Double loop knot recommendations....

[Chad]

I've been unable to find a suitable knot for a (rock climbing) lanyard that I'm making.  I need a double loop knot but each loop needs to hold weight if the other loop were to get cut.  All of the double loop knots I've seen (double loop figure eight, double loop bowline, etc.) do not meet this criteria.  Any recommendations would be greatly appreciated. 

Also, please let me know if I didn't explain this well enough 

Thanks.


Chad

[SS369]

Hello Chad and welcome.

I am certain that amongst us we can give you some ideas with which to experiment.
I feel we need as much info/pictures to assist your request.

Climbing is a fun and potentially dangerous sport and any advice you get should be scrupulously tested by you. Preferably with the aid of others and the use of appropriate "dummy weights".

That being said, I wonder if your needs can be best met by searching for a pre-made harness that is sewn and tested by a climbing equipment manufacturer.

If you would please give a full list of the knots you are disqualifying, we can go with suggestions from there.

SS

[Chad]

Thanks for your reply and concern SS.  I assure you that I don't take my safety for granted, 15 years of rock climbing and no accidents (knock on wood).

Here is what I have used in the past.  The single loop goes around a (sewn) belay loop on the harness.  The problem with this set-up is the lack of redundancy with the single loop I've tied into the lanyard.  I'd like to remake a similar lanyard but with two loops that fit the aforementioned criteria. 


I don't knot the names of all of the double loop knots I've been looking at on-line but with all of them, one of the loops would come undone if the other loop were cut.  I see that a lot of member's refer to Ashley's book when referencing a knot.  I don't own this book but I'll try to get it from the library.


Chad

[SS369]

You are welcome Chad.

That gives us a little more to go on.

The knots that may be posed do require proper dressing and setting of course and may even be a tad bit difficult to tie around your tie in/belay loop.

Investigate the double loop butterfly knot and see if that is doable.
Just a first offer. And yes it will be a challenging tie.
Search function does work pretty well here. Just hang in there (pun intended).

SS

[SS369]

Quick thought to here:
You could tie two rethreaded 8's side by side. It will be bulkier there, but it is well known and you should be able to do that with your eyes closed.

[Chad]

Very true!  Tying whatever knot I decide on is going to be very tricky as I can't tie it on a bight (as most illustrations will show).  I have considered a side-by-side figure eight.  I was hoping to find an elegant, less bulky solution 

I tried the double loop alpine butterfly, no good.


Thanks again.


Chad

[knudeNoggin]

The single loop goes around a (sewn) belay loop on the harness. 
The problem with this set-up is the lack of redundancy with the single loop I've tied into the lanyard.

How is this "problem" an actual problem in practice?
(It apparently has not been in your 15 years; and must not be
troubling others enough such that some "better" knot has been
tried.)  For example, how redundant is your belay harness and
the rope you climb on --are you using a single rope or double?

I need a double loop knot but each loop needs to hold weight if the other loop were to get cut.  All of the double loop knots I've seen (double loop figure eight, double loop bowline, etc.) do not meet this criteria.

I believe that the Figure of 8 double loop that you name will
meet this criteria.  Why don't you?

I can't tie it on a bight ...

Why not?  The lanyard you show has short ends, and so
although you use them, you are getting pretty much the
same "on a bight" tying ease by for example pulling the
ends through the bight of a Figure-of-Eight bunny ears
instead of taking that bight around the bunny ear loops.
But there are knots that can be tied in the bight and which
meet your criterion of redundancy, but I am curious about
how the Fig.of.8 got eliminated, by whose bad word?

*knudeNoggin*

[knot4u]

I have no idea if the Karash Double Loop meets your criteria, but it's a nifty knot.  Also, I only know how to tie this not on a bight.
http://www.karashknot.com/

[Transminator]

Hi Chad

I think the Triple Crown (aka Three-Part Crown in the Bight) [ABOK #1097]
_{source: http://www.layhands.com/knots/Knots_DoubleLoops.htm (scroll down to knot #9)}
meets your criteria. As far as I can see, the loops don't "communicate" directly and therefore the second loop
should remain secure when the second one is cut or only one of the loops is under load.

The source above does not have any strength rate but I estimate it strong enough.
The wikipedia article is only a stub. It quotes the ABOK though: "It is secure and symmetrical, but can jam when tightened."

I have to say that I like this knot and perhaps it deserves more credit then it currently receives. It definitely needs
a more thorough evaluation and testing. I will perform some simple test by tying the knot and putting my weight on both loops
and then one loop at a time to see how it behaves and how bad it actually jams.

Has anyone used or done some test on this knot?
Chad: Do you think it is the knot for you?

I have no idea if the Karash Double Loop meets your criteria, but it's a nifty knot.  Also, I only know how to tie this not on a bight.
http://www.karashknot.com/

I also like the KDL, but the loops communicate as in other double loop knots of that kind.

