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Kinetic rope snapping

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extreme90:
i can understand why h wont use his winch, ill only use my winch's to recover a friend of mine or someone who i know and he just needs a helping hand, cos after it, when your solenoids are smoking, alls you get is  a chears mate, and thats it
my friends offer pay but i refuse cos itw what mate are for,
and that is why i dont carry a KERR and why no 1 hooks one up the the arse end of my 90
the chap in the 90 was a lucky [!Expletive Deleted!] that the rope didnt send anything else hurtling towards him, instanly he was rubbing his head, so that shows how much force was behind that rope,
anyhows such is life and everyone learns
dan

redneck:
Another video clip of kinetic rope letting go, in this one i believe the tow ball or a shackle does the damage  :shock:
http://video.google.fr/videoplay?docid=-3054143592822346647

Mr Bump:

--- Quote from: "davidlandy" ---
--- Quote from: "drmike" ---David - what was with the guy in the red RR hitting the Suzuki in another video you posted. Doesn't he like his truck or something?

Mike
--- End quote ---


He likes his motor , but he is just a nutcase!
--- End quote ---


And he doesn't wear a belt  :roll:  :roll:

Bulli:
Therm, thats what a lot of people think....just wang it in first and hit the load pedal...not the right way though.
If you have traction then you should have the rope nearly taught. Set off at walking pace and when there is no more stretch hit the brakes, theory is the rope contracts recovering the stuck vehicle.
If you have less traction then you should allow more slack...but not a 3 meter run up. The energy stored in a stretched KERR is huge, its the same as the car creates by its movement forward by 3-4 feet.

I have a brand new KERR that has been sat in my recovery box for over a year now and hasnt been used in anger. I will use it when appropriate and have used them before.

I dont think the recovery would have been more successful/safer if a non stretch rope were used .I think he needed winching or poss pulling forward. Its hard to say from a video though and im sure the guys on scene assesed it better than i can

Eeyore:
Okay, quick bit of info re: ropes, knots and hysteresis.

Knotting a rope will reduce it's strength locally by between about 40 and 90% depending on the rope and the knot used. Elasticated ropes, bungees and ropes of a plaited construction are generally in the latter catagory (splicing is a good thing here).

Whilst a rope may support, for example, a ton of load; apply a 70kg load to it quickly (as in a fall situation) and it snaps. It also places significantly more load than the 70kg on the anchor points. F=m X a and all that.

Kinetic rope was desinged to allow significant energy to be transferred to an object (like a stuck tank) whilst reducing the peak strain on the anchor point (t reduces the effective acceleration placed on the anchor points). This is it's job; it goes taut, you keep it taut and keep pulling (as I beleive the Hussars are taught), thus maximum energy can be transferred to the stuck object whilst the peak load is kept in check. The elasiticy is pretty irrelevent thereafter, unless the pulled object is on firm ground and can roll freely.

All the info suggesting that it's the elasticity of the rope that moves the vehicle is sadly misleading - it's the energy of the other vehicle that does the job, the rope just protects the anchor points.

Here's another really cool example - go climbing and use a semi-static rope. Fall off. Kiss your pelvis good bye. However, use a 'dynamic' (i.e. stretchy) climbing rope and you bounce - the load on your pelvis is reduced significantly by the stretch in the rope absorbing that energy.

That said, it doesn't change the application as Bulli describes - start slowly, especially if using shackles and anchor points of limited trust. I would be wary of a snatch from a tow ball too - their load rating is static, not dynamic. It's worth noting that military vehilces (armoured and Landys) generally have some significant anchor points for recovery fitted, unlike a lot of civilian machinery.

Oops, hysteresis, nearly forgot; the kinetic energy you get out the rope will be much less than the energy you put in because of micro-heating of the rope fibres. So again, the recoil of the rope isn't all that large a contributor for freeing the vehicle.

Also as Bulli says, I wasn't there so I'm not judging the posted video, only passing accross some of my thoughts.

Hope some of this helps!

Cheers
 8)
Eeyore

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