Enlengthening SpanSets more longerer

derekleffew

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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.
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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.
 

RonaldBeal

Well-Known Member
Refraining for one week.
Ack! Ack! Gac!
 

Amiers

Renting to Corporate One Fixture at a Time.
I love a good riddle this early in the year.
 

What Rigger?

I'm so fly....I Neverland.
I love this one. Send it!
 

derekleffew

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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.
 

What Rigger?

I'm so fly....I Neverland.
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

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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!
 

JonCarter

Well-Known Member
(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?
 

derekleffew

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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.
 

JonCarter

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

StradivariusBone

Custom Title
Fight Leukemia
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?
 

Crisp image

Well-Known Member
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.
 

StradivariusBone

Custom Title
Fight Leukemia
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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