Winches: Broken wire recoil....

Submitted: Friday, Apr 20, 2007 at 17:07
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A thread earlier this week ended up in some discussion regarding how the wire behaved when it snapped under load whilst winching and several not so wise heads were stating that the blanket, bag, air brake - call it what you like, placed over the centre of the tow wire was unneccesary as when the wire broke it simply fell to the ground.

Well I would like to inform you to proceed with that method at your own peril...

I have just spent an hour x-raying a bloke who was hit in the shoulder and arm by recoiling wire from a snapped winching escapade and he now has numerous small pieces of broken wire embedded in his arm not to mention much bruising and a future with the surgeon methinks to remove the same.

So if all else fails, listen to the guys who teach recovery for a living and so prevent these incidents by education....
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Reply By: Member - Kiwi Kia - Friday, Apr 20, 2007 at 17:45

Friday, Apr 20, 2007 at 17:45
Hi John,
I don't believe the blanket does any good, well, not the size as used by most 4wder's anyway.

I do know that winch ropes fly with the greatest of ease and do kill and maim people ! Education should also include using rated recover hooks on vehicles and not flimsy tie downs !

Can you tell us about what the unfortunate person was actually doing when the accident happened ?
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Follow Up By: tvl - Friday, Apr 20, 2007 at 17:56

Friday, Apr 20, 2007 at 17:56
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Follow Up By: Member - John L G - Friday, Apr 20, 2007 at 18:01

Friday, Apr 20, 2007 at 18:01
As I understand it he was winching a heavily bogged vehicle and whilst noticing that the wire was not in pristine condition, the recovery was still attempted with the subsequent result. Lucky it wasn.t his face in the line of fire methinks...

I have sailed off shore yachts for years and when we sailing maxi yachts in the days before spectra and kevlar ropes, we often used wire for headsail sheets and halyards. We learnt a pretty healthy respect for the stored energy in wire when under extreme load and saw some nasty accidents during big boat regattas. It all happens too fast to duck, if and when it lets go, so careful handling is essential to minimise injury. We never placed ourself in a V of the pull line or next to a loaded wire brace as the consequneces were too great.

The use of a blanket whilst not being heavy, acts more as a foil to entrap the wire and quickly dissipates energy through its volume, probably more so than a heavy object which would only serve to act as a pivot point for the wire to relaunch itself from....

I'm no expert, but I was taught by some..........
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Reply By: Member - Phil G (SA) - Friday, Apr 20, 2007 at 18:30

Friday, Apr 20, 2007 at 18:30
John,
I think the issue here is that airbrakes are useless in preventing recoil.

Thats why heavier objects are being used now - bag full of sand or dirt, heavy chain etc
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Follow Up By: Mike Harding - Friday, Apr 20, 2007 at 19:00

Friday, Apr 20, 2007 at 19:00
Ah! Some common sense - something of a rarity on this forum.

Look... I'm an electronics engineer and know little of the mathematics of mechanical engineering but common sense tells me that I can wave a queen sized blanket through the air without much effort. Now... consider a wire rope with sufficient stored energy to cut bodies in half or propel shackles through Land Cruiser rear doors... it doesn't take a huge leap to suspect the air resistance of a blanket will not stop that wire rope? Corrections, from people who know what they're talking about, welcomed...?

Mike Harding
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Follow Up By: Bonz (Vic) - Friday, Apr 20, 2007 at 22:15

Friday, Apr 20, 2007 at 22:15
The air brake is not a recoil preventer it is to prevent broken bits attached to the end of the rope from flying unimpeded IMHO
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Follow Up By: Member - Phil G (SA) - Friday, Apr 20, 2007 at 23:32

Friday, Apr 20, 2007 at 23:32
Bonz,
Thers no ideal damper, but
Airbrakes do not impede anything, especially flying recovery points and shackles.
They slip down the cable or strap, and fly through the air with ease - they are not parachutes.

