# Enlengthening SpanSets more longerer



## derekleffew (Feb 1, 2022)

So I have lots of 3' and 6' polyester roundsling s, but I really need a couple of ~9' footers to wrap a certain piece. No problem, just "tie" them together end-to-end right? It's harder to explain than to demonstrate, but what one ends up with is basically a square knot. Just with no dead-ends.


Now someone told me I had to derate due to the square knot. Interwebs says effeciary of a square knot is ~45%. So I take my 5300 lb. Spanset, multiply it by 0.45 and get 2385 lb. Is that right? Does it matter if it's Gac-flex? I think it's actually stronger than a normal square knot, in that all four ends are being pulled equally. Yes/no?

Professionals please refrain for one week. Thank you.


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## RonaldBeal (Feb 1, 2022)

Refraining for one week.
Ack! Ack! Gac!


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## egilson1 (Feb 1, 2022)

Great Question!


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## MRW Lights (Feb 1, 2022)




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## Amiers (Feb 1, 2022)

I love a good riddle this early in the year.


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## What Rigger? (Feb 3, 2022)

I _love _this one. Send it!


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## JonCarter (Feb 3, 2022)

It'll work fine for your 2000 lb. load. (But I'll wait for a week.)


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## derekleffew (Feb 8, 2022)

derekleffew said:


> Professionals please refrain for one week. Thank you.


Thank you all for your restraint. Unfortunate that no non-professionals have expressed any interest in the topic. Consider the floodgates now open, to everyone.


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## MRW Lights (Feb 8, 2022)

You keep using that knot.... I do not think it holds what you think it holds...


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## What Rigger? (Feb 8, 2022)

Consult the manufacturing documents, and labels, of your particular roundslings. Proceed with caution, if you must, with off label use. 

(How's that for a start?)


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## egilson1 (Feb 8, 2022)

If only a polyester round sling behaved like a rope……but alas they do not. 

By choking the two round slings together you eliminate the ability of the individual fibers of the sling to equalize the load. This will eventually lead to one fiber overloading and failing, then the next in line will do the same, and so on and so forth until ultimate failure. This is the reason why there is a derating of strength for when the sling is choked around an object. 

The proper way to connect two round slings is by using a connector such as a screw pin anchor shackle. 

And again, great question!


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## JonCarter (Feb 8, 2022)

(Altho not a "professional" in any sense of the word I like to consider myself an RKI and as such have restrained.) Anyway, I agree with egilson1; the slings' load capacity will be diminished when they're bent sharply as shown. Isn't this also true of all ropes and cables, and isn't this one of the reasons for minimum sheave diameters and bend radii for thimbles based on rope diameter?


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## derekleffew (Feb 22, 2022)

Okay, some of you are suggesting I use rope rather than spansets. What kind of knot do you suggest I tie in the ropes to make them into roundslings? My splicing fids are all dull at the moment.


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## JonCarter (Feb 22, 2022)

Well, either sharpen your fids & make a decent long splice, or use some more rope and make several loops and only one square knot.


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## teqniqal (Jun 23, 2022)

Crosby® 253 Sling Saver Screw Pin Sling Shackles - The Crosby Group

Crosby's full catalog for the Crosby 253 Sling Saver Screw Pin Sling Shackles



www.thecrosbygroup.com




Use two to couple slings.


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## StradivariusBone (Jun 23, 2022)

derekleffew said:


> Okay, some of you are suggesting I use rope rather than spansets. What kind of knot do you suggest I tie in the ropes to make them into roundslings? My splicing fids are all dull at the moment.



Are the ropes different diameters?


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## derekleffew (Jun 23, 2022)

StradivariusBone said:


> Are the ropes different diameters?


I hope not! as it's all coming off the same spool. Actually, I was thinking of using some of the old purchase lines that got replaced a few years ago.


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## Crisp image (Jun 23, 2022)

derekleffew said:


> Okay, some of you are suggesting I use rope rather than spansets. What kind of knot do you suggest I tie in the ropes to make them into roundslings? My splicing fids are all dull at the moment.


I would use a triple fisherman's knot to join the 2 ends. This knot has the advantage of not reducing the load capacity of the rope. Now remember that the rule of thumb is diameter squared of the rope will give a WLL (kg) of the rope when it is is new and in perfect condition. This does not apply to kernmantle rope.
Have a great (safe) day
Regards
Geoff

Edit: added weight unit of kg.


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## StradivariusBone (Jun 23, 2022)

derekleffew said:


> I hope not! as it's all coming off the same spool. Actually, I was thinking of using some of the old purchase lines that got replaced a few years ago.



Nuts. I was hoping we'd have to bust out the ol sheetbend. Old purchase line does make good swings though.


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## Richard Green (Jul 10, 2022)

egilson1 said:


> If only a polyester round sling behaved like a rope……but alas they do not.


I must be missing something. Doesn't a roundsling and rope (ok, I assume we're just talking kernmantle ropes these days) behave EXACTLY the same way? That is to say....they both have an exterior shell providing abrasion relief for an inner core of independent fibers carrying the load that will in either case fail prematurely if subjected to uneven loading. Which is another way of saying both ropes and slings derate as soon as you bend them sharply, whether it's over an edge or tying a knot that unevenly stretches the fibers. I'm sure you're right....but I don't think I get what you're saying.


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## egilson1 (Jul 11, 2022)

It has to do with how the fibers move in each one and how much a bend would derate it by. In a rope when the fibers are woven together the movement of the individual fibers along the entire length of the rope are less pronounced. The weave makes the fibers work together locally, and so bending does not reduce the individual fiber strength as much. In a poly sling the fibers need to freely move along the entire "length" of the sling as they loop around to equalize the force amongst all fibers. So they are working together globally, but not locally. This means that a bend or knot will reduce the strength much more than the rope because you are halting the movement of the individual fibers.

I hope that makes sense.


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## Richard Green (Jul 11, 2022)

Huh. First - I somehow had never noticed that a standard static line was also woven - I guess since the ends generally are melted when you cut them I had been labouring under the delusion that the strands ran parallel to each other much like in a sling - which is why I specified a kernmantle rope rather than a traditional woven rope. But of course you're right - both types have a woven core. Learn something new every day. Second: following that, the explanation seems to make sense except that it would appear to explain the opposite condition: if the strands in a sling are independently moving as a single yarn, then as force is applied - let's say as a basket over a an I-beam takes weight - all the fibres should shift to equalize the forces applied. In a rope which is woven the weaving should reduce the ability of the fibres to move which would increase the disproportionate loading as a bend is introduced. As you point out, one is is working globally and the other locally - but local distribution of force is going to make failure under load occur earlier rather than later....right? Again, what am I missing? And thanks for the reply - I'm genuinely interested in understanding this better.


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