Deaths from towballs

[MudRunnerTD]

I applaud him for helping those in need as his paid job, but he does use towballs on some of the recovered vehicles after a rudimentary look around it. Unfortunately it just takes one out of a hundred to go wrong. Other people watch his videos and think it's OK to follow his example.

That right there is the biggest problem. The Professional providing the example to the Pleb. The Pleb cant tell the difference here and will make the Fatal decisions and the Coroner wont care that the Professional provided a Bad Example.

[MudRunnerTD]

I am not advocating use of a towball as a hitch point where the towball is anchored with a thread into a receiver. This type of setup puts rise to potential failure of the treaded element from shear and/or shear and a bending moment as the line of action is raised to the thinner section of the towball. Most towballs have an undercut at the base of the thread where it matches the 50mm head, and this becomes the stress riser, especially as depth of undercut, radius size and surface roughness are unknown.

Additionally we have no idea what the towballs are manufactured from, could be recycled chinese bicycle seats - my towball is from a HT 4140 steel, but I would think a lot are made from a far lower grade.

What I would say is that his towball setup looks like its got 3 different sized balls, welded to a solid receiver bar, and fixed to the front of the towbar hitch using a standard 16mm pin. I would say, his weakest point in all this is either the 16mm pin in a double shear loading or the strap itself. The welded towballs are essentially 50mm pegs and the stress is going thru 3 circumferential welds into the solid hitch. The loading diagram for his hitch is not straight forward to determine actual stresses, however it is possible to get this analyzed using a Strand Stress Analysis package for certainty as it takes away the interpretation of the engineer. We don't know the materials, weld detail, weld procedure or welder certification, NDT taken place etc - there is a lot missing in this picture.

So, is the setup any weaker than using a slot in hitch on our standard towball set-up - I doubt it as ultimately the pin is the weakest element. Even if the receiver was a tube, worst case a thin walled tube, its 'probably' still going to fail on the tow strap rather than the hitch - thats my analysis anyway. On the surface it probably looks worse than it is. Whilst the guy using it claims to assess the loading conditions of the recovery - had to laugh at the h/d ear ring he pulled out for use though - and he does execute his recovery operations in seemingly the worst way, I think he is no worse off than what we do when we use a standard hitch and 16mm pin.

Final parting comment, Don't use a snatch strap on a towball for recovery.

Kinda what i said above but with Bigger words and More brain cells.... ^^^^What He Said ^^^^

[Rossco]

I think if your publishing something to a worldwide audience and its your profession it's a no brainer really. His three ball thingy maybe OK but have seen him on many occasions hooking up to tow balls of vehicles to be recovered, not just on ice with no resistance as he says in Mad Mats vid but giving big American trucks a good yank (no pum intended lol) . .

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[Big Gags]

I finally got my winch fitted up a few weeks ago after it sat in the shed for 3 months or so (although now we are in lockdown and so my only "recovery" so far has been to winch my son in from the driveway across the street so that I at least had some tension on the drum!! I am ex-army and have been involved in engineering numerous vehicles with self-recovery winches and also dedicated Recovery Vehicles. Army has a whole trade stream (Recovery Mechanics AKA Recce Mechs) who's job is to recover vehicles whether they be bogged, battle damaged, or have a malfunction. Army has a Recovery Mechanics Handbook that is basically their bible for recovery and it's actually got some really good guidance in it. Army does not do dynamic recovery using snatch straps but instead uses winches to conduct controlled recoveries. When planning a recovery the Recce Mechs calculate the total pull required which is dictated by a number of things.

The first one is the Ground Type and depending on the type of ground you get a number to divide the vehicle weight by. From memory for hard ground it's a factor of 25 and for mud (bogged to the floorpan) it's a factor of 1. So you take the mass of the vehicle and divide it by the Ground Factor. For example a 10 tonne vehicle would have a Ground Factor of 500 kg for hard ground and 10 tonne for mud bogged to the axles.

