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Recovery Formula...

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Old 07-11-2009, 04:56 PM   #1
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Recovery Formula...

Resistance & Effort Required
There are a few different forms of resistance.
Grade Resistance
Overturning
Mire
Other: Cargo and Tackle

Grade Resistance is created when a vehicle is disabled on a slope. The cause of the resistance is the vehicles weight as it is affected by gravity. This makes the resistance equal to the vehicles weight. I will be using 5500lbs as the example vehicle weight. I believe this is approximately what the double cabs weigh. Correct me if I’m wrong please. So if needing to be recovered on a slope my resistance will be 5500lbs.
Overturning Resistance is the part of the vehicles weight that will act against the effort to upright the vehicle. The cause is the vehicle’s weight beyond the center of gravity which is estimated at ˝ the vehicles total weight. If trying to overturn a Double Cab Toyota resistance would be 5500/2= 2750lbs.
Mire Resistance is created due to the contact of the mud/terrain between various components of the vehicle. A vehicle is considered mired (stuck) when it can no longer propel itself.
Three depths of mire:
Wheel = equal to vehicle weight 5500lbs
Fender = 2x vehicle weight 11000lbs
Cab = 3x vehicle weight 16500lbs

(Remember that the type of mire may cause more or less resistance, ie clay, dry dirt, mud, snow etc...)

If it is to the top of the tire then you can figure that you are in the fender depth realm. If it is up to the hood then you can figure you are at cab level. Obviously if your frame is high centered then you are immediately in the Fender Mire zone since it will be producing resistance as you recover.
Cargo Resistance is self explanatory. What you are packing and who’s fat ass is in the driver’s seat all has to be added to the vehicles weight to be incorporated into your resistance.
Tackle Resistance is the resistance your pulleys have AGAINST you. Yes your tackle will cause some resistance since there is friction as the cable passes through the pulley,however the benefits of using a pulley far outweigh the resistance. The Tackle Resistance is calculated at 10% per pulley used and is factored into the formula AFTER you have done all the calculations to find out what the total resistance against you will be. Nevertheless, it must be calculated because that resistance can be the difference between you working hard and working smart. You could assemble a 2 point rigging and try winching for a while only to find out you needed a 3 point rigging.
Example:
Toyota DC using 2 pulleys- 5500 X 20% or(.20)= 1100 Now 1100+5500= 6600lbs that your winch has to pull when you thought it would only be 5500lbs. 1100 pounds can be the deciding factor on what your rigging configuration will be when you also factor in Mire depth and Cargo.
Resistance Reducing Factors
Pulling in the opposite direction of travel will reduce resistance by 10%. So if you fly into a mud hole head on and are recovered from the rear it will reduce the resistance of the total weight by 10%
Applying power to the mired vehicle’s wheels MAY reduce resistance up to 10% also. I say “may” due to the fact that even though they are turning they may not be getting traction due to clogged tread or slippery terrain. Make your assumption and either subtract the 10% from your weight or not, each situation will dictate. It is still something you need to factor in.
Winches
Know your line pull as opposed to how many wraps are on the drum. For a Warn M8000lb 12V system on the top layer you are only getting 6630lbs.


I went with the 1st layer being the 1st layer you start out with not the last one that will be on the drum when all your cable is out. I know they do it opposite on the websites that post the specs for these winches. You will notice how there is a difference between the winches that are both rated at 9000lbs. one has 25 more feet of wire and this cause it to have an extra layer on the drum which in turn diminishes the 1st layer pulling power by 440lbs. something to keep in mind when buying winches. You can always carry a 25’ extension.
If I was only able to use the 2nd wrap on a 9000i due to terrain constrictions and my 5500lb Taco had 1600lbs of Cargo and Resistance working against me(winch Bumpers, rock sliders, belly skids, non-stock tires, gear stowed in bed and cab etc…, + my 150lbs soaking wet)then I would not be able to recover the vehicle, however with a M9000 I would be good to go and they are both 9000lb winches. Just something to think about.
Anchors and Guy Lines
There is a lot of information and it would be easier if I didn’t just cut and paste from a document you could download on this subject. I found a good one and to download it all you have to do is sign up for an account which is free. It’s just like signing up for an email. You have to click the download icon and then select PDF and it will ask you to sign up. It has good information for when you don’t have another vehicle with you and you need to create your anchor for the winch. This is the link.
http://www.scribd.com/doc/3874179/ch4-Anchors-and-Guy-Lines
That is just chapter 4. if you want you can get the whole Army Riggers handbook here.
Army Rigging Handbook FM 5-125

Resistance and Effort Required Formula
Now that we have talked about all the information lets put it all together to make the formula that will determine the EFFORT needed to recover.
W x M – RF + TR = Resistance
W= Weight
M= Mire
RF= Resistance reduction Factors
TR= Tackle Resistance

So let’s just say we stopped by a scale on our way out to the trail and weighed in at 6500lbs. You have a Warn M8000 winch and the vehicle gets stuck and is mired above its tires just touching the “skirt” of the truck (Fender Depth). We are able to pull the in the opposite direction of travel out of the hole and he will be able to apply power to the wheels and can get traction with them.

