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BigJimnyMeet (North) 2024 (12 Jan 2024)


BigJimnyMeet 2024

14th July 2024
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Re:Re:Recovery adapter.

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29 Aug 2020 19:25 #227515 by CC Baxter
Replied by CC Baxter on topic Recovery adapter.
Just a thought but...
Experience is something, a tractor is everthing
Chris

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29 Aug 2020 19:55 #227517 by 300bhpton
Replied by 300bhpton on topic Recovery adapter.

Roger Fairclough wrote: A KERR can be lethal if the recovery points are weak. Never use one on a tow ball as the forces involved can rip the mountings apart.

Roger


I do not believe this to be correct. A Kerr is far kinder to any mounting point as it isn’t an instant violent snatch. Anyone who has ever used a Kerr vs a regular rope will be able to reconcile this.
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29 Aug 2020 20:06 #227518 by mlines
Replied by mlines on topic Re:Recovery adapter.
Roger is correct, Kerrs can be very dangerous due to the way they store and release the energy. As said, they were designed for the army using tanks recovering tanks.

A number of off road clubs around here have banned them.

They are woven to be elastic. The towing car accelerates away and it's kinetic energy is stored up in the stretched rope. This builds up significant levels of energy that is released in a short burst. A two ton towing vehicle can generate up to 8 tonnes of energy.

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Martin

2003 M13 early KAP build.
3" Trailmaster lift with 1.5 Spacers on front
Customised winch bumper and roll cage
235/85R16 Maxxis Bighorns on 16" Rims, 4:1 Rocklobster, Rear ARB locker and on-board air
Corrected arms all-round, rear disks, Recaro seats and harnesses

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29 Aug 2020 20:19 #227519 by Lambert
Replied by Lambert on topic Re:Recovery adapter.
I would argue that a snatch strap is worse for imparting force into the towed vehicle as the degree of stretch is less. Again its a matter of experience. If you are using a tank grade kerr on a 4x4 then you will have problems. Just like howling off at full chat when you just need a light pull etc etc. Experience.

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29 Aug 2020 20:48 #227522 by 300bhpton
Replied by 300bhpton on topic Re:Recovery adapter.

mlines wrote: Roger is correct, Kerrs can be very dangerous due to the way they store and release the energy. As said, they were designed for the army using tanks recovering tanks.

A number of off road clubs around here have banned them.

They are woven to be elastic. The towing car accelerates away and it's kinetic energy is stored up in the stretched rope. This builds up significant levels of energy that is released in a short burst. A two ton towing vehicle can generate up to 8 tonnes of energy.

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People ban them when not understanding them IMO.

The shock loading is far less with a Kerr. And it is the shock loading that causes recovery points to fail.

You can test it out easy enough. Get a rubber band and a short length of string.

Pinch the rubber band between your fingers (finger & thumb) and “snatch” it with you free hand. Chances are you will retain hold of the rubber band.

Do the same with the string and it’ll be very difficult to keep hold of it.

All the instant shock loading is not good for recovery points. A Kerr is far more gentle. And therefore less likely to cause a failure.

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29 Aug 2020 21:22 #227527 by Roger Fairclough
KERR stands for Kinetic Energy Recovery Rope and as such is made from 8 strand Multiplex nylon rope. It's style of weaving means that it does not kink. A 3 strand nylon rope has the same degree of stretch but will kink if not properly straightened before use. Kinks will reduce the strength.. The rope used to pull out tanks is 65mm in diameter. The army needed a method to get a 60 ton tank out of the muck ASAP and the thought of asking a tank crewman to exit the tank under fire to carefully lay out a 3 strand rope before attaching it was asking to much.
Nylon snatch straps look a lot like lifting straps but are woven to stretch. I have one in the Jimny simply because I had it in my Land-Cruiser. I would tow with it and I might consider a very mild tug but a full blooded gung ho lets show em how it's done is a big no no.

Roger

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29 Aug 2020 21:36 #227529 by Roger Fairclough
300bhpton reckons that a KERR rope is "softer" than a strap and therefore less likely to cause a problem.
Trouble is the gung ho reality of people oozing testosterone who think along the lines "if 10mph is good, then 15mph will be better and then what about 20mph" at which point the rope has stretched to breaking point and...........it breaks.

Roger

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29 Aug 2020 21:40 #227530 by Lambert
Replied by Lambert on topic Re:Recovery adapter.
take the time to have a look at the video I linked. Those are also kerr ropes and other than evident experience of the admittedly American operator they are simple and effective to use and nowhere near 65mm diameter. They are also not life limited like a snatch strap which is only good for about 10 cycles before it becomes a standard extension or lifting strap and not to be used for energy recovery attempts. Also I am not saying that a kerr will work for every recovery just like how a winch or a tractor had limitations. But used appropriately and in a sensible manner a kerr is about as gentle as might reasonably be expected for recovery of a stuck vehicle.

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30 Aug 2020 08:19 #227536 by Roger Fairclough
Lambert.
"Used appropriately and in a sensible manner", your words, unfortunately they rarely go together because the people who use them lack the training to understand how kinetic energy works.Have I used a KERR, yes I have and very successfully too but the point you are ignoring is that there are to many people who don't know how to use them and that is why clubs are banning them. Would I trust that American? no and that answer is all about how he treats his equipment. I suggest you take another look at that video.

Roger

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30 Aug 2020 10:20 #227543 by Lambert
Replied by Lambert on topic Re:Recovery adapter.
I'm a subscriber of matt and have seen most of his videos and it's very rare that he has done damage.

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30 Aug 2020 10:45 #227544 by Roger Fairclough
So by your own admission he has caused damage!
We could argue this case until the sun sets but I have better things to do, so I will bow out.

Roger

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30 Aug 2020 11:34 #227545 by Lambert
Replied by Lambert on topic Re:Recovery adapter.
Regardless of what method of recovery is used, as I am running road tyres my level of stuck is much lower than most so therefore the forces involved in becoming unstuck are noticeably less than if I were running trepadors for example, I simply won't have got as far. Therefore a shackle attachment bolted into my towbar is going to be adequate for the 1160 kg that Dreadnaught weighs.

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