Recovery (non snatch) on tow ball?

Got stuck? How to get unstuck. How to use your Pajero.
User avatar
4ePikanini
Affiliate Member
Contact:
Country: South Africa
Vehicle: 2001 Pajero LWB 3.2 Di-D GLS
Location: East London, South Africa
Posts: 2798
Joined: Sun Jun 14, 2009 9:38 pm

Recovery (non snatch) on tow ball?

Fri Sep 02, 2011 6:34 pm

OK, I know it's a no-no to do a snatch recovery on a towball and I wouldn't dream of it.

What I want to know........

Can the traction (Not engine power as most engines can easily spin all 4 in low range) of tyres create more pulling power than what the towball can handle?

In short : Is it safe to do a pull recovery on a towball? Pin type?
Marius Fourie
MY DIY WEBSITE
2005 Touareg R5 Air & Bi-Xenon
Image
User avatar
jotto
Contact:
Vehicle: Pajero SWB 3200 Di D 2001
Location: Centurion
Posts: 119
Joined: Thu Feb 17, 2011 6:52 am

Re: Recovery (non snatch) on tow ball?

Fri Sep 02, 2011 7:18 pm

Hi Marius

Not safe at all, no matter what. Read this and you will understand the stresses placed on the connection point:

http://www.4x4community.co.za/forum/sho ... hp?t=92189

It is very informative and real case examples of what happens, very nasty :evil:

If you read the whole article, there is a full explanation on the exact forces with e maths behind them.

Hope this helps

Cheers

Johann
Di-D 3200 SWB 2001
User avatar
4ePikanini
Affiliate Member
Contact:
Country: South Africa
Vehicle: 2001 Pajero LWB 3.2 Di-D GLS
Location: East London, South Africa
Posts: 2798
Joined: Sun Jun 14, 2009 9:38 pm

Re: Recovery (non snatch) on tow ball?

Fri Sep 02, 2011 7:32 pm

That thread made me post this one. They all talk about snatching.

I want to know about pulling with a normal tow strap.

Reason I ask is

- I have pulled a fully loaded double axle trailer with dad's touareg V10 and forgot the handbrake on. Pulled away on steep inclines and because of the sheer torque of that monster engine I didn't notice until 2 trips later my boet smelt something and revealed cooking bearings - it didn't break the gooseneck on the VW
- I have pulled a tractor trailer (and the tractor itself) from my pintal and din't experience failure
- We have been on holiday with a huge caravan fully loaded and the towbar was fine. (Dad pulled away in low range on some hills and then stopped and moved to high range once over the hill if I remember correctly)
- I have never seen a report on a failed towball while pulling NOT snatching.

I strongly feel that the power transferred by the engine onto the road by the four wheels cannot provide enough strength to break a towball.

The obvious test would be to have car connected via strong chain to tow ball (other end fixed to immovable object) and have the car pull in low range on tar to see if vehicle starts spinning wheels or towball breaks. (I don't want to be guinea pig due to forces on transmission) - I bet wheels would start spinning first.
Marius Fourie
MY DIY WEBSITE
2005 Touareg R5 Air & Bi-Xenon
Image
User avatar
jotto
Contact:
Vehicle: Pajero SWB 3200 Di D 2001
Location: Centurion
Posts: 119
Joined: Thu Feb 17, 2011 6:52 am

Re: Recovery (non snatch) on tow ball?

Sat Sep 03, 2011 7:27 am

Hi Marius

Agree, while the other object is easily moved, the strain on the ball is not that much. It is when the other object stops moving and people tug at it when things go wrong. Looking at just the strength for towing, i remember some time ago a show where a baKkie towed a Boeing 747, so would suspect it be strong enough while towing a moving object.

Would also like to know the maximum/break point of a tow ball vs weight being towed.

I will bring the chain, who's keen on the 4x4 :twisted:

J
Di-D 3200 SWB 2001
User avatar
4ePajero
Vehicle: 1989 Pajero LWB
Location: East London
Posts: 1347
Joined: Fri Jun 12, 2009 1:59 pm

Re: Recovery (non snatch) on tow ball?

Sat Sep 03, 2011 9:26 am

Yeah, I've read that thread on the Commy forum, and have a few opinions on it.

Firstly, I doubt whether you will break a "healthy" tow ball with a smooth pull.
The vehicle should lose traction long before enough forces to break a tow ball, even with the best tyres.
An emergency stop, with a large trailer/caravan will most probably create larger forces.
Once you start "jerking" though, it turns into a "snatch" and anything can happen!


On snatching, and breaking tow balls / bars:
  • The forces involved in snatching and those involved when towing/pulling, are not of the same order of magnitude.
    Because I prefer to err on the safe side, I would never recommend doing a snatch using a tow bar or a tow ball.
    I doubt however whether the forced involved in a "proper" snatch are large enough to break a "healthy" tow ball.
    The question then is what a "proper" snatch is.
  • I have watched many snatching videos on the web, and am convinced that most of the "experts" don't understand the physics involved fully.
    I am convinced that most snatches (and certainly most of those where breakages occur) happen when the kinetic limits of the snatch rope are exceeded.
    The specification for kinetic ropes usually states that snatch should be done in such a way that it is ensured that the length of the rope should never 110% of it's unstrained length (when new).
    In most snatches this is ignored. The snatch is done in such a way that the kinetic rope exceeds it's kinetic limits, and it then becomes just another "solid" rope.
    When this condition is reached, the recovering vehicle is still moving, and the forces exerted on the rope (and thus all attachments and connectors) FAR exceeds the design parameters of the kinetic rope.
To give an analogy of what happens, imagine this:

You have to "cushion" the weight of a falling mass.
To do this, you place a coil spring in an upright position underneath the falling mass.
As the mass falls, it compresses the coil spring.
NB. Ideally it should stop the falling mass before it is fully compressed.
The momentum of the falling mass is "damped" because of the kinetic properties of the coil spring.
The forces transmitted to the ground through the coil spring are thus also "damped" (the force is applied over a length of time, and not as one impact).