W(6500)X M(2)-RF(20% or.20)+TR(10% or.10)= Resistance
(Or Effort Needed)
6500 X 2= 13000
So we know that there is 13000lbs of resistance working against us. Now multiply that number by the Resistance reduction Factors or RF. 10% for opposite direction and 10% for tires getting traction.

13000 X .20= 2600 So since RF is a help to us we subtract it from the weight.

13000 - 2600= 10400

Now we can figure Tackle Resistance or TR which is a hurt to us so we add it to the weight. We are using 1 pulley so we only have one sheave worth 10% of our resistance weight up to this point which is 10400.

10400 X .10= 1040 We have to add this to our resistance weight since TR is a hinderance to us.

10400 + 1040= 11440

So 11440 is the Resistance that we need to overcome and our Effort (pulling power) must be more than that. Now in this scenario no matter what layer you are at on the drum you will be fine to recover. The first layer is still going to give you 13260 which is greater than 11440.

But what if we couldn’t pull it in the opposite direction of travel and the tires could not get traction? Then 13000, the original weight after mire is calculated, does not get 2600 subtracted from it and the 10% of Tackle Resistance is now 1300 added to 13000 which makes our total resistance 14300 now.

Now all of a sudden we either need another pulley or we need to be able to pay out our line to at least the end of the 3rd layer which will get us 14560lbs of pulling effort according to the Warn specs.

So now you see that just a few changes in the situation can cause you to waste efforts and have to re-rig your gear. MEASURE TWICE CUT ONCE right?

A couple of things to note here…

If any portion of the vehicle qualifies for a certain type of mire then you should safely just consider that your mire depth. Just because the front end is sunk and the rest of the truck isn’t, does not mean your still at wheel depth and “kinda sorta” fender depth. Better safe than sorry so go fender depth.

I realize that sometimes you may be in the bottom third or top third of a mire depth and it will not always be in increments of the vehicles weight but again it is better to round up so we stick with doubling or tripling the vehicle weight to always be safe with our calculations.

You may be asking yourself, How do I know what to put in for Tackle Resistance if I haven’t found out what my total resistance is? At the beginning of a recovery you estimate your mired depth and then multiply it by your vehicle weight accordingly. Then divide it by your winches peak pulling capacity. If I was at fender depth and the vehicle weighed 6500 then it would look like this. 6500 X 2= 13000. 13000/8000= 1.625
So I now know that I need at least 1 pulley. From 0.00 to 0.999 I can get away without a pulley. But even if it is 1.01 I need a 2 point rigging which requires 1 pulley. And at 2.01 I need 3 point rigging. Always round up. This is only a way to estimate. You will find out if you need to up the configuration when all math is done.

Recovery is all math incorporated with the specs and weight of the equipment involved. If you want to guess and check then so be it but we use this all the time and know what is needed when it is needed. Once you get the hang of it and know your vehicles weight when heading out you can almost do it in your head but in some cases you will be cutting it close and need to calculate it out exactly.


Just an FYI on the use of pulleys and your winch's pulling capacity...
When it is said that a winch's capacity is doubled or tripled it is the short way to explain that the work effort the winch needs to put out to pull the load is being reduced so the winch feels like it is pulling less weight than it really is.

A 10000 lb load can be pulled by a 5000 lb winch if a pulley is used (understanding that i am not factoring in tackle resistance, mire or anything else, i am just using an example to get a point across). This does not mean that the winch is pulling at a force of 10000 lbs. The gears are how the gears are. They can only give you 5000 lbs of pull at max. But through the use of a pulley we can reduce the "Resistance" by half.
Notice in the formula that if we use one pulley we doubled the pulling power of the winch. This is the same as saying the Resistance has been reduced by half through the use of one pulley. It just makes the formula easier if you find the resistance and then see how many times you need to double your winch's power to pull that amount. Because then you automatically know how many pulleys you need

In the end YES a 5000 lb winch CAN pull a 10000 lb load if rigged properly. But we all know the winch is not ACTUALLY pulling 10000 lbs. This is really why it is explained as doubling/tripling the winch capacity. its easier understood. but For those of you who may have been misled I hope this clears it up

Now..., a tip for the one person who is comprehending all this on the first read


You can double the power of the winch or "reduce the Resistance" (depending on how you want to look at it) to help out on the power draw. If your winch can handle the load with a one point rigging but it is no trouble to add a block then why not? You will be making the winch pull with less effort and in doing so your winch will require less amp draw which will in turn be easier on your battery life should you not have a very effective power source setup. This will also increase the life of your winch since it will not be working as hard when it is employed.

a Warn 9000i pulling an 7000lb load could easily tackle that resistance. But if you throw a pulley in there then the winch will feel like it is only pulling 4500 lbs and will be drawing less amps and not working as hard.

