Snatch block ratings

[Ed Batchelor]

Got a couple of large snatch blocks, the one (hopefully) pictured below has 15tons on it, now does this 15 ton refer to the winch line pull or the load imposed by the stricken vehicle/immovable object being winched, ie if being used in 2:1 configuration a winch rated at 7.5ton?

Any ideas what sort of age this might be?

[recymech66]

If you have an Estimated pull (EP) of 30 Tons the loading at the head of the apex will be 15 Tons, So... 15 Ton winch on a 2:1 pull will give you 30 Tons.

 

If your EP comes to more than 30 Ton then you will be overloading the Snatch block, however I would be very wary of applying such a load to an item of recovery equipment you have no history of.

 

Edited to add, looks at least over 30 years old, but could be wrong.

Edited April 29, 2009 by recymech66

[paulob1]

hmm not sure this is correct...it is partially dependant upon the position of the snatch block and what you are doing. But the snatch block can only take a load of 15 tons...if you connect for instance the block to a 15 ton vehicle and use a 7.5 ton winch looped around the snatch then that is fine....however if you use it to pull a 30 ton tank it will fail...irrespective of how many loops you have the snatch block is carrying the full weight...of both cables, or the full load...

[Stormin]

hmm not sure this is correct...it is partially dependant upon the position of the snatch block and what you are doing. But the snatch block can only take a load of 15 tons...if you connect for instance the block to a 15 ton vehicle and use a 7.5 ton winch looped around the snatch then that is fine....however if you use it to pull a 30 ton tank it will fail...irrespective of how many loops you have the snatch block is carrying the full weight...of both cables, or the full load...

 

A 30 ton tank would not need a 30 ton line pull to move it unless it was suspended vertically (off a cliff for example). Even if seriously bogged in mud it would probably only need about 15 tons of line pull.

 

Looking a that block it could be arranged to be overloaded using a 7.5 ton line pull winch as follows:-

Snatch block connected to imovable object. Line from winch vehicle wraps around sheave and back to winch vehicle, around another pulley block and back to the snatch block on the load this time terminating on one of the end fixings. This gives three lines at the snatch block each with 7.5 tons load. Total load on snatch block 22.5 tons!

Edited April 29, 2009 by Stormin

[Ed Batchelor]

I understand the physics involved, but not the logic behind the labelling.

My question was how did the military mean the rating to be understood, 15 ton winch pull or 15ton ultimate pull (accounting for 2:1 ratio). It has an attachment either end so could be used in even greater ratios.

A rating on a shackle is straight forward enough but this one has puzzled me.

It must weigh over 2cwt as I can only drag the thing accross the ground!

[Ed Batchelor]

Just been reading a REME recovery manual from the AEC militant website, looks like the rating refers to the load imposed by any 1 run of cable to the snatch block rather than the ultimate load hanging off the other end of it or the sum of all the cable runs. Matador and Pioneer will definately not be overstretching it!

[paulob1]

Think this is getting more confused..

 

In answer to your question, a 15 ton snatch block is the maximum load the snatch can take. fORGET ABOUT LOOPS AND THINGS..THAT IS ALL ABOUT LINE LOADING NOT SNATCH BLOCK LOADS.

 

iF YOU NEED TO MOVE 30 TONS OF TANK YOU WILL NEED A 30 TON SNATCH BLOCK OR TWO 15 TON SNATCH BLOCKS...

 

These are the three Basic newtons laws , the tank will stay put until you apply a force, that force is f = ma..(forget the coefficient of friction).

 

For every reaction there is an opposit and equal reaction. If you pull a tank of 15 tons then snatch block is taking 15 tons...however if you pull a 30 ton tank with a snatch block of 15 tons the snatch block will likely fail...there is massive fail safe in the design but you would be outside of its design spec, irrespective of the number of lines...

 

But as has been said if you use multiple snatch blocks you can offsett some of this...

[recymech66]

Just re-read my post and realised I was talking rubbish, of course if you have an Estimated pull of 30 Tons then the loading at the Snatch block will be 30 Tons but the loading on the ropes on a 2:1 will be 15 Tons as will the loading on the winch, if you have a snatch block which is rated at 15 Tons then that will be the maximum load you can apply to the point were it's connected to the tackle layout. So the maximum winch pull you can apply will be 7.5 Tons.

 

But as I stated before, I would be very, very wary of putting any load on a snatch block were you have no history, it may be damaged, it may have been repaired after failure, you have no idea of weather it may have been overloaded during it's lifetime.

 

I'd suggest working out an estimated pull before any winching task, so at least you have an idea of what sort of load you are applying to your recovery tackle.

