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Old 01-11-2009, 10:33 AM
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Default Winching and Recovery Calculations

Now I know I am probably going to get my head chewed off here but this is what we use at work for recovery.

Total pull required = Rolling Resistance (RR) + Gradient Resistance (GR) + Damage Resistance (DR) + Safety Factor.

RR = Vehicle Weight / Ground Factor when
Ground Factors
Smooth or hard road = 25
Grass = 7
Hard wet sand or gravel = 6
Soft wet sand = 5
Loose drty sand most beaches = 4
Gibber desert = 3
Clay and black mud = 2
Vehicle completely submerged to chassis or higher = 1

GR = Vehicle weight divide by 60 times the angle of the slope or the full weight if above 4 degrees

DR = One locked wheel unable to turn locked up and no drive add 250kg

SF = 25% of the total of RR, GR and DR

So lets say my Patrol weighs 3t is stuck in clay to the axles on a 25 degree slope with one wheel siezed up (monumental stuck)

3000kg divided by 1 (RR) = 3000kg
3000kg divided by 60 times angle of slope (GR) = 1250kg
add 250kg (DR)
Pus a saftey factor (3000+1250+250) / 4 = 1125kg

So my winch is required to pull only 5675kg on a single line add one snatch block and its only 2837.5 kg

so as you can see the only time your vehicle will weigh its total mass is stuck beyond the axles at an incline of greater than 45 degress.

I have worked for nine years with lifting equipment as a rigger and feel confident inthe above calculations.

Feel free to start the hate mail if you wish
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Old 01-11-2009, 11:06 AM
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That all sounds great but my rule is always use snatch block in any winch recovery to save the winch, has not let me down so far.
By your calculations its about right.

cheers.
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Old 01-11-2009, 12:09 PM
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Cool. I just hook up my winch and go, if it doesn't like it, then I go double line.... still no good, I go triple line....

2 many numbers....
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Old 01-11-2009, 01:32 PM
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Quote:
Originally Posted by marin View Post
Cool. I just hook up my winch and go, if it doesn't like it, then I go double line.... still no good, I go triple line....

2 many numbers....
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Old 01-11-2009, 01:54 PM
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I always try to use a snatch block also get the full line out its where the winch wants to be. I only have an 8000lb low mount on my GUIV Wagon and we use winches at work with a rated line pull of under half the GVM (6t winch for 12 t vehicle and 10t winch for a 22t vehicle). I guess what I'm trying to say is that you don't need the biggest winch or even one rated at 1.5 times the weight of the vehicle just use common sense.

I have seen some people say that when you vehicle is bogged to the axle that your vehicle can weigh as much as three times in the winches perspective. I have used these calculations for years and never had anything go wrong.
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Old 01-11-2009, 02:09 PM
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Quote:
Originally Posted by marin View Post
Cool. I just hook up my winch and go, if it doesn't like it, then I go double line.... still no good, I go triple line....

2 many numbers....

I agree, i do the same


Plus why is your petrol bogged?
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Old 01-11-2009, 03:09 PM
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Quote:
Originally Posted by robert1875 View Post
I always try to use a snatch block also get the full line out its where the winch wants to be. I only have an 8000lb low mount on my GUIV Wagon and we use winches at work with a rated line pull of under half the GVM (6t winch for 12 t vehicle and 10t winch for a 22t vehicle). I guess what I'm trying to say is that you don't need the biggest winch or even one rated at 1.5 times the weight of the vehicle just use common sense.

I have seen some people say that when you vehicle is bogged to the axle that your vehicle can weigh as much as three times in the winches perspective. I have used these calculations for years and never had anything go wrong.
Not disagreeing with your numbers at all, just who actually sits there and works out that stuff whilst out wheeling?

