Recovery gear expense justification.

[2011TXPowerWagon]

Why not just use that gator jaw, rated at 32,000 lbs and only $40


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[adeluca73]

Negative, good buddy. This is a pure 2:1 system. Doesn't matter where the end of the line is attached, whether to the vehicle or a ground anchor. If the PULLEY moves, it is a 2:1 system, say 30klbs from our trucks. The lines would carry 15klbs each. Another way to view this is to count the feet needed from your line to move the load one foot. To move the snatch block one foot, you must pull one foot from the winch-side of your line and one foot from the anchor-side of your line. Hence why doubling the pull of the system also halves the speed. We used to do this all the time with rope rescue. All of the anchor-side attachments all go to one "bear paw". We were still capable of 10:1 compound systems.

The literature, some even published in the WINCH 101 section on this site, the Army manual for heavy vehicle recovery (AFMAN), and the Air Force manual for ground aircraft static maneuver, plus any undergraduate vector mechanics texts say otherwise. When the line is attached to the vehicle, the outbound line and the inbound line share 1/2 the total load, thus you're winch is doing 1/2 the work, and you get a 2:1 advantage--called a travelling block or movable pulley. When the load is attached to a fixed point, you're getting 1 lb of pull for every 1 lb of resistance, and the sheave anchor is experiencing 2x the input load. I've attached two Free Body Diagrams to illustrate. But essentially you're correct in the Sheave has to be rated minimally for 2x the max expected load and the shackle attached to the winch has to be minimally rated to 1x max expected load. Max expected load is a function of the vehicle weight, surface coefficient, and ground pitch/gradient.


This is from the DODGE POWERWAGON WINCH MANUAL:

In the illustration above, IF the bitter end of the line is *not hooked to the winched vehicle*, but is hooked to a tree or rock next to it, for each pound of winch force applied, the block will be under *twice* the load, while the line strain will be equal to the line pull. So if you apply a full 12,000 pounds of pull, you are putting 24,000 pounds of stress on the block/anchor. If, however, the bitter end *is* attached to the winched vehicle, the block becomes a "traveling block", even though it is attached to a solid object, because the vehicle itself is actually doing the "traveling", and the load on the *line* is halved, since you are using two lines to "support" the load. In this case, the mechanical advantage is 2/1, so you get 2 pounds pull for each pound of winch effort. Now, since you have two lines splitting the load, let's say it's 10,000 lbs. (you're *really* stuck), the line load is halved to 5000 lbs per line, but the *block* load is still 10,000 lbs because of the parallel line angle factor of 2. As you can see, while the load on the winch is cut in half, as is the line speed for winding, the load on the block is *not*, and is equal to the total line load.

This is why using a properly rated and carefully maintained block is of the utmost importance when winching. In most winching situations, "double-lining" is the best method to reduce stress and strain on the lines and winch motor, at the expense of speed, but may be the *worst* thing you can do from the safety or block standpoint, if your block is not adequately rated or is in poor condition or if you don't know the strength of the anchor or the stall-pull of your winch. The block is being subjected to twice the force of any of the other components, and consequently the winch operator may never know he is exceeding the capacity of the block until it parts and takes his head off. This is especially true when using very powerful winches.

Imagine the stress on a block (and it's anchor as well) when the SUV owner with the Warn 12,000 lb winch double lines to pull his vehicle over an obstacle and sticks a wheel behind a rock, locking the vehicle in place. The winch is already rated for 6 tons single line pull, and adding a traveling block doubles the pulling force to 12 tons. If your snatch block is (as many are) underrated for the winch/line combination, and you have a 6 ton rated snatch block, or even a "really big 8 ton-rated" block, which is commonly sold with RV winches, you still have the potential of block failure because you are using a 6 - 8 ton block with a system capable of exerting 12 tons of force under circumstances where you might not recognize the actual pulling force you are exerting, because you are not really stressing out the winch.

http://dodgepowerwagon.com/glovebox/sna ... basics.php

[DamageWagon]

adeluca thanks for putting those up. I was picturing things wrong in my head with reference to the first model. I'm used to systems where the pulley moves and the vehicle would be static. Opposite of what is happening in our case you are dead on.

