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To some, vehicle recovery is almost as exciting as wreck diving because you get a chance to dive on and maybe even recover something large and man-made that does not belong underwater. Just seeing a vehicle underwater can steer the imagination and can be quite enjoyable to dive around and explore if of course there is no one inside. Because of this, many recovery divers tend to relax around submerged vehicles believing there is nothing to fear. In fact, this is not usually the case.
Underwater vehicle recovery can be a very challenging and dangerous undertaking if not approached and conducted properly. When we take a closer look, it's not locating the vehicle that usually gets us into trouble, it's the actual "making contact" where we see divers getting hurt. Considering the possible hazards involved such as entanglement, entrapment, air expansion injuries during lifting (using lift bags), contamination due to fuel and cargo leaks, or being crushed by the moving vehicle, one can easily see that proper training in vehicle recovery is required. So, because of this, let's slow down and of course, do it right.
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Remember - Plan your dive and dive your plan!
Vehicle entry dynamics
When a vehicle rolls down a ramp or runs off a road, etc. and hits the water, the distance it travels away from its entry point depends on three main factors:
1. The momentum (speed) the vehicle reached prior to hitting the water - The momentum of the vehicle is influenced by the roughness of the surface it is traveling on prior to entering the water, the angle and length of its surface. Also, whether or not the vehicle was under its own power (motor on and accelerator pushed down) or rolling freely, the depth of the water, and by the obstructions it may hit along the way. So basically, the more speed the vehicle has prior to entering the water the farther the vehicle's momentum will carry it away from the entry point.
2. The depth of the water - The depth of the water has a lot to do with how far the vehicle will travel away from the entry point and its final vehicle position (right-side-up or up-side-down). In shallow water the vehicle will usually hit the bottom composition like rock, mud, sand, etc., and stop. If the water is deep enough (two to three feet will usually do it) the vehicle will float until it fills with water and its buoyancy changes and starts to sink. Keep in mind the length of time a vehicle can float can be quite surprising. The longer it floats the farther its momentum and/or current can take it away from the point of entry. If there are no secondary factors like snags, strainers or other obstructions holding the vehicle from traveling, the vehicle can travel great distances before stopping. Usually the person placing the vehicle in the water already knows the water's depth and has chosen a location deep enough to hide the vehicle. As the vehicle descend, the weight of the engine causes the noise to dip. As the vehicle goes under, in shallow water, the vehicle will usually settle to the bottom right-side-up. In water 2 to 3 times deeper than the vehicle is long, the vehicle will usually flip upside down.
3. The strength and speed of the current - The current speed and its strength has a lot to do with how far a vehicle can be moved away from its entry point. It all depends basically on whether or not the depth of the water (usually just above the tires) is enough to allow a strong current to "push" the vehicle. Also, the current speed and strength has to be strong enough to overcome the negativeness of the vehicle and the hold the bottom composition will have on the vehicle. If the vehicle is floating, the current can move a vehicle great distances before it sinks and settles to the bottom. Even then the vehicle can still be moved by strong currents, sometimes for miles before it hits an obstruction or the bottom's contour or composition stops its movement.
So, what does all this mean? It means that a lot of factors are involved in determining the distance a vehicle will travel from its entry point. Understanding them will not only assist you in locating the vehicle, it will help you understand what happened or what could be happening to the vehicle while it is submerged.
Don't get caught with your pants down
Keep in mind that many teams not knowing or understanding the dynamics of vehicle movement in water have been caught with their pants down. After getting a call to search a location for a possible vehicle, they end up searching the immediate area around the entry point only, usually not too far past the end of the concrete boat ramp and of course, don't find the vehicle. They get this idea from the vehicle being so large and heavy, that it could not be far away from where it entered. Believing the vehicle is not in the water, they pack -up and leave, only to find out later through witnesses or the person that actually put the vehicle in the water that it was in the water. The dive team then returns and searches beyond the entry point's immediate area and.... locates the vehicle. What does that say about that team's ability when everyone knows they have already been there and searched once and did not find anything?
Remember - If you understand in the beginning how far you might have to search for a submerged vehicle away from its entry point, you can increase your success rate while decreasing your embarrassments.
Did you know?
If there was some way we could pull the plug and drain our water ways, we'd be amazed as to how many vehicles are actually hiding underwater. Because that's not usually possible, its up to us to thoroughly search our lakes, rivers, ponds, quarries, and oceans by using what we know about submerged vehicles and their movement and good old common sense.
Remember - Vehicle recovery takes training, practice and good communication between everyone involved.
Question - Have you been properly trained in vehicle recovery? If not, why?