this reason, are generally not used in high loading situations.

I think the roping industry has some way to go to break old ways of thinking about knots - and this is understandable given the status quo of traditional knot testing (and knot book authors promoting the notion of 'strength').
I note that Elon Musk is a game changer - a big thinker. He has shaken up the rocket launch industry. The accepted paradigm is you build a rocket, use it once and then throw it away. Elon thinks this approach is 'crazy'. Its like building a Jumbo jet, fly it once to your destination and then throw it away. In a sense, knot testers have a default mindset that you need to pull-it-till-it-breaks - and then you pop the cork from the champagne and celebrate.

I note that some knot testers will declare the MBS yield to be of low importance - and yet, paradoxically, the entire premise behind their tests is to pull-it-till it breaks. On the one hand - their youtube videos show knots being pulled until they yield - but on the other hand, they try to downplay the significance of their tests. I see this as a paradox. Why publish such videos in the first instance if the tester retrospectively tries to downplay the results? What is the ulimate point?

If a knot tester examined something other than the default mindset of 'pull-it-till-it-breaks' - it would be a revelation and history in the making.

I would like to see a two turn grapevine go up against a three turn, if the three turn breaks higher we'll have more to discuss ;-)

Indeed - but I would remind a would-be knot tester that you must use a 'control' and you must perform a sufficient number of tests to build a statistically valid data set. One (1) test is insufficient. Due to time and cost considerations, a reasonable number of tests is five (5). You also need to be very clear from the outset what the objective of the test is. You need to declare this stated objective in plain language.

 

[*useless info*]

Our loads in rigging run way beyond bodyweight and some get high impact drop too. We let loads run thru frictions to slow down sometimes etc. Going large but not too is the production sense on how money is made. This is a ruff and tumble biz, with literally everything on the line with knots in un-inspectable positions; if it ain't already flying thru air .
.
The fascination with knot strength here goes beyond just most 'macho' number; but rather we look to minimize all force multipliers chained against system as a mantra. Basically cuz don't know what the lead input will be when things get going so leave as much room as possible. Everything guesstimated in quick calcs, by a man hanging on synthetic lifeline runs 900degree muffler , passing 600 cutting teeth a second all around frail 1/2" rope holding self and cuts free large wood without injuring rope etc. at pro-duction speeds daily. Average chainsaw bite to emergency room is 110 stitches. We all know some that have gotten far less stitches; that just means there is some poor sucker out there making up for that slackard so we can maintain 110 please!!!!
.
Tho 'least important character'; grooming to strength has revealed much(like auto racing), and gives more ('Max') Headroom of quality/forgiveness. The proper architecture to lay rope in it's 'malleable' /form-able state inside and outside the knot , is just like forming metal to carry properly when hardened to solid. Same architecture rules apply, only just unload rope, not heat like metal to be able to form rope structure.

 

[moss]

I disagree completely.

The MBS yield point of a knot does not tell you anything meaningful UNLESS you are specifically investigating a geometric change or assessing if the knot remains jam resistant right up to the point of failure. And you must use a 'control' - otherwise, your tests are invalid. I am unclear if readers of this thread actually know what a scientific 'control' is?
I would remind readers that #1410 (Offset overhand bend) is an example where 'pull-it-till-it-breaks' tells you nothing meaningful.

There is no load that an individual climber can generate that will reach the MBS yield point of a knot.
A climber cannot even approach the MBS yield point of a simple overhand knot (#46 / #514) or a simple overhand loop/eye knot (#1046). These knots will maximally jam (rather than just initial threshold jamming) - and so for this reason, are generally not used in high loading situations.

I think the roping industry has some way to go to break old ways of thinking about knots - and this is understandable given the status quo of traditional knot testing (and knot book authors promoting the notion of 'strength').
I note that Elon Musk is a game changer - a big thinker. He has shaken up the rocket launch industry. The accepted paradigm is you build a rocket, use it once and then throw it away. Elon thinks this approach is 'crazy'. Its like building a Jumbo jet, fly it once to your destination and then throw it away. In a sense, knot testers have a default mindset that you need to pull-it-till-it-breaks - and then you pop the cork from the champagne and celebrate.

I note that some knot testers will declare the MBS yield to be of low importance - and yet, paradoxically, the entire premise behind their tests is to pull-it-till it breaks. On the one hand - their youtube videos show knots being pulled until they yield - but on the other hand, they try to downplay the significance of their tests. I see this as a paradox. Why publish such videos in the first instance if the tester retrospectively tries to downplay the results? What is the ulimate point?

If a knot tester examined something other than the default mindset of 'pull-it-till-it-breaks' - it would be a revelation and history in the making.


Indeed - but I would remind a would-be knot tester that you must use a 'control' and you must perform a sufficient number of tests to build a statistically valid data set. One (1) test is insufficient. Due to time and cost considerations, a reasonable number of tests is five (5). You also need to be very clear from the outset what the objective of the test is. You need to declare this stated objective in plain language.