On the second model, the important takeaway is that, if you have a movable load such as an 8,000lb truck, and the truck does move and we don't consider any other multipliers - just say we are moving 8000lbs - then the pulley carries 8000lbs and the line carries 4000lbs each side. Sweet! We must also consider the inverse and danger involved here. If the load is massive, or does not move, your winch capacity of 15,000lbf max is now felt by both sides of the line, and the pulley feels 30,00lbf. Dangerous. This is not shown by the diagram, but this scenario is exactly how we set up our most basic rope rescue system. Single pulley, 2:1 mechanical advantage. You pull 2 feet of rope and the load moves 1 foot. You apply 100 pounds force to the rope, the load feels 200 pounds force. This is the system where things break.


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[Bill2014]

Hence my Warn 63490 33,000 pound snatch block and 30,000 pound tree protector.




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[MSCH2112]

Hence my Warn 63490 33,000 pound snatch block and 30,000 pound tree protector.

same here. got 2 of them. they are not cheap but it's stout hardware.

mike

[OffroadTreks]

Dang, now I feel inadequate with my 20000lb ARB snatch block and 26500lb tree saver.

[DamageWagon]

Dang, now I feel inadequate with my 20000lb ARB snatch block and 26500lb tree saver.

It's ok Mike, as long as you have a AAA Card you don't need any of this stuff.....



Right?



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[FordyceCreekTrail]

Ahhh, this reminds me of some good times. Snatch block is something you NEVER use until you need it, and when you do, boy do you need it. Great thing about synthetic is it also takes some weight off the rig, and that can never hurt. Not to mention it floats when you need it to. For some reason under 100' of line never seems to be enough, but over 100 usually gets it done.

[TwinStick]

Maybe because everyone gets a different price. If you order one, or order 20, or order 500 things, you get s different price. It's the 21st century, but that's the same way it's been forever so I don't see why you could get upset at that.


Sent from my safe space

Not upset, just frustrated when people make it more difficult than it has to be. Everyone has heard of bulk pricing. A LOT of other websites have bulk pricing too, but they post them for all to see. How friggin hard is that ?
1-10 $xxx each
11-50 $xxx each
50-500 $xxx each.

See how easy that was.

If someone sold wine, had a website. with a picture of the bottles but had no description of taste or no price & said "If you want to know how much it cost or how it tastes---call us", I'm just thinking they wouldn't sell as many bottles of wine, as if the description & price was right there, that's all.

[adeluca73]

adeluca thanks for putting those up. I was picturing things wrong in my head with reference to the first model. I'm used to systems where the pulley moves and the vehicle would be static. Opposite of what is happening in our case you are dead on.

On the second model, the important takeaway is that, if you have a movable load such as an 8,000lb truck, and the truck does move and we don't consider any other multipliers - just say we are moving 8000lbs - then the pulley carries 8000lbs and the line carries 4000lbs each side. Sweet! We must also consider the inverse and danger involved here. If the load is massive, or does not move, your winch capacity of 15,000lbf max is now felt by both sides of the line, and the pulley feels 30,00lbf. Dangerous. This is not shown by the diagram, but this scenario is exactly how we set up our most basic rope rescue system. Single pulley, 2:1 mechanical advantage. You pull 2 feet of rope and the load moves 1 foot. You apply 100 pounds force to the rope, the load feels 200 pounds force. This is the system where things break.


Sent from my safe space

Hey no problem, I'm glad all that Govn't sponsored education can be used for something productive

A little pentagon down time & PowerPoint are a dangerous elixir...

[adeluca73]

Hence my Warn 63490 33,000 pound snatch block and 30,000 pound tree protector.




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I've got 2x these : https://www.amazon.com/gp/aw/d/B003CG9P ... ref=plSrch

And 1x this one: https://www.amazon.com/gp/aw/d/B004XG3K ... atch+block

[TwinStick]

Is that the "exact" one you have 2 of ? Do you have smaller dia synthetic line on your winch ? The reason I am asking is our Cable is 7/16" & that snatch block is only up to 3/8".

[adeluca73]

Is that the "exact" one you have 2 of ? Do you have smaller dia synthetic line on your winch ? The reason I am asking is our Cable is 7/16" & that snatch block is only up to 3/8".

no, it's a representative of that smitty built style and strength rating.

[TwinStick]

Cool.

[CombatWombat]

I took a Snow Chain from a Semi and shortened it.
My Tires are 315/70r17 that is 35x12.5r17
My Semi Chains are for 315/80r22.5

So just cut it down in length and you have a very Bulletproof Chain for your Money.

Only Tools requiered are Bolt Cutter and Eye Protection.

Greetings from Germany



You can go fast.
I can go anywhere.
Dodge Powerwagon