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Bigger is not better in straps.
You want some stretch as this lowers the impact of a snatch. If you get a 15,000KG strap and pull a suzuki with it there will be minimal stretch and the shock load on the recovery points, drivers, shackles, etc. will be higher. Sure you won't break the strap, but you may pull the bar off.
You should aim to exceed the stated safety margins, but by a minimal amount.
Cheers, Steve
There seems to be a lot of confusion concerning the actual strength and SWL/WLL of Snatch straps, because of the way that sellers/distributors/manufacturers rate their straps. A few points to clear it up:Quote:
Originally Posted by wovenrovings
Min Breaking Strain/Maximum Breaking Strain should READ Guaranteed Breaking Strain (GBS), if a strap is rated at 8000kgs it WILL break at 8000kgs or Less, there is no Safety Factor built in like properly Rated Rigging equipment.
For instance, General purpose heavy duty rigging gear, like Shackles, Wire slings, Chains and Straps have a Safety Factor of 6, i.e. the GBS of the equipment Divided by the SF. Example 6000kg GBS piece of rigging gear has a SWL/WLL of 1000kgs.
If you have a Snatch Strap with a GBS of 8000kgs, I would advise you use a rated shackle of 8000kgs SWL/WLL. that way you will always have the weakest part of the rig being the strap, assuming your Salvage points are up to the job.
Reason, Safety factors are designed to take into account wear and tear on rigging gear, when a shackle is new it is at it's strongest and will deteriorate with use and abuse until it is OBVIOUS that the piece of gear has reached the end of it's safe working life.
One of the easiest ways to bugger a shackle is to have the bow or D part of the shackle to put sideways pressure on the shackle pin. If you have the shackle connected to a salvage point with the pin HORIZONTAL and the pull on the shackle is NOT directly straight ahead the bow will try to pull the pin sideways in it's salvage point hole. Remedy, have your salvage points with the shackle pin hole VERTICAL, that way the shackle body can swivel and align itself with the line of pull, Regards Frank.
Where did I put my soapbox! :p
NO NO NOQuote:
There seems to be a lot of confusion concerning the actual strength and SWL/WLL of Snatch straps, because of the way that sellers/distributors/manufacturers rate their straps. A few points to clear it up:
Min Breaking Strain/Maximum Breaking Strain should READ Guaranteed Breaking Strain (GBS), if a strap is rated at 8000kgs it WILL break at 8000kgs or Less, there is no Safety Factor built in like properly Rated Rigging equipment.
Strain is a measure of deformation Typically defined as the ratio of extension in length divided by the original length.
As such it is dimensionless
The minimum breaking strain would be the smallest amount that item would stretch divided by original length etc and can not be 8,000 kg
The expressions stress and strain are commonly misused
If a strap is rated at 8,000 kg then the MINIMUM load required to break it would be 8,000 kg. IF it fails at less then 8,000 kg when new then the manufacturer is on extremely dodgy grounds re things like trade description etc and is liable to be prosecuted.
When I was involved in making climbing slings etc the rating of a sling etc was determined by doing a series of UTS tests, taking the lowest figure achieved and then dividing it by 1.3. So a sling rated at 2,700 kg when new would be expected to break at a minimum of 3,600 +kg. This way there was a built in safety margin on the slings against any errors in manufacturing. Typically these 2700 slings would break at loads of 4,000 kg+
How the recovery strap people rate their equipment I have no idea. A used strap can easily break at loads less then the quoted as new strength due to abrasion, nicks, interfilament damage, chemical attack, uv degradation and misuse.
IF in doubt about your webbing gear BIN IT
Webbing gear is much more suceptable to damage then the metallic items in your recovery gear (excepting wire winch ropes)
Regards
Brendan
Off my soap box now (again) Am I safe to put it away or should I keep it handy?:p
When 4WDAction had testing done on straps, there were quite a few that failed before their rating also. I'm pretty sure the Supercheap one failed a exceptionally early.
Did they report where the failures occured?Quote:
Originally Posted by Slunnie
If in middle of strap then the webbing was overrated/substandard
If stitching failed then the stitch pattern/thread gauge is wrong
If failed across webbing but close to stitch block (which would be a good typical failure) then the rating of strap was incorrect.
Please note that the way you grip a specimen and how you test them can have a dramatic effect on test results. i.e. use self tightening jaws on webbing strength is drastically reduced. Use bollards and apparent strength can appear to go up with increasing size of bollards
Regards
Brendan
I dont recall if they reported on all of the failures - I don't think they did IIRC. The straps were not gripped with jaws though.
I'm pretty sure they said where the failures occurred for all straps -- all were tested in their full lengths (no half strap tests as some do) using rated shackles both ends of such a size that the strap angle around the pin was <20ยบ as is reccommended to not place undue stress on the stitching etc.
If they did complete it as they stated, it seemed pretty fair and genuine and the results should be reliable and accurate. From what I recall ARB and Just Straps were the best performers, the SuperCrap was appalling and I'd be hesitant to use it to pull a tonka truck from a sandpit....:p
Cool thanks for all the info.. great help
I think I will stick with the 8,000 kg.. seems to be they way to go. If joining two snatch straps, is it best to have two of the same rating?
Thanks
I think 8000kg is very very common, even for full size 4WD's. I've only seen one break and that was a sand bogged loaded Disco with trailer being snatched up a hill by a super loaded LandCruiser 100 series.Quote:
Originally Posted by disco_2008
It doesn't matter if the straps are joined and rated differently.
I am pretty sure when 2 magazines did the tests some did fail below the stated minimum rating. I believe only one snapped the strap itself and the others that failed, failed at the eyelet stitching.