Synthetic rope question

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Originally Posted by FeatherWeightDriver

Apologies for the rant, but if you spend enough time hanging off gear that is saving your life you spend a lot of time thinking about how it works ;)

My other pet hate about SWLs is that the SWL is entirely without context.

Climbing gear (yes sorry here we go again) is rated for different loading configurations:

https://www.aulro.com/afvb/images/im...013/05/906.jpg

But if I load a recovery shackle at 45 degrees or 90 degrees (see below, assuming the pin can't pivot) when will it break? I'm betting well within the SWL, particularly at 90 degrees...

https://www.aulro.com/afvb/images/im...013/05/907.jpg

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ID bet you're wrong....

If you were talking about ally stuff like the climbing gear usually is Id back you but with the steel stuff, not so much.

You'll get deformation of the shackle onto the pin which if its done too tight will bind up the shackle warranting its replacement. Its a moot point at any rate because typically if you're recovering off of a bow shackle at more than 45 degrees off center you're most likely doing it wrong enough to be risking additional damage to the vehicle or other recovery equipement.

I'm always happy to be on the safe side of that line.

It keeps me from "doing it wrong" (as you said)... :)

Here's a shackle tested to failure with both pull force axes rotated by 90 degrees from the usual. It always amazes me how much (non brittle) metal gear stretches before it fails...

[ame="http://www.youtube.com/watch?v=3RrKiuzbuc8"]Super Slings Inc. 5/8" Shackle Break Test - YouTube[/ame]

what your facing off against with ally lifting gear is that all the strenght is in the outside where the hardening is, damage that or deform it and then your basically dealing with the playdough soft ally in the middle.

if you'd like a real world example of why you can trust bow shackles for some good angles lets try this.

Picture doing a 2 leg lift, its a 4t weight so you use a 4t shackle BUT due to lifting height clearance restrictions you need to do the lift running on the limit of slinging angles of 120 degrees. to pull that off you need to have 8T legs hanging from the shackle.

so theres 8T trying to deform the shackle.

As a side tip. If you EVER have a dogger or craney trying to explain that that is a perfectly safe way to conduct a lift walk off. The dimensions of the gear is matched, if you need to rig 8t straps you use an 8t shackle to avoid damage to the straps.


for your video

did you notice that they stated the MBS (which I'm assuming is the manufacturers stated value not a test value) and the test shackle beat out both the stated normal pull and side pull values on the graph at the end?

on the graph

can you spot when the shackle is going through its "plastic" stage? (more questions on that later if you can)

given that the shackle can reduce in diameter 10% before its a write off, where on the graph at the end (nearest 500lb or second) has that shackle reached the point where it (in theory) is deformed past that 10%.?

Yes I did notice the breaking load was give or take the "normal" load direction MBS, but was going to do some more homework to see why that was the case :angel:

Best I can come up with is that the strength across the gate is not too different to the strength across the curved section. As they load roughly evenly with a centre line load, there is also no torque to worry about.

I wonder if that is still true for the 90 degree load in the my earlier diagram? The torque must decrease the strength, but the only reference I can find to loading that way says subtract 50% of the limit load (whichever one you are working in). Source: http://www.dcl-usa.com/wp-content/up...kles_Part1.pdf

As for your other questions, as it has been nearly 20 years since I last "knew" that stuff I will need some more thinking time :(

start by researching torque to yield bolts.

think along the lines of that sinking "why'd the bolt just get easier to turn" feeling some people get just before they take the torque wrench off only to discover no radiating lines when there should be 3 or 6 or no marking when there should be an 8.8 or 10.9.

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Originally Posted by Blknight.aus

what your facing off against with ally lifting gear is that all the strenght is in the outside where the hardening is, damage that or deform it and then your basically dealing with the playdough soft ally in the middle.

if you'd like a real world example of why you can trust bow shackles for some good angles lets try this.

Picture doing a 2 leg lift, its a 4t weight so you use a 4t shackle BUT due to lifting height clearance restrictions you need to do the lift running on the limit of slinging angles of 120 degrees. to pull that off you need to have 8T legs hanging from the shackle.

so theres 8T trying to deform the shackle.

