Sounds good in theory, what about the example of his TPR being 12.9 tonnes and mine being 2.68Quote:
Originally Posted by Blknight.aus
Its too broad a spread.
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Sounds good in theory, what about the example of his TPR being 12.9 tonnes and mine being 2.68Quote:
Originally Posted by Blknight.aus
Its too broad a spread.
Nothing weird about 25% for 15 degree slope. Sin 15 deg ~ .26Quote:
Originally Posted by Hymie
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.
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:
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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)
Shouldn't that be GR= 3000kg/60*40 (2000Kg)Quote:
GR= 3000kg/60*30=1.5 (1500Kg)
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
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Originally Posted by Bushie
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.
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.Quote:
Originally Posted by dhard
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.
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.
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Originally Posted by 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:)Quote:
Originally Posted by Blknight.aus
You got me on the Tirfor, I was thinking Drum/Capstan winches not mechanical jaw apparatus.
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.