Tow Chains for the Deuce

[rwoods]

Sorry, I can't find the picture I used to have showing a clevis with the strap still attached sticking through the head portion of a high rise bucket seat of a Jeep. Ron

 

[Josh]

I use both chains and snatch straps depending on the situation. I have 2 lengths of 15ft 3/4in TANK recovery chain, With a nice end designed to fit into a pintle. Also have 2 20ft 1/2in grade 80? chain, and 8 20ft 2in nylon straps. Along with an assortment of D-rings ranging from 5ton to 40ton.

I normally use the chain for recoveries when 2 or more straps would make the lenth to long. A good chain can come in handy here, because with the hook, you can add a couple feet or all of it depending on how you rig it. When trying to remove a vehicle that 1 width of nylon cant handle, I hook the 3/4 inch chain to my truck, at the end of that I fit a massive 40 ton D-ring, and proceed to attach as many straps as nessassary in it. (Normally 2-3 for trucks up to full sizes), and depending on how the other end is, I will use another 40ton D-ring on the other side mounted directly to the truck.

Never had an issue with the chains, or straps, I need to just go buy a larger strap, but the system I do now works well and see no reason to go buy more stuff. If I break more then 4 of my nylon straps, I plan on buying a 10inch one rated for 100,000lbs, as it would cost about the same to replace.


Also linking snatch straps together with D-rings can be done relativily safely, if winch blankets and forms of securing them to the strap are used properly.

But I defently recomend that durring any recovery, that no one stand with in the backlash of the strap in any direction, and I wont pull out a truck that is truely stuck, with out making sure that people are at a safe distance.

 

[ATC]

This should work:

 

[srodocker]

mmm i need to add this to my list of needed parts

 

[Haggar]

this post looks like it has some good potential for some darwin awards, anybody have any carnage pics/ vid's from improper recovery methods? (no fatality stuff please) mabye some damaged trucks? broken chains? bent stuff?????

It certainly happens. A guy here in MI died a year or two back at a bog, I don't remember if it was a clevis or trailer ball that came loose and killed him.

The wife of an ex club-member of mine got hit by a shackle in the neck, she was in the hospital for a while but survived. There are safe ways to hook straps up without heavy chunks of metal involved.

Its just about proper recovery techniques. Especialy at mud bogs, you see way too much unsafe stuff.

Chains defiantely have their place in recovery, the distinction comes in on how its done.

There's generally two types of recovery: with and without momentum to help.

If you are winching, or connecting up to a vehicle, slowly creeping all the slack out, and then slowly pulling (recovery vehicle has high traction), then chains are fine.

Now, when you are doing a 'snatch' type recovery, where you get momentum built up before the strap/chain/etc goes tight, therefore multiplying the amount of force, THAT is when a chain has a big issue.

If you get into the physics, its all about the impulse


Hehehe, here's a good thread about it on my local 4x4 board. You'll have to wade through lots of silly responses, too. There is some good info towards the end, though.

Another engineering/physics challenge - Great Lakes 4x4. The largest offroad forum in the Midwest

The bottom line is when you get a running start, and then hit the end of that chain, you have a certain amount of impulse. That 'impulse' is considered the amount of work to decelerate your tow vehicle from its speed to zero(assuming you don't yank the guy out successfully). The faster you stop, the harder the hit is, but for less time. Chain stops you *right now* and due to the math, the stresses are astronomical, although they don't last all that long.

Some examples from the above thread: (The thread above is kinda about how fast you'd have to go to break a strap....)

OK, so, there were some numbers in the thread that MCM posted, maybe we can make a practical example.

In this case, it was 20% stretch @ 50% rating.

So, if its a 30 ft, 30klb strap, that'd mean it'd stretch 6 ft @ 15k lbs.

So thats 2500 lbs/ft for a spring constant. Or we can say 3717 kg/m

If thats the case, then the strap should break when it hits 42 ft long (base of 30 + 12 feet of stretch).

So, if we have the equations from before with potential and kinetic energy, then we can solve for velocity V.

V = sqrt ((kx^2)/m)

So if you have mass of 2267kg (5000 lbs), stretch of 3.66 meters

V = sqrt ((3717 * 3.66 * 3.66)/2267)

v = 4.686 m/s = 15.365 feet/sec = 10.477 mph.

Lets see if it was twice as stretchy.. so the spring force is half (1858.5) but the distance travelled is twice as far, until it hits 30k lbs.

V = sqrt ((1858.5 * 7.32 * 7.32)/2267)

v = 6.6277 m/s = 21.73 ft /sec = 14.82 mph


So, as you can see, a stretchier strap will take a 'faster hit' before breaking, because it lowers the peak shock load.

Now, lets watch this get ugly.

Say you have a 20ft chain. It maybe will stretch 2" before snapping.

Say someone is going 10 mph when the chain goes tight..

kx = mv^2/x

kx = f

f = (2267 * 4.47 * 4.47) / 0.0508m (which is 2" of travel)

F = 891,667 kg = 1,966,126 lbs

granted, thats assuming the chain stopped you in 2", and that force isn't for more than a few milliseconds, but its a staggering figure.

