Tow strap vs. Kinetic rope

[7wt]

Worse still, by it's nature, you can't apply the force slowly. You can't pull little by little, while a spotter tells you what's happening. You can't back-off and adjust the angle of pull, or a bit of your rigging.

From my experience you can apply the force slowly. The more the kinetic rope stretches, the slower or more gently it applies the force. The less it stretches, the faster and more abrupt the force is applied. Heres how I see it works, tie a soft rubber band to a rock and pull on it. You will pull a lot before the band stretches enough to move the rock. Now tie three bands together side by side to the same rock and pull with the same force, the rock will move much sooner than it did with one band because the three bands stretched very little. Now if you apply that line of thought to vehicle recovery and use a strap that has little stretch but is still not a tow strap and do a kinetic pull, then the strap will be much harsher than the Masterpull rope that stretches a good amount.

I have a "recovery rope" I bought at an offroad shop in California. It was sold and labeled on the package as a such, not a tow strap. I was under the assumption that it has a decent amount of stretch to it. Well it doesn't really, the thing says on the sewn in label that it shouldn't be used in that manor. It states that it is only a tow rope. Now it is made out of nylon so it will stretch a little but not enough to be considered a recovery strap, which in my book means kinetic recovery. I think it is all a matter of semantics but the fine point lost can get someone seriously hurt or even killed. I promise most people out there, if you use the right rope for the right purpose, you will be a fan of a proper kinetic recovery rope. I keep mentioning Masterpull because that is all I have used and all I really know about. I know Viking makes one as well but it looks to be the same type of rope. Soon, Phil and I plan on doing side by side test of his ARB kinetic strap against my kinetic rope. These test will be done in a measured controlled environment where nothing will be left to chance. Both the strap and the rope are the same length so we will be able to test each out with the same amount of slack with the same amount of acceleration to see which one stretches more, is softer and what not.

 

[muskyman]

From my experience you can apply the force slowly. The more the kinetic rope stretches, the slower or more gently it applies the force. The less it stretches, the faster and more abrupt the force is applied. .

sorry you are wrong...the energy is returned at a rate based on the elongation of the rope based on the diameter. Like a rubber band you can stratch it fast or slow it does not matter the energy returned is based on how far you stretch it(elongation).

You really need to go do some research because your comments are just looking uninformed.

There is no hatred going on there are informed opinions being shared for nthe education of the community.

Breaking stretch: 100 %
Elasticity modulus: 2.5 kN/mm^2


Using these basic figures and a length of 10 metres by a diameter of 25 mm for the sake of the argument, the energy (W) set loose by the breaking of such a rope is in the order of magnitude of 75 tons, when using a 2-ton vehicle. This means that by then your 10 metre rope has a length of 20 metres while snapping back at you, possibly carrying 2 or 3 kg of the other Land-Rover with it. So the word is : "DUCK !"

source=http://www.landroverclub.net/Club/HTML/KER.htm

The problem with Kerr's in general is when the amount of energy released is greater then the failure point of a given recovery point and how the measured failure point relates to the obstruction holding the truck in place.

Say for example a truck bounces into a mud hole and without knowledge of the driver becomes lodged over a large rock in front of the rear axle housing. The truck apears to be just sitting in a mud hole but really that rock prevents the truck from being moved unless a force greater then the amount of force needed to cause a failure of the recovery point is used. What happens next is the kinetic energy recovery rope releases that amount of energy and the recovery point becomes a deadly projectile.

In most cases this does not happen because the force needed to recover the truck is not enough to cause a recovery point failure so the total amount of energy is limited to the amount needed to move the obstructed truck. But very often the amount of energy is available in the elongated strap. Yes the elongated strap can have enough energy stored in it to cause a recovery point failure in what seems like just a gentle pull.

 

[7wt]

sorry you are wrong...the energy is returned at a rate based on the elongation of the rope based on the diameter. Like a rubber band you can stratch it fast or slow it does not matter the energy returned is based on how far you stretch it(elongation).

You really need to go do some research because your comments are just looking uninformed.

I am not a physicist nor do I play one on TV but I am do feel I can comment based on experience. Take a stretchy rope and a non stretchy tow strap, both with equal amounts of slack and equal amounts of acceleration to a set speed and what will you find? You know the one that stretches will store the same amount of energy slower than the one that doesn't stretch. It will also release it slower than the one that doesn't stretch. Rate of elongation is a result of a couple of things, rate at which force is applied and the resistance applied by the stationary object. The rope will only stretch up to the point resistance is overcome. As the stuck vehicle's resistance approaches the point where it isn't stuck anymore, the rope will recover it's elongation at that same rate. Where am I wrong with this?

