Proof of necessity for correct recovery techniques

[FJ40-GARAGE]

I bet that got his attention..

I am really happy no one got hurt..

Its not always like that..............:whoops:

As part of the 2008 Transoriental Rally, a terrible accident occurred yesterday morning in Russia at 7:25 a.m. local time (5:25 a.m. FT - 3:25 a.m. GMT), on the route of the special stage.

The official Chinese driver of the Team Zhengzhou Nissan, Xu Lang, stopped to help another vehicle that had got stuck. The towing cable broke and struck Xu Lang full force in the face.

Assistance was rendered very quickly by the surgeon who had been aboard the immobilized vehicle, and later by the Transoriental's physicians. The medical helicopter arrived 10 minutes after the accident. Suffering from multiple neurological injuries, Xu Lang was transferred to the hospital in Orenburg (Russia) in serious condition.

Well-liked by all, this fine professional racer succumbed to his injuries this morning.

Zhengzhou Nissan and the Team Dessoude, all deeply affected by this tragedy, extend their sincere condolences to his family and friends.

Rally : Xu Lang succombed to his injuries - RAID WRC - Rally-Live.com

 

[Awl_TEQ]

So, f=ma
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? ]

Because the velocity of the pulling vehicle is added to the equation - If it takes 50#'s of force to stop a vehicle from 5 mph it will take 2500#'s to stop the same vehicle from 10 mph. ALL OF THAT FORCE is transmitted through the strap to the anchor point of the stuck vehicle in THE FRACTION OF A SECOND BEFORE the force overcomes it's inertia. It doen't matter whether you use a chain, cable, synthetic rope or snatch strap. If you use your forward momentum to increase the force you cannot regulate the forces applied and can very quickly overcome the anchor points and make things airborne.

[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 - but over what time frame? Do you use a winch to slowly apply 5k-6k-7k-8k-8.5k and then the truck moves or take a run at the slack in a snatch strap from 2-5-8-15mph. With a winch you can apply force in a linear progression but with a snatch strap it is an exponential progression of applied force. The snatch strap will "find that load" AFTER the inertia of the stuck vehicle is overcome.



[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.]

Correct with a caveat - the snatch strap does reduce the impact of the pulling force by spreading it over a greater amount of time - BUT that time is still very short - fraction of a second - and now you have a loaded rubber band.

[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. ]

YES - because the force applied is squared when the speed is doubled (or duration of application is halved).

I DO agree with the following statements

[I have seen many more chains cause issues than snatch straps.]

[All extraction has an inherent risk to it.]

[If a snatch strap is used cautiously, it is a simple and very effective recovery tool.]

[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..] To a safe limit - there is a line that can be crossed and that line is subjective and different for every application.

Bottom line is this IMO. Every situation requires different action. If you are stuck in 3" of slick muck on level ground use a snatch strap. I carry two and they are not evil. But if you are up to the middle of the door in heavy clay and mud get a winch (or two).

 

[FJ40-GARAGE]

No matter what and how, always keep distance and tell bystanders to move away!

Just found another interesting report on the web.
Corporate Author : ASSOCIATION OF SCIENTISTS AND ENGINEERS OF THE NAVAL SEA SYSTEMS COMMAND WASHINGTON DC

Personal Author(s) : Prentice,George ; Miles,Andrew

Report Date : MAR 1986

Pagination or Media Count : 12

Abstract : When a long thin tensile member is loaded until it breaks, it will snap back in the direction of pull. It matters not if that tensile member is made of rubber, synthetic fiber, wire or glass; it is going to snap back. The only variable in this phenomenon is the speed that it will snap back. Synthetic fiber rope snaps back at about 700 feet/sec; wire rope at about 450 feet/sec. Therefore, both ropes are deadly to anyone standing near them when a failure occurs. In the early 1980's several synthetic fiber ropes did fail. In one nine month period three sailors were killed and four had one or both legs cut off. This report outlines the approach taken by NAVSEA to reduce the number of accidents resulting from synthetic line snap back. The most effective short term solution is to make personnel aware of the dangers involved in linehandling and the proper procedure for handling the lines to avoid injury due to snapback. For long term solution to the problem, the development of a low snapback line is the only sure way to go. A Kevlar-Nylon combination has been tested in the laboratory and will shortly undergo field testing on a U.S. Navy ship.

Descriptors : *ROPE, HAZARDS, NAVAL PERSONNEL, TENSILE PROPERTIES, NYLON, FAILURE, BOAT AND SHIP SAFETY, SYNTHETIC FIBERS.

Subject Categories : MARINE ENGINEERING
SAFETY ENGINEERING

Distribution Statement : APPROVED FOR PUBLIC RELEASE
Found here

 

[Mace]

Because the velocity of the pulling vehicle is added to the equation - If it takes 50#'s of force to stop a vehicle from 5 mph it will take 2500#'s to stop the same vehicle from 10 mph. ALL OF THAT FORCE is transmitted through the strap to the anchor point of the stuck vehicle in THE FRACTION OF A SECOND BEFORE the force overcomes it's inertia. It doen't matter whether you use a chain, cable, synthetic rope or snatch strap. If you use your forward momentum to increase the force you cannot regulate the forces applied and can very quickly overcome the anchor points and make things airborne.

But the velocity of the pulling vehicle is only adding additional force that is required to extract the stuck truck. You are not "stopping it", once the truck is pulled free, the differential speeds between the two trucks begins to reduce the forces seen by the stuck truck. You can regulate the forces, you just have to not apply as much skinny pedal juice and do not take a 50' run.