Imagine however, that the coil spring is to "soft", and cannot support the falling mass!
The coil compresses fully before the mass is stopped.
The damping effect still occurs, but the mass is still falling when the coil is fully compressed.
The coil spring now acts the same as a solid piece of steel, and the momentum of the mass is transferred to the ground without any further damping effect.
You can now realistically expect damage to all the components involved: mass, coil and the earth!

Summary:
I doubt whether a "smooth" pull will break a tow bar/ball.
Gerhard Fourie
If you want to shoot somebody, make sure you aim at his head, not your own foot.
Me
Image
User avatar
Bigwill
Vehicle: 2004 Pajero 3.2 DID SWB
Location: Gauteng
Posts: 276
Joined: Mon Sep 28, 2009 11:41 am

Re: Recovery (non snatch) on tow ball?

Sat Sep 03, 2011 12:27 pm

Well I once had a bad experience that certainly put my gooseneck tow ball to a severe stress test when I was unfortunate to barrel roll my camper trailer of about 1.2 tons. In spite it rolling over about 5 time the tow coupling did not come off and neither did the ball break off. It had a swivel coupling and also did not effect the car much. As it rolled over onto the roof the top front corners of the trailer were ploughing into the soft gravel road surface leaving trenches behind large enough to plant potatoes in. In my opinion those that break so easily had flaws in. Mine has now proved itself and I am happy to continue using it now pulling a Echo Chobe.
From the photos you can see how the tow bar itself pulled away from the bumper under the force. It used to have the bumper protection plate right up against the bumper
How did it happen you may ask. Well I’m still not sure. Factors of influence were low inflated tubeless tyres on the trailer and non-tubeless rims, speed a little high for corner, anti-skid on the Paj caused slight breaking that swung the trailer tail out. It happened in Kaokoland a few years ago. Had to desert the trailer there.
DSC_9874.JPG
DSC_9874.JPG (44.66 KiB) Viewed 6434 times
DSC_9865.JPG
DSC_9865.JPG (46.7 KiB) Viewed 6434 times
DSC_9762 - Copy.JPG
DSC_9762 - Copy.JPG (65.73 KiB) Viewed 6434 times
Willie from Jo'burg
White Gen 3 SWB Pajero 3.2 DID
User avatar
HBannink
Affiliate Member
Contact:
Vehicle: Pajero gen2 3l lwb
Location: Johannesburg
Posts: 434
Joined: Sat Jun 13, 2009 1:22 am

Re: Recovery (non snatch) on tow ball?

Sun Sep 04, 2011 2:20 am

I would never encourage one to use a tow ball as recovery point, having said that, there is no way that I will leave a fellow human stuck in the bundu just because he or I don't have the rated and accepted recovery points on a vehicle. A gooseneck is designed with the forces of towing in mind and I think the pin type hitches are a bit stronger than them. If I only had a gooseneck I would wrap the recovery strap around the tow bar and make sure that in the event of failure there is no flying bits and that includes the strap as well.

Safety is no accident but I think some folks tend to take the rating thing a bit too far. I do not know how to work a slide rule and formulas and such have never been my strong point, especially when I or one of my friends are stuck. Then the old instincts set in and we improvise to recover the vehicle in such a way that in the event of failure no one gets hurt and that includes both vehicles. Even if it is not a perfect recovery it would be safe.

Years ago we had a minimum force rule in the police and that would be my argument in a recovery, don't grab the snatch rope or winch first, rather start with the trusted old spade and work up from there. Most situations can be resolved with the help of a spade and hi lift.

One point to remember is that the nylon pull straps have some elasticity in them and if they break they can fly off in some direction so it is wise to put some form of damper on them as well.
Henk Bannink

Some people are wise, some people are otherwise
User avatar
buurman
Vehicle: Pajero Gen 2 3500 V6 2001
Posts: 28
Joined: Tue Jan 18, 2011 8:26 am

Re: Recovery (non snatch) on tow ball?

Tue Sep 06, 2011 8:05 am

I found this comparison on http://www.offroadexpress.co.nz/Forums/ ... 49&t=19886
Just for interest sake

I have carried out several hook tests on a test rig.
The bighorn hook with 10mm bolts snaps the bolts around 5 tonne
Drilled out to take 12mm bolts the hook snaps, nowhere near the drilling, at around 6 tonne
The Black Rat Black hook snapped around 5 Tonne
The Black Rat Chrome hook straightened around 5 Tonne
The Supa Cheap Ridge Rider Black hook snapped around 8 Tonne
The Bush Ranger Black hook straightened around 5 Tonne
3/4 shank towball snapped around 8 Tonne
The Snatchmaster hooks from Cookes straighten around 9.8 Tonne, this opens a new can of worms as the M12x1.75 bolts broke first.
Pintle Hook/Nato Coupling stripped the 10mm mounting bolts ie Patrol, around 12 Tonne
Pintle Hook with 12mm 8.8 bolts stalled the test rig around 20 Tonne
The Pintle tests were a straight on pull, an angled pull would load 2 bolts more with a leverage factor accross the mount face
All these tests were a increaseing load pull, not a snatch which could lower the results.

Return to “Techniques (Driving, Recovery etc)”

Login · Register

Login  •  Register