Winching Formulas

[Hymie]

Has anybody read Australian Four Wheel Drive Monthly, particularly Pat Callinans article on how to winch and calculate how much force is needed to extricate a bogged Forby?
What a load of rubbish!!
Read Pats "formulas" for calculating required pulls then sit back and consider a few thing I'm going to teach y'all.
Pat is right on a few things, there are 4 types of resistance to take into consideration.
1. Rolling Resistance, this being the resistance to motion given the surface the vehicle is on, ie, Bitumen, Grass, Sand or Mud
2. Gradient Resistance, the effort required to overcome gravitys pull on an incline
3. Damage Factor, did you damage anything that might increase resistance tomotion, rip a tyre off a rim, bend a steering arm etc.
4. Add a safety margin.

To work out rolling resistance, take the weight of your vehicle and divide it by a. 25 for bitumen or concrete
b. 10 for gravel
c. 7 for grass
d. 5 for sand
e 2 for mud

To work out Gradient resistance,
a. calculate the slope
b. Factor 1/60th of a tonne for every degree of slope

To work out a Damage factor,
throw in 25% of the vehicles mass for every damaged wheel.

Safety Factor is 25% of the total of all of the above.

This will give you a Total Pull Required. (TPR)

Sooooooo.
Using the example in the magazine of a 3.3 tonne GU Towning a 1 Tonne Camper trailer Bogged to the chassis.

RR= 4.3/2= 2.15 Tonne
GR=0
DF=0
Total =2.15 Tonne
Safety Factor 2.15/4=.53 Tonne

TPR=2.68 Tonnes

A whole lot less than the 12.9 Tonne quoted!

Lets do another,

Blknight.aus has a fully loaded Big Red of around 3 Tonne stuck on a muddy slope of around 40 degrees. ( sorry Dave, hope you don't mind)

RR= 3/2 = 1.5
GR= 3000kg/60*30=1.5 (1500Kg)
DF=0
Total = 3.00
Safety Factor = 3.00/4=.75
TPR=3.75 Tonnes

Now you know why Tirfors are so much fun:)

[Blknight.aus]

Has anybody read Australian Four Wheel Drive Monthly, particularly Pat Callinans article on how to winch and calculate how much force is needed to extricate a bogged Forby?
What a load of rubbish!!
Read Pats "formulas" for calculating required pulls then sit back and consider a few thing I'm going to teach y'all.
Pat is right on a few things, there are 4 types of resistance to take into consideration.
1. Rolling Resistance, this being the resistance to motion given the surface the vehicle is on, ie, Bitumen, Grass, Sand or Mud
2. Gradient Resistance, the effort required to overcome gravitys pull on an incline
3. Damage Factor, did you damage anything that might increase resistance tomotion, rip a tyre off a rim, bend a steering arm etc.
4. Add a safety margin.

To work out rolling resistance, take the weight of your vehicle and divide it by a. 25 for bitumen or concrete
b. 10 for gravel
c. 7 for grass
d. 5 for sand
e 2 for mud

To work out Gradient resistance,
a. calculate the slope
b. Factor 1/60th of a tonne for every degree of slope

To work out a Damage factor,
throw in 25% of the vehicles mass for every damaged wheel.

Safety Factor is 25% of the total of all of the above.

This will give you a Total Pull Required. (TPR)

Sooooooo.
Using the example in the magazine of a 3.3 tonne GU Towning a 1 Tonne Camper trailer Bogged to the chassis.

RR= 4.3/2= 2.15 Tonne
GR=0
DF=0
Total =2.15 Tonne
Safety Factor 2.15/4=.53 Tonne

TPR=2.68 Tonnes

A whole lot less than the 12.9 Tonne quoted!

Lets do another,

Blknight.aus has a fully loaded Big Red of around 3 Tonne stuck on a muddy slope of around 40 degrees. ( sorry Dave, hope you don't mind)

RR= 3/2 = 1.5
GR= 3000kg/60*30=1.5 (1500Kg)
DF=0
Total = 3.00
Safety Factor = 3.00/4=.75
TPR=3.75 Tonnes

Now you know why Tirfors are so much fun:)

dont mind at all, your numbers are on the money as per the Raeme book of recovery...

what was in the mag that pat had done differently?