As a side tip. If you EVER have a dogger or craney trying to explain that that is a perfectly safe way to conduct a lift walk off. The dimensions of the gear is matched, if you need to rig 8t straps you use an 8t shackle to avoid damage to the straps.


for your video

did you notice that they stated the MBS (which I'm assuming is the manufacturers stated value not a test value) and the test shackle beat out both the stated normal pull and side pull values on the graph at the end?

on the graph

can you spot when the shackle is going through its "plastic" stage? (more questions on that later if you can)

given that the shackle can reduce in diameter 10% before its a write off, where on the graph at the end (nearest 500lb or second) has that shackle reached the point where it (in theory) is deformed past that 10%.?

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A shackle pin or body can wear up to 10% before condemning, but if there is an area that has waisted due to stretching you wouldn't worry about if was 10%, you would scrap it immediatley.
In the scenario above with the 8 tonne slings you would not use a shackle to connect the slings to to the crane hook, you would either use a manufactured sling with one piece round or oblong style "rings" which are usually connected to a larger crane hook ring. You certanly would not use a shackle on the crane hook with slings at any angle over 45 degrees. Shackles may be used at the other end of the slings as long as they were being loaded in the straight ahead line.
I was watching (on Austar) a while back a recovery of a 20ft container supposedly weighing around 20 tonne from a ditch on the side of the road, they used a 4 leg chain sling and because of the angle of the container one of the hooks couldn't be connected to the container pin holes on one corner. So they used a large shackle, looked to be 50/60mm in thickness in the pin hole and they fitted another shackle into the side of the "D" shackle body then hooked up the sling hook. These shackles were in the 20 tonne SWL range. The crane lifted the container and when it was about 10' off the ground the shackle that was jambed in the container pin hole, and being pulled sideways broke and the load fell to the ground and the mobile crane flipped over backwards, no one was injured. Another case of a load equal to the SWL of the shackle snapping well before its GBS because it was not designed to be used the way it was, Regards Frank.

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Originally Posted by Tank

A shackle pin or body can wear up to 10% before condemning, but if there is an area that has waisted due to stretching you wouldn't worry about if was 10%, you would scrap it immediatley.
In the scenario above with the 8 tonne slings you would not use a shackle to connect the slings to to the crane hook, you would either use a manufactured sling with one piece round or oblong style "rings" which are usually connected to a larger crane hook ring. You certanly would not use a shackle on the crane hook with slings at any angle over 45 degrees. Shackles may be used at the other end of the slings as long as they were being loaded in the straight ahead line.
I was watching (on Austar) a while back a recovery of a 20ft container supposedly weighing around 20 tonne from a ditch on the side of the road, they used a 4 leg chain sling and because of the angle of the container one of the hooks couldn't be connected to the container pin holes on one corner. So they used a large shackle, looked to be 50/60mm in thickness in the pin hole and they fitted another shackle into the side of the "D" shackle body then hooked up the sling hook. These shackles were in the 20 tonne SWL range. The crane lifted the container and when it was about 10' off the ground the shackle that was jambed in the container pin hole, and being pulled sideways broke and the load fell to the ground and the mobile crane flipped over backwards, no one was injured. Another case of a load equal to the SWL of the shackle snapping well before its GBS because it was not designed to be used the way it was, Regards Frank.

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you dont always happen to have custom slings for doing certain jobs. sometimes you have to make the gear as you go.

I think know the show you were watching and if memory serves they were trying to lift a 40ft container not a 20 (which is why the gear didnt reach) and they were well past the 120 degree limit when the shackle broke

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Originally Posted by Blknight.aus

you dont always happen to have custom slings for doing certain jobs. sometimes you have to make the gear as you go.

I think know the show you were watching and if memory serves they were trying to lift a 40ft container not a 20 (which is why the gear didnt reach) and they were well past the 120 degree limit when the shackle broke

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Dave in the lifting scenario, if I didn't have a manufactured sling to do the job then I would do away with the shackle on the crane hook. I would put the eyes of the sling on the crane hook and if the crane hook size allowed it I would use a shackle in each eye and put those on the crane hook, Regards Frank

what I want to know is, who takes their friggin crane 4x4ing in the first place :p

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Originally Posted by uninformed

what I want to know is, who takes their friggin crane 4x4ing in the first place :p

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I prefer my Heavy-Lift Helicopter to escort my tougher trips :D