Richard Mumford-yoyoman
Been here a while
- Location
- Atlanta GA
Knots for joining two ropes for life support
- Thread starter Phil
- Start date
Phil
Carpal tunnel level member
- Location
- Oak Lawn, IL
Thanks for putting this out there 
If strength were the #1 consideration, how would a bowline on a bight (on the end of each rope, around each other) rate? It seems like it's got to be a darn strong knot. I love the bowline knot, and with two loops to share the load, seems like this would be a winner. Fugly and bulky but I bet it would test very strong...
evo
Been here much more than a while
- Location
- My Island, WA
With a bowline the loop isn’t the part that fails. It’s the tight bend within the knot itself or just before the knot which ruptures. This is why a double fisherman’s is so strong, the bends are beyond the high friction area
Richard Mumford-yoyoman
Been here a while
- Location
- Atlanta GA
As strong as if you welded two pieces together. ;-)
*useless info*
Participating member
- Location
- usa
Seems to be like stiffer more delicate 'glass' fibers at critical loading to me in imagery.
Like feels the backpressure of the coming arcs and stretch losses as goes into friction arcs carry outside of knot some. Forces are higher outside of knot, and runs into impacts of change at full force just outside of knot and fails as 'glass' rods bend some and elasticity stops too so can't help mediate.
Like feels the backpressure of the coming arcs and stretch losses as goes into friction arcs carry outside of knot some. Forces are higher outside of knot, and runs into impacts of change at full force just outside of knot and fails as 'glass' rods bend some and elasticity stops too so can't help mediate.
Thanks for doing these tests and posting the results, Yoyoman! Very cool to see exactly how different knots fare under load.
So I guess the only advantage of putting the Bowline on a bight is somewhat more wear/chafing resistance when you have a double bight...?
I did some Googling around to see the comparative strengths of knots, and it seems that no one really tests the bowline on a bight ... just the bowline ... which leads me to believe that in ultimate breaking strength, there is no advantage to putting it on a bight.
Interesting stuff...wish I could rig a load cell to test this stuff at home. As an offshore fisherman, I've done some testing of knots in monofilament (only in thin stuff since my spring scale doesn't go above 50#) ... I've always thought the Australian Braid/Plait was superior to the Bimini Twist for putting a doubled line before the leader, but in the testing I've seen they're pretty close and in some tests the Bimini Twist tests higher...a lot of guys use a Spider Hitch instead of a Bimini or Australian Braid but I don't have much faith in that...not to go too far off-topic...
agent_smith
New member
- Location
- Townsville
The MBS yield point (ie Strength) of a knot is irrelevant.
There is no load that an individual climber can generate that will reach the MBS yield point of a knot. I'm assuming that the type of ropes used will be human rated - and intended for life critical applications (eg conforming to EN1891, etc).
The notional concept of 'strength' is all pervasive and is the default mindset of knot testers. There is little imagination beyond pull-it-till-it-breaks, and then declare (or assume) a 'winner' based solely on the criterion of the MBS yield achieved. The concept of knot 'efficiency' actually has nothing to do with MBS yield. The metrics for 'efficiency' are; footprint (ie volume/bulk), the amount of rope required to form the knot structure, resistance to jamming, utility, level of security and stability, and whether the knot is tiable-in-the-bight (TIB).
What matters most is that a selected knot is resistant to the following loading profiles:
1. Slack shaking
2. Cyclic loading
3. Flogging
4. Circumferential (hoop stress) loading (for eye knots).
If a particular knot can withstand these types of loading profiles, then it can be deemed to be 'inherently secure'.
Not many knots can withstand all four of these loading profiles - but some can.
For a deeper dive into knot theory, it may be of interest to view the technical papers at this website:
PACI
www.paci.com.au
'Bowlines' at #2 in the table
Offset overhand bend (#1410) is at #3 in the table
Zeppelin bend is at #4 in the table.
RyTheTreeGuy
Branched out member
- Location
- Canada
Am interested in the content however, it seems to be password protected
LordFarkwad
Branched out member
- Location
- Chatham Co.
RyTheTreeGuy
Branched out member
- Location
- Canada
Unsure if serious. But, in case you are...
Lol...I just quickly hit the link out of excitement and didnt read the bold print...blew my load before the foreplay
*useless info*
Participating member
- Location
- usa
The PACI is an incredible resource and effort. And quite a list of authors.
.
Agent_Smith and knudeKnoggin may be 2 of the best knot minds on planet.
