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General => General Discussion => Topic started by: Jason B on June 04, 2012, 09:30:04 PM

Title: The Dangers of snatch straps and the forces involved.
Post by: Jason B on June 04, 2012, 09:30:04 PM
A luky escape for this poor fella, not that the accident was caused by a recovery, but it just goes to show the forces involved.

Regards


Jas

http://www.lorellasprings.com.au/rhettsaccident.htm (http://www.lorellasprings.com.au/rhettsaccident.htm)
Title: The Dangers of snatch straps and the forces involved.
Post by: BigJules on June 04, 2012, 09:32:14 PM
Nasty.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Paul (SA) on June 04, 2012, 09:36:37 PM
Leaves me lost for words. OMG
Title: The Dangers of snatch straps and the forces involved.
Post by: Black Diamond on June 04, 2012, 09:39:51 PM
Gee that's a lucky escape. Poor bloke I can only imagine how that would have felt on impact. Chain on the end of the strap?? Bad move.

Bd
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Sicilianmama on June 04, 2012, 09:52:21 PM
Omg, that's awful, poor fella wouldn't have known what hit him, he's very lucky to still be alive
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: brickiematt on June 04, 2012, 09:58:19 PM
Holy Shit
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Swannie on June 04, 2012, 10:02:03 PM
Very very lucky man to be alive.
Greg
Title: The Dangers of snatch straps and the forces involved.
Post by: Kevo on June 04, 2012, 10:34:42 PM
Leaves me cold. Very lucky to be alive.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Jon on June 04, 2012, 10:49:39 PM
What is the purpose of towing the tyre?
Surely the added traction required to do so would cause the track to chop up more?

Anyway, very lucky bloke from the sounds. Anything letting go under load is not good.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Jason B on June 04, 2012, 10:53:48 PM
What is the purpose of towing the tyre?
Surely the added traction required to do so would cause the track to chop up more?

Anyway, very lucky bloke from the sounds. Anything letting go under load is not good.

Thought that my self, however apparently its to smooth the tracks over again to prevent errosion from both wind and rain when they get it. Not sure how effectice it would be.

Regards

Jas
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: SteveandViv on June 04, 2012, 11:47:18 PM
You see that a lot up here as well and we also saw it over in QLD last year. The tyre chops the top of the corrugation off and it does make a fair bit of difference. You can only use a chain or winch cable for this as any strap will soon be rubbed through. Fairly unusual to break like that.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Barrabart on June 05, 2012, 01:56:48 AM
Thanks for posting this Jason, always good to remind all of the potential dangers involved with loading up straps etc, especially when "bush fixes" are thrown into the mix....... Glad the young fella is on the mend, very lucky fella.
Title: The Dangers of snatch straps and the forces involved.
Post by: britts on June 05, 2012, 06:11:40 AM
That's 1 lucky bloke, do you mind if I post this on our club 4wd forum?
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Symon on June 05, 2012, 06:12:31 AM
The chain wasn't the problem, it was the strap.  A chain should have been used instead of the strap, or a sling, or anything that doesn't store a heap of energy.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Humbolt on June 05, 2012, 07:25:13 AM
My thoughts go out to him and also his family who had to go through that ordeal.
I am sure they have learned a valuable lesson and are grateful everyone is still alive!
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Jason B on June 05, 2012, 11:59:53 AM
That's 1 lucky bloke, do you mind if I post this on our club 4wd forum?

I am sure that is fine mate, its on the web.


Regards


jas
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Desert lover on June 06, 2012, 09:23:04 AM
Thank goodness there were people with him to render first aid.... I do hope his recovery is complete and quick...
Desert Lover
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Patr80l on June 06, 2012, 04:25:54 PM
Looked up the location on Google Maps.   They are on the Gulf of Carpentaria... a long way from anywhere.
He was very lucky; the only first aid equipment they had was toilet paper.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Squalo on June 07, 2012, 08:27:15 AM
You see that a lot up here as well and we also saw it over in QLD last year. The tyre chops the top of the corrugation off and it does make a fair bit of difference. You can only use a chain or winch cable for this as any strap will soon be rubbed through. Fairly unusual to break like that.

