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majid_sabet
Feb 21, 2008, 8:05 AM
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Last year during some rope training, I ran in to an interesting discovery while applying tensions on fig 8 knot and shortly after, I began purchasing some mechanical stuff to build a mini size electromechanical puller that I could synchronize to a digital camera and mini size camcorder while conducting pull test . Finally and after spending good amount of time on drilling, machining and assembling, the Sorbat made rig was ready to test its first victim, the fig 8 knot.
What was so special about the fig 8 knot that made to conduct this test?
During tensioning a fig 8 knot , I noticed that the free string of a fig 8 (where you tie a backup knot) creates an open loop during tensioning phase where one of the strings is not evenly compressed with the rest of the fig 8 bends, therefore, only portion of the fig 8 knot or one of the bend is taking the load . This could be caused by
Lack of string movements within the entire bends as tensions begins to build up.
I also noticed that most string movements are within the first bend (where the load is applied) and if the fig 8 was about to fail, the most logical place will be close or around the first bend in the direction of the load and not the other side where you tie in.
So, here are few pictures from the mini size puller. The string leading to backup knot has an opening loop that can be seen in several photos. Since this puller was not strong enough of to break the rope or to pull larger size ropes, I used a smaller size (3-5mm) cords instead. I marked the beginning of the rope movement with an arrow so you could track the cord movements in and around each bend. Of course more detail tests are needed to understand what is happening within the fig 8 knot during tensioning phase but for now, that is all I got to share with you guys.
The homemade electromechanical puller
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Tensioning a different size cord
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edit to add more images.
(This post was edited by majid_sabet on Feb 22, 2008, 7:28 AM)
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ozoneclimber
Feb 21, 2008, 9:32 AM
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Very interesting, I've noticed that that happens when I take a big lead fall or sometimes in some of my gear while I'm scrubbing a route.
I'm curious as to how much it compromises the strength of the knot, if at all, and if so, could there be a better knot. Double Bowline, etc...
Definitely curious...
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Adk
Feb 21, 2008, 11:51 AM
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Interesting Majid but.....no arrows????!!!!!!!!
I take it that it is always that same strand of rope in proximity to the knot? I believe I have seen thing in the fig 8 in falls as well.
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corson
Feb 21, 2008, 1:00 PM
Post #4 of 32
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Registered: Oct 16, 2005
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majid_sabet wrote: Last year during some rope training, I ran in to an interesting discovery while applying tensions on fig 8 knot and shortly after, I began purchasing some mechanical stuff to build a mini size electromechanical puller that I could synchronize to a digital camera and mini size camcorder while conducting pull test . Finally and after spending good amount of time on drilling, machining and assembling, the Sorbat made rig was ready to test its first victim, the fig 8 knot. What was so special about the fig 8 knot that made to conduct this test? During tensioning a fig 8 knot , I noticed that the free string of a fig 8 (where you tie a backup knot) creates an open loop during tensioning phase where one of the strings is not evenly compressed with the rest of the fig 8 bends, therefore, only portion of the fig 8 knot or one of the bend is taking the load . This could be caused by Lack of string movements within the entire bends as tensions begins to build up. I also noticed that most string movements are within the first bend (where the load is applied) and if the fig 8 was about to fail, the most logical place will be close or around the first bend in the direction of the load and not the other side where you tie in. So, here are few pictures from the mini size puller. The string leading to backup knot has an opening loop that can be seen in several photos. Since this puller was not strong enough of to break the rope or to pull larger size ropes, I used a smaller size (3-5mm) cords instead. I marked the beginning of the rope movement with an arrow so you could track the cord movements in and around each bend. Off course more detail tests are needed to understand what is happening within the fig 8 knot during tensioning phase but for now, that is all I got to share with you guys. The homemade electromechanical puller [URL=http://imageshack.us][IMG]http://img509.imageshack.us/img509/6493/picture001fy3.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img339.imageshack.us/img339/6335/picture003ti5.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img83.imageshack.us/img83/6001/picture004fw5.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img292.imageshack.us/img292/8805/picture007zu6.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img514.imageshack.us/img514/2088/picture019jq9.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img406.imageshack.us/img406/848/picture020fq5.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img406.imageshack.us/img406/9835/picture021sp3.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img252.imageshack.us/img252/7865/picture022qc6.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img252.imageshack.us/img252/3743/picture023ej6.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img512.imageshack.us/img512/8691/picture026zj3.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img252.imageshack.us/img252/9523/picture027lt8.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img512.imageshack.us/img512/1962/picture028th2.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img179.imageshack.us/img179/2163/picture029fn0.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img212.imageshack.us/img212/7826/picture030bv2.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img206.imageshack.us/img206/639/picture032xa9.jpg[/IMG] Tensioning a different size cord [URL=http://imageshack.us][IMG]http://img151.imageshack.us/img151/1332/picture101ss4.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img208.imageshack.us/img208/7685/picture103la0.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img208.imageshack.us/img208/7534/picture105tx1.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img403.imageshack.us/img403/8559/picture107cz5.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img208.imageshack.us/img208/3511/picture103pb5.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img177.imageshack.us/img177/5480/picture096sg2.jpg[/IMG] [URL=http://imageshack.us][IMG]http://img176.imageshack.us/img176/1319/picture111ww1.jpg[/IMG][/URL edit to add more images
Dude,you really need to get laid!!!!!!!!!