.
i do think chasing strength has brought us many things in it's wake, but can be as real world as auto racing for development. Also to guide to keeping loading lower.
>>if not as 'strong' at same job; would look for higher side forces loading against rope not to task column, so system (rope, support, devices etc.) carries at higher tension for same job, more chance of fail of weakest link X; more potential damaging power release if fail.
-kc
.
Agent_Smith and knudeKnoggin may be 2 of the best knot minds on planet.
.
i do think chasing strength has brought us many things in it's wake, but can be as real world as auto racing for development. Also to guide to keeping loading lower.
>>if not as 'strong' at same job; would look for higher side forces loading against rope not to task column, so system (rope, support, devices etc.) carries at higher tension for same job, more chance of fail of weakest link X; more potential damaging power release if fail.
-kc
Last edited:
Those are interesting papers, thanks for posting them up!
timmysaint
New member
- Location
- Ontario
EDK.
Watched a re-traced figure 8 roll on a couple of brother's rapelling of Kerkesslin Falls a few years ago. My climbing partner stepped on the tail while it way rolling, with his crampon, which might have saved a life.. Here's more food for thought:
“They had been using a flat figure 8 backed up with overhands all the way down the route. [Kautz] tied the same knot, no doubt, but didn’t back it up, or it would not have come untied. A flat overhand is the preferred knot for tying two ropes together for rappelling, but the figure 8 looks more substantial so it gets used, too. But a flat figure 8 can walk and unwrap itself when loaded. If the tails are too short, it can walk right off the ends of the rope.”
https://rockandice.com/climbing-accidents/rappel-knot-fails-climber-falls-to-death-on-the-goat-wall/
EDK is easy to tie, and less likely to snag.
Watched a re-traced figure 8 roll on a couple of brother's rapelling of Kerkesslin Falls a few years ago. My climbing partner stepped on the tail while it way rolling, with his crampon, which might have saved a life.. Here's more food for thought:
“They had been using a flat figure 8 backed up with overhands all the way down the route. [Kautz] tied the same knot, no doubt, but didn’t back it up, or it would not have come untied. A flat overhand is the preferred knot for tying two ropes together for rappelling, but the figure 8 looks more substantial so it gets used, too. But a flat figure 8 can walk and unwrap itself when loaded. If the tails are too short, it can walk right off the ends of the rope.”
https://rockandice.com/climbing-accidents/rappel-knot-fails-climber-falls-to-death-on-the-goat-wall/
EDK is easy to tie, and less likely to snag.
moss
Been here much more than a while
- Location
- Carlisle, Massachusetts, U.S.
Watching the double fisherman's test I believe the reason it breaks so well is that the structure (coils) of the knots allows the tightening to continue well into the test. At some point there's no more to give and the cover then core breaks. The EDK was a strong example of an opposite principle, when a knot has a crossing part or firm choke point that occurs early in the loading cycle, it has nothing to give, the crossing part cuts the rope at lower load numbers. Zeppelin also showed this feature. Another way to look at the double fisherman's is that it has cordage "in reserve" in the coils with no dominant choke point, it keeps on tightening/stretching through the coils until it's a welded nut and finally breaks.
If this is true I'd predict that a triple fisherman's will break at even higher numbers. it has more to give before lock-up occurs.
Great work once again, thanks Richard.
-AJ
If this is true I'd predict that a triple fisherman's will break at even higher numbers. it has more to give before lock-up occurs.
Great work once again, thanks Richard.
-AJ
moss
Been here much more than a while
- Location
- Carlisle, Massachusetts, U.S.
Triple fisherman's is even easier to untie after "normal" use as a life support knot, the load is more dispersed through the additional coils.
-AJ
-AJ
agent_smith
New member
- Location
- Townsville
This is an example of a source of misinformation because it is unclear as to precisely which knot structure is being referred to. A lay person could misinterpret the meaning...
'Retraced F8' could mean either #1411 (Flemish bend / F8 bend) or, it could mean Offset #1411.
If #1411, it cannot capsize - because it is inherently secure (assuming the person actually tied it correctly).
If Offset #1411, then yes - it can capsize, particularly if unequal rope diameters are united - and the larger diameter rope is positioned underneath the thinner rope.
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.
Dan Lehman has advocated the use of small color coded 'tracer threads' being woven into various rope segments which act as visual 'markers'. Upon completion of the load test, the tracer threads could then be investigated to help pinpoint the point from where failure propagated.
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