Recovery and Towing

[Tony B]

============

 

And in physics I suppose the word energy has to come in - amount of work that can be performed by a force (and I suppose the control of the energy during the application - thinking of KERR snatch recovery). All gets a bit complex - so many factors.

KERR Kinetic Energy, the energy imparted to an object by movement. A KERR rope acts like a spring. The movement applied by the towing vehicle stretches the rope this is then stored as POTENTIAL. As the inertia is overcome the 'spring' then moves very fast increasing the A in the formula, hence more force. Same as snatch towing, The formula for Kinetic energy is Mass x velocity squared over two

[Richard Farrant]

 

remember U bolt against "U"nstressed cable.

 

One of my older work colleagues from way back, had a saying, "You never put a saddle on a dead horse".

[cosrec]

In the CCKW manual they suggest using a fixed object to winch the vehicle too so as to place some load on the cable as its being wound back on the winch drum , there is also a split block that can be fabed that would mount on a vertical 2x4 which has a single bolt through a second 2x4 which runs upward at an angle from ground across the bumper to provide a drag load and guide that a person moves to feed the cable back on to the winch drum in even layers , these methods require two people to do as the WWII American winches did not incorperate a cable laying on system , I think those came along on the Vietnam era and newer vehicles.

 

Before during and after the war britans milatery spent a great deal on RD into getting winch ropes to wind on correctly under load. Ranging from the pendalum rig they retro fitted to the DT 980/981 trucks to the overley complicated mechanism they fitted on the scammells and Leyands Guys with horizontal winches. The nearest to a good solution was developed as you state by the US when it introduced i believe the M62 wrecker with a sort of inverted pendilum rig on both front and rear winches. All these ideas were never complete success however as they ignored a basic fact a winch must have the correct fleet angle between its self and the load it is winching or its fairleads. Modern day civilian wrecker designs have over come this to a degree by mounting twin narrow drum winches high up on the boom but still need operator intervention at times to keep things in order. Unless they start building wrecker chassis 90ft long with drum at one end and fairleads at the other or move over to constant line pull capstan winches we are stuck with the fact that safe operation of these winches is down to operator knowledge

[cosrec]

Very useful information, Cosrec :thumbsup:

 

What's your take on snatch block pulley diameters? Some recovery type blocks look way too small for my liking.

 

It should be noted that some recovery block pulleys look as if they will accept a larger diameter rope than their design size, due to the wider mouth of the rope groove - which are intended to reduce damage if the rope pulls sideways. It is the radius of the bottom of the groove which is critical for safe operstion, and which determines diameter of rope to be used.

 

 

Hi i was going to leave Snatch blocks for a while but thought i must give a little warning. A long time ago i bought ten snatch blocks from a dealer in North Yorks These new and still in greased wrapping I was made up and knew i had got a bargin. To discribe them they where very well made quality pieces of kit. The actual pully was made of alloy with four drilled holes in it The pulley was approx 10 inch in dia the side check plates were also of alloy around it was a steel strip 2.5 inch wide main frame with a swiveling hook attached. The side gate to get the rope in and out was secured with one of those antiluce fasteners. we put 4 on each of two heavy wreckers we had which were equipped with twin 6 ton hydraulic winches. they had no makers markings on them nor any SWL. They were worked hard over the next 5 years and never gave any problems

A well documented article then appeared in our trade magazine AVRO news a recovery operator (who ceased trading very shortly after)in the states had been on a recovery righting an overturned artic. A snatch block had let go killing a state trooper and blinding another. the next edition showed a line sketch of the snatch block and what to look out for The pully was machined to accept 1 1/2" fibre rope its safe working load was 1.5 ton

Guess what i had 10 of them did any more survive

[cosrec]

Ok so now we are in a position to actually winch something got a good winch with good rope on it with an end thats safe to fasten to. How about before using it we work out how much or little the vehicle will actually pull. Take for example the pioneer guessing its wt is 12 tons

Using the calculations we have we can work out that stood on level road with hand brake on disabling back wheels and no front brakes

WT 12 x Damage resistance 4 divided by total wheels 6

it will slide back at a bit over 8 tons not a great amount for what is a relativley big vehicle.

Try those scotch blocks that come with the pioneer this will disable the front wheels

WT 12 x Damage resistance 6 divided by total wheels 6

thats better it will take a little over 12 tons to move it now but a little more would be handy

Stiff leg/spades add 1/3 to 1/2 to what a vehicle will hold.

Take the scotch blocks out and put them under the rear most wheels winch with handbrake of until almost ready to go over the top put handbrake on bring cables for scotch blocks together with a shakle and hang on to crane take tension on crane you now have the equal of a set of stiff legs. get some one to press brrakes to disable them recalculate

WT 12 x Damage resistance 6 divided by total wheels 6 x 1/3

16 tons getting a bit more like it perhaps another two stiff leg spades would help.

