Sizing snatch blocks for linkage/ tractor winches

[wills-mill]

Evening all,

 

What sort of loading factor are forestry winches rated at? A '6 tonne' winch is not a lifting tool capable of lifting 6 tonne, so what do you do when it comes sizing snatch blocks, which are usually rated as per lifting gear?

 

Heaviest usage for a forestry winch would be using a snatch block attached to the load and the end of the winch line brought back to anchor point near to tractor- so doubling the line pull I believe at the snatch block.

 

I've been looking at an 8 tonne forestry winch, but how necessary is it to use a rated lifting snatch block with a 16 tonne WLL? The winches seem to use a 12 or 13mm wire rope, and the snatch blocks (for 'just' 8t) are on 16 to 19mm rope or above. The 15t block in the link below is for 19 to 22mm wire rope.

 

Is it all academic? Is tractor stability the biggest limiting factor?

 

http://www.liftingsafety.co.uk/product/heavy-duty-rigging-snatch-block-2808.html

Edited November 24, 2014 by wills-mill
forgot to put the link in.....

[mendiplogs]

Evening all,

 

What sort of loading factor are forestry winches rated at? A '6 tonne' winch is not a lifting tool capable of lifting 6 tonne, so what do you do when it comes sizing snatch blocks, which are usually rated as per lifting gear?

 

Heaviest usage for a forestry winch would be using a snatch block attached to the load and the end of the winch line brought back to anchor point near to tractor- so doubling the line pull I believe at the snatch block.

 

I've been looking at an 8 tonne forestry winch, but how necessary is it to use a rated lifting snatch block with a 16 tonne WLL? The winches seem to use a 12 or 13mm wire rope, and the snatch blocks (for 'just' 8t) are on 16 to 19mm rope or above. The 15t block in the link below is for 19 to 22mm wire rope.

 

Is it all academic? Is tractor stability the biggest limiting factor?

 

HI WILL as you may no a say 6TON winch will only pull 6ton on empty drum mate so when you have 50mt on drum your only pulling say 3ton thanks jon

[wills-mill]

HI WILL as you may no a say 6TON winch will only pull 6ton on empty drum mate so when you have 50mt on drum your only pulling say 3ton thanks jon

 

Thanks Jon I've just done the sensible thing and had a search around- found this little lot-

 

http://arbtalk.co.uk/forum/general-chat/56220-snatch-block-winch-how-large-do-i-need-2.html

[agrimog]

stick to 2 1/2 times your max pull and youll not go far wrong, bigger is always better

[Brushcutter]

Welcome to the minefield of big winch blocks.

 

I've been looking for a 20 tonne block that fits a 13/14mm rope. Nothing i've found comes close. They also weigh loads making them impractical to lug into the woods.

 

Of course you put a 20tonne bock on a basketed 10t sling to a 20 tonne shackle onto the block. Now of course you have to then find an anchor point that is rated to 20 tonne. Oh wait trees aren't rated.......

[wills-mill]

I suppose the question we should be asking is "what's the WLL of 13mm wire rope" then go from there.

 

EDIT: Mainco Wire Ropes Ltd, Wire Rope Specialists | MWR - Wire rope breaking load tables

 

That gives a SWL of 2 tonnes ish. For lifting/hoisting (rated at a fifth of the breaking strain). Any idea what that is stretched out to for plain old dragging?

 

This problem is going to run and run.

Edited November 24, 2014 by wills-mill

[JimE]

Most of the pulleys we sell are rated as say '3 tons'. But that is 3 ton line pull, the actual hook on that pulley is 6 tons. So normallly use a 3 ton block with a 3 ton winch and it is ok to use with a doubled line.

As Jon says, a 3 ton winch only actually pulls about 3 ton when the cable is fully unwound, when its all the way in maybe only 1.5 tons anyway.

[wills-mill]

Most of the pulleys we sell are rated as say '3 tons'. But that is 3 ton line pull, the actual hook on that pulley is 6 tons. So normallly use a 3 ton block with a 3 ton winch and it is ok to use with a doubled line.

As Jon says, a 3 ton winch only actually pulls about 3 ton when the cable is fully unwound, when its all the way in maybe only 1.5 tons anyway.

 

Sounds fair enough, as long as we can have it in writing

 

I need to come and see you at some point soon Jim, so I'll see what you've got available.

[mendiplogs]

Sounds fair enough, as long as we can have it in writing

 

I need to come and see you at some point soon Jim, so I'll see what you've got available.

 

HI WILLS you only need to look at the igland winch site they tell you mate thanks jon

[Logan]

HI WILLS you only need to look at the igland winch site they tell you mate thanks jon

 

hello jon, went and had a look on igland site and could only see a odd mix of funky looking blocks, thought they'd have bit more info too?

 

Cheers, John.