Having re-read what I wrote that prompted your response, it did not properly convey what I was trying to say. If the stuck vehicle's resistance and force applied by the pulling vehicle is such that it can overcome the breaking strength of the rope then you are in for quite the show. I stand behind what I said but it did need clarification. If the force applied isn't overcome by the resistance of the vehicle then what I said makes perfect sense in the recoveries I would use it in, ie mud and sand. Both of these will release energy at a fairly smooth rate. So again, as you approach the rate where the stuck vehicle's resistance will be overcome, the forces stored in the stretch rope will decrease. The slower it's friction is overcome, the slower the release in energy. This is assuming the towing vehicle is not accelerating and is moving at a steady rate, something I always do as it's predictable and measured.

For the most part, I think we are saying the same thing or at least understanding the same principals involved. What I failed to do was explain how I do what I do, steady rate and all. Again, all of this is outside a textbook, it's all experience and observations so I may be wrong in one or the other or both. I will allow for that.

Say for example a truck bounces into a mud hole and without knowledge of the driver becomes lodged over a large rock in front of the rear axle housing. The truck apears to be just sitting in a mud hole but really that rock prevents the truck from being moved unless a force greater then the amount of force needed to cause a failure of the recovery point is used. What happens next is the kinetic energy recovery rope releases that amount of energy and the recovery point becomes a deadly projectile.

Proper assessment of the situation would reveal the rock and immediately disqualify the Kinetic rope as a useful tool.

 

[muskyman]

Proper assessment of the situation would reveal the rock and immediately disqualify the Kinetic rope as a useful tool.

How do you do that if the truck is up to the doors in mud?...throw on the diving equipment and crawl under the truck?

I have been reading your posts on this and I think you may intend well but have a poor idea of what is at play

Have a great day !

 

[7wt]

How do you do that if the truck is up to the doors in mud?...throw on the diving equipment and crawl under the truck?

I have been reading your posts on this and I think you may intend well but have a poor idea of what is at play

Have a great day !

If I still have a poor understanding of what's at play then by all means correct me. I would welcome that as anything that helps me or others be safer offroad does us all good. Of all the things I said in response to your comments, you found the above quote the only thing to correct? I restated my stand to make it more clear, if I am wrong the do your best to show us all why. I can take it.

 

[michaelgroves]

Recently at the last OEX training, we used a Masterpull rope to pull a very stuck truck out of some deep and sticky mud. I was absolutely shocked with the results. It was the easiest, smoothest and safest recovery I have ever done. The rope did exactly what they say it does, it delivered a nice soft pull that freed Streakerfreak's truck post hast. Now we did slowly ramp up the energy used by starting with a slow run with a very small amount of slack in the rope. When that didn't work, we did it a little faster with a little more slack until we found the right amount of energy to free him.

7Wt,

This description of the way you use your KERR is absolutely by the book, and as safe as you can be when using a KERR. Even so, as Muskyman says, if you're pulling someone out of a mud-hole, and unbeknownst to you, there's a rock or tree stump in front of his axle, then even using the KERR progressively, each successive pull using more slack/acceleration, you're going to end up with something nasty happening. Granted, if you have a lot of experience using that specific KERR with that particular truck, you might start to realize that something is amiss, and bring out the hi-lift instead. But even with experience, it's hard to judge how much extra force you are applying by adding a few extra feet of slack to the next run.

I am not a physicist nor do I play one on TV but I am do feel I can comment based on experience. Take a stretchy rope and a non stretchy tow strap, both with equal amounts of slack and equal amounts of acceleration to a set speed and what will you find? You know the one that stretches will store the same amount of energy slower than the one that doesn't stretch. It will also release it slower than the one that doesn't stretch. Rate of elongation is a result of a couple of things, rate at which force is applied and the resistance applied by the stationary object. The rope will only stretch up to the point resistance is overcome. As the stuck vehicle's resistance approaches the point where it isn't stuck anymore, the rope will recover it's elongation at that same rate. Where am I wrong with this?

I believe I can see what you are saying: there's the same energy released when you accelerate the tow-vehicle by a given amount, but the stretchier the rope, the more slowly that enery is released. (An extreme would be a wire rope, which would shed all the energy at once as a shock load, and break something immediately).

The logical flaw in here is that with a wire-rope (or the less stretchy rope), the pulling force stops when you reach the extent of the stretch (assuming no movement of the stuck truck). If there's another 10m of stretch, that's the equivalent of another 10m of run-up!

Proper assessment of the situation would reveal the rock and immediately disqualify the Kinetic rope as a useful tool.

Of course, if you could see the rock, you'd use something other than a KERR! But since when can you see anything under your vehicle when you need a KERR?