Thats why the recent change was made to cable dampers, which have some weight, and weight can dampen a runaway cable, strap or shackle.
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Follow Up By: Bonz (Vic) - Saturday, Apr 21, 2007 at 08:18

Saturday, Apr 21, 2007 at 08:18
Yer Phil I reckon thats right, dampeners for competitions have always had to be a specific weight, like the Ironman and ARB ones u can buy. I reckon theyre OK and would affect the flight of a cable, even a heavy blanket would be good too
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Reply By: Member - Hughesy (NSW) - Friday, Apr 20, 2007 at 19:21

Friday, Apr 20, 2007 at 19:21
About 9 months ago I had to pull a mates bogged Malloo ute out of a salt lake. He was a long way out and I didn't have enough, cable, strap to reach him. Anyway some blokes from a local station came out with about 40m of old cable coiled onto an old split rim. I didn't like the look of it but had no option. Thinking it was going to break I tied the now empty cruiser split rim to the wire rope using some 8mm poly rope. When the cable did snap it broke that 8mm rope like it was a cotton thread and the rim moved about an inch (the distance the cabel recoiled was amazing). From that point on I've realsied that a little bag weighing maybe 3kg that people hang over the rope aint going to do much to prevent the wire flicking around.

Mind you Myth busters did do a test to try and cut a pig carcuss in half doing a set up of this thing. They used huge cable and bigger forces than you could ever do with a 4x4winch but it never did more than leave a nasty ring around the pig. But when you watch the rope whipping around the pig in slow-mo the energy in it would certainly kill you.
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Follow Up By: Member - Kiwi Kia - Friday, Apr 20, 2007 at 20:28

Friday, Apr 20, 2007 at 20:28
I agree with Mike and the others who seem to have a consensus here that there is a problem out in 4wd land. Some people who are held up to be experts are perpetuating a myth - that a small bag used to carry tools in will somehow stop a cable moving at about 100 kph from flying through the air ! Experts my as..., they are just passing on what some one told them in the long distant past. However, I do agree that at the very least an object thrown over a live winch rope will act as a flag and warn people that a rope is connected between the vehicles.
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Reply By: Member - Mark P (VIC) - Friday, Apr 20, 2007 at 20:45

Friday, Apr 20, 2007 at 20:45
The use of an air blanket, bag what ever is to reduce the recoil so the force is applied downward (the ground offers greater resistance to air) reducing injury to the upper body if the thing breaks. That is to say if u are in the way, which you shouldn't be to start with. It won't stop it but it will slow it down.

Note the injury specified in the post. Upper body, lucky he didn't lose an eye.
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Follow Up By: Member - Steve T (NT) - Friday, Apr 20, 2007 at 21:11

Friday, Apr 20, 2007 at 21:11
Hey Mark.

Last year in Arnhemland, I saw what happens to a cable 100mtrs long, it was Between a grader and an 6.5 t OKA .

When the cable snapped the first time it was unreal, next time we put a beach towel over the cable, it snapped a second time the difference was amazing.

The third time we got it out, next time a cable is involved I'm using a towel or similar.

To those post's above you can draw your own conclusion.

Cheers Steve.
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Reply By: Member - Kiwi Kia - Friday, Apr 20, 2007 at 21:39

Friday, Apr 20, 2007 at 21:39
Hi John, If you are implying that a towel works, well if you saw it then ok. But, I have seen a fold out recovery kit holder secured with velcro tapes on a steel winch rope and it may as well not have been there ! It was no use at all, the rope was just a blur and slapped up the front of the vehicle leaveing whip marks on the front of the bonnet.
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Follow Up By: Member - Kiwi Kia - Friday, Apr 20, 2007 at 21:40

Friday, Apr 20, 2007 at 21:40
Ooops, The above was meant for Steve.
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Follow Up By: Member - Steve T (NT) - Friday, Apr 20, 2007 at 21:51

Friday, Apr 20, 2007 at 21:51
Hey Kiwi Kia

The original snap the cable sprung back about 75 mtrs and looked lethal.

The second time it sprung back about 20/30 mtrs with way less force, as the cable hit the ground and slowed considerably.

Cheers Steve.
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Follow Up By: Member - Mark P (VIC) - Saturday, Apr 21, 2007 at 10:04

Saturday, Apr 21, 2007 at 10:04
I agree with you steve.

What is operating is basic physics. It takes very little downward force applied to the cable to push it to the ground. So yes a towel will work. But with everything, there are caveats. That is the length of the cable and force applied and the height from the ground. The towel, air brake what ever not going to be as effective if its in a situation where the cable is 6 feet off the ground for example.

The issue is it will help reduce the effect, and it is I believe dangerous to say to other members, visitors and newbies (like me) that your wasting your time. Unless you can show me the physics that it doesn't work I'm going to put something over the cable and have the cable placed low and safe.