 

[Haggar]

All that said, I keep proper sized chain (I use 3/8" properly rated for Jeeps/trucks), and use it as a choker, winch rigging, etc. Just don't use them to snatch.

Its funny, that most people respect/fear winching, but the majority of accidents that I see are caused by something failing during a snatch attempt. On smaller vehicles, most of us are switched over to synthetic rope for the winches, for the deuce, the 1/2" cable is far stronger than the shear pin. But with snatch-recoveries, you never know how good the strap is, or the guy's anchor point. You see people do idiotic things like hook to trailer balls. Makes a **** of a sling-shot...

 

[Kohburn]

heck, I've had a 1" wratchet strap (not used for towing or snatching, just tiedown) put a hole through my liscence plate when it let go.

stored energy can be pretty dangerous.

 

[emr]

Another really good post with alot of good info, even for us older guys, it is always good to be reminded of the what can and does happen.....

 

[Kalashnikov]

If you are using chain is should be suited to the application. You do not get a chain rated for 16,000lb breaking strength and use it to move 16,000 lbs. You should select the chain grade and size depending on the working load limit.

Grade 43 5/8 chain has a 13,000lb WLL.
5/8 grade 70 has a 15,800lb WLL.
5/8 Grade 80 has a 18,100lb WLL.
1/2 grade 100 has a 15,000 WLL.

I have used straps and chains as well. I perfer the method mentioned earlier of putting a tire in between the chains. I've been using a motorcycle tire between two chain for fullsize trucks and it has been the best method by far for snatching. CHains don't store kinetic energy like straps so there is much less force when a chain breaks. I'd prefer properly rated chain and a tire over straps. You don't have to worry about the chains rotting, UV rays, getting cut, etc.

 

[NRG]

If you are using chain is should be suited to the application. You do not get a chain rated for 16,000lb breaking strength and use it to move 16,000 lbs. You should select the chain grade and size depending on the working load limit.

Grade 43 5/8 chain has a 13,000lb WLL.
5/8 grade 70 has a 15,800lb WLL.
5/8 Grade 80 has a 18,100lb WLL.
1/2 grade 100 has a 15,000 WLL.

I have used straps and chains as well. I perfer the method mentioned earlier of putting a tire in between the chains. I've been using a motorcycle tire between two chain for fullsize trucks and it has been the best method by far for snatching. CHains don't store kinetic energy like straps so there is much less force when a chain breaks. I'd prefer properly rated chain and a tire over straps. You don't have to worry about the chains rotting, UV rays, getting cut, etc.

Just to clarify, are you saying that you take the chain and run it through a tire so if the chain snaps the tire will stop or slow down the snapping force?

 

[ODdave]

i think he is hooking the chains to each side of the tire (making it a link in the chain)

 

[Kalashnikov]

Just to clarify, are you saying that you take the chain and run it through a tire so if the chain snaps the tire will stop or slow down the snapping force?

No, there is a chain from one vehicle that the end is hooked around the tire. Another chain from the other vehicle gets hooked around the other side of the tire. The tire acts like a rubber band.

And to prevent anything with a hook from flying up into the air, point the open end of the hook facing the sky so if it slips off it will going towards the ground.

 

[Bob H]

...................................................................

And to prevent anything with a hook from flying up into the air, point the open end of the hook facing the sky so if it slips off it will going towards the ground.

Exactly!
Very important even when not jerking on it. be it a chain, cable, strap, rope doesn't matter.

 

[sigo]

Great info. The pirate 4x4 link is outstanding too. I'm probably going to make myself a little smartcard with some of the formulas and bits that I may need during a recovery op.

Army FM 4-30.31 (or Marine MCRP 4-11.4A) is the current manual for vehicle recovery. They combined recovery and battle damage assessment and repair into one FM.

 

[NRG]

No, there is a chain from one vehicle that the end is hooked around the tire. Another chain from the other vehicle gets hooked around the other side of the tire. The tire acts like a rubber band.

And to prevent anything with a hook from flying up into the air, point the open end of the hook facing the sky so if it slips off it will going towards the ground.

Wow I would of figured the tire would just tire apart. Very interesting.

 

[blybrook]

Wow I would of figured the tire would just tire apart. Very interesting.

If you use the wrong tire, it will. When I pulled out the dozer (as mentioned above), we used an old tire from the dump truck as our "link". For vehicles, I typically use a 16" steel belted radial tire unless the only thing handy is a 15".

They'll wear out after a couple uses, so use an old tire, then turn it into a potato planter! It'll be pretty much ready for the dump anyway, might as well get some extra use out of it.

 

[srodocker]

make sure if you use a chain or a strap you hook onto something that wont brake...i've seen a chain wrap around my buddys nice f250 and squish is like a tin can after trying to pull his cousin out because his hook up point snapped not the chain.