[Sweeney]

I also thought about ABOK #1097 - removing one loop leaving 2 short stubs seems to work OK though the test I've just done was hardly scientific. I like this knot because of the splayed loops (which can be increased though it becomes more difficult to tie) eg to make part of a chatelaine for holding keys. ABOK # 1070 (Double Anglers Loop which is easier and quicker to tie) may also do the job depending on how much stress you want to place on the remaining loop and for how long.

Barry

[SS369]

"Tying whatever knot I decide on is going to be very tricky as I can't tie it on a bight (as most illustrations will show)."

I am unsure I understand this statement above.

In fact I only know how to tie the double loop butterfly on the bight. If this is truly and correctly the issue, I would be glad to help you figure that out.
And since you want a more "elegant solution" than two side by side figure 8's, I think that would satisfy. Just the requirement of two loops is going to bulk your chosen knot some in any case.

IMO, if there is tension on the rope, then there will be many 2 loop knots that will satisfactorily be secure.

Is it just the aesthetic aspect?

SS

[DerekSmith]

#1979 and the Triple Crown both suffer from a loop to loop translation via a wrap around the two SP's.  Although better than the Spanish, if one loop broke, then there is opportunity for the loose end to translate through.

From your image, it looks as if you are casting a simple overhand onto the bight to create the loop, so the loop is formed by two parallel overhands.  This is a servicable enough knot, but if I had done it, I think I would have opted for a two strand MWK, and here-in lies the basis for my offering.

But first, the solution you seek, should not only offer isolation between the loops, but also needs to be reasonably neat and not bulk up excessively.

To provide the necessary isolation, try simply tying a Bowline using the bight, passing the bight end through you belay loop (creating the twin loops), then tie a BWL effectively making twin BWL's in parallel.  This arrangement has the weakness of the BWL, in that the 'end' can feed back into a slack BWL knot and fail the whole assembly.  Fortunately, when tying the BWL on the bight, the end is in fact a small loop and the two lanyard lines can be passed through it to prevent it ever feeding out through a slack BWL.  What you then have created is two independent BWLs, such that if one loop breaks it has no impact on the other, yet because they are made together, each lanyard line is held by its partner.  A lanyard who's loop is broken is still attached via the parallel BWL to its neighbours loop.

This brings me to my final proposal using the MWK as mentioned before.

Middle the cord and tie a two strand MWK to create a single small loop.  Pass this through the belay loop (creating the twin loops) then loosen the MWK and tie the two SP's into the MWK to create a four strand MWK.  Finally, finish the lanyard ends to the 'binas.

Here you have it (one 'bina lanyard shown foreshortened)



You even get a small third loop for free for direct attachment or tools etc.

Derek

[roo]

I've been unable to find a suitable knot for a (rock climbing) lanyard that I'm making.  I need a double loop knot but each loop needs to hold weight if the other loop were to get cut.

I'm not going to rehash the comments and questions that have already been mentioned, but I would avoid the Karash Double Loop for the reasons discussed here:

http://igkt.net/sm/index.php?topic=1953.msg13611#msg13611

One double loop knot is mentioned at the bottom of this page:
http://notableknotindex.webs.com/midspan.html

A double splayed loop is shown here (use a stopper knot on the free end):
http://notableknotindex.webs.com/dsplayedloop.gif

It starts out with a Butterfly Loop:
http://notableknotindex.webs.com/butterflyloop.html

One other option is to make a Butterfly Loop (or another loop of your choice) for the first anchor point, and then using the excess line from the loop, hitch to the second point with a Gnat Hitch.

[Transminator]

#1979 and the Triple Crown both suffer from a loop to loop translation via a wrap around the two SP's.  Although better than the Spanish, if one loop broke, then there is opportunity for the loose end to translate through.

In theory, yes, but does that actually hold true in real rope?
The tests I did so far indicate that the friction is so high that it will not actually happen but of course that needs to be clarified before
using it in any potentially lethal operation such as mountain climbing or rescue scenarios.

[DerekSmith]

In theory, yes, but does that actually hold true in real rope?
The tests I did so far indicate that the friction is so high that it will not actually happen but of course that needs to be clarified before
using it in any potentially lethal operation such as mountain climbing or rescue scenarios.

I have 'borrowed' Dave's image and coloured the weakness in blue.



I grant you that I am talking principle rather than practice.

BUT  the blue line shows that in principle there is very little holding it in place if one loop gets cut.  The key problem with practice is that the exact outcome of a physical test depends upon so many variables that you would be very hard pressed to identify them all, let alone test them.  Yes, in one rope with one tyer, the result might lock itself well and appear to be fully satisfactory.  But, cut the left loop and bias the load on the right loop onto its blue leg and ask yourself how high from the ground you would be prepared to hang, let alone fall, onto that right loop ?  Remember, if the left loop is cut, it effectively becomes an 'end' and the knot must take up a new geometry with the load now just on one loop.

Principle suggests that if it is relatively easy to translate rope from one loop to the other, then perhaps the knot is exposed to this potential weakness, and it is this very weakness that Chad is attempting to design himself away from.

Derek