4WD Recovery

4x4 Africa - RecoveryDuring his first lesson in mud driving, our aspiring off-road driver Bud wanted to know what role off-road tyres played in how easily 4WD vehicles got stuck, and conversely, what role the use of the correct off-road tyres for a particular purpose played in recovering a bogged down 4×4. At the time Bud asked the question, the Instructor invited Bud to attend the series of lectures he was going to present on the subject of 4WD Recovery, and remembering Bud’s question, the Instructor opened the lecture by repeating it for the benefit of all the club members present.

Off-road Tyres and 4WD Recovery


“OK guys, some time ago Bud wanted to know what role off-road road tyres played in how 4WD vehicles get stuck, as well as how they relate to 4WD Recovery. Well, the short answer to this is that there are no short answers to this; no two recovery situations are ever the same, but there are some things that bear on the issue, so let us look at them one at a time:

• Off-road tyres:

4x4 tyre-pressure“Off-road tyres are the way they are because their particular construction and characteristics are meant to prevent 4×4’s getting stuck by providing the maximum amount of traction in any given situation, provided of course you use the right off-road tyres for that specific application. However, in the off-road environment anything can happen, and even the most experienced off-road driver can get stuck no matter the type of off-road tyres he may be using. Nevertheless, some types of off-road tyres, such as the narrow bias-ply tyres used with split rims, will almost always sink into mud long before mud tyres will, so if you are using bias-ply tyres, be extra careful of any sort of muddy terrain, because you are more likely to get stuck since the narrow tread width cannot support the 4×4’s weight on the mud as easily as wider mud tyres can. Not that mud tyres cannot get you stuck though, but their greater width coupled with their specialized tread pattern means that you are less likely to get stuck.”

“Bias-ply tyres can cope with some deflation, so they are not so much of an issue on sand, and many off-road drivers successfully use them on sand, but remember that bias-ply tyres are best used in rocky terrain or terrain where sharp rocks and stones can destroy the sidewalls of mud or sand tyres, but even so, you are always better of using the correct type of off-road tyre for any given type of terrain, but with that said, any 4WD vehicle with any type of off-road tyres can potentially get stuck in any, or several, of a million different places.”

• Off-road tyres and 4WDrecovery:

“In an ideal world, no 4WDwould ever get stuck, but the world not being ideal, means that 4WD vehicles get stuck all the time, so, to answer the second part of Bud’s question, yes, off-road tyres can have a bearing on how easy or difficult 4×4 recovery is.”

“Regardless of the method used to tow a bogged down 4WD out of mud, sand, or whatever, you should always remember that unless the bogged down vehicle has lost power or cannot assist in the recovery attempt because of mechanical issues, the bogged down 4WD should always assist in the recovery attempt, by at least spinning the wheels if there is no traction. The towing force should always just be enough to move the stuck 4WD into a position from where it can exit the obstacle under its own power, and this is of course where off-road tyres come in: say you are recovering a vehicle that is stuck in mud; if it has mud tyres, you will need a much smaller towing force to get it moving if it uses its own power to assist since by virtue of their design, mud tyres will find traction much sooner and much easier than if it had for instance, sand or all terrain tyres. best-recovery-tool-tyre-pressure-gaugeThe same goes for a 4WD that is stuck in sand: sand tyres rely on the high number of edges in the tread to find traction, and if it had mud tyres, the smaller number of edges in the tread will make finding traction so much more difficult.”

“The art of towing a 4WD out of a hole depends more on skill than on brute force: all you require is just enough “pull” to get the bogged down 4WD moving, from which point it will almost always get out under its own power. You do not have to jerk it all the way out of the obstacle, in fact, if you do that, you are almost guaranteed to break something, so next we will talk about towing stuck 4WD vehicles out of holes:”

Snatch, or Kinetic Straps


“Do not confuse towing straps with kinetic straps: an ordinary towing strap may also be woven but it does not have the ability to stretch to the same degree as a proper kinetic strap. There is also a difference in length, and for good reason: towing straps are limited to around 4 meters because that is what the law prescribes, whereas kinetic straps on the other hand, can be anything from 9 to 11 meters in length.”