[Hymie]

dont mind at all, your numbers are on the money as per the Raeme book of recovery...

what was in the mag that pat had done differently?


Should be, I helped proofread it...
Pat had a formula where if a vehicle is bogged to the rims add 100%
To the Hubs 200%
To the chassis 300%
Some weird 25 percent for every 15 degree of slope formula
and so on...

[DeeJay]

Good thing Pat doesn't design shear pins :cool:

[Slunnie]

An 8mm 8.8 shear pin would never be a problem. :lol2:

[Barra1]

Should be, I helped proofread it...
Pat had a formula where if a vehicle is bogged to the rims add 100%
To the Hubs 200%
To the chassis 300%
Some weird 25 percent for every 15 degree of slope formula
and so on...

Thanks Hymie.;)

You have just given me another reason as to why I don't bother to read the damn magazine. Qualifying the facts as you have done doesn't seem to be in their vocabulary.:(

And little wonder I sold the tirfor! I'm an old codger and it did seem a lot of hard work - now I know it WAS hard work!:(

[Slunnie]

I think its more important to take on board all of the information that you can, and then make your own judgements on its relevance or value rather than cut off an information conduit based on a human error. Monthly amongst the other mags have a lot of value despite their errors.

[Blknight.aus]

JOOC...

i wonder if you did the numbers he was using up like a table and did the same for the Raeme book maths if his wouldnt look the same but cover lower values with a broad spectrum. Sort of like a ready reckoner for when you just dont have the time to do the math...

[CraigE]

I have not read the article but there is so much differing opinion on calculations and safety margins it is not funny. In emergency response rope rescue we work with a 8:1 safety margin so there is no possibilty of failure. Excessive in some people views, Yes but likliehood of equipment failure is absolutely minimal even with damaged equipment. Some people operate a lot closer to the equipment tolerances with success. Who is right or wrong. Neither really but I know what safey margin I would follow.

[twitchy]

everything is way underrated in the crane industry as well........... but that might be so I don't drop 15ton on ya Mellon :p

[Hymie]

JOOC...

i wonder if you did the numbers he was using up like a table and did the same for the Raeme book maths if his wouldnt look the same but cover lower values with a broad spectrum. Sort of like a ready reckoner for when you just dont have the time to do the math...

Sounds good in theory, what about the example of his TPR being 12.9 tonnes and mine being 2.68
Its too broad a spread.

[Bush65]

...Some weird 25 percent for every 15 degree of slope formula...
Nothing weird about 25% for 15 degree slope. Sin 15 deg ~ .26

Nowhere near as weird as your 1/60 tonne per degree. That is real weird because it does not take account of variations in vehicle weight.

Neither account for the fact that sin is not a linear function of slope.

But there are so many variables that you may as well pull figures out of the air for real world off road winching situations.

[Bushie]

Maybe its as easy as a typo (I haven't read the article) - given that almost nothing (in journalism) is proof read.

As you demonstrated typos are easy to make :eek:


Blknight.aus has a fully loaded Big Red of around 3 Tonne stuck on a muddy slope of around 40 degrees. ( sorry Dave, hope you don't mind)
GR= 3000kg/60*30=1.5 (1500Kg)Shouldn't that be GR= 3000kg/60*40 (2000Kg)

As others have said surely the weight of the stuck vehicle has to come into the gradient bit somehow, otherwise it works the same for a Landy and a Leopard tank.



Martyn

[Hymie]

Maybe its as easy as a typo (I haven't read the article) - given that almost nothing (in journalism) is proof read.

As you demonstrated typos are easy to make :eek:

Shouldn't that be GR= 3000kg/60*40 (2000Kg)

As others have said surely the weight of the stuck vehicle has to come into the gradient bit somehow, otherwise it works the same for a Landy and a Leopard tank.

