Has anyone ever had a 4,000kg winch strap fail?
Submitted: Tuesday, Jun 06, 2006 at 11:06
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Scubaroo
Looking for some real world experiences here - has anyone ever had a 4,000kg winch extension strap fail? Under what circumstances? Hand winch or vehicle mounted? Had the strap done much work prior to failing?
I've got a hand winch, and am thinking a 20m or 30m 4,000kg will be sufficient - I know I could potentially exceed that load by using a snatch block on a winch, but my thoughts are that I wouldn't be using the two in conjunction. It's more of a "just in case" item rather than something I ever plan on using (no point having a hand winch if the nearest tree is more than 20m away and you've only got a 20m cable), and I'm trying to justify to myself spending almost double the money for the same length 6,000kg straps - an item that will likely never be used. Spend enough money on stuff I *do* use.
Reply By: Rosco - Qld - Tuesday, Jun 06, 2006 at 11:25
Tuesday, Jun 06, 2006 at 11:25
First off. What size (capacity) hand winch have you got. The reason I ask is I doubt you will ever approach 4 Tonnes with a hand winch, even with a snatch block.
You will most likely bust your freckle long before then ... ;-)) or certainly the shear pin in the winch.
Cheers
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Follow Up By: Scubaroo - Tuesday, Jun 06, 2006 at 11:35
Tuesday, Jun 06, 2006 at 11:35
ARB Magnum - I think the pin is rated to 1.6t - which should fail first.
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Follow Up By: Scubaroo - Tuesday, Jun 06, 2006 at 11:38
Tuesday, Jun 06, 2006 at 11:38
Presumably the *maximum* load that could be applied with a snatch block is 3.2t (11mm cable around a snatch block should not decrease the load rating of the cable because of the bend). I'm looking at a "Just Straps" brand winch strap, which are rated 10% below their tested minimum break load - so a 4,000kg strap has a minimum 4,400kg breaking load (at least when new). All of their straps rate
well in the comparison tests that get conducted.
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Follow Up By: Rosco - Qld - Tuesday, Jun 06, 2006 at 11:43
Tuesday, Jun 06, 2006 at 11:43
There you go. I think you've answered your own question. Seems to me you have an adequate factor of safety with a 4000 kg strap. Of course you would always use an air brake in any event ..
Cheers
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Follow Up By: Scubaroo - Tuesday, Jun 06, 2006 at 12:17
Tuesday, Jun 06, 2006 at 12:17
Thanks Rosco - just needed someone to validate my line of thinking.
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Reply By: Sand Man (SA) - Tuesday, Jun 06, 2006 at 12:12
Tuesday, Jun 06, 2006 at 12:12
In the words of Professor Julius Somner Miller, "WHY IS IT SO?"
Why is a "Snatch Block" called such?
You don't "snatch" with it at all. It merely reduces the pulling effort of a cable going through it.
So, it should be called a "Winch Block" because it is used with one, either manually, electrically, or Hydraulically driven.
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Follow Up By: Scubaroo - Tuesday, Jun 06, 2006 at 12:15
Tuesday, Jun 06, 2006 at 12:15
Good question! I've always called them a snatch block, but winch block is probably used more commonly.
Anyway, where's the "block" bit come from? There's nothing square about them - it's a pulley!
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Follow Up By: Rosco - Qld - Tuesday, Jun 06, 2006 at 12:27
Tuesday, Jun 06, 2006 at 12:27
I think you'll find they're called this due to the fact they are openable and can be "snatched" over a cable, rather than have to thread the cable through, as is the case with a normal block.
Absolutely nothing to do with "snatch" recoveries.
Cheers
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Follow Up By: Member - MrBitchi (QLD) - Tuesday, Jun 06, 2006 at 13:21
Tuesday, Jun 06, 2006 at 13:21
Snatch Block Basics
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Follow Up By: hoyks - Tuesday, Jun 06, 2006 at 13:47
Tuesday, Jun 06, 2006 at 13:47
And they are called a 'block' because back in the bad old days on sailing ships, the pulleys for hoisting the sails and the tensioning stays on the masts were made out of blocks of wood with holes and grooves bored through
the block that the rope ran through.
No wheels were used in the middle of the pullies as the only material they had was steel and it tended to rust up and fail at sea and most times was inaccessible in order to do maintenance.
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Follow Up By: Pajman Pete (SA) - Tuesday, Jun 06, 2006 at 14:33
Tuesday, Jun 06, 2006 at 14:33
Snatch - because you can 'snatch' a bight of the rope or line.