I don't think it was unusual - it was a literally a bomb waiting to go off. Snatch strap and chain - joined by fencing wire? One of the dumbest snatch strap accidents I've ever heard of. Just sorry that the guy who had nothing to do with putting that contraption together was the one who copped the chain in the head. The person/s responsible should never be allowed to handle that sort of gear again, they are simply not to be trusted with it.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Redback on June 07, 2012, 09:05:26 AM
I don't think it was unusual - it was a literally a bomb waiting to go off. Snatch strap and chain - joined by fencing wire? One of the dumbest snatch strap accidents I've ever heard of. Just sorry that the guy who had nothing to do with putting that contraption together was the one who copped the chain in the head. The person/s responsible should never be allowed to handle that sort of gear again, they are simply not to be trusted with it.

Yep absolutely agree, what were they thinking!!

Baz.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: SteveandViv on June 07, 2012, 09:08:13 AM
Yep absolutely agree, what were they thinking!!

Baz.

Not a whole lot I'd say 
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Big Nath on June 07, 2012, 09:21:30 AM
I don't think it was unusual - it was a literally a bomb waiting to go off. Snatch strap and chain - joined by fencing wire? One of the dumbest snatch strap accidents I've ever heard of. Just sorry that the guy who had nothing to do with putting that contraption together was the one who copped the chain in the head. The person/s responsible should never be allowed to handle that sort of gear again, they are simply not to be trusted with it.

I dont think this is a fair call. In the bush, ya do what works with what you have got. Yes in hindsight a silly idea. The problem is it has worked for the past 20+ years. These accidents are never good, the thing is they happen.

The tyre must of hooked on something, the wire (assume it was 2.5mmHT) has a breaking strain of some 1100LB. 

Your right, he was a very lucky bloke and yes DUMB idea.

Cheers!!
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Squalo on June 07, 2012, 09:46:09 AM
When lives are at stake I'm not going to mince words. I'd bet my CT that the fencing wire went on as a stop-gap solution and was simply left there.

The injured man could have been saved by one of these, not hard to come by. Or just weld the chain closed - a one million acre property will have a welder, and someone who knows how to use it - or how about just using a webbing strap, or a rope... anything but a snatch strap!

(http://product-image.tradeindia.com/00364650/b/2/-D-Shackles.jpg)

Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Big Nath on June 07, 2012, 09:58:24 AM
And your probably right.

lets hope all of those still using this technique change over before any other injuries or worse occur.

its hard to explain to people whats worked for many many many years is now not safe.

Cheers!!
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Patr80l on June 07, 2012, 02:41:59 PM
It's one thing to cobble together a repair with fencing wire to get you home, it's quite another to make this a design component for ongoing use.   There are laws covering homicide by negligence.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: GeeTee on June 07, 2012, 02:56:43 PM
When lives are at stake I'm not going to mince words. I'd bet my CT that the fencing wire went on as a stop-gap solution and was simply left there.

The injured man could have been saved by one of these, not hard to come by. Or just weld the chain closed - a one million acre property will have a welder, and someone who knows how to use it - or how about just using a webbing strap, or a rope... anything but a snatch strap!

(http://product-image.tradeindia.com/00364650/b/2/-D-Shackles.jpg)

I'm not sure if a picture of a cheap, bright-plated, unrated D shackle is appropriate in this thread!   
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Bird on June 07, 2012, 03:22:36 PM
Put together by AJ and his team yrs ago..

http://www.whyalla4wd.org.au/Shackles.html (http://www.whyalla4wd.org.au/Shackles.html)


Checking Stretch of Snatch Strap.

If all the Kinetic Energy of the Recovering 4WD is transferred to Elastic Energy in the Snatch Strap then the stretch of the strap can be determined. (Assuming no losses due to friction)

From Energy Conservation,

Kinetic Energy of Recovering 4WD = Elastic Energy in Snatch Strap
KE4WD=PEStrap
3472 J = 1/2 k x2
therefore x = 0.579m
or approximately 6% extension.

And from Hookes Law the Force Stored in the Snatch Straps is,
F = kx
= (2.075 Tonne/m) (0.579m)
= 1.2 Tonne



Determine Speed of Shackle if Snatch Strap Breaks.