 

[I Leak Oil]

So is a kinetic rope rated in a similar fashion to a coil spring? For example 1 inch of compression would require 500 lbs of force (the KERR would be 1 foot of elongation yielding 8000 lbs. of force)? Is it linear or is it more progressive? I can't imagine the rate at which it is stretched has anything to do with the amount of force that is returned. Being stretched 1 foot in one second or 1 foot in one minute would result in the same amount of force being applied to the stuck vehicle, assuming the stuck vehicle doesn't budge.

 

[michaelgroves]

I think that all that determines the amount of energy in the rope (until the stuck vehicle moves or something breaks), is the amount of power that's applied, and for how long. A stretchier rope will result in a longer duration, thus more energy. A lighter vehicle (for a given amount of power), will accelerate to a higher speed during run-up, but will decelerate more quickly too as the rope stretches, so mass shouldn't affect the energy.

The amount of actual stretch in a given rope should be an almost perfect indicator of the energy stored in the rope (until it breaks or the stuck vehcile moves), but I shouldn't imagine it's linear. You're right about the time taken to stretch it not being relevant.

 

[7wt]

I believe I can see what you are saying: there's the same energy released when you accelerate the tow-vehicle by a given amount, but the stretchier the rope, the more slowly that enery is released. (An extreme would be a wire rope, which would shed all the energy at once as a shock load, and break something immediately).

The logical flaw in here is that with a wire-rope (or the less stretchy rope), the pulling force stops when you reach the extent of the stretch (assuming no movement of the stuck truck). If there's another 10m of stretch, that's the equivalent of another 10m of run-up!

That is what I am trying to say. I would also like to point out that a stretchy rope will protect both vehicles from shock loads resulting in a smoother recovery. 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.

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. I know I failed in assuming everyone would do the same. I know there are those who would see that there is a good amount of slack in the rope and accelerate to a fast speed and keep accelerating until the stuck vehicle was freed or something broke. Everyone knows that is not a recipe for success. Hopefully the process I outlined and used sheds a little more light on my earlier statements. If used properly, the kinetic rope is not only safe but a very effective and quick means of recovery.

As far as the shock loads go, a stretchy rope will slow the tug down gently where as the wire rope will stop it immediately providing the stuck vehicle is not freed. By slowing down over a given distance, the tug is imparting less force than it would otherwise. 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.

 

[muskyman]

The progressive thing sounds great and controlled on the internet and all but there is a reason why the military uses this as a recovery method intended for armoured vehichles.

http://www.youtube.com/watch?v=HEtuO-Mh9Lg

The forces at work are huge, because these straps are designed to elongate and store energy you are able to transfer loads way in excess of what many recovery points are designed for.

This is not hate for kerr it is just fact being brought to the attention of people that may choose to use this method of recovery.

 

[muskyman]

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. .

Please stop, you just keep making incorrect statements.

Force is energy here and a longer run with more speed stores and transfers more energy. There really is no easy and accurate way to calibrate the amount of energy you are putting on the recovery points unless you know the amount of force needed to move the stuck truck.

 

[muskyman]

could you make more mistakes then this one?

http://www.youtube.com/watch?v=Q8lMxYnGIrw&feature=related

 

[Abel Villesca]

Yikes! I kept expecting a maiming or death at any moment. It was a bad scene from the start with the dangerous winching procedures.

 

[7wt]

could you make more mistakes then this one?

Look pal, you know good and well I am not advocating the actions in that video. You continue to read what you want in my statements and refuse to look at it with an open mind. I asked you several times to correct my statements if they are wrong and all you can muster up is a bunch of inbred brits in deep mud driving like morons. I am no longer eating from your troll pie.

 

[emmodg]

KERR is not the "wonderful, safe, warm and miraculous" recovery tool that many instructors say it is. Use it when you have assessed the situation and have deemed a recovery STRAP as ineffective. It SHOULD NOT be your 1st "go-to" when it comes to effecting a recovery that will involve ELASTIC FORCES. Have you tried jacking and stacking, sand ladders or other tractive devices? How about throwing a floor mat down? Have you tried lowering tire pressure? Have you tried weight shifting by wheel "sawing"? ALL these things should have been at least thought of first before you go grab your $250 KERR or $60 strap! Try a simple tow 1st, if that doesn't work THEN try imparting kinetic energy with the proper tool: recovery strap or KERR. Safe recovery starts with using your head FIRST! It amazes me how many people you see immediately grabbing some kind of recovery tool before they even THINK about a plan of attack!

I have yet to see an up-armored 1151 or 52 HMVEE lose a vehicle designated recovery point with KERR or nylon strap. (I've seen them rip off mirrors and break side window frame hinges trying to learn a hasty recovery!)