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Follow Up By: Member - Kiwi Kia - Saturday, Apr 21, 2007 at 10:31

Saturday, Apr 21, 2007 at 10:31
Hi Mark, Here is some basic physics :-))

If someone fires a rifle (horizontal) and at the same time another person drops a bullet from the same height, which one hits the ground first ?
Answer, they both reach the ground at the same time, gravity doing it's work.

Gravity effects the recoil drawing the rope downwards but the speed of the whiplash can still do a lot of damage before it reaches the ground. So, as you say it depends on the height of the rope above the ground and direction of pull.
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Follow Up By: Member - Mark P (VIC) - Saturday, Apr 21, 2007 at 11:10

Saturday, Apr 21, 2007 at 11:10
Hi Kiwi,
Don't mean to lol, but I will lay odds the bullet gets there first. You're now talking about different physics.

Bullet Fired from gun
.22 rimfire cartridge 1200 - 1500 fps
.22 centerfire cartridge 2400 - 3000 fps

Gravity of a bullet being dropped
On Earth, objects do not fall at constant speed, as your statement suggests. Gravity accelerates objects toward the center of the Earth at 32.2 ft/sec/sec (which can also be written as 32ft/sec2). In other words, an object's velocity will increase by 32.2 ft/sec (or 9.8 m/sec) each second the object is falling until it reaches its terminal velocity, which you can think of as a speed limit. Terminal velocity is reached when air friction equally opposes the force of gravity. Different objects will have different terminal velocities, depending upon their shapes. (caveat again: this has little to do with what the cable snapping question because of it's height from ground, it just sounded good, lol)

Terminal velocity is a hell of a lot less than 2400 fps say, if it were more then I suggest you don't go bungee jumping.

I am sure some of this is on wiki, as I have just plagiarised it.

Now the big question what is the bullets final velocity if its dropped at say 50 feet???

Regards

Mark.

P.S. Don't stand under the bullet that is being fired.
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Follow Up By: Member - Mark P (VIC) - Saturday, Apr 21, 2007 at 11:12

Saturday, Apr 21, 2007 at 11:12
Addendum: Bullet gets there first is the one from the rifle, lol.
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Follow Up By: hoyks - Saturday, Apr 21, 2007 at 16:41

Saturday, Apr 21, 2007 at 16:41
OK then.

We are standing on a perfectly flat horizontal plane.

A bullet is fired from the barrel of a rifle parrel to the horizontal plane.
The moment the projectile leaves the barrel, another bullet is dropped from the same height as the barrel with a forward velocity of 0m/s.

In this situation, regardless of the projectiles horizontal velocity, both it and the dropped bullet will accellerate toward the ground with at -9.8m/s per second and both hit the ground at the same time. One will just do it a long way from where it was launched.
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Follow Up By: Member - Kiwi Kia - Saturday, Apr 21, 2007 at 16:46

Saturday, Apr 21, 2007 at 16:46
Hi Mark, This could get interesting :-))

As far as I remember my physics;

The only thing constant and uniform to both actions is gravity which as you say is 32 feet per second per second. Every other force or interference is meaningless to the answer to the question asked.

The velocity of the bullet fired horizontally has nothing to do with the force of gravity acting on the bullet.

Because the bullets are falling such a short distance neither will reach terminal velocity.

My physics says they should both reach the ground at the same time under the influence of gravity albeit at some horizontal distance from each other.

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Follow Up By: Mike Harding - Sunday, Apr 22, 2007 at 21:05

Sunday, Apr 22, 2007 at 21:05
Sounds reasonable to me Kiwi - and confirms why, when I fire my rimfire .22 over a lake, it hits the water sooner than I think it should.

Mike Harding
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Reply By: Member - Mark P (VIC) - Saturday, Apr 21, 2007 at 11:22

Saturday, Apr 21, 2007 at 11:22
oops, Just re read it u said "horizontal", the principal still stands apply a small vertical force and the bullet will head down. Given it's velocity it will get there pretty quick and into the ground where it's speed will be reduced greater than that of wind resistance. Depending on variables height, force ect it is difficult to say which one hits the ground first.

Wouldn't like to be the one applying the force to the bullet. lol.

