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  1. #41
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    Default Re: DANGER! energy absorbed on snatching!

    Thanks Alex

    Johan,
    The feeling of a quick stop, was by no means a dead stop. To amplify the feeling of a sudden deceleration was, as pointed out by Alex, due to the non linear effect of the rope. Also in most recoveries; the recovery vehicle only loose momentum before the stuck vehicle become un-stuck. In our experiment, we exceeded the usual 20 km/h and the bloekom was going nowhere.

    I also make use of snatch straps (ARB and TJM) and the RopeWorld rope is certainly "smoother" in a recovery.
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  3. #42
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    Default Re: DANGER! energy absorbed on snatching!

    .......when we moved to softer sand, on top of a dune, to set-up for a real-life recovery, not pulling trees....

    We bogged a D4D Hilux Single Cab, on purpose, loaded with mountain rescue kit and lots of extras. When I say bogged, it was on the chassis, with all 4 wheels spinning to clear all sand from underneath and hanging free. Weight was; vehicle weight of 1900 kg plus an assumed 500 kg for a total of 2400 kg odd.

    The Patrol was again used. After a few dummy accelerations to get to as close as possible to the "standard" 20 km/h recovery speed I was ready. The recovery line was straight ahead and not in the same tracks as the practice. We also had a very slight incline, less than 5 deg. This time a snatch strap was used, with 2 meter slack.

    We recorded 2.7 ton and the HiLux was un-bogged. The Patrol "dug in" due to the soft sand and did not move further than the HiLux's wheel base. The rear wheels made it to the holes previously dug by the front wheels....

    So what shall we conclude from this...?
    Is sand snatch recoveries really that dangerous...?
    But then we also broke a kinetic rope at less than 30% of advertised rating, which had the potential to cause serious damage if there was a shackle (or more) at the end of a 9 meter rope that's under 3 ton load at the time of breakage.
    I would still say yes, but more due to sub-standard recovery points or attachment of them.
    The rope still left a serious dent in the rear door... as we only secured all metal parts by lanyards.
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  4. #43
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    Default Re: DANGER! energy absorbed on snatching!

    Cheers
    Last edited by Bean-Bone; 2016/06/06 at 09:26 PM.
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  5. #44
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Bean-Bone View Post
    I have noticed that some recovery gear meets sans specs but note to what reference that spec is or is the gear derated because of reference to lifting requirements and not snatching or pulling or recovery requirements. In my option it is not poor quality but at least a reference. Engle pofadder equipment is a very good equipment in terms of reference and safety factor. If I put a load cell in between the two vehicles and note the pulling snatch or inertia strength. It is like a slow blow fuse. What would the result be.
    there are no SANS specs for recovery or pulling gear.

    the best you'd get is a maximum line pull rating.

    OHS legislation only covers lifting gear - not pulling gear.

    A load cell is a measuring device. thats all. it's purpose is to measure load, it's not safety equipment.

    I would note that the pofadder is sheathed , which would have prevented Kiri's damage to his tailgate, and conventional wisdom (not regulation) on recovery ropes and straps is to make sure it is 'damped' by means of a bag or simiar draped over the line.

    The Pofadder is rated as a 13ton breaking force rope - it will not break at a load of 13 000 kgf

    it's good gear - I have one - and it is sheathed, which is an advantage over the Kiri's recovery rope. but it's pretty much the same thing otherwise.

  6. #45
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    Default Re: DANGER! energy absorbed on snatching!

    [QUOTE=Apocalypse;3252951]there are no SANS specs for recovery or pulling gear.

    the best you'd get is a maximum line pull rating.

    OHS legislation only covers lifting gear - not pulling gear.

    A load cell is a measuring device. thats all. it's purpose is to measure load, it's not safety equipment.

    I would note that the pofadder is sheathed , which would have prevented Kiri's damage to his tailgate, and conventional wisdom (not regulation) on recovery ropes and straps is to make sure it is 'damped' by means of a bag or simiar draped over the line.

    The Pofadder is rated as a 13ton breaking force rope - it will not break at a load of 13 000 kgf

    it's good gear - I have one - and it is sheathed, which is an advantage over the Kiri's recovery rope. but it's pretty much the same thing otherwise

    cheers
    Last edited by Bean-Bone; 2016/06/06 at 09:26 PM.
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  7. #46
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    Default Re: DANGER! energy absorbed on snatching!

    I have never seen the Pofadder. When you say it is sleeved, is that the entire length? So the sleeve will have to be nylon too, to allow stretching with...?

    In regards to putting a dampener over the snatch rope; in hindsight, something to consider. I have used and abused snatch straps over many years, like uprooting tree stumps, but never broke one, till the test. It will however have to be something that can be fastened to the rope, as tightening of the rope in a snatch will send it flying upwards at some speed....

    When it comes to kinetic rope strength (rating) vs vehicle weight, where do we draw the line for overrating and losing the kinetic effect and shock loading? Example, snatching a little Suzuki with an 11 ton rope....

    ARB recommends 2 to 3 times the vehicles weight, some trainers in SA recommends 3 - 4 times the GVM.
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  8. #47
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Kiri View Post
    I have never seen the Pofadder. When you say it is sleeved, is that the entire length? So the sleeve will have to be nylon too, to allow stretching with...?

