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Snatch Straps and Kinetic Recovery.

Some day inevitably your four wheel drive is going to get bogged. Snatch straps have revolutionized 4x4 recovery. The strap is attached to a strong point on the bogged vehicle and to one on the recovery vehicle with a few feet of slack in between.

[snatching, jpg]
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The recovery vehicle takes off, usually in 1st or 2nd low. As the strap becomes taught it stretches, storing kinetic energy from the recovery vehicle and transferring it to the bogged vehicle, popping it free - hence kinetic recovery. The bogged vehicle should generally have its wheels rotating to assist.

A bogged vehicle can be snatched forwards or backwards. The recovery vehicle should ideally be on firm ground so that it does not itself become bogged.

Snatch straps are potentially dangerous and the operation should be treated with great care. The strap is nothing less than a giant catapult. The forces generated are of the same order of magnitude as the vehicle's weight - ie. they are measured in tons.

Only straps that are specifically designed for vehicle recovery and that pass appropriate national standards (e.g. ASA) should be used. The straps are elastic and the technique will not work with any old rope! Straps should be treated carefully and worn ones must be discarded. A strap can loose its elasticity under repeated use and some have special stitching or threads to show when this has happened.

The strap must be attached to towing-points that are well able to withstand the huge forces generated. Shackles should not be used to attach straps, only adequate towing strong-points. Ordinary tow-balls are not designed to withstand these forces. Most bull-bar manufacturers do not approve their bars for use as attachment points for snatch straps. Kinetic recovery is quite capable of ripping a bull-bar, or a weak towing-point, clean off a vehicle (seen it) particularly if the chassis is rusted.

If an anchor point is detached during recovery, the heavy metal object becomes a lethal projectile which is quite capable of punching a hole right through vehicle bodywork and through any person that happens to be in the way. The strap alone can inflict serious injury if it breaks. For these reasons, innocent bystanders should be kept well away.

A snatch strap should not be used to extend a winch cable during recovery operations precisely because it stretches and thus stores energy: Winching hardware and cables could be "launched" if the cable or the strap broke. The ideal winch cable does not stretch at all although they all do a little bit.

Sometimes one strap is not long enough for the job. A shackle must never be used to join two straps. Even if the shackle is plenty strong enough, one of the straps might break, launching the shackle with a force of tons.

[joining two straps] two

There are three ways to join two straps together if really necessary. The first way is to pass one strap through the eye of the second strap, doubling the first strap up to give a total length of 1.5 straps. The second way is to pass each strap through the eye of the other to give a combined length of 2 straps. If you do join two snatch straps by this method, but do nothing else, it will be almost impossible to separate them after use as they will have tightened up and become locked together. The trick to avoiding this problem is to insert a small, light, wooden stick between them before use (picture). Note that the stick does not carry any load as such; so it will not break and it does not matter if it does, and it is easily slipped out after use thus providing just enough slack to separate the two straps easily - bingo. A better alternative is to use a rolled-up magazine or newspaper (diagram) instead of a stick (softer!), but read it first as it may be destroyed in separating the straps. The third way is to pass one strap through an eye of the 2nd strap and then through its own eye to make a combined length of two straps (this is topologically equivalent to method two). As in the second method, a rolled-up magazine can be inserted at the tight spot to ease separation after use.

Snatch straps are a wonderful invention. The most extreme examples are used to recover bogged army tanks, mind you those straps are thicker than your leg.
- © L. A11ison © 1995, 2000

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