4x4 Recovery that went horribly wrong - Page 2





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  1. #21
    Beans Guest

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    Simon you can purchase these hooks at any 4x4 shop for about R65.00 these are chrome ones. Welding The problem with welding is that it changes the hardness of the metal making some brittle like glass. If one looks at the the snear snap off pressure of bolts i would rather bolt mine on. Looking quickly at the tow bar it was bolted to a plate which was welded to the bumper which could be say 1.5 to 2.5 mm round tube, plus taking into effect the rust issue of the round tube

  2. #22
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    Quote Originally Posted by vizzerman View Post
    Also, why not put up ones bonnet in a snatch recovery? People always do so when whinching, why not snatching?
    Do you realy think a tow ball (or whole hitch) coming at you at xyz Km/hr will be stopped by a thin 0.6mm plate

    I think not.......
    "A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster "
    By Jeremy Clarkson (I think)

  3. #23
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    I agree that bolting is the best, my recovery eye is however welded to my plate. I attach a picture to explain in more detail. As you can see the welding is around all 4 edges of the eye plate. The holes on the side is where my tow ball adapters bolts onto for towing, also not shown is 2 lower support arms that reinforce the tow ball for towing at the lowest setting. the wire you see there is just me not having bothered to rewire my tow bars plug.
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    Currently: 2009 Mitsubishi Triton 3.2 D/C 4x4
    Previously: 1996 LR Defender 110 V8



  4. #24
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    Quote Originally Posted by BigRed View Post
    Do you realy think a tow ball (or whole hitch) coming at you at xyz Km/hr will be stopped by a thin 0.6mm plate

    I think not.......
    Offcourse not, but heck I would rather have it there than not. Anything to absorb the worst momentum. Those poly straps will also probably snap, but anything is surely better than nothing? Hmm ok maybe not snap. What sort of force can a 5kg tow hitch generate?
    Last edited by vizzerman; 2007/11/19 at 09:26 PM.
    Currently: 2009 Mitsubishi Triton 3.2 D/C 4x4
    Previously: 1996 LR Defender 110 V8



  5. #25
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    You cannot snatch with a bonnet open. might loose your bonnet. Make sure you have good recovery equipment. Add proper recovery points, and if you think you can weld, you cant. Stay away and pay someone who can! Use a blanket on your recovery!
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  6. #26
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    Quote Originally Posted by BigRed View Post
    Do you realy think a tow ball (or whole hitch) coming at you at xyz Km/hr will be stopped by a thin 0.6mm plate

    I think not.......
    Oh c'mon Kai - think about it... an open bonnet which is allowed to buckle will absorb a lot of energy. It's not solid but pretty pliable so will spread the impact before it hits the windscreen and the windscreen will absorb the rest.

    Lets face it.. a buggered bonnet and a busted windscreen is better than being maimed, or worse, dead.
    2015 Pajero Sport 4x4
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    Carpe Diem Scrotum
    Give a man a beer, waste an hour. Teach a man to brew, and waste a lifetime!

  7. #27
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    Quote Originally Posted by Engel View Post
    You cannot snatch with a bonnet open.
    Make sure you have good recovery equipment.
    Add proper recovery points,
    Use a blanket on your recovery!
    Good points
    "A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster "
    By Jeremy Clarkson (I think)

  8. #28
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    Quote Originally Posted by Engel View Post
    You cannot snatch with a bonnet open. might loose your bonnet.
    Aha, thank you, that would be a good reason! Whats next? Duck under the dash? Begs the question though, loose a bonnet or your head? Has anyone ever seen a bonnet ripped off?
    Last edited by vizzerman; 2007/11/19 at 09:42 PM.
    Currently: 2009 Mitsubishi Triton 3.2 D/C 4x4
    Previously: 1996 LR Defender 110 V8



  9. #29
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    That guy can thank his lucky stars that that ball ricochetted off the bonnet. It changed the angle enough to miss him.

    Kai, the bonnet alone might not stop it, depending where it catches it, but it will absorb some of the energy, thus giving you a better chance.

