/ "Reversed" fig-8 knot strength?

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999thAndy on 15 Jan 2014
An ordinary fig 8 knot has a breaking strength of ~80% of the rope strength.
http://www.bethandevans.com/pdf/8_strength.pdf

Does anyone know what this would change to if instead of re-threading the fig 8 starting at the bottom (nearest to the climber) the fig 8 was re-threaded from the top (nearest the belayer)?

I've done a search but can't see any data/results.

Cheers

Andy
crayefish - on 15 Jan 2014
In reply to 999thAndy:

That would just be the Flemish Bend described in the pdf no?
999thAndy on 15 Jan 2014
In reply to crayefish:

The Flemish bend is shown joining 2 ropes, not making a loop which affects the directions of forces in the knot.
crayefish - on 15 Jan 2014
In reply to 999thAndy:

Yep. But if the two ends (of different ropes) were joined in a loop as if it was all one rope and then loaded from two opposing directions within the loop, you'd be in that same scenario I think...

If it was just to be loaded in the same way as the fig 8 when tying into a harness, I don't see why you'd use the knot over a normal fig 8. I'd expect that fact that the loading is bending the knot over would affect its strength probably.

What sort of loading scenario are you thinking of?
999thAndy on 15 Jan 2014
In reply to crayefish:

Just thinking of ways to keep the dead end of the rope pointing at the climber (to keep it out of the way when clipping)
crayefish - on 15 Jan 2014
In reply to 999thAndy:

Turn your fisherman's stopper knot into a larger version with more turns? (I am sure there is a more technical way of saying that! lol) Or use a bowline of course.

I'd be wary about messing around with the fig 8 tie in knot personally.
climbwhenready - on 15 Jan 2014
In reply to 999thAndy:

So creating a 180 degree kink where the rethreading begins? Can't be good.
Dan Arkle - on 15 Jan 2014
In reply to 999thAndy:

A ring bend is a good knot for this. Its unusual but approved by the American Alpine Club IIRC

http://www.youtube.com/watch?v=Au8KiUS4RCc
origamib - on 15 Jan 2014
In reply to 999thAndy:

I can't imagine it would affect the strength much more then a standard figure 8, its still the same shape and same turns etc, in theory it's still putting strain on the rope in exactly the same places as a figure 8. unless of course you load it differently... Not sure what the advantage is exactly though if you're tying in! just tie off your slack better...
999thAndy on 15 Jan 2014
In reply to climbwhenready:

Yes, it creates a 180 deg kink, but not in the live rope.

I was interested to know if anyone knew of test results for it TBH, more out of idle curiosity than anything else.
999thAndy on 15 Jan 2014
In reply to origamib:

The load would be applied differently so I'd have thunk it would affect the strength ...
999thAndy on 15 Jan 2014
In reply to Dan Arkle:

Not as strong as a fig 8 (says google)
Joonsy - on 15 Jan 2014
In reply to 999thAndy:

having read that link and if i understand you correctly i would think tying 'reversed' as you suggest would be a very weak knot, my guess is about equivalent to an overhand knot, far weaker than a rethreaded 8 tied normally. I presume you mean when the climber ties in a rethreaded 8 to harness your suggestion is starting the rethreading from belayer end of rope not the part of rope that goes through the harness. Tying as you suggest when loaded the knot would have the same characteristics and look similar to an overhand knot, reading that link it is the severe bend you put on the rope that makes knots weaker, and your suggestion has put a very severe bend in the knot when loaded just like an overhand knot, a normal rethreaded 8 does not put such a severe bend in the knot, and regarding your comment of finished loose end coming towards climber instead of away well the loose end does not take any load, it is the loaded ends that are important as to the strenght of knot. I have looked at that video in that link showing ring bend and once again it has excactly the same features of an overhand knot when loaded, if he had tied a normal rethreaded water knot instead it would be much stronger, the finished end would be going away from climber but that really doesnt matter at all, if you really want the finished loose end to go towards the climber then a bowline does that.
stewieatb on 15 Jan 2014
In reply to 999thAndy:

> Yes, it creates a 180 deg kink, but not in the live rope.