Try throwing a sleeper each side in the back bogie arrange it so that the top is sitting on the top of the rear most axle and under the second axle this will mean as you winch back with handrake of to top of the scotch block the second axle will try and climb over the rear axle. You have now created the second set of stiff legs do the sums again

WT 12 x Damage resistance 6 divided by total wheels 6 x 2/3

20 tons to move it lot better. Feeling greedy and want more though. Any thing in the calculations that can help us. How about adding a bit of gradient resistance. Before rigging up scotch blocks and putting sleepers in try putting truck down that dyke side that happens to be in right place dont need much of gradient to increase pull by 1/2 that will give you another 6 ton thats 26 tons of holding power.

So for only a little work and and some thought we have increased our holding piont from 8 to 26 tons.

Also given you a problem if you want to utilise it the winch aint big enough.

[Stormin]

So for only a little work and and some thought we have increased our holding piont from 8 to 26 tons.

Also given you a problem if you want to utilise it the winch aint big enough.

 

Isn't all that holding power now good enough to make use of the snatch blocks you claimed were almost useless previously and effectively increase the pull of the winch?

[cosrec]

 

Isn't all that holding power now good enough to make use of the snatch blocks you claimed were almost useless previously and effectively increase the pull of the winch?

thats exactly the piont i am making i never said the blocks were usless i was angling at what is the point in using needlessly when the truck would slide back anyway

[Stormin]

 

As for Kerr, you are storing up potential energy in the rope that is released as the casualty comes unstuck. The stored energy is directly proportional to how far the rope is stretched before the casulaty unsticks. You can only store so much energy by driving forward using the grip of the tyres on the tow vehicle provide and the stored energy in the rope can never exceed what could be achieved by using a normal Hawser or chain if used just as a rope ( ie trying to tow the casualty out).

 

 

Not sure I can agree with the last sentence. If I KERR rope is no more effective than using a dead tow why were they developed?

[N.O.S.]

I thought the whole point about KERR was that it enabled you to transfer the momentum (ah - extra energy ) of the moving tow vehicle into a snatch pull with far less risk of ripping off rope anchor points or breaking tow rope than if you tried a snatch pull with chain or non-stretch rope.

[Jack]

Keep posting cosrec some of us are learning something

 

I Second that!

[rbrtcrowther]

I'm really enjoying this thread tons of good info being passed round:D i shows what can be dpne with a little thought. I can never remember which way the saddel and U bolts are ment to be fitted and always end up wandering of to find the book. So thamks for the saddel and dead horse thingy.

 

Having now got our scammell set up with good holding points and up to 26T we now realize what a rubbish winch we have and the skin will remain firmly on the rice pudding cos we can't put the snatch blocks back to the scammell or we might pull the arse out of it. We should have brought a propper truck with a rated ground anchor to put the snatch blocks to:-)

 

Can't wait for us to get on to compound rigging as i really need to brush up on the ratings and losses ect.

 

Keep it coming i love it:thumbsup:

[Mk3iain]

I Second that!

I second that second!

[gritineye]

 

Take the scotch blocks out and put them under the rear most wheels winch with handbrake of until almost ready to go over the top put handbrake on bring cables for scotch blocks together with a shakle and hang on to crane take tension on crane you now have the equal of a set of stiff legs. get some one to press brrakes to disable them recalculate

WT 12 x Damage resistance 6 divided by total wheels 6 x 1/3

 

As a Pioneer has no front brakes and you have removed the front scotches, surely damage resistance remains 4/6, also I'm thinking the angle of the cables to the crane would be too steep for the scotches to work effectively, or am I missing summat?

[croc]

Ok so now we are in a position to actually winch something got a good winch with good rope on it with an end thats safe to fasten to. How about before using it we work out how much or little the vehicle will actually pull. Take for example the pioneer guessing its wt is 12 tons

Using the calculations we have we can work out that stood on level road with hand brake on disabling back wheels and no front brakes

WT 12 x Damage resistance 4 divided by total wheels 6

it will slide back at a bit over 8 tons not a great amount for what is a relativley big vehicle.

Try those scotch blocks that come with the pioneer this will disable the front wheels

WT 12 x Damage resistance 6 divided by total wheels 6

thats better it will take a little over 12 tons to move it now but a little more would be handy

Stiff leg/spades add 1/3 to 1/2 to what a vehicle will hold.

Take the scotch blocks out and put them under the rear most wheels winch with handbrake of until almost ready to go over the top put handbrake on bring cables for scotch blocks together with a shakle and hang on to crane take tension on crane you now have the equal of a set of stiff legs. get some one to press brrakes to disable them recalculate

WT 12 x Damage resistance 6 divided by total wheels 6 x 1/3

16 tons getting a bit more like it perhaps another two stiff leg spades would help.