[Stormin]

So the maximum winch pull you can apply will be 7.5 Tons.

 

 

 

Remember that block could be rigged for a triple line pull so the max line pull would be 5 ton to reach max load at connection.

All lifting equipment is rated as a safe working load so there is built in over capacity to allow for shock loads, wear and tear, etc.

Question is how much of that overcapacity is left after many years of use and abuse?

[paulob1]

7.5 tons line pull, ie say a 7.5 tons winch, if used with three pulley blocks could potentially pull 30 tons.......safely, as long as the two pulley blocks are attached to the tank...

 

I think in reality the pulley block will not have been that badly affected unless it has been really badly treated. (would show signs of misuse) I would as always proceed with much caution when using a pulley block of unknown history....make sure you are nowhere within line distance if it were to give way...and in my humble opinion under no circumstances use it for lifting, just use it for winching...

[antarmike]

Suggested reading

 

Vehicle Recovery

A practical manual for the Heavy-vehicle driver fleet operator and recovery specialist

 

R J Grice

 

Pub. Newton and Butterworth.

 

Type of surface Pull required to move

 

Road 1/25th Vehicle weight

Grass 1/7th ""

Gravel 1/5th ""

Soft Sand 1/4 ""

Shallow Mud 1/3rd ""

Bog 1/2 vehicle weight

 

Then you need to concider gradient factor.

 

Rule of thumb 1/60th Of Vehicle weight for every 1 degree of slope, up to 45 degrees, above this angle add the whole weight of the vehicle.

 

eg. Thirty ton Casualty up a 30 degree slope, Shallow mud surface.

 

Grade resistance for 30 degrees 30 x 1/60 X30 = 15 Tons

 

Surface resistance 30 x 1/3 = 10 Tons

 

Total pull required 15 + 10 = 25 Tons.

 

I swear by the Fellows 15 Ton block. The plate on them declares them to have a SWL of 15 Tons and that they have been proof tested to 45 Tons. I have never broken one..(yet)

Edited April 30, 2009 by antarmike

[antarmike]

Grice quotes as safe figures for an average 10" dia sheave for 3/4 cable 8 tons on the becket and 4 tons in each rope run.

 

For a 12" sheave to suit 7/8 cable 10 Tons on the becket and 5 tons in each wire.

 

for a 14" sheave for 15/16 cable 10 Tons on the Becket and 6 1/4 Tons in each wire.

 

(if the last case doesn't seem to add up, frictional losses in the spindle bearing are probably why...)

Edited May 1, 2009 by antarmike

[recymech66]

We have just replaced all our Fellows as they wouldn't certify them at 45 Tons, bearing in mind the new MAN SV® can winch 50 Ton 2:1 we now have a new Snatch block rated at 50 Tons.

[poppypiesdad]

Could you not get the snatch block tested by someone like

 

http://www.phutcheon.co.uk/load_testing.html

 

and then you would have a useable safe peice of kit ?

 

Jamie

[recymech66]

Could you not get the snatch block tested by someone like

 

http://www.phutcheon.co.uk/load_testing.html

 

and then you would have a useable safe peice of kit ?

 

Jamie

 

I guess you work for Phutcheon then

[poppypiesdad]

no m8 In Scotland the idea of a tester like them

the only one that stood out from google

[MilitantGraham]

All the information you need is here.

http://www.aecmilitant.co.uk/downloads/recoverymanual.pdf

 

There's nothing like a discussion about winching to bring out misunderstandings and old wives tales.

A military 15t snatch block is rated at 15t per line. It can be used to give a 3:1 pull with a 15t winch for a total of 45t.

If you need a 30t winch to move a 30t tank, how come I can push a 2t Land Rover ?

 

I wouldn't worry about getting a snatch block tested, just a visual check for obvious damage.

Have you had the U bolts and shackle pins connecting your axles to your truck porofessionally tested ? The consequences of failure are far more serious.

[Ed Batchelor]

Agree 100% with your post militant graham, took the liberty of reading the comprehensive recovery manual on the militant website which makes it quite clear that each line can take 15ton ie 45ton max on this pulley hence my last post.

Regards

Ed

[recymech66]

I think people are getting confused over the 30 Ton tank needing a 30 Ton winch, You can have a 62 Ton Challenger 2 bogged in, but it may only require a winch pull of 30 Ton in order to extract it. Hence if you had a winch rated at 30 Ton single line pull great, but if you only had a 15 Ton winch then you would need to insert a Snatch/Pulley block giving you a 2:1 pul of 30 Ton, doubleing your 15 Ton winch, or 2 Snatch/Pulley blocks giving a maximum pull of 45 Ton 3:1.

