All I am trying to do is explain what I have experienced. I have improperly used a tow strap in the past before I knew any better and I have used a kinetic rope and I can tell you which one is better and safer to use.
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If used properly, the kinetic rope is not only safe but a very effective and quick means of recovery.
I think we'd all agree a properly used kinetic rope is safer than using a tow-strap
as a kinetic rope!
I would always use my brand spanking new rope in this way, first use it a tow rope by taking out the slack and slowly using the tug to pull out the stuck. If that didn't work but came close, I would add a very small bit of slack and accelerate to a low speed for a gentle "pop". If that didn't work I would increase the slack a small bit and accelerate to the same low speed for a slightly larger "pop". If that didn't work I might decide to increase the speed reached. If done this way you can slowly and accurately add more force until you reach the amount needed to free the stuck without adding more energy to the system.
This is the safest way to use a KERR. But still, how do you know when to stop adding more force? Or how much force you
are adding? The energy in the rope is not only related to your run-up-speed, but how much throttle you apply while it is stretching. (If your run-up speed is the same, then extra slack makes no difference, btw. Then all that counts is how much power you apply as you stretch the rope).
The energy of the moving tug is stored in the rope but it will soon reach a point where it is constant and not increasing as it would if the tug didn't slow down. The tug will eventually stop if the other vehicle is not freed resulting in no further increase of energy generated. It's just stored in the rope. Now lets say that amount of stored energy is just one pound over the resistance acted upon the stuck vehicle then that energy will slowly move the stuck vehicle. It won't do it with an abrupt release of energy but a slow steady and degreasing release. That is why I said what I said. Again, I may be wrong but all I am trying to do is try explain what I know happened. I really don't see how I missed it but I really want to be corrected if I did as my safety is involved.
The energy stored in the KERR by the tug continues to increase as long as the tug continues to move forwards. And yes, if that energy is more than that required to free the stuck vehicle, then it
will move it. And if that energy is
not enough to move the vehicle, then it will eventually break something.
I am pretty sure we both understand the mechanism here - the part I think you are missing is that there is no reasonable way to predict (and therefore control) the
maximum force exerted by a KERR.
The point both Muskyman and I are making is that the forces involved in a KERR recovery are far higher and less predictable than other methods and that's a two-edged sword. It can make a serious "stuck" appear childishly simple to extract, under what
seems like perfect control, but in fact you are dealing with unbelievable forces. As long as you recognize that, that's half the battle won. My specific point was that when you have a reasonable alternative (winching, say), that should be your first approach because it involves predictable maximum forces.