Try throwing a sleeper each side in the back bogie arrange it so that the top is sitting on the top of the rear most axle and under the second axle this will mean as you winch back with handrake of to top of the scotch block the second axle will try and climb over the rear axle. You have now created the second set of stiff legs do the sums again

WT 12 x Damage resistance 6 divided by total wheels 6 x 2/3

20 tons to move it lot better. Feeling greedy and want more though. Any thing in the calculations that can help us. How about adding a bit of gradient resistance. Before rigging up scotch blocks and putting sleepers in try putting truck down that dyke side that happens to be in right place dont need much of gradient to increase pull by 1/2 that will give you another 6 ton thats 26 tons of holding power.

So for only a little work and and some thought we have increased our holding piont from 8 to 26 tons.

Also given you a problem if you want to utilise it the winch aint big enough.

 

Have a look at this video someone posted of me winching a lorry at the end of a wet rally.

 

At the first position I did not have enough grip and was sliding backwards. I did not have scotches with me so all I could do was reposition with the back wheels on harder ground and the front wheels down a slope. (this was across the access track for the rally field, I didn't use it at first as I didn't want to block it)

The repositioning was enough to do the job, it was then only hindered by the driver trying to "help" by driving his wheels. The video stops at the point I was getting out to give him a bollocking. Also note at about 50 seconds the bloke who wanders over to the rope, he was one of the "marshals" but presumably keeping people out of the way didn't include himself.

 

A note on the scotches, they are not designed to just disable the front wheels, when used properly there is a cable from the scotch to the chassis, instead of the drivetrain and suspension taking the load from the winch to the ground, the load is taken via the cables to the scotches. On soft ground with the scotches properly seated each one forms a frontal area of about 6" x 14" and provides quite a good anchor, depending on the ground.

Given that the winch on a Pioneer is rated at 8 ton the scotches alone should be adequate for anything you would do with it.

On late Explorers the winch rating had been increased to 15 ton, the only modification being the cutout. The same winch was fitted to the Milly 3 recovery, I know of one where the winch drive was sheared when using the ground anchor (presumably the cutout was disabled) so, stong as these winches are they will break (or cutout) if overloaded. Whilst it is possible to increase the holding power, there is little point in doing so vastly in excess of the winch rating.

[Stormin]

Whilst were on the subject of winching and recovery.

 

What are peoples opinions on these end fittings to winch ropes as oppposed to the usual thimble?

[ATTACH=CONFIG]33320[/ATTACH]

 

Are they as strong as modern cable end fittings? Are they correct to World War Two period?

Are they still available?

 

I suppose the advantage they had is that they could be re-rigged onto the end of a broken cable in the field. They also leave the end of the cable tidy with no loose end or sharp wires to bite into hands.

[N.O.S.]

I use these fittings for a tough duty application. But they are not threaded - they have a very shallow taper into which the rope is fed, then unravelled and the lot filled up with whitemetal. As solid as you'll get.

 

I think it would be a certainty that the threaded variety like your example are still available. In fact I'm not really sure how they are attached in your example.

 

WW2? I would imagine very possible.

[Stormin]

I use these fittings for a tough duty application. But they are not threaded - they have a very shallow taper into which the rope is fed, then unravelled and the lot filled up with whitemetal. As solid as you'll get.

 

I think it would be a certainty that the threaded variety like your example are still available. In fact I'm not really sure how they are attached in your example.

 

WW2? I would imagine very possible.

 

 

Some details here.

http://news.thomasnet.com/fullstory/Wire-Rope-Fittings-eliminate-need-for-swage-press-479682

 

Sounds like there is a plug pushed up the centre of the rope to allow the compression fitting to work against something. I've seen them listed in stainless steel intended for yacht rigging, or architectural support systems but nothing as big as for 3/4 wire winch rope.

 

Another similar type here:-

 

http://www.s3i.co.uk/swagelessterminals.php

Edited August 24, 2010 by Stormin

[cosrec]

As a Pioneer has no front brakes and you have removed the front scotches, surely damage resistance remains 4/6, also I'm thinking the angle of the cables to the crane would be too steep for the scotches to work effectively, or am I missing summat?

Quite right and thanks for pointing out if you look at my post i did put a a bit in about getting someone to press the brakes and disable the front axle but my grammer got mixed up and more important i had completely forgot there are no front brakes from there on all calculations are out by 4 tons. For recovery the scotches work best when they are pulling down hard on the chassis as the load comes on the pull down transfers an amount of the line pull into load on the axle which in turn will cause more wieght to go on to the scotch. If the scotch has a good hold you can end up transfering wieght of the front end and on to the rear causing even more sinking of the scotch.

[cosrec]

Have a look at this video someone posted of me winching a lorry at the end of a wet rally.