Then there is a damage factor. There are various factors depending on the extent of the damage. From memory there is a factor added for each seized wheel which I think for 10 tonne vehicle is 500 kg per wheel. For example's sake let's say that one axle is locked due to a busted diff so the damage factor is 1000 kg.

Finally there's a gradient factor which is vehicle mass x angle of slope (degrees) / 60 and so for say a 15 degree estimated slope the gradient factor for a 10 tonne vehicle is 2.5 tonne.

So total pull in this example is 10 + 1 + 2.5 = 13.5 tonne

However, there is then a 25% safety factor added and so the total pull required is 13.5 x 1.25 = 16.875 tonne but they round it up to the closest tonne so in this recovery a 17 tonne pull is required.

Then they workout the recovery layout. Let's say they had a 10 tonne winch and so they decide to do a 2:1 recovery. Again I remember this because I have dealt with it a few times (although I was not a Recce Mech) but due to the inefficiencies of the tackle a 2:1 recovery actually only gives you 1.8:1 which in this case meets the requirement.

The dedicated recovery vehicles carry suitably rated chains, sheaves (snatch blocks), and bow shackles to setup the recovery. Initial light tension is applied (once tension is applied, nobody is allowed to step over a recovery rope and at no time is anybody allowed to stand in the "V" formed by a 2:1 recovery) and then all recovery attachments are physically checked by the Operator. The Operator is behind a protective screen and a danger exclusion zone is cleared for 1.5 times the distance between the two vehicles and only after all this is in place can they start winching.

So what are my lessons learnt from this experience (and the ones I will apply when using my winch in anger):

- Always try to do 2:1 recovery where possible to reduce the tension on the winch and the rope (and put up with it being half as fast as a single pull)
- Always determine what the weakest point in the recovery layout is and make sure it's strong enough!!
- Always use rated bow shackles and rated recovery points
- Always use an equalisation bridle and use both recovery points on the front of the vehicle for every recovery
- Always use a damper on the rope in case it does snap
- Keep everybody else well away from the recovery activity
- Check everything at least twice (once after applying initial tension)
- Only use a snatch strap as a last resort and if needed then use minimum recovery speed and rated recovery points
- Never, ever use a towbar for any recovery activity!!!

Once we are allowed out I think I will go out for a familiarisation session and do a couple of winch pulls just to familiarise myself with everything and make sure that everything works OK.....looking forward to it!!

[PeeBee]

Excellent content, thanks very much.

[mudnut]

Army does not do dynamic recovery using snatch straps but instead uses winches to conduct controlled recoveries.

I am hearing that sort of statement more and more. Some Youtube presenters dealing with 4wds, advocate not using snatch straps at all, or only as a last resort.

Thank you for all that knowledge, Big Gags.

[BillsGU]

The British Army use snatch straps – but only on armoured vehicles. The rules are everyone inside the vehicles and all hatches shut before the snatch is attempted. Because they are heavy vehicles they use seriously large straps – but it is quick and safe if procedures are followed.

[Big Gags]

The British Army use snatch straps – but only on armoured vehicles. The rules are everyone inside the vehicles and all hatches shut before the snatch is attempted. Because they are heavy vehicles they use seriously large straps – but it is quick and safe if procedures are followed.

Funnily enough I am currently working as a contractor on an Armoured vehicle program. Towing and Recovery Points for armoured vehicles in Australia need to meet a DEF(AUST) standard but that refers to the STANAG 4478 standard and this is no doubt what the UK vehicle recovery points would meet. The STANAG needs each individual tiedown/lifting/recovery point to be strong enough to withstand a force of 1.5 x GVM in the vertical direction (for lifting and for lift-tow) and also in a 22.5 degree cone around a line drawn parallel to the vehicle axis. So each individual point can withstand 1.5 x GVM and when you have for example a 40 tonne armoured vehicle it means that each point is rated for 60 tonne!!! There are also specific clearance angles around the points and specific dimensions of the points (to ensure that the suitably sized A-Frames and tiedown/lifting equipment can be used!!