When you buy your gear, you buy the stuff that is rated appropriately, you maintain your equipment/gear, and then you rely on experience/other peoples experience/your senses (eg sound the winch is making, what you can see, if your winch starts to smell like its burning up, if you hear noises that don't sound right) and common sense to tell you what is the right way to winch in a particular situation and what is the right gear to use (lets not start any debates on common sense lol)

Understandably in a work situation, you need to cover your arse by having done all the calcs/lift studies/JHA's/JSEA's/THA's/Take 5's......
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Old 01-11-2009, 04:04 PM
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There just seems in my opinion a lot of misconceptions about what size winch to use when i was chasing a quote to rebuild my winch at 4wd shops i was constantly being told i should not use this winch on my patrol as it is grosely underated and being told if i value the safety of my wife and kids i shouldat least be putting a 12000lb'er up the front, and that i an irresponsible 4wder for not using the appropriate sized winch,i understand that they were probably trying to make a sale but there just seems to be a lot of people out there who can't get their head aroung the physics of it all.
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Old 01-11-2009, 05:27 PM
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I agree with Marin..

I've seen plenty of patrols (EG my old club) with 8000 lows going nowhere winching... and plenty with 9000's struggling.my 10k warn struggled few times too. Sometimes you dont have access to put in a second block, eg sand driving isnt the easiest place.

Difference in price/weight of 8000/9000 isn't spit.

If your happy with your 8000, stick with it.

YMMV.
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Old 01-11-2009, 06:19 PM
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considering my 8000lb is about ten years old i'm pretty happy i haveseen blokes go back to a 4wd shop within 2 to 3 months of bying a 12000lb and its cactus cos they don't know how to use and care for a winch
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Old 01-11-2009, 06:35 PM
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Quote:
Originally Posted by robert1875 View Post
considering my 8000lb is about ten years old i'm pretty happy i haveseen blokes go back to a 4wd shop within 2 to 3 months of bying a 12000lb and its cactus cos they don't know how to use and care for a winch
Im not saying you need a ****box 12,000. But I wouldnt go near under 9000, and if 10k's werent so heavy, I'd go another one of them.
.
If you buy cheap **** you get cheap ****.

Anyway this is just going to go round in circles.
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Old 01-11-2009, 07:41 PM
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I dont think 8000lb is to small for a patrol. This was a very popular size for many years before all the cheap 12000 came on the market. Now everyone thinks that if you dont have a big ass winch it wont pull you out of a bog
The ratings are a safety rating, not a how easy/fast it will get you out rating.
Even highmounts as used in comps are 8000lb in there standard form.
Out of interest Warn recommends a winch rating 1.5 the weight of your vehicle.
You will know fairly quickly if you need to use a snatch block or not lol.
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Old 01-11-2009, 08:16 PM
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for the record they weren't these cheap winches they were warn 12000lb. i doesn't matter if you have the biggest or badest winch or whatever it is for that matter if you don't look after it, it won't look after you a little maintenance and sympathy on your equipment will go a long long way. if its good enough for a comp vehicle to run and 8000lb hi mount why does a 4wd shop say an 8000lb low mount is so much worse, 8000lb's is still 8000lb's. i know they modify them. i had one shop tell me to put one of the new warn motors in it and it'll be like a 10000 or even a 12000lb for stall rating but the cable will still only be 8mm or 3/8.

i just wanted people to know is that there are standards out there for winching.

here is another one, in my scenario up the top while the snatch block did half the load on the winch it didn't on the anchor how many people out there use 6t or higher shackles and other recovery equipment i know that a 3.2t shackle wontgive at anywhere close to these loads but hey safe working loads and all.
cheers.
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Old 01-11-2009, 08:29 PM
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Aren't the SWLs generally about 1/3 or 1/4 of the failure rating?
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Old 01-11-2009, 08:59 PM
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about 1/5 i was told on my riggers course unfortunately the likes of warn don't have to abide by these but its still a sake working stress go over it and somebody gets injured or worse watch out for the legalities even in our hobby.
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Old 01-11-2009, 09:35 PM
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It's a good post and good info. I think my heaviest rated shackle is 4.7t. It doesnt take too long to blitz that.

I guess thats why it's important to always watch the safety issues.

Coroners and coronial investigators are so humourless these days.
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Old 02-11-2009, 08:26 AM
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Quote:
Originally Posted by robert1875 View Post
here is another one, in my scenario up the top while the snatch block did half the load on the winch it didn't on the anchor how many people out there use 6t or higher shackles and other recovery equipment i know that a 3.2t shackle wontgive at anywhere close to these loads but hey safe working loads and all.
cheers.
yay . i win.. i use 6.5 t bow shackles and made a high tensile recovery hitch to go into the towbar that suits my shackles.
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Old 24-12-2009, 02:32 PM
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I just seen this thread almost identical as what I have been taught. I was told that the safety factor is 4 for shackles for lifting and two for dragging, so a shackle that will deform at 18.8t will have a WLL/SWL of 4.7t but when dragging a vehicle that same shackle will have a RLL (recovery load limit) of 9.4t.