snatch-recovery strap“The reason for this should be obvious; it is because it provides a safe distance between the two vehicles. Kinetic straps work so well because an 11 meter long strap can stretch more than 1 meter, and it is when this stored energy is released that most of the pulling power is delivered, something that makes it possible for even relatively small vehicles to pull much heavier ones out of holes. This also has the effect of reducing the stresses and strains on both vehicles, however, kinetic straps can break under extreme pulling forces, and it is therefore important that if the towed vehicle is serviceable, it should assist in the recovery as much as it is able to, because a kinetic strap that breaks under strain can whip back with enough force to knock out a windscreen, or worse, seriously injure by-standers by breaking arms and legs should they be in the way of a recoiling strap.”

• Precautions when using kinetic straps:

“However, kinetics straps are safe enough if you use some common sense on the one hand, and observe the tried and tested safety procedures on the other:

• Condition of the kinetic strap:

“First check the condition of the kinetic strap: it should have no cuts, abrasions, tears, knots, or foreign objects embedded in it. Any one of these conditions will reduce the effectiveness and strength of the strap to the point of uselessness.

• Attachment points:

do-not-use-tow-ball-for-recovery-point“For obvious reasons, you should never, under any circumstances use attachment points on either 4WD that is not rated and approved by the manufacturer for towing or recovery purposes, especially not towing balls. The problem with towing balls is that they are only designed to handle a maximum load of around 3.5 tons, which is sufficient for towing trailers or caravans, but the forces involved in 4WD recovery can be as high as 9 or 10 tons, and sometimes even higher. You can imagine what will happen when a towing ball snaps off and is flung back at the towed 4WD by a fully stretched kinetic strap: it will hit the towed vehicle at a speed faster than a 9 mm bullet, which means that if it hits the driver, or anyone else, that person is dead, so never use a towing ball as an attachment point for a kinetic strap- you may not survive the recovery attempt.”

“However, kinetic straps can break even under the best conditions, so to minimize the risk of personal injury, open and support the bonnet of the stuck vehicle; if the strap snaps and recoils, it will hit the open bonnet instead of the windscreen. Also place a blanket, sleeping bag or if you have one, a purpose made piece of heavy canvas over the kinetic strap halfway between the two vehicles: whatever you use, this will slow down both ends of the strap in the event it breaks. This is a tried and tested method of reducing the chances of injuries, so use it.”

“Another thing to do is to attach the kinetic strap to the back end of the towing 4×4: this provides the driver of the towing vehicle with extra recovery-tow-hookprotection should the strap break, because the strap end has other places to hit than a big windscreen, but speaking of attachment points: never tie the kinetic strap around anything by using any kind of knot. If you have to use anything to attach the kinetic strap to anything, only use D-shackles that you bought from a reputable off-road supply store, and make sure they are rated to cope with loads of at least 12 to 15 tons. Also make sure that the kinetic strap is not kinked or wound up along its entire length before any strain is placed on it: these straps are designed to stretch and it cannot do that efficiently if it is not flat along its entire length. If it is not flat, it is more likely to break than haul your mate’s 4WDout of the mud, so be sure to check for that.”

Winches


“Using a winch is sometimes the only viable method of 4WDrecovery, because it could happen that no other off-road vehicle could get close enough to use kinetic straps, or you might be alone, with no other 4WD available to pull you out of the muck, but with that said, there are some things you need to know about using winches, of which the single most important is the fact that if you do not know what you are doing, a winch is several orders of magnitude more dangerous to use than anything else and has killed and injured more people than any other method of 4×4 recovery, so, let us talk about some of the issues:

• Attachment points and anchors:

recovery-hooks“There are many ways to rig a winching line with single pulls, double and triple pulls, directional pulls, and some others, but the single most important factors in all of these arrangements are that all equipment should be rated for the job, in good condition, but above all, securely fastened to all points involved in the operation.”