Block - because originally all 'pulleys' were cut from a solid block of wood:
Cheers
Pete
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Follow Up By: Pajman Pete (SA) - Tuesday, Jun 06, 2006 at 15:32
Tuesday, Jun 06, 2006 at 15:32
Not quite hoyks, Brass and bronze sheaves were used at least as early as the 1560s. You may be thinking of 'deadeyes' -
Pete
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Follow Up By: Mike Harding - Saturday, Jun 10, 2006 at 07:34
Saturday, Jun 10, 2006 at 07:34
Site Link
Excellent link Mr Bitchi - thanks for that, I learned some very interesting stuff.
Mike Harding
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Reply By: HJ60-2H - Tuesday, Jun 06, 2006 at 12:31
Tuesday, Jun 06, 2006 at 12:31
Yes, quite a few. Used in recovery at competition events. Got to th epoint that we now only use 8K ones. They dont fail under normal use, but are still the weakest link in a recovery set up so can be set up to be safe when they do fail.
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Follow Up By: ro-dah-o (WA) - Tuesday, Jun 06, 2006 at 22:11
Tuesday, Jun 06, 2006 at 22:11
I wouldnt think that it is always the weekest link in a recovery set up.
If I had a 1.6tn shackle and a 4tn extension strap, the weakest link in my set up is certainly the shackle.
I would agree that they are the most prone to breakage, but not the weakest link per say.
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Follow Up By: HJ60-2H - Tuesday, Jun 06, 2006 at 22:40
Tuesday, Jun 06, 2006 at 22:40
True. If I were to use a boot lace it would be the weakest link. Or perhaps an unated shackle. The thought of using anything less than a 3.2T rated shackle scares me. If I saw a 1.6T shackle in a recovery set up I'd be walking away from it all. Each to their own though.
A 3.2 T rated shackle will break around the 4 x its rated capacity. A strap will break before 2 x its rated capacity.
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Follow Up By: Scubaroo - Tuesday, Jun 06, 2006 at 23:57
Tuesday, Jun 06, 2006 at 23:57
Most straps break just below, at or just over their rated capacity judging by the mag tests. The strap rating can pretty much be considered the failure point. A shackle has something like a five times safety factor - basically anything over 3.2t should be good, it's just a matter of picking the size you need.
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Follow Up By: ro-dah-o (WA) - Wednesday, Jun 07, 2006 at 08:41
Wednesday, Jun 07, 2006 at 08:41
1.6tn was only used as an example.
I am the same, never use a shackle with a swl of less than 3.2tn.
scubaroo is right about the safety factor. The swl is calculated on the MBL (mean break load) of the device. If memory serves me right, the mbl is divided by a factor of 5 for hardware (shackles and snatch blocks etc) and 8 for soft ware (extension straps, ropes, etc). This is set out by standards australia.
I know it relates to rope and industrial rescue equipment, but not 100% sure about recovery gear. How
well policed is the sale of recovery gear?? Does it have to meet any stringent indusrty satandards? This is a debate question, but a genuine 'I dont know' sort of question.
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Follow Up By: HJ60-2H - Wednesday, Jun 07, 2006 at 11:31
Wednesday, Jun 07, 2006 at 11:31
Generally the gear we typically use in 4wd recovery is the same used in industrial lifting and hoisting, shackles, blocks, cables etc. So the standards that apply to this industry and policed by Workcover and the like apply.
Though a recovery strap labeled as a "4WD strap" is probably excluded from the above.
There arent that many Australian Standards that are enshrined in law so although they exist you dont have to meet them in most cases, though is is usually sensible to do so. Lifting & hoisting and electrical safety ones are (fortunately) one of the few that are required to be complied with under the law.
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Follow Up By: ro-dah-o (WA) - Wednesday, Jun 07, 2006 at 12:02
Wednesday, Jun 07, 2006 at 12:02
"There arent that many Australian Standards that are enshrined in law so although they exist you dont have to meet them in most cases,"
thats what i was afraid of. Its a shame as the potential for injury would be quie high, and the consequences high
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Follow Up By: Mike Harding - Saturday, Jun 10, 2006 at 07:51
Saturday, Jun 10, 2006 at 07:51
My understanding is that Oz standards only apply to "lifting" equipment. 4WD recovery equipment is "pulling" equipment and, as such, any ratings given to it are what the seller thinks is a good idea. Of course this doesn't preclude someone selling lifting shackles (say) for 4WD work but if a strap is _not_ certified for lifting then it's rating is, in reality, anyone's guess.
btw even Oz standards do not provide the guarantee many assume - I bought a number (120) electrical enclosures rated to IP66 (rain proof) which let water in due to one bad design fault and another bad manufacturing fault - caveat emptor.
