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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I've posted before about using a shackle the way it was designed to be used, in that case involving a 8.0 tonne GBS snatch strap and a shackle with a GBS of 17.5 tonne, with the snatch vehicle off centre to one side (probably 30 to 40 degrees).
In this case the shackle was torn apart and the shackle pin travelled 50+ metres and broke the cast iron hinge on the back of a Stage 1 LR. the shackle body disappeared in to the scrub.
So the point here was that 17.5 tonne GBS exploded and the supposedly weakest link, the 8 tonne GBS snatch strap, survived intact. So misusing the shackle that was engineered and designed only to be used in a straight ahead pull ends up the weak link, instead of the strongest.
In your diagram the recovery point is thick enough to stop the actual pin shank jambing in the hole, but the majority of recovery points on 4WD's are about half that thickness, allowing the shackle pin to janb on a much smaller surface are.
Easy way to tell if a shackle has been abused is if it is harder to undo the pin, if you can't undo it with your fingers then the body of the shackle or the pin has been bent.
I've seen riggers and 4WD'ers misuse a shackle and have to undo the pin with a podgy bar or a shifter, luckily most times the pin will not screw back into the shackle body and is disposed of (with a gas axe). BTW the SF for a Lift or device that lifts people is 10, so you should feel OK about getting in a lift, Regards Frank.

Hey Frank I knew you would like the shackle post have had that discussion with you before:D

Hello Geoff, I understand you have a Disco now, you haven't got rid of "the Booger" have you, love that truck and when are you coming down this way again.
Bloody shackles, I was watching 4WD Action on Aurora channel 183 on Austar the other night. Roothy and his mates tearing up the countryside, getting bogged rigging up to pull a 3 tonne nissan/toyota piece of crap up a hill, when they threw a tree strap aound a tree with one eye on the pin of the shackle the other eye on the side and the hook from the winch cable on the opposite side, talk about morons that should know better, passing on dangerous practices on to the general public, anyway got any pics of the new machine, Regards Frank.

Regarding the aluminium thimble being a bad choice of material, would it not depend on what type and spec aluminium before writing it off ?

My thought on SWL...based on stall rating of winch.

Rope 2:1
Rigging and attachments 4:1
This ensures the rope is the failure point if any as that is much safer than a failure of the rigging.

With proper care of the rope you will not see failure with reasonable life by the time you see normal abrasion as require replacement, you will be within a safe fatigue loading for a 2:1 safety factor.

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Originally Posted by Red90

With proper care of the rope you will not see failure with reasonable life

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Agreed - proper care and use within the design envelope.

I found this vid (apologies for those who have seen it before) illustrating why it is a bad idea to use rope / straps with knots in them. Especially without a dampener.

That's a decent size dent in the back of the car for "only" strap impact.

Australia's Best 4WD BOGS - YouTube

(action starts at 8:23)

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Originally Posted by Tank

Hello Geoff, I understand you have a Disco now, you haven't got rid of "the Booger" have you, love that truck and when are you coming down this way again.
Bloody shackles, I was watching 4WD Action on Aurora channel 183 on Austar the other night. Roothy and his mates tearing up the countryside, getting bogged rigging up to pull a 3 tonne nissan/toyota piece of crap up a hill, when they threw a tree strap aound a tree with one eye on the pin of the shackle the other eye on the side and the hook from the winch cable on the opposite side, talk about morons that should know better, passing on dangerous practices on to the general public, anyway got any pics of the new machine, Regards Frank.

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Still got the s111 got the d1 just to play with:D hoping to get down your way soon the disco is much faster than the booger

Yes, but the SIII looks the part, be good to see you and the young fella down here again, Regards Frank.

The alloy thimble does look solid, but where it counts, inside of the eye of the rope the alloy doesn't look to be any thicker than a steel thimble, I have never seen any thimble made of anything other than steel.
The eye of the rope is the most vunerable part of a winch rope, if you look at breakages of otherwise undamaged rope you will find the most breakages occur at the eye that doesn't have a thimble to protect the rope fibres. I have seen ropes actually melt at the eye (without thimble) and fuse into a solid.
I don't think an alloy thimble would be strong enough to handle the type of forces imposed on a steel thimble, Regards Frank.

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Originally Posted by Red90

My thought on SWL...based on stall rating of winch.

Rope 2:1
Rigging and attachments 4:1
This ensures the rope is the failure point if any as that is much safer than a failure of the rigging.

With proper care of the rope you will not see failure with reasonable life by the time you see normal abrasion as require replacement, you will be within a safe fatigue loading for a 2:1 safety factor.

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SWL is a Safety Factor used because the first time you use or abuse a new rope it's GBS becomes less and each use or abuse diminishes the GBS of the rope.
Now if you use 2:1 SF on a rope that has say 10tonne GBS by loading it to 5 tonne then you are putting more stress and damage than if you used a SF of 5:1, so in theory the 5:1 loaded rope should last longer than a 2:1 loaded rope.
Because a rope is tested in a laboratory to destuction to find it's GBS, how in everyday use do you determine the ever diminishing GBS of a rope that has had a severe shock loading, been dragged over abrasive surfaces and through mud, what would the GBS be of this rope after it had been subjected to this sort of work.
Only way of knowing what the GBS is of a well worked rope would be to test it to destruction in a Lab test.
Point being that SWL's are there to cover this type of Use/Misuse or abuse as it is impossible to guess how far the GBS has dropped from when the rope was new.
Dyneema 12 strand rope has the same strength as wire rope of the same diameter, wire cable rope for a winch will (should be) IWRC 7 strands, with 19/24 wires per strand. Dyneema rope has some advantages, 90% lighter, it floats and doesn't kink, wire rope, heavier, doesnt float, not affected by sunlight or abrasion, does kink.
But diameter for diameter they are the same strength (quoting the company that manufactures Dyneema), so if you stick to the limits of a SWL/WLL and maintain your rope you will get a longer safer life from your rope or cable, Regards Frank.