    My question is why, with so many people and vehicles around didn't they winch him out. Snatching is such a violent and dangerous way of recovering that it should only be used as a VERY last resort.

    Why only after the incident did they suddenly follow the common sense recovery, backwards, where he came from, and where there would be least resistance. Those front wheels are dug in almost level to the ground. The forces involved to snatch him out of there is diffucult to calculate, but I can assure you anything less than a bulldozer would not have moved him.

    Came very close to a "Darwin Award" case this....and it's normally the guy doing the pulling that comes up with a "Grab my beer, let me "help" this guy out of there"

    I stand a looong way away when these antics start.
    Sakkie Coetzee

    Some people say I have a "short temper"....I see it as swift and assertive reaction to Bull!

  10. #30
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    Quote Originally Posted by SimonB View Post
    an open bonnet which is allowed to buckle will absorb a lot of energy. It's not solid but pretty pliable so will spread the impact before it hits the windscreen and the windscreen will absorb the rest.

    Lets face it.. a buggered bonnet and a busted windscreen is better than being maimed, or worse, dead.
    Agreed, but a 0.6 or thinner pice of steel (and in the case of most turbo diesels a large plastic scoop) will absorb about as much energy as a 4mm windscreen that is designed to deflect impact.

    At the end of the day, prevention is far better than cure...
    "A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster "
    By Jeremy Clarkson (I think)

  11. #31
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    Quote Originally Posted by BigRed View Post
    ...prevention is far better than cure...
    You've got my vote on that one.

    But doesn't matter how you look at it, looking at those pics they should never even have ATTEMPTED a snatch.
    Last edited by Sakkie; 2007/11/19 at 09:48 PM. Reason: S.O.S.
    Sakkie Coetzee

    Some people say I have a "short temper"....I see it as swift and assertive reaction to Bull!

  12. #32
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    Quote Originally Posted by BigRed View Post
    At the end of the day, prevention is far better than cure...
    Too true, I think that we just get too complacent sometimes, too relaxed. Things go wrong even when you have the best equipment and expertise, so always treat with respect and have a plan in place for when the worst takes place?
    Currently: 2009 Mitsubishi Triton 3.2 D/C 4x4
    Previously: 1996 LR Defender 110 V8



  13. #33
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    Here are some examples of recovery points I've fitted to my vehicles, some I've bought and others I've made myself.

    The recovery hook Beans was referring to as fitted to my hilux:
    Note the grade 12.9 M12 bolt. It has a shear force of 17 tons per bolt. I ONLY use grade 12.9 on recovery points....I'm not even taking chances on normal grade 8.8 hi tensile bolts. I also make sure that only one of the however many bolts I use can take the full load of the recovery, because due to the slight differences in hole pitches there can be a moment where all the load is only on one bolt.
    I've done some violent recoveries with the hooks, and no problems so far. In the last pic we tested the recovery points by digging the lux in down to the chassis and then recovering it without the wheels spinning....it took the landy 4 attempts to get the lux out.










    The recovery points I did for the front of my Isuzu which came with a factory Nudge-M bumper, but had no recovery points. These plates were designed in my CAD program and under stress analysis failed at 13 tons, so they will be stronger that a 8 ton breaking strain snatch strap. Again note the grade 12.9 bolts. This time M10 to match the holes in the chassis with a shear force of 12.2 tons each.








    This is the rear bar and recovery points I did for the rear of the Isuzu. The bracket are bolted to the chassis with 4 M12 bolts either side and there are bolts not only into the side of the chassis, but from the bottom as well to prevent the brackets from moving on the play around the bolts. The brackets themselves are 12mm waterjet cut plates and the pipe is 1.5" schedule 80 pipe, which can easily take the weight of the vehicle.






    (EDIT: Don't worry, the bolts were replaced by longer ones the next day...these are too short)


    This is a big recover point I designed for my friend's disco. Behind the flimsy Nudge-M there are brackets made from 80X10 flatbar that runs through to the chassis members. The brackets are attached to both chassis members with 4 M10 grade 12.9 bolts. Then the blocks are bolted to the brackets with 4 M12 bolts.

