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Where When How March/April 2017 : Page 97

Water is an intriguing substance that makes life possible, but it’s such a common commodity that we often take it for granted. Maybe we shouldn’t. Recent droughts in this country and around the world have demonstrated the vulnerable nature of man without H2O. The average American uses about 168 gallons of water a day and will personally drink around 16,000 gallons during his lifetime. As divers, water is not only necessary for consumption, it’s also the most important ingredient for our sport. There seems to be a natural human affinity to water. Maybe this is because it comprises the majority of our body’s com-position. Whatever the attraction, water holds a great emo-tional appeal for most of us, and perhaps this is why we take the training, pack the equipment, and head for the dive site. If you’re taking up diving to go fishseeing, and you regard water simply as a medium you look through, like air, then water might seem like a simple subject. It may be simple, but there’s a lot more to it than meets the eye. Water has some amazing properties that, in their way, are as intricate and as wonderful as anything you’ll see underwa-ter. And to make every dive safe, water’s effect on diving fun-damentals need to be understood and respected. Water is a dense medium. It’s almost 800 times denser than air. This density creates a tremendous capacity for sound transmission. Sound waves travel through water at speeds ap-proaching 3,300 mph. This is why it’s difficult, if not impossi-ble, for divers to determine the direction of underwater noise. We’re designed to locate a sound’s direction by which ear picks it up first. The mind can easily decide direction when sound is traveling at or below 750 mph, but at supersonic speeds, it’s impossible. Underwater noise not only travels faster, it also travels far-ther. For example, a whale’s low frequency song can be audi-ble to human ears up to 45 miles away. Before man became the ocean’s major noisemaker, disrupting the natural sounds, whales communicated over hundreds, and probably thou-sands, of miles. Since the submerged diver can’t tell a noise’s direction or distance, it’s impossible to determine the location of moving boats. You don’t know where they are, and unless you’re flying the diver’s down flag, they sure don’t know where you are. That’s why it’s so important to show the flag on every dive. It’s also a very good idea to stay in visual contact with your dive buddy. Since you can’t rely on your underwater hearing for di-rection or distance, if your buddy gets out of sight, you may hear him banging his tank, but you won’t know which way, or how far, to look. Water has other subtleties, and they often determine the way you see – or don’t see – things. For example, because water more evenly diffuses light, shadows don’t appear the way they do on land. On a bright and clear dive, diffusion can make things look different in a way that you can identify but not exactly explain. Underwater, objects appear to be 25 percent larger and closer than they really are. This means your depth perception can be off, so you need to adjust accordingly. Any diver who catches lobsters isn’t necessarily exaggerating when he tries to explain how much bigger they were during the submarine battle. These size and distance changes are caused by refrac-Reprinted with permission from Dive Training -Photos and Illustrations provided by Dive Training Visit the Turks & Caicos Islands at MARCH/APRIL 2017 • • • • • 97

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