Proof of necessity for correct recovery techniques

[png62]

Narrow escape from serious injury - a very worthwhile viewing.

TASSIE 4WD :: Tassie 4wd Online

I trust this is treated as educational and not turned into a witch hunt on the poor bloke this happened to. I read into his report and clearly see his mistake but thought proof of the failure of an inappropriate recovery technique is a worthy reminder to the casual/unwise.

I POST THIS IN THE HOPE THAT IT MAY SAVE SOMEONE, SOMEWHERE, SOMEDAY.

Take care out there folks.

Argghhhh !!! - Bugger - didn't realise until too late - it's password protected, I will try to overcome and repost with images - in the meantime here is the text reported on that site.
Cheers

Went for a weekend trip with a couple of friends last weekend down around the Arthur River region and had a good time until 2 mates got bogged in the sand nose to tail, i reversed back unrolled my ARB 11000kg snatch strap put one end on my bus and hooked the other loop on the cast iron tow hook (no shackles used) on my mates flat tray cruiser.
Went through a normal text book snatch procedure and "TWANG" the snatch strap hit my back doors and the hook which had broken went through my back window,ripped my roof lining,went through the sunvisor hit the roof,shattered the front window and smashed a hole in the dash and landed on the seat behind me.
My missus and i was the only people in the car and are very lucky to be alive. Everyone was so shocked on what had happened we packed up and went home with a horrible gut feeling of what could have happened.
Upon closer inspection of the tow hook we found that it had a tiny fracture where it had let water in rusting on the inside making it weak. After the trip all 4 4wd owners have removed there old hooks and replaced them with new ones.
Even though we used all the correct recovery equipment accidents still happen. I have sinced learnt from this accident that i will no longer carry passengers on a recovery mission and am installing a cargo barrier to hopefully stop any objects from coming through from the back (hopefully never again) .
The over all damage was $9000 which is nothing compared to someones life.
I urge to everyone check your recovery gear and hooks regurlary because i would hate this to happen to anyone else."

 

[AdventureBuddies]

That is a mistake that anyone could make - thanks for sharing.

 

[mkaustin]

That is the exact reason I like the idea of an additional tether of webbing on the winch cable then attaching it to another anchor near the recovery point. Saw this on a video somewhere and thought that was an outstanding idea.
1" tubular webbing (like climbers use) is dirt cheap (30 cents/ foot) and can hold 4000 lbs. (8000 lbs when doubled in this intended application). They make a 2" webbing (60 cents/foot) that can hold 6700 lbs (13400 lbs doubled). 20 ft of webbing is more than enough.
Attach the webbing to the winch cable about 1-2 feet behind the hook w/ a prusik knot. (look it up, it's super simple) and then attach the other end to something a little bit away from the recovery point. Like the shackle or bumper mount on the other side or another recovery point on the other side of the bumper.
If the recovery point breaks loose like this one did, the webbing would catch the flying cable and drop it to the ground. The reason for attaching webbing away from the recovery point is in case the force of the flying hook manages to be greater than the strength of the webbing, the hook is thrown to the side and not directly at the pulling vehicle like the above case.
I'll have to search to find an image example of what I'm trying to explain.
This should be a requirement to all attempted recoveries, just like not standing anywhere near the cable or where it can reach.
It's a lot like having the safety chains on the trailer. Would you tow a trailer w/ only the hitch and not safety chains?

 

[flintknapper]

Exactly why I don't use "snatch" straps. Too much possibility of overloading something with the tremendous "spike" of energy developed.

Tow straps are fine, but "stretchy" snatch straps are a recipe for disaster IMO.

Anytime you have to "jerk" a vehicle to recover it, means you have the wrong equipment for the job.

 

[Mace]

Anytime you have to "jerk" a vehicle to recover it, means you have the wrong equipment for the job.

I disagree completely. There are times where there is no choice and you do have to bump it. But, the same forces will occur if you have good traction and are pulling hard.
It is important that you keep in mind all of your recovery equipment. Everything needs to be up to par.

 

[Clutchee]

Anytime you have to "jerk" a vehicle to recover it, means you have the wrong equipment for the job.

Sorry........ but no

While at the ACT 08 this year, in deep mud ( like 38 sx's below mud)
you have to yank, yes, each situation has it resolve but a "tug" can and will extract a vehicle safely. We did use winches a lot but those can have their failures too.

And in this case a " previously failed" tow hook was the cause not the yank

 

[Mace]

also, there are differences between snatch straps and tow straps. Keep that in mind..

 

[flintknapper]

I disagree completely.

That is your prerogative.

There are times where there is no choice and you do have to bump it.