Martyn


Well spotted on the typo Martyn, I stand corrected.

The formula I use, Weigh/60*Gradient takes the weight of the casualty into account, trust me 1/60th of a Leopard is a tad more than a 60th of a Landrover.

The TPR formula I gave in the posting is the standard recovery formula as used by British and Australian Army Recovery Mechanics since WW2.

One thing I didn't mention, is that the formula is only applicable up to 45 Degrees, after that it is a lifting task and the full weight applies.

[dhard]

Just another thing too ponder from memory i think winches are only rated for pulling not lifting. Any gradient over 5 deg is more like lifting so therfore the winches power would be substantially reduced i.e 10000 pound winch would rapidly only effectively have 1000 pounds of pull. Trifor style winches on the other hand are rated as lifting devices so what they say is what they can actually lift vertically assuming you are strong enough to use them.

[Hymie]

Just another thing too ponder from memory i think winches are only rated for pulling not lifting. Any gradient over 5 deg is more like lifting so therfore the winches power would be substantially reduced i.e 10000 pound winch would rapidly only effectively have 1000 pounds of pull. Trifor style winches on the other hand are rated as lifting devices so what they say is what they can actually lift vertically assuming you are strong enough to use them.

See the above post, over 45 degrees is a lift.
A winchs' pull is rated for a single line pull off the bottom layer of rope, regardless of being used for either lifting or pulling.
Terminal tackle, i.e snatch blocks, shackles, chains etc are rated for lifting.
This is called the Safe Working Load, (SWL) an is the maximum lifting load that can be placed on the tackle.
Recovery Load is the SWL multiplied by 2.
If the angle of pull is less than 45 Degrees Recovery Load applies, over 45 Degrees, Lifting SWL applies.

[dhard]

must have posted at the same time as didn't see your post 5 deg might be a bit low but 45 deg sounds pretty high. Though it must be pretty accurate if that is what the army use. I think i read about this once in lro mag on winching will check it if i can get it back from my mate and I'm sure they were pretty clear in stating that electric winches are only rated for pulling not lifting.

[Blknight.aus]

See the above post, over 45 degrees is a lift.
A winchs' pull is rated for a single line pull off the bottom layer of rope, regardless of being used for either lifting or pulling.
Terminal tackle, i.e snatch blocks, shackles, chains etc are rated for lifting.
This is called the Safe Working Load, (SWL) an is the maximum lifting load that can be placed on the tackle.
Recovery Load is the SWL multiplied by 2.
If the angle of pull is less than 45 Degrees Recovery Load applies, over 45 Degrees, Lifting SWL applies.


ohhh got to ping you here... not all are rated for lifting...

my 1.5t tirfor is rated to 2.5t of force but it is plated for a SWL of 2.5t and a lifting limit of 1.5...

some slings appear identical but have different load ratings on them untill you look closely and have a look at how the sling configuration is laid out some will be lifting some will be drag...

The ADF playing it safe run all slings as lifting slings but just occasionally some stuff will come through as dual use...

[Hymie]

ohhh got to ping you here... not all are rated for lifting...

my 1.5t tirfor is rated to 2.5t of force but it is plated for a SWL of 2.5t and a lifting limit of 1.5...

some slings appear identical but have different load ratings on them untill you look closely and have a look at how the sling configuration is laid out some will be lifting some will be drag...

The ADF playing it safe run all slings as lifting slings but just occasionally some stuff will come through as dual use...

Fair enough, We had no nylon slings in my time. I'm a chain and wire rope man myself:)
You got me on the Tirfor, I was thinking Drum/Capstan winches not mechanical jaw apparatus.