If your anchor points are not up to the job, they will break at 8 or 10K no matter how that force is applied (barring a shock load)

Yes - but over what time frame? Do you use a winch to slowly apply 5k-6k-7k-8k-8.5k and then the truck moves or take a run at the slack in a snatch strap from 2-5-8-15mph. With a winch you can apply force in a linear progression but with a snatch strap it is an exponential progression of applied force. The snatch strap will "find that load" AFTER the inertia of the stuck vehicle is overcome.

Does a winch apply force in a linear fashion? I really doubt that it does. An electric winch does provide maximum torque right off the bat, but there is a lot more to it than that. Donno actually, might be interesting to find out.. According to the link below the forces do increase in an exponential format, but honestly, who gets up to 20 mph in a snatch situation?? I mean really?? Go take a tape measure and see how far it takes to get to 20 mph. It is not that far, but it is further than a 20' snatch strap.

Agreed that you can apply the forces a winch provides a bit easier with a button, but some gradual test pulls with the snatch strap will tell you what you need to know as well. Use your head in a bad situation. That is waht safety is about.

Correct with a caveat - the snatch strap does reduce the impact of the pulling force by spreading it over a greater amount of time - BUT that time is still very short - fraction of a second - and now you have a loaded rubber band.

The rubber band is an issue. That is why you have to make sure that your recovery equipment is in good condition.


Bottom line is this IMO. Every situation requires different action. If you are stuck in 3" of slick muck on level ground use a snatch strap. I carry two and they are not evil. But if you are up to the middle of the door in heavy clay and mud get a winch (or two).

Agreed

 

[Niner]

had a winch been attached to the same hook in this case the same result more than likely would have occured. even with a steady pull there is a certain amount stored energy in the wire rope of the winch.

 

[flintknapper]

had a winch been attached to the same hook in this case the same result more than likely would have occured. even with a steady pull there is a certain amount stored energy in the wire rope of the winch.

Absolutely not! While winch cable (wire rope) will exhibit a certain amount of stretch (usually under 1.7% at breaking point) it pales in comparison to a snatch strap.

As a practical experiment do the following:

Take a piece of string, attach it to a paper clip and pinch the PC between your thumb and index finger. Pull on the string (steadily) until you have think you have exerted 1 lb. of pressure and then let the PC slip through your fingers (note the result).

Now, take a rubber band (substitute it for the string) and repeat the steps above. Please come back here and tell us what you found.

 

[Mace]

And if something was draped over the strap (like a winch cable) it would snap back differently.

But if the equipment was up to par, it would not have happened at all. Think of what could have happened even if a winch was being used if the extraction was along the side of a 40' cliff??

Make sure that your recovery equipment is up to par, that is the main lesson to be learned here.

 

[flintknapper]

And if something was draped over the strap (like a winch cable) it would snap back differently.

But if the equipment was up to par, it would not have happened at all. Think of what could have happened even if a winch was being used if the extraction was along the side of a 40' cliff??

Make sure that your recovery equipment is up to par, that is the main lesson to be learned here.

Mehhh, forty feet ain't nuthin!

 

[Mace]

Mehhh, forty feet ain't nuthin!

lol

 

[MarcoPolo]

Is this a video?

Do you have to log into the site to see? I don't want another password to remember...

 

[SouthBostonFJ40]

I just saw a video on youtube of a jeep being winched and it had a weighted bag in the middle of the cable span so that if it did break, the weight of the bag would slow the cable down. The hood was also up just in case.

 

[Niner]

Mehhh, forty feet ain't nuthin!

And if something was draped over the strap (like a winch cable) it would snap back differently.

But if the equipment was up to par, it would not have happened at all. Think of what could have happened even if a winch was being used if the extraction was along the side of a 40' cliff??

Make sure that your recovery equipment is up to par, that is the main lesson to be learned here.

The real problem is we all have to assume that everyone has their equipment up to par. Unfortunately not everyone does and I'm not exacly sure most would catch a cracked hook.

 

[Awl_TEQ]

Some of you may have seen this in chit-chat (two threads that I know of) but I am curious what Mace and Flintknapper think. Not really a "snatch strap" but more of a technique issue I believe. This is the kind of thing I was refering to in these quotes....


{Bottom line is this IMO. Every situation requires different action. If you are stuck in 3" of slick muck on level ground use a snatch strap. I carry two and they are not evil. But if you are up to the middle of the door in heavy clay and mud get a winch (or two).}

{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....}

YouTube - Jeep lost its top

No one hurt (phisically anyway) so we can laugh at this poor bugger..... but what if the cage ripped out of the floor and was flung in the direction of the crowd??





.

 

[MarcoPolo]

YouTube - Jeep lost its top

LMAO

 

[Mace]

Some of you may have seen this in chit-chat (two threads that I know of) but I am curious what Mace and Flintknapper think. Not really a "snatch strap" but more of a technique issue I believe. This is the kind of thing I was refering to in these quotes....


{Bottom line is this IMO. Every situation requires different action. If you are stuck in 3" of slick muck on level ground use a snatch strap. I carry two and they are not evil. But if you are up to the middle of the door in heavy clay and mud get a winch (or two).}

{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....}

YouTube - Jeep lost its top

No one hurt (phisically anyway) so we can laugh at this poor bugger..... but what if the cage ripped out of the floor and was flung in the direction of the crowd??





.

that was one of the dumbest recoveries I have ever seen.

 

[Awl_TEQ]

Funny though

 

[bad_religion_au]

I just saw a video on youtube of a jeep being winched and it had a weighted bag in the middle of the cable span so that if it did break, the weight of the bag would slow the cable down. The hood was also up just in case.

the cable dampeners (weighted bag) are pretty much mandatory in aust