“With winches, the pulling forces could approach and in some cases exceed 20 tons or more, and given the fact that steel winch rope is much heavier than a kinetic strap, the destruction that could follow if an attachment point snaps or becomes undone, is dozens of times worse than anything that could happen when it happens with a mere kinetic strap. Many people have had limbs severed by whipping steel winch ropes, and dozens have been killed, but for all that, a winch is sometimes an indispensible 4WD recovery tool, and the only real challenge lies in learning to use it safely.”

“Almost all accidents and fatalities involving winches have occurred because worn or substandard equipment were used, or basic safety considerations were not observed, so, if you want to fit winches to your 4×4’s, there are some basic tips and techniques concerning winches and associated equipment that will help you make the most of its capabilities:

• Type of winch:

“The type of winch is not really an issue but what is important is that it should have a rated capacity of at least 5 to 6 tons, and that it must have a remote control function, because it allows you to operate the winch from a point far away from the winch itself. High capacity winches may require more input energy than a lower rated one but the higher rating it has, the longer it will last. Low rated winches may be cheaper, but its low pulling power means that it works close to its rated capacity every time you use it, whereas a higher rated winch gets the job done without overworking the motor or pump, regardless of whether the winch is purely electrical or hydraulic. So, get the highest rated winch you can afford, or have room for on your 4WD.

• Rigging equipment:  

“It can be a tricky business pulling a bogged down 4WD out of a hole with a winch, especially when you are alone. With another 4WD present it is often just a case of attaching the winch rope to the stuck vehicle, and starting the winch, but it is not always that easy. However, it is when there are no conveniently placed anchorages such as trees or large boulders within easy reach that things can get complicated.”

recovery equipment“It is sometimes necessary to use snatch blocks, which are pulleys within very strong frames, to change the direction of the pulling force because the only suitable anchoring point might be inconveniently placed. So, say for instance, there are two vehicles and one gets stuck: one of the vehicles might be able to approach the obstacle at an angle, from which it might be possible to attach a winch rope to the stuck 4WD via a snatch block, always off course, using a tree strap to prevent damage to the tree, if a tree is used as the anchoring point. Depending on the distance and the angle between the stuck 4WD and the anchoring point, the recovery vehicle can than pull the stuck 4WDup to the point from where the snatch block could be removed and the rope attached to the stuck vehicle directly, to pull it all the way out of the muck.”

“But there is another way to approach the same problem: instead of running the winch rope to another vehicle via a snatch block, you can use the same snatch block to run the rope back to a rated recovery point on your own 4×4. The doubling of the rope doubles the pulling power of your winch but it takes twice the time, but that should be the last thing you should worry about; your primary concern should be making sure that all 4WD recovery techniques and methods are performed safely.”

“Yet another way of recovering your stuck 4WDis to use a triple line pull; which is similar to the double line pull, but this method uses another snatch block attached to the front of your 4WD through which the winch rope is run back to the anchoring point. Although this method triples the pulling power of the winch, it takes three times as long as a single line pull, but it is rarely necessary to use this method. However, the method you decide to use depends entirely on the terrain, whether you are alone or not, the weight of the stuck 4×4, and the rated capacities of the winch and the type of rope you have, which could be steel or woven synthetic materials.”

“A particular situation might dictate the recovery method, but whichever method you use, you should always remember that the “stuck weight” of a 4WD could exceed the gross vehicle weight several times.”

At this point the Instructor handed round some pamphlets with what appeared to be flow charts on them, one of which is reproduced here:

4WD Recovery - Gradient Resistance Chart

 

 

4WD Recovery - Vehicle Surface Resistance Chart

Flow charts by: http://www.pirate4x4.com/tech/billavista/Recovery/

Bud could not make out what the pamphlets were about, but just as he was going to ask what the table represented, the Instructor continued:

“OK, so you remember that I told you to weight everything you load onto your 4×4? Well, this is where it gets important to know what your 4WD weighs when you go off-road, because winch manufacturers will often tell you to buy a winch that is rated at 1.5 times your gross vehicle weight, which in most cases is not nearly enough to pull you out of a bog, and for the following reasons:”

• Err on the heavy side:

“Very few people can accurately judge the weight of anything, especially a loaded 4WD, and unless you have had your fully loaded 4WD weighed on a weigh bridge, you have no idea what its all-up weight is, which is the single most important factor to consider when you get ready to use a winch to pull it out of a seemingly bottomless mud pit. If you know what the weight is, fine, but if you do not, add the carrying capacity to the empty weight, and just to be sure, add 300-400 kg. It is better to err on the heavy side than to rig a line that could become undone, or snap, but worse, try to pull a stuck 4WD with a winch that is not up to the job.”