I understand scientific methodology, I’m simply stating a hypothesis based on observed phenomenon. That’s how the scientific process begins.

You are overstating the irrelevance of break testing. We know that our body parts will break before these knots will. I’ll speak for myself, I like to know the actual and relative strengths of the knots I trust my life to. As you said yourself it is one characteristic among several that we use to decide on the appropriate use of a given knot.
-AJ

 

[DSMc]

... MBS yield testing is largely irrelevant and a meaningless exercise.
However, if MBS yield testing was done with a specific purpose in mind - for example to investigate the precise location from where fracture propagates - this would be meaningful...

Sorry, but this is such a load of crap. A statement based on the assumption that if you don't reach a system's MBS, it is somehow less relevant?

Virtually everything we do in this aerial-access industry is based on knowing and working within a safety zone. We do not work at the limits of our equipment. One can only postulate that the MBS of knots is irrelevant because the testing has already been done and patterns have been noted. Past testing cannot be relied upon, however, when new ropes are constantly coming to market.

Knowing where a knot fails or what strand of the fiber gives way first will change nothing for the field worker. It is only relevant if you are designing rope weaves or inventing new knots. Also, the assumption that because testing is done on strength, all other aspects and interactions are being ignored is ludicrous.

 

[agent_smith]

A statement based on the assumption that if you don't reach a system's MBS, it is somehow less relevant?

My statements are specifically addressing the default mindset of 'pull-it-till-it-breaks' - and the relevance of doing this. If you take a snapshot of all of the knot tests performed all around the world - they invariably all run the same theme; 'slow pull-till-it-breaks'. There appears to be no other way of conceptualizing how to test knots.

Virtually everything we do in this aerial-access industry is based on knowing and working within a safety zone.

Every roping industry states the same thing.
It is sufficient to state (and assume) that all hand tied knots in a modern synthetic rope will reduce the MBS of that rope by 50%. Regardless of knot choice - even the alleged 'worst' knot, 50% reduction factor covers them all.
As a thought experiment, I could happily use #1046 (Overhand loop knot / Overhand eye knot) as my default end-of-line fixed eye, and still meet this 50% reduction factor. Of course, all of my knots will jam - but for the purposes of this thought experiment, it is simply to point out that the simple and humble #1046 will meet all safety requirements.

Knowing where a knot fails or what strand of the fiber gives way first will change nothing for the field worker.

This points to the fundamental premise behind the entire crop of knot testers around the world. What exactly are they trying to prove? When they conduct yet another default mindset 'slow pull-it-till-it-breaks' test - what revelation has been uncovered?
We could save them much time and effort by simply declaring all knots to reduce the MBS yield of a rope by 50%. Even the alleged 'worst' knot still meets this 50% criterion.

My point - which you missed - is that if you are going to perform a default 'pull-it-till-it-breaks' knot test, you must have a clear and concise stated objected - a reason why.
Several funded research teams have attempted to pinpoint the precise location where fracture propagates from within a knot structure. It has been attempted on several occasions by different scientific teams. None have been able to pop the champagne cork.
So this is one reason for performing such a test - to try to advance our collective scientific knowledge in this area.
For the average roping industry worker - it doesn't mean much. It is pure theoretical research to advance our understanding of forces within a knot structure. And this type of research can pay dividends for rope manufacturers who have the ultimate goal of building and selling a better rope
The other reason for 'slow pulling-till-it-breaks' is to probe the effect of geometric changes within the knot structure. For example, the jury is still out on the effect of adding 3 rope diameters inside the nipping loop of a 'Bowline'. Tests could be designed to investigate this further.

I might also add that virtually all knot testers around the world appear to follow the same mindset of 'slow pull to failure'. They typically use a hydraulic ram of some sort which has a defined 'stroke' (travel) and cross-head speed (rate of pull).

Rarely do you see dynamic style testing of knots - where sudden injection of force is applied.
If you stop and think about it, dynamic load tests more closely mimic operational reality - in that if something went wrong while working at height, it usually results in a sudden injection of force into a system.
I have yet to witness a falling climber fall in slow motion - at the cross-head speed of a hydraulic ram. Or perhaps for this forum, an out-of-control falling piece of tree vegetation - falling at the minuscule speed of a hydraulic ram.

At least the committee behind EN892 (for rock climbing / mountaineering) got the basics right - although the 80kg limit for the test is coming under increased scrutiny (and that will shake up the rope manufacturing industry). The committe behind EN1891 also require a (smaller) drop test...

Within my lifetime, it is difficult to see any changes to the default paradigm behind knot testing. The status quo will prevail for some time to come. Although unlikely, some knot testers might have a lightbulb moment and begin to investigate something other than the 'slow pull-it-till-it-breaks' mindset. Worthy objectives include (but not limited to); jamming threshold, instability threshold, the effects of slack shaking and cyclic loading.

I once came across a famous philosophical phrase:
“All truth passes through three stages: First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as self-evident".