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reg
Feb 21, 2008, 1:57 PM
Post #5 of 32
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corson wrote: majid_sabet wrote: Last year during some rope training, I ran in to an interesting discovery.......... Dude,you really need to get laid!!!!!!!!!
 - no pic's with arrows - plz!
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nainsin
Feb 21, 2008, 2:13 PM
Post #6 of 32
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Hi, Majid could u do the same test, but with the fig 8 tied with the follow thru laying on the inside of the first 8 thanx
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easton
Feb 21, 2008, 3:20 PM
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nainsin wrote: Hi, Majid could u do the same test, but with the fig 8 tied with the follow thru laying on the inside of the first 8 thanx
I agree, I think. Are these knots dressed properly before you start pulling? The pink rope does not appear to be, and it is hard to tell from the pics of the other rope.
I have fallen on, and even used one to pull stumps out of my yard and cars out of snow and never had this happen with an 8.
On a side note, I even got the 8 to untie after pulling the car out of snow the other day.
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patto
Feb 21, 2008, 3:24 PM
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Great work! 
However all this simply suggest is that the final rethread in unloaded and superfluous. For this reason a backup is even 'extra' superfluous and unecessary. I never bother with a backup for a figure 8.
In terms of function the figure eight is not an elegant knot. That is it is topologically inefficient and has superfluous loops. In comparison a clove-hitch, fishermans and bowline are much more efficient in their use of knot topology.
However topologically efficiency isn't a particularly desired charactaristic in climing. What is more important it strength efficiency and ease of tying, inspecting and loosening. A figure 8 excells at all of these except knot loosening.
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WVUCLMBR
Feb 21, 2008, 3:53 PM
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Pulling car out of snow? Looks like I finnaly found a use for my new Petzl rope......
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potreroed
Feb 21, 2008, 5:10 PM
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The last pass through on a figure 8 is redundant--all the work is done by the first loop through.
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majid_sabet
Feb 22, 2008, 7:30 AM
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nainsin wrote: Hi, Majid could u do the same test, but with the fig 8 tied with the follow thru laying on the inside of the first 8 thanx
You mean two cords attached with fig 8 then pull from end to end?
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nainsin
Feb 22, 2008, 11:53 AM
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no the same knot that is the fig 8 on the bight , but lay the follow thru on the inside of the first (starting) fig 8, this way the first fig 8 which tightens tightens down on the second inner 8 , thanx
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basilisk
Mar 1, 2008, 5:55 AM
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patto wrote: Great work! However all this simply suggest is that the final rethread in unloaded and superfluous. For this reason a backup is even 'extra' superfluous and unecessary. I never bother with a backup for a figure 8.
This is one of the reasons the AMGA no longer requires the backup knot. The Fig 8 is inherently redundant.
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trenchdigger
Mar 10, 2008, 3:11 PM
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nainsin wrote: no the same knot that is the fig 8 on the bight , but lay the follow thru on the inside of the first (starting) fig 8, this way the first fig 8 which tightens tightens down on the second inner 8 , thanx
I've heard some claim that the eight tied "backwards" with the loaded strand to the outside is weaker.
These guys claim otherwise: http://onrope1.com/Myth6.htm
Som valid test data would be interesting, though I am doubtful that Major Sorbet could provide any valid data.
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robdotcalm
Mar 10, 2008, 3:33 PM
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basilisk wrote: patto wrote: Great work! However all this simply suggest is that the final rethread in unloaded and superfluous. For this reason a backup is even 'extra' superfluous and unecessary. I never bother with a backup for a figure 8. This is one of the reasons the AMGA no longer requires the backup knot. The Fig 8 is inherently redundant.
The reason for the backup is to make sure there's enough tail after tying the fig. 8. It's a procedure to make sure that you don't overlook having a long enough tail.
r.c
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Jbitz
Mar 10, 2008, 4:22 PM
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Interesting Majid. This makes me curious about how the double bowline would behave with and without a Yosemite finish.