• Actual weight vs. stuck weight:

“No matter what the weight of your 4×4, if it is stuck, it could weigh several times that, and that is what the flow charts are about. This is information collected from several military recovery manuals, and has in some cases been tested under combat conditions, where there is no time to muck about, so it is reliable, and it could save not only your life, but those of your passengers and your 4WD as well.” “However, knowing what your 4WD weighs is not enough: you also need to understand some of the terminology used on those pamphlets. For instance, what does rolling resistance mean, and how does it change from situation to situation?”

isuzu-recovery - Stuck weight“Rolling resistance is the resistance an object has to movement; which in the case of even a loaded 4×4, can be little enough to overcome by pushing it, all the way to a force equal or greater than several times its gross weight when it is stuck, or damaged in some way. In 4WD recovery there are four types of rolling resistance to keep in mind when calculating the force needed to overcome this resistance. So, assuming you have arrived at a reasonably accurate assessment of the weight of your stuck or damaged 4×4, you must apply the following principles in calculating the final force, or total force required, which is measured in kilograms, so you do not have to apply complicated conversion factors.”

• Surface resistance:

“Based on the weight you arrived at, which is different for all 4×4’s, but serves as a datum, or base line figure in all cases irrespective of what is, a 4WD on a hard, level surface you will need a force equal to 10% of that figure to move it. If it is on sand or gravel, you will need a force of 33% of your baseline figure to move it.”

• Damage resistance:

“If the 4WD is damaged, say for instance the wheels cannot rotate, you will need a force equal to 66% of your baseline figure to move it on a level surface. This figure already includes the 10% of surface resistance so you do not have to add it to the 66%.”

• Stuck resistance:

“If you are stuck to the depth of the sidewalls of your tyres, i.e., to the level of your rims, you need a force equal to 100% of your baseline figure; if you are stuck to the level of your hubs, you need 200% of the baseline figure, and if you are stuck up to your floor plates, you need 300% of the baseline figure. These figures include those for damage resistance so you also do not have to add it to the figure for stuck resistance.”

• Gradient, or uphill resistance:

“If you are on an incline, you need to add the following corrective factors to the resistance figures:
• 15° —- add 25% of the baseline figure to the total adjusted for resistance.
• 30° —- add 50% of the baseline figure to the total adjusted for resistance.
• 45° —- add 75% of the baseline figure to the total adjusted for resistance.”
“If you are on level ground, you only use the figure adjusted for resistance, you do not need to apply any correction.”

• Gradient, or downhill resistance:

“Going downhill is a little easier; here you subtract the same amounts that you added for uphill recoveries, thus:

• 15° —- subtract 25% of the baseline figure to the total adjusted for resistance.
• 30° —- subtract 50% of the baseline figure to the total adjusted for resistance.
• 45° —- subtract 75% of the baseline figure to the total adjusted for resistance.

• Total force required:

recover-suzuki“So, as you can see, it is of critical importance to know how much your loaded 4WD weighs, give or take a few kilograms either side. It should also be clear that based on these calculations, a winch that is rated at only 1.5 times your gross vehicle weight will have a hard time pulling you along anything other than a hard level surface. The problem with winches is that there is no regulation of the industry, which means that a supplier cannot be held liable if an inadequate or underrated winch fails and somebody is injured or killed as a result. That is why I told you in the beginning to get the biggest and highest rated winch you can afford, or have the room for. The strongest off-road winches are rated at around 8000 kilograms, which should be enough to get you out of almost any situation.”