If all the Elastic Energy of the Snatch Strap is transferred to Kinetic Energy in the Shackle then the peak Speed of the Shackle as the Snatch Strap returns to it's 9.0m length can be determined. (Assuming no losses due to friction)

From Energy Conservation,

Elastic Energy in Snatch Strap = Kinetic Energy of Shackle
PEStrap = KEShackle
1/2 k x2 = 1/2 m v2
where k = spring constant
x = distance stretched (meters)
m = mass of shackle (kg)
v = velocity of shackle (m/s)
1/2 (20750N/m) (0.579m)2 = 1/2 (0.68kg) v2
v = 101m/s

or Peak Speed of Shackle   v = 364 km/h  
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Rumpig on June 07, 2012, 03:54:09 PM
. Just sorry that the guy who had nothing to do with putting that contraption together was the one who copped the chain in the head.
where does it say he had nothing to do with putting it together?
being it's his property the accident happened on, wouldn't you think he knew exactly what was happening?
i was on that property a few months after the accident happened, and was having a drink with Rhett at his bar whislt he told me all about what happened, to look at him you wouldn't believe the person in the first photo is one and the same. Rhett was having some vision problem still at the time back then, but other then that looked pretty healthy to me. his boy (it says grandson in the article , but i pretty sure he was his son?) was driving the vehicle, Rhett saw what was happening but couldn't get him to stop in time, the rest is history.

The tyre must of hooked on something, the wire (assume it was 2.5mmHT) has a breaking strain of some 1100LB.
according to the conversation i had with Rhett, that's exactly what happened. the tyre got hooked or wedged on / between something (i can't remember exact details) and he didn't have time to tell his son (who was driving) to stop (or he didn't stop in time) before that accident happened. being the kid driving was only something like 16 years old from memory, it'll be a lesson he'll never forget after nearly seeing his old man die right in front of him.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Jason B on June 07, 2012, 09:25:54 PM
In addition to the shackle, a winch extention strap would also be alot safer as it wouldn't store the energy that a snatch strap would.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Squalo on June 08, 2012, 06:51:12 AM
where does it say he had nothing to do with putting it together?
being it's his property the accident happened on, wouldn't you think he knew exactly what was happening?


Hi Rumpig, I read the account of the accident quite a few months ago and did not remember the exact details - thanks for clarifying, and good to hear that he is recovering so well. I'm also appreciative of the fact that the accident details are online - they will get some flack about it, but it will also save others from making the same mistakes.

Here's why I am so hardnosed about snatch strap misuse - that little head sticking up in the back of my car is my daughters - 5 years old at the time. She was supposed to be ducking down low in her seat, but kids being kids...  you can see that the strap is at full extension with my car having been pulled over a metre to the left under tension. I nearly had a heart attack when I saw this pic, and I've always cleared the vehicle of extraneous occupants since this occasion. I didn't get them out because we were on a rising tide at Hook Point and literally only had minutes to save the other vehicle, but now I know better!

I got away with making a huge mistake there, and I'd hate to ever think that someone else might make a similarly disastrous mistake simply because I'd kept my mouth shut about the dangers of snatch straps.

(http://farm6.static.flickr.com/5210/5228973130_1f33146599_b.jpg)
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Rumpig on June 08, 2012, 10:42:23 PM
Here's why I am so hardnosed about snatch strap misuse -....

all good with me mate, if more people were hardnosed about snatch straps, then we wouldn't see some of the "accidents" that we see in the media at times. a lot of people don't realize how dangerous they are, they just think connect it up and floor it to extract a stuck vehicle, if they had half an idea they'd know speed has nothing to do with safely using a snatch strap.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: jim-m-72 on June 18, 2012, 09:36:20 PM
Not good to see someone hurt like that but it is good to see him getting better and hope a lesson learned by all about saftey
Jim
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Squalo on June 18, 2012, 10:30:56 PM
July edition of 4x4 Australia has a spread on Corella Station, Rhett discusses the accident in one paragraph.
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Grunta on June 20, 2012, 06:17:31 AM
Not good

I always use a dampener bag over my snatch strap
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: cheif carlos on June 20, 2012, 10:41:17 AM
one thing to think about if you have wagon have a cargo barrier, they will reduce/stop this sort of thing from happening if you don't have gear piled to the roof. for those with a ute umm.

from a safety point of view they could place a board at the back of the car which could be mounted in the tow hitch for easily removal. make the tyre mount to this so that it cannot be used without the board.

Sorry I am stuck in safety mode all the time. I have seen too many idiots doing stupid things and not willing to listen to what other people have to say.

Jason
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: BigJules on June 20, 2012, 01:42:15 PM
I was watching a clip from All 4 Australia on youtube, his snatch strap broke and really smashed up his rear door. The damage done was like hitting a roo, and without even a shackle involved.

This one.
Australia's Best 4WD BOGS (http://www.youtube.com/watch?v=ZSlOH7LHVxk#ws)
Title: Re: The Dangers of snatch straps and the forces involved.
Post by: Symon on June 20, 2012, 02:56:05 PM
Hardly surprising considering there was a knot in the strap!  Doesn't that derate the strap by a third or something?