[MudRunnerTD]

I finally got my winch fitted up a few weeks ago after it sat in the shed for 3 months or so (although now we are in lockdown and so my only "recovery" so far has been to winch my son in from the driveway across the street so that I at least had some tension on the drum!! I am ex-army and have been involved in engineering numerous vehicles with self-recovery winches and also dedicated Recovery Vehicles. Army has a whole trade stream (Recovery Mechanics AKA Recce Mechs) who's job is to recover vehicles whether they be bogged, battle damaged, or have a malfunction. Army has a Recovery Mechanics Handbook that is basically their bible for recovery and it's actually got some really good guidance in it. Army does not do dynamic recovery using snatch straps but instead uses winches to conduct controlled recoveries. When planning a recovery the Recce Mechs calculate the total pull required which is dictated by a number of things.

The first one is the Ground Type and depending on the type of ground you get a number to divide the vehicle weight by. From memory for hard ground it's a factor of 25 and for mud (bogged to the floorpan) it's a factor of 1. So you take the mass of the vehicle and divide it by the Ground Factor. For example a 10 tonne vehicle would have a Ground Factor of 500 kg for hard ground and 10 tonne for mud bogged to the axles.

Then there is a damage factor. There are various factors depending on the extent of the damage. From memory there is a factor added for each seized wheel which I think for 10 tonne vehicle is 500 kg per wheel. For example's sake let's say that one axle is locked due to a busted diff so the damage factor is 1000 kg.

Finally there's a gradient factor which is vehicle mass x angle of slope (degrees) / 60 and so for say a 15 degree estimated slope the gradient factor for a 10 tonne vehicle is 2.5 tonne.

So total pull in this example is 10 + 1 + 2.5 = 13.5 tonne

However, there is then a 25% safety factor added and so the total pull required is 13.5 x 1.25 = 16.875 tonne but they round it up to the closest tonne so in this recovery a 17 tonne pull is required.

Then they workout the recovery layout. Let's say they had a 10 tonne winch and so they decide to do a 2:1 recovery. Again I remember this because I have dealt with it a few times (although I was not a Recce Mech) but due to the inefficiencies of the tackle a 2:1 recovery actually only gives you 1.8:1 which in this case meets the requirement.

The dedicated recovery vehicles carry suitably rated chains, sheaves (snatch blocks), and bow shackles to setup the recovery. Initial light tension is applied (once tension is applied, nobody is allowed to step over a recovery rope and at no time is anybody allowed to stand in the "V" formed by a 2:1 recovery) and then all recovery attachments are physically checked by the Operator. The Operator is behind a protective screen and a danger exclusion zone is cleared for 1.5 times the distance between the two vehicles and only after all this is in place can they start winching.

So what are my lessons learnt from this experience (and the ones I will apply when using my winch in anger):

- Always try to do 2:1 recovery where possible to reduce the tension on the winch and the rope (and put up with it being half as fast as a single pull)
- Always determine what the weakest point in the recovery layout is and make sure it's strong enough!!
- Always use rated bow shackles and rated recovery points
- Always use an equalisation bridle and use both recovery points on the front of the vehicle for every recovery
- Always use a damper on the rope in case it does snap
- Keep everybody else well away from the recovery activity
- Check everything at least twice (once after applying initial tension)
- Only use a snatch strap as a last resort and if needed then use minimum recovery speed and rated recovery points
- Never, ever use a towbar for any recovery activity!!!

Once we are allowed out I think I will go out for a familiarisation session and do a couple of winch pulls just to familiarise myself with everything and make sure that everything works OK.....looking forward to it!!

Hi mate, thanks for your input.

Have a look at this thread also as the first section provides some good references for your average 4wdriver relating to some of the math you have applied above.

http://www.nissanpatrol.com.au/forum...e-Fundamentals

[mudnut]

I did try sending an Email, with a picture of the Yota tailgate, but I don't think it my Email is working. Anyone want to reply to him?

https://www.youtube.com/watch?v=exlh8H4eH-0