I have my recovery book in my car all the time. It also goes into the mechanical advantage of using snatch blocks but as you put it through you encounter friction and it reduces the 'actual mechanical advantage' ie: two block 1.8 to 1, 3 blocks 2.5 to 1, 4 blocks 3 to 1, but it also shows you how to do direct and indirect compound tackle layouts so using 2 snatch blocks you can get a 4 to 1 pull ratio but an actual ratio of 3.2 to 1 taking into account friction.

An interesting point that seems to create confusion around the blokes I go wheeling with is that if you use a snatch block on a fixed anchor and attach to a vehicle being moved (first order lever in physics) you dont gain a mechanical advantage, but if the block is attched to a vehicle being recovered and the hook back to an imovable anchor you get that mechanical advantage back (second order of lever). Another example self recover attach a block to an anchor and the hook to another anchor no mechanical advantage, attach a block to an anchor and back to yourself mechanical advantage gained, so in order to gain mechanical advantage the block should move closer to the effort (winch).

It all gets so confusing when you delve deeper into the physics involved in recovery, my head hurts now. Just some more info for those people who are interested.
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Old 24-12-2009, 04:38 PM
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Quote:
Originally Posted by vaughnGU4 View Post
I just seen this thread almost identical as what I have been taught. I was told that the safety factor is 4 for shackles for lifting and two for dragging, so a shackle that will deform at 18.8t will have a WLL/SWL of 4.7t but when dragging a vehicle that same shackle will have a RLL (recovery load limit) of 9.4t.

I have my recovery book in my car all the time. It also goes into the mechanical advantage of using snatch blocks but as you put it through you encounter friction and it reduces the 'actual mechanical advantage' ie: two block 1.8 to 1, 3 blocks 2.5 to 1, 4 blocks 3 to 1, but it also shows you how to do direct and indirect compound tackle layouts so using 2 snatch blocks you can get a 4 to 1 pull ratio but an actual ratio of 3.2 to 1 taking into account friction.

An interesting point that seems to create confusion around the blokes I go wheeling with is that if you use a snatch block on a fixed anchor and attach to a vehicle being moved (first order lever in physics) you dont gain a mechanical advantage, but if the block is attched to a vehicle being recovered and the hook back to an imovable anchor you get that mechanical advantage back (second order of lever). Another example self recover attach a block to an anchor and the hook to another anchor no mechanical advantage, attach a block to an anchor and back to yourself mechanical advantage gained, so in order to gain mechanical advantage the block should move closer to the effort (winch).

It all gets so confusing when you delve deeper into the physics involved in recovery, my head hurts now. Just some more info for those people who are interested.


What he said!!

i use the rule when setting up the snatch block for determining if it give mechanical advantage (which is the point of using it) is - "If it aint spinning then it aint doing nothing". It is just being used to change direction of the pull... The snatch block wheel must be rotating to be adding mechanical advantage..

I understand the posts above regarding "If the winch is struggling then its too heavy and add a snatch block" At the end of the day the point of the info here is for people to actually understand HOW BIG the weight can GET! The rolling weight with all the factors can get to the limit of your winch very quickly, no problem put in a snatch block. You will find the limit of your winch extension strap next and without thinking about it.

The main thing that people need to take away from the "Numbers Game" above is to think about how your vehicle is bogged and how much heavier it is than a rolling car, how much suction is in that bog hole, how steep is that hill. I have seen stuff break a few times and it aint good! "hit it a bit harder", "give it another go", "she'll be right mate" Just dont cut it

Big recoveries need consideration of the situation far more than they need Brute force. consideration and discussion may find a better way.
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Old 24-12-2009, 05:25 PM
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Pardon my ignorance, but is there such a thing as a "maximum current limiter" for winches, to avoid burning out the battery and electrics, or is this not what happens or not neccessary? Ive never had the pleasure of seeing a winch stop due to overload, not from memory.
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