trewhella winch

[skyhuck]

Are people really suggesting these hand winches have a 10 tonne pull capability??

 

Or that a load of 10 tonnes would not destroy them??

 

I find it hard to believe that its a 10T pull, that three times that of the largest Tiror!!

[David Humphries]

 

I have a picture I stole from here, but I can't find it now. It was one Monkey-D posted once.

 

 

These perchance...........

 

 

 

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[Andy Collins]

Are people really suggesting these hand winches have a 10 tonne pull capability??

 

Or that a load of 10 tonnes would not destroy them??

 

I find it hard to believe that its a 10T pull, that three times that of the largest Tiror!!

 

I'm guessing that at 10 ton pull would be correct as this would convert to 4.54® tonne and looking at its dimensions this would be feasable

[Treewolf]

I've just dug out the instruction booklet that Trewhella kindly sent me. It makes no mention at all of capacity, line pull, etc, but does say:

 

"NUMBER OF MEN. One man often works a winch, but two are better. Never allow more than three men on the lever, or a broken rope may result. Even two big men can apply quite as much power as is good for the ropes."

 

Later in the instructions:-

 

"Take care when releasing a heavy load. It is absolutely essential to employ the same number of men as were required to apply the load. If not held firmly, the lever will swing violently, which is dangerous."

 

Andy, I fear that I have to take issue with your calculations

 

10 tons = 10 * 2240 lbf = 22,400 lbf

10 tonnes = 10 * 1000 kgf = 10,000 kgf = 10,000 * 2.2 lbf = 22,000 lbf

 

Comparing the size of the original Trewhella rope to the rope on the Husky 8 on my Defender suggests that a 10-ton line pull would be well within the capability of the rope. I do have somewhere a copy of the old British Standards for standard lifting/pulling tackle and wire ropes, and if I can find it I will see what it has to say.

 

I am sure also that one of the films produced by the Army Kinematographic Service in the 1940's and released on VHS video in the 1990s (either "Scammell Recovery" or "Armoured Recovery") includes a sequence of Trewhella winches being used to recover something very big and heavy, and very stuck. I dont know if anyone has put these on YouTube, but I'll see if I can lay my hands on a copy.

[nepia]

Comparing the size of the original Trewhella rope to the rope on the Husky 8 on my Defender suggests that a 10-ton line pull would be well within the capability of the rope. I do have somewhere a copy of the old British Standards for standard lifting/pulling tackle and wire ropes, and if I can find it I will see what it has to say.

 

 

I'm not sure the rope itself is the limiting factor in the whole setup is it? I seem to remember that the 16mm rope for my Tirfor has a nominal breaking strain of ?25 tons - could be wrong there - but the point is that with a smoothly applied load it's not the rope that's meant to go bang first.

[Treewolf]

I'm not sure the rope itself is the limiting factor in the whole setup is it?

 

The other thing to consider is the factor of safety. A device used for pulling needs a lower FoS than one used for lifting. A device used for lift people needs a higher FoS still.

 

I seem to recall that Tirfors are rated for lifting but not lifting people. This means (and I can't be sure that I remember my FoS correctly, it's been a long time) that the FoS is probably about 5, so the rope on a 3-ton Tirfor probably has a breaking load of around 15 tons. Tirfor of course also fit a shear pin in the handle linkage so that you cannot (in theory at any rate) overload it.

 

Vehicle winches are almost always rated only for pulling with an FoS of 2, and not for lifting (FoS 5). This is the reason why a typical vehicle winch has a cable of only about 10mm diameter, roughly half the size of the equivalent Tirfor cable. (The other problem of course is that if the winch was to be rated for lifting, it would need the thicker cable, which would mean a correspondingly bigger drum, which makes it so big and heavy it wouldn't fit on the front of a vehicle.

 

I am not sure what would break first with a Trewhella loaded to the point of destruction. I suspect that the rope would be the weak point (well, I reckon my back would fail first!) since the construction of the winch itself is massive.

 

It shouldn't be too difficult to work out roughly the line pull simply by measuring the distance of movement of the handle and the corresponding movement of the rope, and using this factor to multiply the force a normal person can apply to the handle. Friction losses are largely unquatifiable, but it woudl give an idea. If I get the chance today I will dig one out and investigate.

[Steve Mack]

I am not sure what would break first with a Trewhella loaded to the point of destruction. I suspect that the rope would be the weak point (well, I reckon my back would fail first!) since the construction of the winch itself is massive.

 

I'd say you'd be right there, but I'd like to meet someone that broke one.

 

I bought the big Tirfor after I got rid of mine, no comparison really. I still have it.

 

Monkey-D, thanks. [the monkey winch thread]

 

Did you use a snatch block with yours? I did. Fun times, that's why I don't have any pictures. Too busy working.

 

I just found this. RAEME Know-how ~ TofC ~ Applied Engineering Solutions in Operations and in the Field 12 ton straight pull, I wonder what we pulled with the extension and snatch block.

[Andy Collins]

I stand corrected, thanks for the correct info:thumbup1:

[Treewolf]

Done some measuring with one of mine today.

 

Without including all the maths (which I am happy to do if anyone wants it), the 'velocity ratio' of a Trewhella is approx 120:1 pulling on the first layer of the drum and using the standard 5' handle held 6" from the end.

 

Assuming that 1 bloke can apply 100 lbf to the handle (which is conservative for a well-built fellow) and discounting friction losses, 100lbf on the handle would result in 12,000 lbf on the rope, which is roughly 5 tons.

 

To get a load of 10 tons on the rope, ie 22,400lbf, would require a load of under 200 lbf on the handle, which should be easily achieved by two moderately strong men.

 

There is no doubt in my mind that you could easily load one up to 10 tons and more.

[Andy Collins]

Anyone fancy knocking up a vid of one of these behemoths working? I'd love to see it working to its potential