 

MilitantGraham is quite right you dont need to get the Snatch block tested. But under Loler 98 Regulations it should be thoroughly inspected/examined every 6 months.

 

And it would take a brave man to go putting 45 Tons on a snatch block with an unknown history.

 

Just my opinion. Great discussion though.

[MilitantGraham]

Isn't LOLER just for lifting equipment though ?

Military snatch blocks and shackles normally have "For Recovery Use Only" marked on them to make it clear they do not meet the 5:1 safety factor required for lifting equipment.

Compare a miltary recovery 15t bow shackle with a regular 15t shackle. The one intended for lifting is designed to hold a static load of at least 75t without deforming and is huge compared with the recovery one which has a much lower safety factor.

There probably is a testing standard for recovery equipment, but as I have never done it professionally, I have never come across it.

We have everything from trolley jacks and axle stands to vernier calipers and torque wrenches tested and certified at work so I would imagine there's a similar process for winch ropes and equipment.

Like so many things, that phrase "hire and reward" must come in to it. You can winch your mates truck out of a mud hole for free, but once you start charging or employing people you will need all sorts of certificates, qualifications and insurance.

 

The confusion over winch capacities isn't helped by the makers of cheap and nasty winches and tow ropes claiming a 2 tonne "rolling load" capacity.

Going by the figures Mike posted above and in the REME manual, a 2t rolling load on a hard level surface with all the tyres inflated needs less than 100kg of force to get it moving. Hence my earlier comment about one person being able to push a Land Rover.

[Richard Farrant]

Military snatch blocks and shackles normally have "For Recovery Use Only" marked on them to make it clear they do not meet the 5:1 safety factor required for lifting equipment.

 

There probably is a testing standard for recovery equipment, but as I have never done it professionally, I have never come across it.

We have everything from trolley jacks and axle stands to vernier calipers and torque wrenches tested and certified at work so I would imagine there's a similar process for winch ropes and equipment.

 

Graham,

 

I used to be involved in the annual testing of winches on military equipment, ( recovery vehicles, trucks, plant, ARV, etc) while working for REME, also mobile cranes and other lifting equipment. The safety factor for winching tackle is 2:1, hence the difference in size of shackles, pulley blocks, etc. as you pointed out. From memory, last involved about 13 years ago now, was that shackles, pulley blocks, snatch blocks, and ropes are tested on manufacture and certificates issued, after that, the periodic inspections are carried out, in the Army it was annual and on the items I mentioned, are visual only, but if the original test certificate is missing, lost, etc. then the item has to be scrapped as it has no history. There would be identifying numbers on item and certificate. We had to test the winches on full load pull to check cut outs and warnings, also correct functioning, ropes were inspected before and after this test.

[recymech66]

We now (MoD) treat Recovery equipment as Lifting equipment Hence LOLER 98 and as Richard Farrant says, in respect of Shackles, Pulleys, Chains, strops etc they are subject to a periodic inspection as Accessories currently 6 months, when refering to cranes, winches, Palletisers, Trolley jacks etc as Appliances they are subject to an Annual load test.

[recymech66]

A failed snatch block.

 

 

 

[antarmike]

I was looking at Fellows blocks at the W/E. The old Mk111 block ( forged or cast steel??) is rated at a SWL of 15 Tons, Proof Load 45 Tons, But the latter welded Fellows blocks are rated SWL 15 Tons, Proof load 30 Tons....

[nptimber]

All the information you need is here.

http://www.aecmilitant.co.uk/downloads/recoverymanual.pdf

 

There's nothing like a discussion about winching to bring out misunderstandings and old wives tales.

A military 15t snatch block is rated at 15t per line. It can be used to give a 3:1 pull with a 15t winch for a total of 45t.

If you need a 30t winch to move a 30t tank, how come I can push a 2t Land Rover ?

 

I wouldn't worry about getting a snatch block tested, just a visual check for obvious damage.

Have you had the U bolts and shackle pins connecting your axles to your truck porofessionally tested ? The consequences of failure are far more serious.

At last someone who knows what they are talking about

[nptimber]

I was looking at Fellows blocks at the W/E. The old Mk111 block ( forged or cast steel??) is rated at a SWL of 15 Tons, Proof Load 45 Tons, But the latter welded Fellows blocks are rated SWL 15 Tons, Proof load 30 Tons....

Good job i put a padlock and chain on them PINCHER FINCHER had his eyes on them all weekend , but i did notice all the bolts were loose on the track box on the pioneer , perhaps his master plan was to nick the whole box ?