“However, do not take these 8 tons of pulling power as gospel, because there is no standardized rating system for winches. Nevertheless, what is true in all cases is that ratings for winches are valid only when there is only one layer of rope on the drum. As the cable is wound in, the diameter of the drum gets bigger; this decreases the pulling power of the winch due to the changing gear ratios, of which the drum diameter is an element. In practical terms this means that the pulling power of your winch decreases every time a new layer of rope is added to the drum; so, keep this in mind especially when you are recovering a 4WD on an incline. Almost anything can happen during a 4×4 recovery and if that something suddenly increases the rolling resistance to the point where either the winch or the rope fails; you could lose your 4WD if it rolls back down the hill. You could also injure or kill people, so be careful, and always remember that a winch’s pulling power is never constant; it decreases as the cable is wound in.”

Winch Ropes


“This brings us to winch ropes, which are without any doubt the least understood but the most abused item in almost all 4WD recovery kits or setups. You can have the most powerful winch in the world, but if you have a damaged or underrated rope, you seriously risk injuring or killing someone.”recovery

“There are no major differences between the wire ropes used on 4WD winches and those used in industry, except that off-road winches are more often than not supplied with aircraft-grade ropes, but the technical aspects of wire rope covers a huge field; literally thousands and thousands of pages of published literature, so, I can only give you some pointers about the general care and use of the wire rope on your winches. For more information on the technical aspects of wire rope manufacture and usage applications, I highly recommend you each get a copy of the manual published by the Wire Rope Technical Board, or other sources, and that you learn as much as you can because wire ropes kill the people who stop respecting them.”

“Nevertheless, there are some things you can do to keep your wire rope in good shape, which does not cost anything and can save your life, provided you remember the following points:”

• “Wire ropes are machines and they wear out: if it is worn out, abused, damaged, not properly maintained, and subjected to loads it was not meant to handle, it WILL break, and could kill someone.”

• “With regular use, wire ropes naturally lose some of their strength and capability, and this rate of deterioration is accelerated by abuse and poor maintenance of the rope.”
• “The published minimum breaking strength of wire ropes ONLY applies to NEW ropes that have not previously been subjected to any load.”

• “The minimum breaking strength of wire ropes applies only to ropes pulling in a straight line where both ends of the rope are unable to rotate, which can break even new, previously unused ropes. The SAFE WORKING LOAD (SWL) of steel ropes is not the same as the minimum breaking strength, and should never be used as an indicator of a wire rope’s minimum breaking strength. Moreover, the minimum breaking strength only applies to ropes tested under laboratory conditions. Anything you add to a wire rope, such as rope terminations, eyes, sheaves, hooks and the like, REDUCE the breaking strength, which means that the rope on your winch has a minimum breaking strength significantly under that of an equivalent rope that does not have all the stuff you have on yours.”
• The safe working load of a wire rope is determined by dividing the minimum breaking strength by a design, or safety factor, which is different for all installations and types of work expected of the rope. For instance, a design factor of say, “5”, means that the minimum breaking strength of a particular rope must be divided by 5 to arrive at the safe working load that can be applied to that rope. The responsibility of finding the safe working load for any wire rope you intend to use on your winch rests solely with you. However, you do not have to rely on guesswork; proper, reliable safe working loads for all wire ropes have been determined and published by large industrial concerns such as OSHA, ANSI, ASME, and others. You should NEVER install and use a rope for which the safe working load has not been properly determined by using information from established sources. WIKIPEDIA is not a reliable source for this kind of information.”

• “Although the breaking strength of a wire rope increases slightly after its initial first few uses, they do eventually wear out and will lose their strength faster the more they are used, and unless you are an engineer that specializes in wire rope, do not evaluate the condition of a wire rope by just looking at it: have it checked and assessed by a specialist in the field, or even better, replace the rope if there is any doubt about its condition.”
• NEVER apply loads to a wire rope that exceeds the safe working load, not even by a marginal amount, because the overload can damage the rope in ways that may not immediately visible. The fact that the rope survived the overload can never be taken to mean that the rope will not break even under future loads that may be significantly lower than its safe working load.