If you have ONLY a snatch strap with you this is no doubt true. Otherwise, there are always "choices". The reason snatch straps are so popular is that they are cheap, easy to carry, and any idiot with a lead foot and 20 feet of slack can generate tons of (unregulated) force with which to extract someone.

But, the same forces will occur if you have good traction and are pulling hard.

No Sir! In a proper extraction/recovery ONLY the amount of force necessary to recover the vehicle should be used.

You can not control the forces applied to vehicles/recovery points with a snatch strap the same way you can with a tow strap, chain, or winch cable. IMO, vehicles should never be snatched (regardless of the equipment used), it is dangerous, foolish and only points to the need for the correct tool.

It is important that you keep in mind all of your recovery equipment. Everything needs to be up to par.

Here we agree.

 

[flintknapper]

also, there are differences between snatch straps and tow straps. Keep that in mind..

I believe I alluded to that in my first post.

 

[flintknapper]

And in this case a " previously failed" tow hook was the cause not the yank

I am quite aware of the actual item that "failed". My point of course...is that a tow strap, chain or cable (used with slow and constant force) would not have resulted in a tow hook being "launched" with the force that it was.

In fact, I would wager in this case that it would have simply fell off (or within feet of the vehicle).

A snatch strap virtually guarantees a "rubber band" effect anytime it (or recovery points fail). Not to mention the unnecessary "spike" forces placed upon a vehicle when they are improperly used (which is common).

Yes, they are cheap, they are easy to carry, they "can" be relatively safe to use IF both vehicles involved have adequate recovery points, IF the forces applied are well under the limits of the strap, IF there is no other safe method available (winch, etc), and IF there is not an idiot at either wheel.

Lot of "ifs".

The off-road world is chock full of horror stories involving failed equipment because someone tried to "snatch" a vehicle out.

 

[Albin]

Where are the pics?

And did he really use a "cast iron tow hook"?

 

[Awl_TEQ]

I'm with flintknapper on this. Anytime I've seen someone take a run at yankin' out a stuck vehicle I cringe and stay far away. No one yanks my truck. On the trail there is often a "get er done" attitude and sometimes not enough emphasis placed on safety. Some guys tend to charge ahead with what they have in hand rather than pause and reflect to find a better way. Nine times out of ten (or even 99/100) all is well - but that one time....

My kids wheel with me so I don't bash through the bush at Mach 10.

 

[flintknapper]

It is each persons choice of course, but I simply do not like Snatch Straps for the majority of recovery scenarios.

For those not aware of the "spike" forces involved... look at the chart below...and apply the weight and speed of your cruiser to the figures (typical 80 series probably falls in the 5,000-6,000 lb. range). Just look at an "average" pull:

http://performanceunlimited.com/documents/img143.gif

There is no reason to exert that kind of unregulated force on a vehicle, its just begging for trouble IMO.

 

[Mace]

if a vehicle is stuck it takes a certain amount of force to extract it. Simple physics right?

A snatch strap will only provide the necessary force to extract it cannot exert more force than that. The only exception is when there is a time variable to the extraction.

A chain when used in a snatch situation will provide a considerable more stress than a snatch strap..

 

[flintknapper]

if a vehicle is stuck it takes a certain amount of force to extract it. Simple physics right?

Correct.

A snatch strap will only provide the necessary force to extract it cannot exert more force than that.

Incorrect.

The only exception is when there is a time variable to the extraction.

Now you're catching on. Here is where the dilemma lies (control of forces applied). The "time" involved in which a force is applied is known as the "impulse". The impulse can be rapid (as with snatching with a non/low stretch device (tow strap, cable, chain) or it can be a bit longer (using a device such as a snatch strap).

The problem IMO...arises when you endeavor to SNATCH a vehicle in order to achieve linear momentum (move the mass).

The "snatch" technique is what I am primarily opposed to. A snatch strap (by design) encourages this type of extraction technique. You simply can not control the amount of energy applied (when snatching) like you can with a non/low stretch device and apply the forces at a slow and constant rate.

Apparently, some folks think a snatch strap will regulate itself and apply only the amount of force necessary to move the vehicle. This completely ignores the force impulse (spike) that occurs just before the vehicle begins to move. This energy can be over 60,000 lb. ft.

A chain when used in a snatch situation will provide a considerable more stress than a snatch strap..

Yes and No! A snatch strap does absorb some of the energy (the amount is negligible). What happens here is that the "impulse" (time of force applied) has changed. With a chain, tow strap, cable....you feel the "jerk" because the force is realized in a fraction of a second. With a snatch strap the force is applied over a longer period of time and "builds". The strap first stretches, peak load is attained, then the strap contracts (assuming movement of one vehicle or the other). But, make no mistake...the energy involved is the same.