The 180* kink is inside the harness loop - so it is on the live rope. It will massively decrease the strength of the loop.
Joonsy - on 15 Jan 2014
In reply to stewieatb:

absolutely, to purposefully weaken a knot for no need is madness.
999thAndy on 15 Jan 2014
In reply to stewieatb:

From the link above

Rejected: Knots Break Because of Severe Curves Inside the Knot
Day commented that “It is sometimes asserted that the breaking strength of a knot
depends on the radius of the sharpest curve within the knot.” (15) It may also be inferred that
the Alpine Club report would support the idea that a knot breaks at a severe curve inside the
knot. And Ashley observed that “One of the ‘laws’ quoted in dictionary and encyclopedia
knot discussions … is that ‘the strength of a knot depends on the ease of its curves’ ” (30).
Ashley’s experiment with the Bowline Bend dramatically refutes the idea that severe curves inside a knot weaken it. Except in knots of the core-and-wrap construction, curves well inside a knot do not directly affect either the strength of the knot or the place where they break. For
example, a Bowline does not break at the severe curve where the arms of the hitch cross. This is because the load that falls on the gentle curve at the entry point is virtually 100%, while the load at the hitch is considerably less than that.
999thAndy on 15 Jan 2014
In reply to Joonsy and the thread:

I'm not proposing to climb on such a knot, nor suggesting anyone else does. I'd just like to know if such a knot has been tested, and if it has, what were the results.

Anyone?
stewieatb on 15 Jan 2014
In reply to 999thAndy:

The bend is in the *loop* not in the *knot*. Also from you link above, "It appears to be true that a rope is weakest just outside the entrance to a knot." That is exactly where your proposed knot would create a severe kink.

When loaded, the effect of the two strands of rope leaving the belayer's end of the figure-8 being pulled in massively different directions is that the knot will deform, decreasing its effective strength. It's very similar to the load placed on a figure-8 by using it as an abseil knot to join two ropes - something we don't do any more, because the knot tends to invert and slip when this is done.
stewieatb on 15 Jan 2014
In reply to 999thAndy:

> I'm not proposing to climb on such a knot, nor suggesting anyone else does. I'd just like to know if such a knot has been tested, and if it has, what were the results.

> Anyone?

It has not been tested because it's blindingly obvious to anyone who understands knots that it's a poor idea.
martinph78 on 15 Jan 2014
In reply to 999thAndy:

> Just thinking of ways to keep the dead end of the rope pointing at the climber (to keep it out of the way when clipping)

I don't understand this. How long is your dead end?
999thAndy on 15 Jan 2014
In reply to stewieatb:

So from your evidently extensive knowledge of knot theory, please could you tell me what the strength of the knot is, and how you arrived at your figure.

Thanks in advance

Andy
Joonsy - on 15 Jan 2014
In reply to 999thAndy:

tie the knot as you suggest and in a seperate piece of rope also tie a normal overhand knot as you would when joining two lengths of rope together, weight them and examine both and you will see they have the same characteristics, the severe bend on loaded ends is causing the weakness and this bend is actualy trying to force the knot to open hence the concern as to the knot rolling, the overhand is known to be about 50% weak so i would think your suggestion would be very similar because tying as you suggest the knot behaves just like an overhand, not good.
stewieatb on 15 Jan 2014
In reply to 999thAndy:

20%, by pulling it out of my arse.
andrewmcleod - on 15 Jan 2014
In reply to stewieatb:

> 20%, by pulling it out of my arse.

You may want an offset knot, such as an offset overhand/Euro Death Knot, to avoid catching on any edges as it is removed.
Andy Chubb - on 15 Jan 2014
In reply to 999thAndy:

If I understand your post of 14.51 correctly then I think the answer is to use the figure of 8 'with Yosemite finish'. This involves tucking the dead end back through the knot so it points towards the climber. I use it all the time.
Instructions via this link
http://blog.alpineinstitute.com/2008/11/figure-eight-follow-through.html

Hope that helps

LizS on 15 Jan 2014
In reply to Joonsy:

Also just tried tying a fig8 "reversed", put a load of stress on it and it's trying to capsize itself so agreed, not good.
David Coley - on 15 Jan 2014
In reply to 999thAndy:

As my second experiment of the night, I tied a reversed fig 8 at the wall tonight and bounced on it a few times. It didn't fail. However, the falls were very low impact and the thing looked like it was going to capsize. I know this isn't a real pull test, but it didn't look good. Which is a shame, because it is a very nice looking knot - before it is loaded.

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