    Last edited by Barto; 2007/11/20 at 09:01 AM.

  14. #34
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    How much did it cost to have that point machined for the Disco? Looks fantastic.
    Currently: 2009 Mitsubishi Triton 3.2 D/C 4x4
    Previously: 1996 LR Defender 110 V8



  15. #35
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  16. #36

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    Quote Originally Posted by vizzerman View Post
    Also, why not put up ones bonnet in a snatch recovery? People always do so when whinching, why not snatching?
    With snachting, the stuck vehicle should be accelerating in the same gear as the recovery vehicle. So when the stuch vehicle is freed, it would be nice to see where you should stop, before you ram the recovery vehicle from behind.

    This in itself does not make it conducive to having the bonnet open.

    IMHO anyway
    Wade Bowman
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  17. #37
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    Quote Originally Posted by iHilux View Post
    With snachting, the stuck vehicle should be accelerating in the same gear as the recovery vehicle. So when the stuch vehicle is freed, it would be nice to see where you should stop, before you ram the recovery vehicle from behind.

    This in itself does not make it conducive to having the bonnet open.

    IMHO anyway
    I agree 100% with Wade!

    It's ok when you're winching because it is slow and controlled, but snatching is fast and violent and an open bonnet could be a very big problem. If you're really feel putting your bonnet up, you'll have to strap it down, because the jolt could fold the bonnet over your roof.
    I've done snatch recoveries where the jolt was so violent the loose rubber trim on my dash ended up behind the rear seat and I had a stiff neck for a few days.....it that case the bonnet would have flown back as well and smashed my windscreen and roof....never mind that I probably would have hit a tree as I was being towed out of the muck.

  18. #38
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    Zantus.

    Sorry mate, but them bolts showing in your second last pic are too short. There should always be thread showing out of the nut once tight, even if you are using grade 12.9
    "A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster "
    By Jeremy Clarkson (I think)

  19. #39
    Beans Guest

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    Why should one recover in reverse as you are not winching. firstly it puts strain on your diff Crown wheel and pinion. Then you have the speed ratio problem. I would rather recover using the recovery vehicle rear to the front of the recovered vehicle if possible.

  20. #40

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    I saw someone ask what sort of speed that tow ball assembly would be doing. Here's a very rough estimate:

    The snatch rope is essentially a spring. The force exterted by a spring is F=kx where k is the spring constant and x is the distance the spring is displaced.

    Ideally one would have to know what k is for a snatch strap and how far the rope had been streched to know the force at the moment of failure. Obviously we dont that.

    But lets just guess at a force. Lets assume the force applied was at least equal to the weight of the Hilux lets say 2 tons which is 20kN (kilo Newtons).

    Now even though the force broke the tow ball off, the rope is still streched at the moment after failure so the spring is still streched and thus that force is still present, except now it is applied to the tow ball assembly alone, not the entire vehicle.

    F = mass x acceleration. Lets assume that tow ball assembly has a mass of 3kgs. Then the initial acceleration would be 6.67 km/s^2 (thats an enourmous acceleration).

    The rope would only accelerate the tow bar while it still was streched, not accross the entire distance separating the tow vehicles. Lets assume it had been streched by 2 meters.

    V^2=U^2 +2as where U=initial velocity (lets assume the Range Rover was close to stationary at that momement so this is zero) a=acceleration and s = distance accelerated. (strictly speaking you cant really use this equation because it assumes a constant acceleration which isnt true due to the accelerating force diminishing as the strech in the rope decreases, so I'll use an average acceleration of half the initial acceleration.)

    V = (2 x 3,333 x 2)^0.5 = 115.5 m/s = 416 km/h

    That would be the speed of the towball after it had travelled 2 meters, from then on it would be slowing down due to the drag of the now slack snatch rope. But being a heavy chunk of steel it wouldnt slow down by much before it hit the Hilux. I would say impact velocity would be anywhere between 200 and 350 km/h.

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