[Blknight.aus]

same applies on all equipment depending on how its rigged...

lets look at a drag line VS as lift line... lets pretend that we know that we need exactly 1000kg of pull to make it move along the ground and due to the magic of the hypothetical situation it needs exactly 1000kg to lift it up...

most dragline applications only require a 2x safety factor so while in theory I would get away with a 1000kg winch and line to pull it the OH+S side of it requires 2000kg of pull so everything must be able to deal with 2t (assuming a continuous rate single line pull ala capstan winch)

Now for lift your safety factor becomes 5 so to lift it you now need 5000kg of pull.

in the real world this is done by taking the nominal breaking strain of an item and deviding it by its nominated safety factor which for chains, wire ropes and shackles is 5 because you can guarentee that some idiot is goint to try an use one to lift what he should be towing..

due to the decreasing cost of manufacturing gear and the increasing costs of ticketing inspecting and stamping to 2 differing standards 90% of gear comes marked with a single SWL or WLL which is what it can lift, safely.

If you ever get chance to see a set of 10% test to destruction tests being done I highly reccomend you take it... hearing and seeing a bit of 2 inch diameter SWR playing itself like a guitar string is an amazing thing.

[Tank]

same applies on all equipment depending on how its rigged...

lets look at a drag line VS as lift line... lets pretend that we know that we need exactly 1000kg of pull to make it move along the ground and due to the magic of the hypothetical situation it needs exactly 1000kg to lift it up...

most dragline applications only require a 2x safety factor so while in theory I would get away with a 1000kg winch and line to pull it the OH+S side of it requires 2000kg of pull so everything must be able to deal with 2t (assuming a continuous rate single line pull ala capstan winch)

Now for lift your safety factor becomes 5 so to lift it you now need 5000kg of pull.

in the real world this is done by taking the nominal breaking strain of an item and deviding it by its nominated safety factor which for chains, wire ropes and shackles is 5 because you can guarentee that some idiot is goint to try an use one to lift what he should be towing..

due to the decreasing cost of manufacturing gear and the increasing costs of ticketing inspecting and stamping to 2 differing standards 90% of gear comes marked with a single SWL or WLL which is what it can lift, safely.

If you ever get chance to see a set of 10% test to destruction tests being done I highly reccomend you take it... hearing and seeing a bit of 2 inch diameter SWR playing itself like a guitar string is an amazing thing.
In a general answer to questions about capacites of winches, whether lifting or towing, a winch's capacity to tow or lift is governed by the cable fitted to it.
A winch capable of lifting 100 tonnes fitted with a 5 tonne Guaranteed Breaking Strain (GBS) (SWL 1tonne) wire cable has a SWL capacity of 1tonne. The problem with winch sellers is, in most cases they quote the capacity of their winches as the GBS of the cable fitted. Never is it OK to sell a product like winches and ancillary equipment by quoting it's GBS, because people will believe that they can work up to and beyond the GBS. Safety Factors (SF) are used because once a cable has been used and sometimes abused it loses some of its strength, so the SF is used to determine the SWL so people wont kill themselves or someone else. SF vary depending on there use or application, for instance a cable used as a guy rope holding up a tower could have a SF of 2 or 3 depending on conditions, in the middle you have slings and winch cables for towing or lifting with a SF of 5 or 6, at the top is a cable used in a lift which carries people, they have a SF of 10. So if you work to the SWL or Working Load Limit (WLL) and use common sense you should stay safe, Regards Frank.

[Tank]

same applies on all equipment depending on how its rigged...

lets look at a drag line VS as lift line... lets pretend that we know that we need exactly 1000kg of pull to make it move along the ground and due to the magic of the hypothetical situation it needs exactly 1000kg to lift it up...

most dragline applications only require a 2x safety factor so while in theory I would get away with a 1000kg winch and line to pull it the OH+S side of it requires 2000kg of pull so everything must be able to deal with 2t (assuming a continuous rate single line pull ala capstan winch)

Now for lift your safety factor becomes 5 so to lift it you now need 5000kg of pull.

in the real world this is done by taking the nominal breaking strain of an item and deviding it by its nominated safety factor which for chains, wire ropes and shackles is 5 because you can guarentee that some idiot is goint to try an use one to lift what he should be towing..

due to the decreasing cost of manufacturing gear and the increasing costs of ticketing inspecting and stamping to 2 differing standards 90% of gear comes marked with a single SWL or WLL which is what it can lift, safely.

