So, Snatch.........

[sae70]

....Blocks then


WHY

The swing away snatch block that came with my winch raised a few eyebrows at Lincomb

It got well used and seemed to work fine

Although there is no markings on it I believe it to be one of these;


6 tonne Snatch / Pulley Block

http://www.winch-it.com/winchaccessories/8-6-tonne-snatch-pulley-block.html

Here's some photos of my one

So I've started to look at whats available, but really do I need to be going for a 12 tonne snatch / pulley block


It's a good price, but it's nearly a foot long with a 4" diameter pulley and weighs over 3Kg

http://www.winch-it.com/winchaccessories/7-12-tonne-snatch-pulley-block.html

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=261099725055

Maybe I should be going for something this size

 

[Ben]

That one youve linked to is very similar to mine.

I think i paid £10 for it at the 4x4 show.

 

[Jon Wildsmith]

What rating is your winch Steven? When you double line pull the snatch block is subject to double the winch pull as is whatever you've secured the snatch block with and to. No mention of if the 6 ton on yours is SWL or max load though. For a wire rope the diameter of the pulley would be important as well but I don't think that's really an issue with plasma rope.

 

[sae70]

My winch is a 9.5TDS and is rated at 9500lbs

9500lbs / 4.25Tons

4309Kg / 4.31Tonnes

I thought that adding a snatch block into a winching operation just decreased the effort that the motor has to make by half and thus the current draw on the battery by half by changing the gearing by 2:1 My winch has a gearing of 173:1 with a single line pull but with the snatch block in place I thought that this changes the gearing for my winch to 346:1 thus reducing the effort by half, but not doubling the capability of the winch?! It will always be a 9500lb winch no matter how many snatch block one puts in surely?

 

[Jon Wildsmith]

Yes the winch will always be 9500lb, but when you double the line, you get that pull (ignoring losses) on both lines which (roughly) doubles the force pulling you out the muck. The pulley block and everything it's attached to gets the full force, as does your winch mount / chassis mounts if the winch and return rope fixing point share a common mount as they often do. Imagine your truck needs 6000kg to pull it out of a hole. Your winch can easily deliver that via a double line pull, but it is still taking 6000kg of pull to get your truck moving and the pulley end gets the whole 6000kg. Stall your winch on a double line pull and that's 8618kg (ignoring losses!) on your snatch block and fixings.

 

[Paul_Humphreys]

Do a search for Black Rat ones, quite good.

 

[sae70]

My winch is a 9.5TDS and is rated at 9500lbs

9500lbs / 4.25Tons

4309Kg / 4.31Tonnes

I thought that adding a snatch block into a winching operation just decreased the effort that the motor has to make by half and thus the current draw on the battery by half by changing the gearing by 2:1 My winch has a gearing of 173:1 with a single line pull but with the snatch block in place I thought that this changes the gearing for my winch to 346:1 thus reducing the effort by half, but not doubling the capability of the winch?! It will always be a 9500lb winch no matter how many snatch block one puts in surely?

I'm happy with what I've said here and hope that it makes sense for everyone

But I'm afraid I don't agree with some of what you've said here Jon I'm sorry to say

Yes the winch will always be 9500lb, but when you double the line, you get that pull (ignoring losses) on both lines which (roughly) doubles the force pulling you out the muck. The pulley block and everything it's attached to gets the full force, as does your winch mount / chassis mounts if the winch and return rope fixing point share a common mount as they often do. Imagine your truck needs 6000kg to pull it out of a hole. Your winch can easily deliver that via a double line pull, but it is still taking 6000kg of pull to get your truck moving and the pulley end gets the whole 6000kg. Stall your winch on a double line pull and that's 8618kg (ignoring losses!) on your snatch block and fixings.

As you say my winch will always be a 9500lb / 4309Kg capable winch no matter how many snatch blocks one uses. Assuming as you, that my winch will stall at it's designed maximum operating load of 4309Kg during a very onerous snatch blocked winching operation and go no further the pulling force on the snatch block will be 4309Kg!!! It can't be any more as my winch has stalled at it's maximum plated load. If this is the case then the pulling force on each of the two ropes heading back to the truck from the snatch block, one from off of the winch drum and one from off of the hook securing point back on the truck will each be 50% of the stalled pulling force of 4309Kg on the snatch block, so each rope will have a load of 2154.5Kg on itself!!! Ignoring losses of any kind of course.

This is why I understand it to be advantages to use a snatch block during winching as it reduces the load on everything but the snatch block by half.

Interestingly on that basis the little 'ol 6Tonne (6000kg) snatch block I have is well capable of being used with my winch, is it not

 

[AndyCook]

thats a very 'ickle snatch block , so i went and checked mine last night - thankfully its rated at 11,000kgs.... and quite big too, 25cm long

 

[Toby]

Hi Steven,

I'm sorry, but I'm afraid Jon is right and you're wrong; go back and read the last part of your argument again - you say the load on each rope heading back to the car will be 2154.5kgs - fair enough, so the the rope going into the winch has only 2154.5kgs tension on it, in which case the winch won't stall will it? It will keep pulling until it stalls at 4309kgs at which point you'll have 4309kgs on each length of rope adding up to 8618kgs on the snatch block and whatever its attached to...

Obviously this ignores the losses and the fact that the winch probably doesn't stall exactly at its rated pull.

When a snatch block lets go you definitely don't want to be in the way.

All the best,
Toby
1990 HDJ80
1994 HDJ80

 

[sae70]

Hi Steven,

I'm sorry, but I'm afraid Jon is right and you're wrong; go back and read the last part of your argument again - you say the load on each rope heading back to the car will be 2154.5kgs - fair enough, so the the rope going into the winch has only 2154.5kgs tension on it, in which case the winch won't stall will it? It will keep pulling until it stalls at 4309kgs at which point you'll have 4309kgs on each length of rope adding up to 8618kgs on the snatch block and whatever its attached to...

Obviously this ignores the losses and the fact that the winch probably doesn't stall exactly at its rated pull.

When a snatch block lets go you definitely don't want to be in the way

Ah, I saw this when you posted it up, but had to go away and stretch my head around the topic again I started out knowing very little about the subject, did a bit of reading, spoke with a couple of people who had their own ideas, thought I'd sussed it and then.............mmmmmmmmmmmm

Cut a long story short I ordered three 9.1Tonne snatch blocks this afternoon following a visit from Giles with his two pulley blocks

From what I can make out these are the same ones sold by MachineMart

http://www.ebay.co.uk/itm/350189353711?ru=http%3A%2F%2Fwww.ebay.co.uk%2Fsch%2Fi.html%3F_sacat%3D0%26_from%3DR40%26_nkw%3D350189353711%26_rdc%3D1

I do need to go away and have a good think about whats been said here with regards to the potential loads generated during winching with a snatch block

 

[Paul_Humphreys]

Just to add, if you have used a snatch with a stell rope/wire then it is recommended that you do not use it with a synthetic rope.

Paul