But, back on topic I still say throw something over the cable.
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Reply By: R Send - Saturday, Apr 21, 2007 at 16:27

Saturday, Apr 21, 2007 at 16:27
A liitle story to add some colour to this thread. Some while ago I worked offshore on the oil & gas fields. The barge we were on was lifting a 1600 ton module with two steel tugger lines between the ends of the module and winches on the barge to stop rotation of the module.

Unfortunately a swell came up whilst the load was in mid air, and the module started to swing. Things of this size tend to move extremely slowly but once they are moving it is not good news.

Anyway one of the tugger lines snapped under the loads, close to the attachment point on the module - about 50 metres of 1" cable suddenly became airborne, twisting in every direction (a bit like a garden hose when the tap is full on). The overall direction was back towards the barge! Most people ducked behind the wave surge barriers (nice and meaty, for obvious reasons) but one poor crew member caught the force of the flying cable across the top of his head removing his most of his scalp.

A rapid evacuation by helicopter and the guy made a good recovery with most of his hair growing back.

Now I know this was on a bigger scale than our caravan situations but it serves to reinforce the potential dangers that lurk, and the need for care and attention by all concerned. That broken cable can go in any direction regardless of gravity!

R Send
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Follow Up By: Member - Mark P (VIC) - Saturday, Apr 21, 2007 at 16:45

Saturday, Apr 21, 2007 at 16:45
Didn't you place a towel over the cable first. ;-)

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Follow Up By: Member - Kiwi Kia - Saturday, Apr 21, 2007 at 17:02

Saturday, Apr 21, 2007 at 17:02
Hey Mark,

Rotfl, my point exactly ! No b...... (great Australian adjective)... use at all :-))

The only thing you have going for you if a cable breaks is the unpredictability of the direction of travel of the rope. If it goes down or any direction other then towards you then it's luck and has nothing to do with the towel. If the forces do not have any upwards component then gravity will take it down at a rate of 32 ft/sec/sec and not the towel.
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Reply By: Member - Fizz (NSW) - Sunday, Apr 22, 2007 at 19:02

Sunday, Apr 22, 2007 at 19:02
Beware! A little knowledge can be dangerous.

Most of the "physics" above is a mixture of invalid assumptions and unwarranted over-simplifications. All the above refer to simplified models where the mass of the objects being discussed can be considered as being concentrated at a single point.

The dynamics of compound bodies - such as a flying steel rope - are vastly more complex, and cannot be analysed by simple mathematical models. In fact, the behaviour of a flying steel rope would be virtually chaotic, and unable to be predicted with any degree of accuracy. Chaotic motion is unpredictable because small differences in initial conditions magnify up into big variations in subsequent behaviour. So length, thickness, tensile strength etc of the rope, tension in the rope, the pattern of breaking of the strands, angle to the horizontal, and a host of other variables will affect the resulting motion in a way no one can predict.

The best law to take account of is Murphy's one, and always assume the worst possible outcome.

That being said, If one could predict where a break could happen, one could attach weights each side of the possible breakpoint such that the resulting rope ends were attached VERY strongly to the weights, and the weights were such that the momentum of the recoiling rope would be dissipated by the inertia of the weights, then there probably would be no big drama if the rope snapped. The difficulty would be to know where the break would be, how heavy the weights would need to be, and how they could be attached to the rope so they could not come adrift. (The momentum of the rope isn't just "mass x velocity" because the rope is a compound object with all its "parts" moving in slightly different directions at different velocities)
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Follow Up By: Mike Harding - Sunday, Apr 22, 2007 at 21:11

Sunday, Apr 22, 2007 at 21:11
I'm sorry... but analytical observation of physics issues is not permitted on this forum - much better to guess or, ideally, site something you or your mate observed.

Mike Harding :)
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Reply By: Middle Jeff - Sunday, Apr 22, 2007 at 20:49

Sunday, Apr 22, 2007 at 20:49
Hi All

I am a great believer in throwing a towel or something loose over the cable, not the rigid ARB or recovery bag types. I have seen two cables snap one was an old tree puller and the other a 4WD winch, the tree puller had nothing on it and I was lucky as it went by me it sliced my jeans open just below my knees but never touched me, the second I was watching and the guys doing it just threw a towel over it and at the time I thought what a joke, but when it snapped the towel got caught up in the cable and the cable started to wrap around the towel but it only did it because it was soft. I think a rigid one would not catch it only slide along it.

So that is my two cents worth.

Have fun

Craig
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