The big problem with a snatch strap though, is that it's elastic properties virtually guarantee a rubber band effect if something breaks. SAFETY is the entire reason we are having this discussion.

Bottom line: Snatching=bad! There are better ways.

Yes, those "better ways" are often more expensive, more time consuming, require more effort, etc...that is why they often thrown aside. Some off roaders have gotten lazy and unconcerned about safety over the years. Many more have just been damned "lucky". I hope that luck holds out.

As concerns safety/techniques when performing a vehicle recovery, I implore everyone to use the BEST/SAFEST technique and not the SIMPLEST/CHEAPEST.

Its for your own good.

 

[dwh84]

Why was there a hook on the snatch strap in the first place? On my snatch straps there is just a loop which prevents this from being an issue. Just my thoughts on it.

 

[flintknapper]

3711305]Why was there a hook on the snatch strap in the first place?[/COLOR] On my snatch straps there is just a loop which prevents this from being an issue. Just my thoughts on it.

There wasn't. I think you may have misread the accounting.

The "hook" was on the vehicle.

 

[Mace]

Now you're catching on. Here is where the dilemma lies (control of forces applied). The "time" involved in which a force is applied is known as the "impulse". The impulse can be rapid (as with snatching with a non/low stretch device (tow strap, cable, chain) or it can be a bit longer (using a device such as a snatch strap).

The problem IMO...arises when you endeavor to SNATCH a vehicle in order to achieve linear momentum (move the mass).

The "snatch" technique is what I am primarily opposed to. A snatch strap (by design) encourages this type of extraction technique. You simply can not control the amount of energy applied (when snatching) like you can with a non/low stretch device and apply the forces at a slow and constant rate.

Apparently, some folks think a snatch strap will regulate itself and apply only the amount of force necessary to move the vehicle. This completely ignores the force impulse (spike) that occurs just before the vehicle begins to move. This energy can be over 60,000 lb. ft.

So, f=ma. (and that chart is misleading..)
You agree that it only takes a certain amount of force to extract a stuck truck. Then you say the force on that stuck truck is increased by using a snatch strap.. Which is it? How can the peak force placed on the stuck truck change because of a snatch strap? If it takes 8K worth of pulling power, the snatch strap will find that load and then the truck will begin to move. Once you over come the "stuck" factor. The truck is rolling and the forces are reduced.

Yes and No! A snatch strap does absorb some of the energy (the amount is negligible). What happens here is that the "impulse" (time of force applied) has changed. With a chain, tow strap, cable....you feel the "jerk" because the force is realized in a fraction of a second. With a snatch strap the force is applied over a longer period of time and "builds". The strap first stretches, peak load is attained, then the strap contracts (assuming movement of one vehicle or the other). But, make no mistake...the energy involved is the same.

It is not a "absorbed" issue. It is the application of force on the stuck truck. with a chain that "jerk" is the total load applied at once. With a snatch strap, the total load is gradual, putting less stress on the components. Shock loads are tremendously hard on things. The snatch strap reduces shock loads. It also allows a 3K sammy to pull with a greater force than its static mass would allow.

The big problem with a snatch strap though, is that it's elastic properties virtually guarantee a rubber band effect if something breaks. SAFETY is the entire reason we are having this discussion.

And a winch cable has elastic properties as dones a chain, but they are still in use today. Switching to a syn winch line is a much safer and better idea because of safety. Throwing away your extraction chain is also an excellent idea. I have seen many more chains cause issues than snatch straps. All extraction has an inherent risk to it. That is why you prep your equipment and use the proper tool for the job. If a snatch strap is used cautiously, it is a simple and very effective recovery tool. And sometimes is all that is possible to use. It is not the devil incarnate and is not built to kill a person.

When using a standard strap you do not put tension on the strap then floor it. When ysing a winch, you apply force slowly you do not just close your eyes and push the button. When using a snatch strap, you give it a little power and see what happens. If more force is necessary you give a harder tug.. Proper use of the equipment is the key..


The rubber band effect is an issue, but not if a coat or something was placed over the strap before the pull. Just like a winch.

 

[FJ40-GARAGE]

Must be the missing pictures........

Found here: http://www.exploroz.com/Forum/Topic...=/Forum/Default.aspx?s=1&ky=%22Snatch%22&pn=1

 

[Mace]

Must be the missing pictures........

Found here: Proof of necessity for correct recovery techniques @ ExplorOz

I bet that got his attention..

I am really happy no one got hurt..