    In regards to putting a dampener over the snatch rope; in hindsight, something to consider. I have used and abused snatch straps over many years, like uprooting tree stumps, but never broke one, till the test. It will however have to be something that can be fastened to the rope, as tightening of the rope in a snatch will send it flying upwards at some speed....

    When it comes to kinetic rope strength (rating) vs vehicle weight, where do we draw the line for overrating and losing the kinetic effect and shock loading? Example, snatching a little Suzuki with an 11 ton rope....

    ARB recommends 2 to 3 times the vehicles weight, some trainers in SA recommends 3 - 4 times the GVM.
    Here is a pic of the pofadder - here I'm using it as a damper over the winch cable.

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    Effectively you put twice as much sleeve as there is rope over the rope - so, on a 10m rope you use 20m of nylon sleeve. it bunches up, but as you pull it opens with it. and bunches up again.

    If the rope breaks in the middle the sleeve absorbs the stored energy and it just slithers apart.

    I loop a lanyard over each end, and attach that to the other recovery point, so if it break at the loop (or the shackle or the recovery point) the lanyard keeps it all tidy....

    If your recovery strap is too highly rated, it won't stretch and you'll get higher forces stored - too low and it will break obviously

    I'd guess it also depends on the material.

    I had a 14ton Kinetic strap - it was hard as hell. Was not pleasant being recovered with that if the guy got too happy with the throttle.

    The Pofadder is 13ton breaking force - but it's really stretchy in comparison, and gives a nice soft recovery.

    I think the recommendations are pretty much thumb sucks / Full of **poo** guesses from various people - I've never seen anyone do an actual load test prior to this , with real world results.

    the load exerted on the rope is all about the weight of the recovering vehicle, not the stuck vehicle. so pitching up with a strap 'rated for your Jimny' at 6 tons breaking force, hooking it to a fully laden 3000 kg Wrangler and letting him give it gas for the full 15m and the jimmy remains stuck means the rope will go right through the Jimny...
    Last edited by Apocalypse; 2016/06/07 at 01:05 PM.

  9. #48
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    Default Re: DANGER! energy absorbed on snatching!

    Thanks Alex, Pofadder looks good and would certainly work as a dampener and "container" when the unlikely happens.
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  10. #49
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Kiri View Post
    Thanks Alex, Pofadder looks good and would certainly work as a dampener and "container" when the unlikely happens.

    I really think it would be very meaningful to publish some proper results with real life empirical testing as you've done.

    You say you tested some kinetic straps at the same time? how did that turn out?

  11. #50
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Kiri View Post
    ... resurrecting a sticky and an old thread...

    Recovery force calculations can be made quite accurately, but we will always wonder what would it be in "real-life"
    So a few of us set out to Atlantis Dunes, equipped with a 10 ton load cell and some recovery gear.
    The expected force at 20 km/h: about 3 ton.

    1st "real-life" test was as follows:

    Load Cell: Calibrated 10 ton with peak hold function.
    Vehicle: 4800 Patrol wagon (petrol 6 cyl), Weighing 2700kg (3 people, including extras.....)
    Tyres: 285/70R17 Cooper STT Pro
    Tyre pressure: 0.6 Bar, front and rear
    Surface: Damp compacted sand. (back of Atlantis, where the big Bloekoms are)
    Anchor point for Load Cell: One very large Bloekom, 10 Ton Tree-protector, plus 2x safety lanyards.
    Patrol recovery points: 2x bolted on chassis (calculated at minimum 6 ton each) with 8t Equalizer, plus 2x safety Lanyards on towbar PIN (not ball)
    Spliced Kinetic rope from Rope World: new 9 meter long, rated at 11 ton breaking. Expected stretch at recovery, +30%
    Slack in rope: 2 meter
    Speed: to be determined but by accelerating as fast as possible in 2nd Low

    And the result was:

    1st surprise was the max speed obtained: 35km/h

    Load at peak: 4.27 ton
    Rope stretch: 45% (Total length = 13 meter)
    Rope, recovery length/time: forgot to check at intervals, but a few days later it was at 9 meter

    2nd Test:
    (After we decided that maximum acceleration in the Patrol was to much)

    Spliced End Kinetic Rope no. 2: Used but with no visible defects (bought from a big name 4x4 outlet)
    Rope Rating: 11 Ton, 9 meter long.
    Vehicle: Patrol as above
    Speed: 20 km/h; achieved by no slack in the rope and slowly building up to 20 km/h

    Result:

    Load at "peak": 3.04 ton, and then the rope broke at the load cell end of the splice point!!