• Never apply “shock” loads to a wire rope by jerking it- first, because the shock load cannot be accurately measured or assessed, which could cause the rope to break, and secondly, the rope can also break when the shock load is released, which could kill someone.”
• The lubricant in the core of the rope is squeezed out after prolonged use of a rope, and must be replaced on a regular basis. However, this is not something you can do yourself, so have it done by a specialist rigging shop to prevent damage to the rope.”

• “Inspect the entire length of the rope for broken strands and other damage after each use, but always wear heavy leather gloves whenever you handle the cable for whatever reason. Broken strands are extremely sharp and can cause severe cuts, so be careful. Nonetheless, a rope with broken strands, kinks, or any type of visible damage should be destroyed by cutting it into pieces. A damaged wire rope is dangerous and must NEVER be used for any purpose whatsoever.”
• “It is your responsibility to ensure that each and every fitting, such as rope terminations, hooks, sheaves and other equipment used in conjunction with your cable, complies with the minimum efficiency ratings for that fitting in your specific application. A winch rope with all its fittings constitutes a mechanical system, and the safety, reliability, and suitability of that system depends on the integrity of all its components, so make sure that the system does not contain any weak links, such as hooks and other fittings that were made in China, or other places in the Far East.”

• Lastly, if you have been through deep water or driving in rain, unwind the rope and dry it off: once a wire rope has started to rust, it become dangerous and there is no saving it. The only remedy is replacement, so look after your wire rope, and it will look after you.”

Synthetic vs. Wire Rope


“You may have heard of synthetic winch ropes that are made of high-grade polyethylene, and that are not as dangerous as steel ropes: that may be true, but it also has disadvantages.”
“However, there is a lot to be said for synthetic rope; it is up to 40% stronger than a steel rope of comparable diameter, but for all that, it is much more susceptible to damage by chafing, extreme heat, dust abrasion, and it holds water, which could possibly damage the winch drum in the long run. But from a purely safety perspective, synthetic rope is a much better option, since it does not store as much energy as a steel cable, which means that if it breaks and the ends hit people, they won’t get killed, or lose limbs. Also, you do not have to wear gloves when you work with it, but not only that- it is a whole lot lighter than a wire rope, which makes it easier to rig pulling lines in difficult conditions.”
“But then again, the winch drum brake can damage synthetic rope if the temperature of the drum gets to about 65o Celsius, and depending on who made the rope, temperatures of 140° Celsius can actually melt synthetic rope. It is difficult to see how a winch can get that hot, but anything is possible, so just keep that in mind.”
“If safety and ease of use is your primary motivation for getting synthetic winch rope, by all means, do so, but remember that not all winches can accept it: some winches use a different method of fastening the cable to the drum, so make sure your winch is compatible with synthetic rope before you spend thousands on a rope you cannot use. However, don’t forget that wire rope is much more durable that any synthetic rope, but if you follow basic safety and maintenance procedures both types of rope will give satisfactory service for a long time.”

Some final thoughts on 4WD recovery


recovery-pointsThe best thing to do before you have to use a winch regardless of the type of rope it has, is to sit down, think about the problem, brew up a cup of tea, think about the problem and its various possible solutions some more, and only then start rigging pulling lines. Thinking about how to best to recover your 4WD will often reveal several options, one of which is almost always better than the first one that came to mind. Rushing into a 4×4 recovery, especially in Africa, where you mostly have no one but yourself to get out of difficult situations can lead to mistakes in judgement and calculation, which could have fatal results, given the large forces involved.”
“There are several excellent training institutions in South Africa that can teach you all you need to know about 4×4 recovery, of which this club is one. However, we prefer to teach 4WD recovery techniques in the real world, along with practical off-road driving skills during our regular long distance trips through Southern Africa. During these trips we also teach you the basics of bush mechanics, tyre repair, and how to use reduced tyre pressures to help prevent you getting stuck. These trips are expensive but we believe them to be the best place to learn about the off-road driving experience, so book for the next one now.”

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