(This post was edited by Jbitz on Mar 10, 2008, 8:28 PM)
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trenchdigger
Mar 10, 2008, 7:18 PM
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Jbitz wrote: Interesting Majid. This makes me curious about the double bowline with a Yosemite finish would behave with or without the double fisherman backup knot. [image]http://www.rockandpaddle.com/l_doublebowline.gif[/image]
The reason for a backup knot with the bowline is not for strength on a single pull, but for security of the knot in general use. The bowline/double bowline more easily unties itself during use and therefore requires a backup knot. For knots that do not require a backup, a hand-width of tail is the most commonly accepted minimum tail that I've heard.
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majid_sabet
Mar 10, 2008, 7:42 PM
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trenchdigger wrote: nainsin wrote: no the same knot that is the fig 8 on the bight , but lay the follow thru on the inside of the first (starting) fig 8, this way the first fig 8 which tightens tightens down on the second inner 8 , thanx I've heard some claim that the eight tied "backwards" with the loaded strand to the outside is weaker. These guys claim otherwise: http://onrope1.com/Myth6.htm Som valid test data would be interesting, though I am doubtful that Major Sorbet could provide any valid data.
Looking at some of the training images that these onrope guys had published in their web site, I think they need to get some serious training themselves and I would not count of their expert opinion.
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petsfed
Mar 10, 2008, 8:37 PM
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Majid, I see what you're trying to illustrate, but the only time I've found that to happen is when I improperly dress my figure 8 (which is quite visible on your first photo of the second rope). Given that the figure-8 is the knot I use to connect my rope to the anchor for my slackline tensioning system, I'd like to think that the knot sees high enough loads for that to be an issue.
Compare
to
and you'll see what I mean.
Given all of that, you're right in pointing out that most of the figure-8 and certainly the safety knot are largely superfluous and the only way the safety knot adds additional strength to a figure-8 is when it is cinched down next to the main knot so as to minimize the amount of creep that can occur under load.
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knudenoggin
Mar 11, 2008, 4:08 PM
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In reply to: I've heard some claim that the eight tied "backwards" with the loaded strands to the outside is weaker. These guys claim otherwise: http://onrope1.com/Myth6.htm
--to wit:
THAT should give a good clue that they lack such!
For they show the incredibly stupid *flat* image of a Fig.8, where the
parallel strand never cross each other (but only jointly cross themselves
at points); this is a form of knot that anyone should be able to quickly see
is unsustainable in rope (it can partly obtain in tape)!! And, finally, in
their current remarks, they recognize this. Which one should hope would've
moved them to look further, and wise up re knot images. --but not yet
(their On Knots Tech Tips section has for a lonnng time been "Cpming soon" [sic]).
My surmise is that their counter-assertion re the "10%" difference
is directed at the e-book Life on a Line by Dave Merchant, which says:
In reply to: Important Note on Direction ... The problem is that the Figure-8
can be tied backwoards, resulting a in a loss of up to 10% of the strength.
Surprisingly few people kno this, so you can guarantee that at least 50%
of the knots you will encounter are incorrect. Look carefully at the picture
above ...
LoaL goes on to say
In reply to: ... though in tests it can be difficult to prove this reliably !?
... --if you get a jammed knot with one very tight loop and one protuding section [i.e., what Majid remarks at] ,
you can bet that it was tied the wrong way round.
Which last remark isn't fully cognizant of the "Perfect Form" shown above
by Lehman; there, what one gets with a knot not well set (by pulling
on the end hard) is a laterally bulging knot--the heavily loaded part
compressing against a too-loosely (un)set parallel strand. Lyon Equipment
shows and tested this Perfect form by loading each end; they found no
difference in result, but I'll guess that they didn't set it so deliberately as
I specify above (they simply applied a load uniformly to all ends at once).
Interestingly, LoaL shows the Perfect Form used for all of the trio
Fig.8 bend (rope-2-rope), Directional Fig.8, & Bunny Ears. In these cases,
they show the end loaded that takes the inner curve (as Majid shows, contary
Lehman's loading). .:. --short attention span?! 
So,
petsfed wrote: Majid, I see what you're trying to illustrate, but the only time I've found that to happen is when I improperly dress my figure 8 (which is quite visible on your first photo of the second rope).
Note that torsion seems to make the legs of the EYE take the LoaL form,
which can be seen e.g. in Outdoor Knots cover photo!
(And it might be a more easily untied version.)
*kN*
(This post was edited by knudenoggin on Mar 12, 2008, 1:57 AM)
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Dry_Hands
Mar 18, 2008, 2:12 AM
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FAIL
That knot looks horrible. A sloppy knot will yield poor results. Hand tighten the knot and this will not happen. The knot will behave fine.
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I fixed it. I should proofread it before I hit the post reply button. Oh well, the information you posted is still a good thing to point out. 
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