Mike Harding
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Reply By: robak (QLD) - Tuesday, Jun 06, 2006 at 13:14
Tuesday, Jun 06, 2006 at 13:14
I have a question for all you physics gurus as I can't totally get my head around it. By using a snatch block do you:
a. double the force on the strap
b. half the force on the strap
c. the force remains the same
Consider a simillar scenario where a 10L bucket of water is hanging off a tree branch on one strap. The force on the strap is 100N.
If you add another strap the force is 50N on each strap. That's easy.
But if you pull the strap through a snatch block and both ends to the bucket (and tie the snatch block to the branch), is the force on each end of the strap 50N or 100N?
R.
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Follow Up By: Member - MrBitchi (QLD) - Tuesday, Jun 06, 2006 at 13:26
Tuesday, Jun 06, 2006 at 13:26
See "Snatch Block Basics" above.
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Follow Up By: Rosco - Qld - Tuesday, Jun 06, 2006 at 13:29
Tuesday, Jun 06, 2006 at 13:29
50N
2 ropes = load/2 per rope
3 ropes = load/3
4 ropes = load/4
...... and so on. Thats basically how a block and tackle works, hence with double and single sheaves it would only take 25 Kg effort to lift a 100 Kg load.
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Follow Up By: robak (QLD) - Tuesday, Jun 06, 2006 at 15:33
Tuesday, Jun 06, 2006 at 15:33
Thanks guys
I was just a bit confused as Scubaroo said that he may exceed the 4000kg load if he uses a block.
Cheers
R.
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Reply By: Rod W - Tuesday, Jun 06, 2006 at 14:33
Tuesday, Jun 06, 2006 at 14:33
Yes I've busted a 4000kg winch strap, and thats with 3.25tonne rated shackles in the set-up. I was winching out a tree stump.
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Follow Up By: Scubaroo - Tuesday, Jun 06, 2006 at 15:02
Tuesday, Jun 06, 2006 at 15:02
Electric winch I guess?
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Follow Up By: Rod W - Tuesday, Jun 06, 2006 at 15:05
Tuesday, Jun 06, 2006 at 15:05
Nup! using a hand winch.
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Follow Up By: BBB - Saturday, Jun 10, 2006 at 07:16
Saturday, Jun 10, 2006 at 07:16
Regardles of the rating on the strap you must keep them clean at all times if they are frayed or have dirt or grit in them ther integreaty is compromised and they can fail under very litle load.
BBB
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Reply By: macca172 - Tuesday, Jun 06, 2006 at 19:08
Tuesday, Jun 06, 2006 at 19:08
Very interesting reading guys! Im about to buy my "first recovery kit" and would be interested in your guidance. Firstly, my vehicle is to be fitted with a 9,500lb winch, from here what do I need in my kit ie; strap ratings, "D" shackle ratings etc etc?
Much appreciate any advice.
Macca
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Follow Up By: Scubaroo - Tuesday, Jun 06, 2006 at 20:59
Tuesday, Jun 06, 2006 at 20:59
Minimum would be a tree trunk protector (happy with the ARB (
http://www.arb.com.au) one I have, Just Straps (
http://www.juststraps.com.au) make great gear too), a 4.7t bow shackle to join the ends of the tree trunk protector, and an air brake of some description to lay over the winch cable to act as a dampener in the event of it breaking. Depending on the hook size on the end of the cable, you could either thread the shackle pin through the gape of the hook, or through the crimped loop on the cable.
The tree trunk protector, shackle and dampener is the *bare minimum* gear you need to use the winch.
If you've no recovery experience, a recovery course would be a good idea.
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Reply By: ro-dah-o (WA) - Tuesday, Jun 06, 2006 at 22:06
Tuesday, Jun 06, 2006 at 22:06
yep, seen one break. it was on a hand winch.
Would put it down to inappropriate care and storage. It was stored in a trunk on the back of a ute along with spare oils and the like.
Be aware of contaminants!!
Any extension strap is prone to fail, if it is not cared for properly i.e. allowed to fray, shock loaded repetitevely, contacted with contaminants, left dirty or full of sand etc etc.
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