    Thereafter we moved to the soft sand, as the STT Pro's found too much traction on the "black" damp sand....
    Hi

    Something is wrong with your calculations. A patrol cannot accelerate to 37km/h in 2m. The loading at 37km/h is also wrong against a dead stop like a tree
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  12. #51
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Kiri View Post
    Thanks Alex, Pofadder looks good and would certainly work as a dampener and "container" when the unlikely happens.
    The sleeve protects the rope from getting sand in. If sand enters the rope hardens and breaks. Nylon does not stretch. It compresses the weave, and that gives it stretch.
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Engel View Post
    Hi

    Something is wrong with your calculations. A patrol cannot accelerate to 37km/h in 2m. The loading at 37km/h is also wrong against a dead stop like a tree
    I would guess that a rope that stretches by 4m would allow the vehicle to continue accelerating for at least 2m of the 4m - it would only start slowing the vehicle down (negative acceleration) at some point during it's stretch.

    so that's 4m or so.... 35km/h comes up surprisingly easy, especially on a short ratio...

  14. #53
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Apocalypse View Post
    I would guess that a rope that stretches by 4m would allow the vehicle to continue accelerating for at least 2m of the 4m - it would only start slowing the vehicle down (negative acceleration) at some point during it's stretch.

    so that's 4m or so.... 35km/h comes up surprisingly easy, especially on a short ratio...
    That means 35 to 0 in 2m? and all that with 4t load? no way. When I have time I will do the calculations and energy involved. You have a huge problem recovering at 35km/h. But wait. I will prove it
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  15. #54
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    Default Re: DANGER! energy absorbed on snatching!

    If the speed was taken from the vehicle's speedo meter, it could be registering standard speed as if in normal high gear. Meaning the speed is not read from the wheels, but somewhere from the gearbox before transfer case reduction.

    So begin dit...

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    Default Re: DANGER! energy absorbed on snatching!

    Not even a GTR Skyline with launch control on a racing track with slicks can beat that acelleration
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  17. #56
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    Default Re: DANGER! energy absorbed on snatching!

    So to make a Skyline take off quicker, add a low ratio transfer case...

    What is the problem here, to split hairs over a kilometre or two, or the fact that 4.27 ton load was achieved in a snatch test under unlikely good conditions. By good conditions I mean, the recovery vehicle had a very good surface for traction and achieving higher speed than normal. To add to this, the stuck vehicle in this case was a tree.

    A more normal off-road condition snatch was also done. Recovery and stuck vehicle were both on soft sand. 20 km/h was the speed (please just take the speedo and gps observer's word for that; as we took the full 9 meter strap length to ensure the speed is as close to 20 as possible). And as per my previous posts, the +_ 2.4 ton loaded HiLux, flat on it"s belly gave a 2.7 ton recovery load, with a 9 meter, 8000 kg strap, snatched by a 2.7 ton Patrol.

    The aim of the "tests" were to determine a few things (other than having fun), recovery rope stretch, rope recovery time, recovery load under a variety of conditions, like slack distance (speed)... Then we also did rolling resistance and drag resistance with tyre pressures from on-road pressure down to 0.6 bar.
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  18. #57
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    Default Re: DANGER! energy absorbed on snatching!

    A load cell is a straining device and cannot function in the application you used it in, it will also give you false readings as it cannot record a snatch load reading accurately.

    I have no problem with the fun part of it. But technically the info is way off
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  19. #58
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    Default Re: DANGER! energy absorbed on snatching!

    It's certainly more info than I've ever seen before!

    I suppose it depends on the load cell reading speeds, but generally speaking the ones I have used are very fast - the ones we used years ago sent a reading 1000 times per second. I would think a peak load function would be reasonably accurate?

    the readings are pretty much in line with what I would expect from ropes with good elasticity -kinetic straps with less stretch will certainly return far higher figures.

    As mentioned though, it would be great to do later tests with more accurate readings , rope stretch and speed /deceleration figures specifically.
    Last edited by Apocalypse; 2016/06/10 at 07:50 AM.

  20. #59
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    Default Re: DANGER! energy absorbed on snatching!

    Quote Originally Posted by Engel View Post
    A load cell is a straining device and cannot function in the application you used it in, it will also give you false readings as it cannot record a snatch load reading accurately.

    I have no problem with the fun part of it. But technically the info is way off
    Engel

    The load cell was calibrated and manned by the supplier, who also perform stress and breaking stain tests for safety gear. There is nothing wrong with using a load cell in this application. And as quoted by Alex too, the peak hold function was used, eliminating human interference or slow reaction. Surely the test could have been completely professional, by fitting the Patrol with velocity transducers, high speed motion sensors, radar speed measurement and the list goes on..... then connect all of that to an event plotter to give millisecond charting. But not too many have done the little we have done, and if they did, they are keeping it to themselves.
    Here is an article where Mitsubishi Australia did it in a similar fashion; by hooking a load cell (ONLY) to a Pajero to prove that snatch recoveries do not take that much load.... http://www.outbacktravelaustralia.co...oading-on-test

    As a kinetic rope manufactures and supplier, surely you must have done some practical tests yourself, to backup the calculations, what are your findings, please share and how you did them...??
    Last edited by Kiri; 2016/06/10 at 01:06 PM. Reason: ...spelling
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  21. #60
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    Default Re: DANGER! energy absorbed on snatching!

    A Stellenbosch student was killed over the weekend in the Northern Cape during a recovery when the cable snapped.Another recovery gone wrong.
    http://www.netwerk24.com/Nuus/Algeme...ansie-20160612

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