 

[moss]

Agent Smith it's worth noting the specific climbing style/orientation of mainstream rope and harness tree climbers. Everything is considered "work positioning" ie: no one is taking a fall. Dynamic testing is not as relevant to tree climbers as say rock/alpine or industrial climbers who build shock absorption into their systems whether through dynamic lines or shock absorbing lanyards. A "slow pull" is fine, we're interested (for life support gear) in static strength values more than multiplied dynamic loading. Certainly in rigging.... dynamic values are very important. In these discussions about knot testing it's best to be clear whether a person is talking about PPE or rigging scenarios.

 

[agent_smith]

A "slow pull" is fine, we're interested (for life support gear) in static strength values more than multiplied dynamic loading.

Moss- I m happy for you to be content with the default mindset of 'slow-pull-it-till-it-breaks' mindset.
I am also happy to make the distinction between the 3 forms of fall-protection systems:
1. Travel restraint
2. Positioning (or 'work positioning')
3. Fall-arrest.

It is patently obvious that positioning systems are default for tree canopy work. Same goes for ISO 22846 rope access work - which also uses 'positioning' as the default method of fall protection.
This is stating the obvious.

I think at this point, no matter what evidence is tendered to the contrary - there will be those individuals who will defend their right to a belief pattern (which is understandable). If you have held a lifelong belief pattern - and had no reason to ever question it - it will be emotionally and psychologically untenable to alter that belief pattern overnight. Telling people that the Earth was not at the center of the solar system would earn you a death sentence at one point in Earths history.

It is an interesting proposition to note that given that most technical work at height is done using positioning systems - with the mass of just one person - at what operational load could that person expect to subject his/her hand tied knots? If everything is 'positioning' - and the assumption is that no one is ever going to 'free-fall' - and that all knots (even the worst knot) reduces the MBS of the rope by 50% - what is the stated objective of a 'slow pull to failure test'?
How would a person using a positioning system reach the MBS yield point of a hand tied knot?
It is an interesting question.
Then again, if you take the view that a free-fall is within the realm of possibilities, does this alter the paradigm for the knot tester?

 

[Mowerr]

I know Rich will pull used hitch cords or used stuff for us I find interesting, sometimes he's been able to set up a harness a lot of us use and break the rope bridge sometimes the bridge was used or he'd be testing different stopper knots. Almost Everytime he breaks rope is for a reason.
I don't even think I've watched any other guys videos of break testing but his videos are great I think.

 

[Woodwork]

How would a person using a positioning system reach the MBS yield point of a hand tied knot?

I bet being in the Circle of Death on a big chairing tree would come close!

 

[climbstihl]

I bet being in the Circle of Death on a big chairing tree would come close!

Unless you are not part of that circle (both ends clipped to front ring) you probably would be be dead before any knot gives.

 

[moss]

Moss- I m happy for you to be content with the default mindset of 'slow-pull-it-till-it-breaks' mindset.

Not at all. I'm not the poster boy for break testing.

It is patently obvious that positioning systems are default for tree canopy work.

Nothing is patently obvious, I don't know how much you know or don't know about the details of rope and harness tree climbing.

I simply stated that I observed that the tightening of the coils in the double fisherman's knots in Richard's break test seemed to slow the process of reaching failure compared to other knots he tested. That's all. I find that very interesting.

The double fisherman's broke a fair amount higher than other "rope joining" knots that Richard tested, I find that interesting as well. If I was a cordage/knot scientist I might design some experiments to learn more.

What Richard does when he breaks things is not useless. Something useful can be observed and could lead to formal scientific inquiry if anyone feels so moved.
-AJ

 

[Chaplain242]

Agent Smith it's worth noting the specific climbing style/orientation of mainstream rope and harness tree climbers. Everything is considered "work positioning" ie: no one is taking a fall. Dynamic testing is not as relevant to tree climbers as say rock/alpine or industrial climbers who build shock absorption into their systems whether through dynamic lines or shock absorbing lanyards. A "slow pull" is fine, we're interested (for life support gear) in static strength values more than multiplied dynamic loading. Certainly in rigging.... dynamic values are very important. In these discussions about knot testing it's best to be clear whether a person is talking about PPE or rigging scenarios.

Agree, but I for one feel that restraint is an area worth studying for an arborist, but so is dynamic testing. I have spoken to witnesses of dynamic rope accidents and those scenarios can apply to treework as much as anything else.

To be honest as far as accidents go, I have seen more accidents to do with habitual/casual mistaken use of equipment ( ie no visual check before committing), false positive evaluation of condition of equipment (she will be right approach) than failure of new non-faulty ropes... and I don’t often see regular all encompassing discussions about those... these are discussed in review of stories shared if at all (many near misses and accidents are not discussed due to regulatory body consequences, even insurance implications in some industries - aircraft industry regulations actually don’t take a big stick approach to ensure the maximum safety level can be reached by hearing a large proportion of accident/near miss accounts...)

One look at Facebook groups blindly criticising the victim of a near miss or accident ensures that many stories aren’t shared and who knows (but God) how much valuable information isn’t taken into account regarding techniques/equipment....