 

At the first position I did not have enough grip and was sliding backwards. I did not have scotches with me so all I could do was reposition with the back wheels on harder ground and the front wheels down a slope. (this was across the access track for the rally field, I didn't use it at first as I didn't want to block it)

The repositioning was enough to do the job, it was then only hindered by the driver trying to "help" by driving his wheels. The video stops at the point I was getting out to give him a bollocking. Also note at about 50 seconds the bloke who wanders over to the rope, he was one of the "marshals" but presumably keeping people out of the way didn't include himself.

 

.

Well done i would have given the driver an upping as well. I know you were not anywhere near your limit on rope but the vidieo shows how well meant help is rocking the scammell and could under the wrong circumstances have caused damage.

A little tip on loaded artics where you have a nice big area to work. Oftence instead of trying to pull the complete lot out at once reposition so that you are at almost 90 degrees to the front of unit then winch the artic will jackknife round fairly easily with out even moving the trailor keep winching and its still an easy pull because the length of the trailer from neck to first axle acts as a lever and screws the trailor out across the ruts you might have to keep reposition and start again the other way but using this method you can get some heavy artics out of deep mud with a relativly small winch.

[julezee001]

Given that the winch on a Pioneer is rated at 8 ton the scotches alone should be adequate for anything you would do with it.

On late Explorers the winch rating had been increased to 15 ton, the only modification being the cutout. The same winch was fitted to the Milly 3 recovery, I know of one where the winch drive was sheared when using the ground anchor (presumably the cutout was disabled) so, stong as these winches are they will break (or cutout) if overloaded. Whilst it is possible to increase the holding power, there is little point in doing so vastly in excess of the winch rating.

 

The reason for the extra anchoring well in excess of the winches maximum pull, is that the rating is for a single line pull. If you fit a snatch block it will almost double the pull, giving the Pioneer close to 16 tons, and the Explorer close to 30 tons. The classic training video shows a Pioneer with a series of snatch blocks in place, I think giving almost 40 tons pulling a Churchill sideways out of a ditch. Very impressive!

 

Jules

Edited August 24, 2010 by Marmite!!
quote tags

[N.O.S.]

... I've seen them listed in stainless steel intended for yacht rigging, or architectural support systems but nothing as big as for 3/4 wire winch rope....

 

They're out there - and they come at least twice as big as this one! They are assembled just as I described, and you can use resin instead of spelter now.

 

Another useful termination is the wedge socket - useful for quick repairs.

 

Hope we're not treading on your toes posting stuff like this, Cosrec - perhaps you were planning a whole post on terminations :blush: Keep it coming!

[cosrec]

Not treading on my toes i like to learn as well

[gritineye]

A little tip on loaded artics where you have a nice big area to work. Oftence instead of trying to pull the complete lot out at once reposition so that you are at almost 90 degrees to the front of unit then winch the artic will jackknife round fairly easily with out even moving the trailor keep winching and its still an easy pull because the length of the trailer from neck to first axle acts as a lever and screws the trailor out across the ruts you might have to keep reposition and start again the other way but using this method you can get some heavy artics out of deep mud with a relativly small winch.

 

I was told this same trick by a farmer, now sadly deceased, he was very fond of telling how he pulled three very stuck tractors and a trailer, all chained together, that had resisted all attempts at recovery all day. He pulled the lot out in one go with his Fordson Major, as each one came out sideways it joined in pulling and so on..

[croc]

Well done i would have given the driver an upping as well. I know you were not anywhere near your limit on rope but the vidieo shows how well meant help is rocking the scammell and could under the wrong circumstances have caused damage.

A little tip on loaded artics where you have a nice big area to work. Oftence instead of trying to pull the complete lot out at once reposition so that you are at almost 90 degrees to the front of unit then winch the artic will jackknife round fairly easily with out even moving the trailor keep winching and its still an easy pull because the length of the trailer from neck to first axle acts as a lever and screws the trailor out across the ruts you might have to keep reposition and start again the other way but using this method you can get some heavy artics out of deep mud with a relativly small winch.

 

Like this, this time it only needed the brakes.

 

[croc]

The reason for the extra anchoring well in excess of the winches maximum pull, is that the rating is for a single line pull. If you fit a snatch block it will almost double the pull, giving the Pioneer close to 16 tons, and the Explorer close to 30 tons. The classic training video shows a Pioneer with a series of snatch blocks in place, I think giving almost 40 tons pulling a Churchill sideways out of a ditch. Very impressive!

 

Jules

 

Here is the edited version of that video,

note the use of ground anchors as well as snatch blocks, only one line runs to the Scammell. If you use a block it is better not to attach it to the winch vehicle if you can avoid it. Also remember that there can be a big difference between towing points, lashing points and recovery points. Edited August 24, 2010 by croc