Author Topic: Redundant Sling Join  (Read 488 times)

Moss

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Redundant Sling Join
« on: June 17, 2019, 03:02:46 AM »
Hello,

I believe I have discovered an efficient way to join two slings or loops of cord so that the failure of any one of the four strands joined will not compromise the join (I say "join" because I don't know what to call it).

I needed this kind of join for rock climbing, trying to avoid using carabiners.  The girth hitch or the climbers hitch would not do because they are not redundant.  Obviously, there are many bends I could use on a bight, but I wasn't satisfied with their bulkiness and appearance and efficient use of cord.

I'm not sure how to assess the structure for redundancy or if there is a more efficient way to join slings redundantly.  It is reminiscent of a bowline on a bight or a dogshank.  I'll attach a low resolution picture and a link to a crappy video ;D.  Thanks for your input! 

https://youtu.be/q9DYhEKy0VU

agent_smith

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Re: Redundant Sling Join
« Reply #1 on: June 17, 2019, 04:15:47 PM »
Thanks for posting this sling 'joining problem' Moss.

I have to comment that it is pointless to try to create what you describe as a 'redundant sling join'.

Do you realize that if any single 'leg' of the sling either left or right of the central join is cut or breaks - this would trigger total failure of the entire sling assembly.

I am assuming that each end termination of the sling will be united and interconnected to a carabiner.

To improve safety, you would need to tie an 'isolation knot' at each end termination of the sling system. This will isolate each leg of the sling, left and right of the join.
However, even with an 'isolation knot' - each eye created by the isolation knot is also vulnerable to failure. Meaning that if one of the 'eyes' fails - the entire sling system still fails.

The only truly 'redundant' method is to have two (2) entirely separate 'slings' - so that if one sling fails, the other survives intact.
I refer to this as 'no single point of failure'.

Moss

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Re: Redundant Sling Join
« Reply #2 on: June 17, 2019, 05:13:52 PM »
Agent Smith,

You are right, I did not describe the problem completely.

What I do at the other ends of the slings is tie them together into one overhand loop (creating two loops).  In other words, I gather the two end bights and tie an overhand knot.  This is referred to as a master point in climbing.  So the problem really is at the join.

I should have clarified that from the beginning.  Thanks for correcting me.  I will post a picture when I get a chance, my nomenclature is a little shoddy.
« Last Edit: June 17, 2019, 05:19:50 PM by Moss »

Moss

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Re: Redundant Sling Join
« Reply #3 on: June 17, 2019, 06:37:11 PM »
Here is a picture of the problem:

Dan_Lehman

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Re: Redundant Sling Join
« Reply #4 on: June 17, 2019, 11:38:23 PM »
Thanks for this!  --which I think is something I've not
previously fiddled (but I could be forgetting), and which
is a nice structure to keep in mind.  I'd like to see how
it fares with webbing.   :)

The redundancy aspect is, as Agent_Smith observes,
not something all so likely ever making a difference.

--dl*
====

agent_smith

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Re: Redundant Sling Join
« Reply #5 on: June 18, 2019, 04:10:01 AM »
Moss, something else that you may wish to consider is that you can unite the 2 rope slings by tying an end-to-end joining knot with bights.
That is, you tie the knot in the same way as normal - but with bights.

I have done this on many occasions for a number of end-to-end joining knots eg:
[ ] Zeppelin bend tied with bights
[ ] #1053 derived Butterfly bend tied with bights
[ ] #1431 Sheet bend secured with a 'Scotts lock' (in fact, a Scotts lock also secures the regular #1431 Sheet bend).

The only disadvantage with tying a knot with bights is the amount of rope consumed (it is therefore less efficient). But, if you have ample length of cord/rope to work with, it is an effective method.

Quote
In other words, I gather the two end bights and tie an overhand knot.  This is referred to as a master point in climbing.
I prefer the term 'load focal point' - which is a more accurate term.

I would again point out that when you tie the 2 slings ends (terminations) together to form a 'double eye', this actually isolates each leg of the sling (one leg is isolated from the other leg) - provided of course that the end-to-end joining knot is secure.
It seems a pointless exercise to try to engineer the end-to-end joining knot into having further redundancy... Do you realize this?
« Last Edit: June 18, 2019, 04:14:57 AM by agent_smith »

Moss

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Re: Redundant Sling Join
« Reply #6 on: June 18, 2019, 01:47:31 PM »
Agent Smith,

I do understand how the legs are isolated by the overhand knot at the load focal point. 

Consider the following: imagine my two slings are joined with a girth hitch, then the length of the two slings is draped around a boulder and the ends are joined into a load focal point with an overhand (as described and illustrated earlier).  Now, if one leg of either of the slings is cut, the girth hitch will slip and the whole system fails.  This is the issue I'm dealing with.  I hope that makes sense, I will attach a picture of the failing system.

The first picture is of the failing system, the second (with my join or with any other bend made with bights as you mentioned) will presumably not fail.
« Last Edit: June 18, 2019, 01:49:30 PM by Moss »

Moss

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Re: Redundant Sling Join
« Reply #7 on: June 18, 2019, 02:18:57 PM »
Here is a more elaborate diagram with a real plastic boulder.  I hope it is legible.

Of course, Agent Smith's solution may be more practical overall, especially to the average user.  Still, there are some situations where one must glean every inch of extension without sacrificing redundancy.

agent_smith

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Re: Redundant Sling Join
« Reply #8 on: June 18, 2019, 03:09:47 PM »
Quote
Consider the following: imagine my two slings are joined with a girth hitch
A 'Girth hitch' does not qualify as a secure end-to-end joining knot (obviously).
Not sure why you felt the need to use it as an example? Using a girth hitch would put you in the running for a 'Darwin award' (if no single point of failure was a crucial objective).

Quote
Of course, Agent Smith's solution may be more practical overall, especially to the average user.  Still, there are some situations where one must glean every inch of extension without sacrificing redundancy.

Forming an end-to-end rope join by tying with bights is indeed a practical solution.
As I stated, the drawback with this approach is the amount of rope consumed to form the join.

If you really wanted to maximize the overall length of your rope 'sling' - you should untie all of the knots so there are no 'slings' to begin with. Then join both lengths of cord with a Zeppelin bend, to make one long length.
Next, form a round sling by using another Zeppelin bend.
Pass the entire round sling around the anchor (eg tree or boulder) and then unite the 2 end terminations with a simple overhand knot of perhaps an F8. This isolates both legs of the sling.
Job done.

I might add that my approach as described solves the problem of uniting the 2 round slings - because now there are no round slings to unite! The 'problem' has been engineered out of the system. I like Zeppelin bends because they consume minimal rope, are totally jam resistant and secure and stable. Obviously, you need to be proficient at tying a Zeppelin bend :)
« Last Edit: June 18, 2019, 03:12:03 PM by agent_smith »