Just another tip to throw out there.


Here are some rigging configurations:
I've actually had to use the 4 point rigging before.




One more Note:
A Pulley is only going to enhance your pulling power when employed at sharp angles. This will always happen when the pulley is attached to the vehicle that needs recovered and the line is ran through it and then back to the vehicle with the winch. Just because you are simply using one does NOT mean you are reducing the resistance by as much as you think you are.

When using a pulley that is attached to a natural or man made anchor point just to get a better pulling angle on the vehicle that needs to be recovered, (like in the MonkeyProof's post on this page), you may not be receiving the full potential that the pulley can give you depending on how it is rigged. Pics will explain below.

This rigging will give you the least amount of resistance reduction however it may be the only practical way to recover the stuck vehicle given the predicament you may be in.


With the rigging below you will be doing much better however depending on the terrain it may be impractical. But knowing this adds a bit of knowledge to your tool box should you need to get a better angle on a vehicle that needs to be recovered.

Instead of thinking only about how to get a better angle on the vehicle, you can be thinking of how you can get that angle AND reduce the resistance as much as possible in the process.

Remember this may be impractical depending on the situation. In the service we always say "The situation dictates everything"!

As for the percentage of reduction to the resistance VS the degree of the angle from the pulley, I am not a mathematician but i'm sure there is a way to apply a formula to it. We all get the point though.



You can get fairly exact with this once you get it down but you will have to learn on your own what situations call for what type of rigging. If the mud you are stuck in is clay and apt to cause a suction action to the vehicle it may increase the resistance more than you initially thought.

Some people have a knack for certain situations while some people have a knack for other situations. It depends on what we have been subjected to in our lives. I have had the privlege of conducting recovery ops in various environments thanks to the Corps with my MOS being LAV's and I still haven't seen it all. So we can all learn from each other that is for sure...

Everyone put in your thoughts. Any corrections or additions and we'll edit this puppy. (Its been done once... it can be done again)
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Old 07-11-2009, 05:16 PM   #3
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So if the train leaving Chicago on track 7 at 55mph is heading towards Omaha.....
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Old 07-11-2009, 05:23 PM   #5
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Yeah there is a lot of info but once you get the hang of it it really isnt that much. just take a couple wuick seconds and your on your way.

Not tanks, overhead view of an LAV. i was gonna look for some Toyota pics and insert but i had been typing for a while...call me a quitter
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Old 07-11-2009, 05:25 PM   #6
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Quote:
Originally Posted by gjbonner View Post
Yeah there is a lot of info but once you get the hang of it it really isnt that much. just take a couple wuick seconds and your on your way.

Not tanks, overhead view of an LAV. i was gonna look for some Toyota pics and insert but i had been typing for a while...call me a quitter
I call that good head work- Not quitting. Good use of resources!!
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Old 07-11-2009, 06:33 PM   #8
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That is the reason that I bought the biggest winch I could for my work truck along with a snatch block to double it up.
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Old 07-11-2009, 07:04 PM   #11
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Quote:
Originally Posted by Brunes View Post
Yeah...I was shopping winches the other day....and I was trying to figure out wtf I was going to need a snatch for and what kind of rating I wanted.

I think now- I'll be getting a far heavier winch than I was looking at...and at least a pair of snatches...

a snatch block is essential to have for recovery other then using it to reduce load pull..can allow to use a winch and odd angles to conduct a recovery...

here's my buddy Tim who attemted the "Gate Keeper" at Calico...twisted his rear driveshaft and debeaded 2 tires all withing 2 minutes...if we didn't have that snatch block, recovery would've been next to impossible..




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Old 07-11-2009, 08:28 PM   #12
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good post monkey proof...i kinda left out the stuff about dead lines and not exceeding your fall line force. Maybe i'll get around to editing that.

also you gave me an idea. either we can post them on here or make a thread for it but what about crazy recovery operation pictures like Monkeyproofs or even just simple ones. it could give a newbie at this stuff some ideas on how to think outside the box.
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Old 07-11-2009, 09:52 PM   #14
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Excellent writeup. Sticked for reference.
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Old 07-11-2009, 10:22 PM   #15
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Quote:
Originally Posted by timmer View Post
if that wire rope breaks the hefty guy in the white is going to be about 8 pounds lighter really quick when the lash takes off his fricking head
that one particular pic was taking while setting everything up...believe me and you..everyone was WAY clear once the actual wenching haha started!
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Old 08-10-2009, 10:26 PM   #18
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+1 to rep, thanks for the info man

Josh
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Old 08-11-2009, 09:15 PM   #19
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Old 08-11-2009, 10:15 PM   #20
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so what happened to all the other stuff that i had posted in this topic? was tooo much?, too involved? it certainly was not "off topic" as it all was all on topic with winching operations and recovery.
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