Thread: Synthetic rope question

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:



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...

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.

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.

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.