If you ever get chance to see a set of 10% test to destruction tests being done I highly reccomend you take it... hearing and seeing a bit of 2 inch diameter SWR playing itself like a guitar string is an amazing thing.
Dave, I used to work at Cockatoo Island Dockyard in Sydney and I used to build my own slings for specailised lifting projects, like lifting Gun Turretts of Destroyers, or power generator turbines, biggest cable was a 4" dia 60' long slings for the floating crane Titan for lifting large Ball and Rod mills, was good fun testing the swages on the test bed, never had one go pop though, thank christ, Regards Frank.

[rmp]

Has anybody read Australian Four Wheel Drive Monthly, particularly Pat Callinans article on how to winch and calculate how much force is needed to extricate a bogged Forby?
What a load of rubbish!!
Read Pats "formulas" for calculating required pulls then sit back and consider a few thing I'm going to teach y'all.
Pat is right on a few things, there are 4 types of resistance to take into consideration.
1. Rolling Resistance, this being the resistance to motion given the surface the vehicle is on, ie, Bitumen, Grass, Sand or Mud
2. Gradient Resistance, the effort required to overcome gravitys pull on an incline
3. Damage Factor, did you damage anything that might increase resistance tomotion, rip a tyre off a rim, bend a steering arm etc.
4. Add a safety margin.

To work out rolling resistance, take the weight of your vehicle and divide it by a. 25 for bitumen or concrete
b. 10 for gravel
c. 7 for grass
d. 5 for sand
e 2 for mud

To work out Gradient resistance,
a. calculate the slope
b. Factor 1/60th of a tonne for every degree of slope

To work out a Damage factor,
throw in 25% of the vehicles mass for every damaged wheel.

Safety Factor is 25% of the total of all of the above.

This will give you a Total Pull Required. (TPR)

Sooooooo.
Using the example in the magazine of a 3.3 tonne GU Towning a 1 Tonne Camper trailer Bogged to the chassis.

RR= 4.3/2= 2.15 Tonne
GR=0
DF=0
Total =2.15 Tonne
Safety Factor 2.15/4=.53 Tonne

TPR=2.68 Tonnes

A whole lot less than the 12.9 Tonne quoted!

Lets do another,

Blknight.aus has a fully loaded Big Red of around 3 Tonne stuck on a muddy slope of around 40 degrees. ( sorry Dave, hope you don't mind)

RR= 3/2 = 1.5
GR= 3000kg/60*30=1.5 (1500Kg)
DF=0
Total = 3.00
Safety Factor = 3.00/4=.75
TPR=3.75 Tonnes

Now you know why Tirfors are so much fun:)

Having tested recovery loads using a load cell those numbers are about what I measured, except that I made rolling resistance 2.5% on flat bitumen at road pressures -- it reads like 25 above. My figure for de-bogging a GU with camper trailer and not driving (we actually did it, not just theory) was equal to the weight. However we did not dig it out at all, if you do that loads are dramatically reduced. There will never be an exact figure but 12 tonnes to remove that GU/camper....it'd need to be sucked down into the most glutinous mud.

[Bush65]

So if I understand this, Robert measured the recovery force of a GU and camper trailer bogged to the chassis as approximately equal to the weight.

So about 4.3 tonnes

Hymie calculated the recovery force as 2.15 tonne

So the required recovery force was double the theoretical value from using Hymie's method.

[dobbo]

by the time you've calculated the load required to remove the bogged vehicle, you could have grabbed a shovel, removed some of the material bogging the vehicle and placed it in feed bags, free with horse food so not free (it costs your soul, an arm and a leg) place the bags in front of the bogged or floating with no traction wheels and drive out.

[rmp]

Yes, but whenever forces are mentioned the qualifiers need to be stated; my figure was with no stuck vehicle driving, and no attempt to reduce load by digging out at all. If there was some even basic digging my figure would be the same as Hymie's.