Where When How March/April 2017 : Page 96
WATER It’s the medium of life and the pursuit of happiness STORY BY EDWARD M. SIDNEY 96 • • • • • MARCH/APRIL 2017 “Where When How -Turks & Caicos Islands” TONY WORKMAN ILLUSTRATION
Edward M. Sidney
It’s the medium of life and the pursuit of happiness
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 composition. Whatever the attraction, water holds a great emotional 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 underwater. And to make every dive safe, water’s effect on diving fundamentals 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 approaching 3,300 mph. This is why it’s difficult, if not impossible, 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 farther. For example, a whale’s low frequency song can be audible 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 thousands, 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 direction 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 refraction, which is simply a change in the angle and speed of light as it goes from the water through the airspace in your mask. To see this illusion in your kitchen, look at the difference in an object halfway submerged in a glass of water.
Size and distance are not the only changes that water makes. Colors change, too. As you descend, the light becomes increasingly blue, which affects the way colors are perceived. That’s part of diving’s beauty. Although sunlight can descend to almost 600 feet, most of the light doesn’t make it past the first 30 feet. Sunlight is the combination of all the different colors (frequencies) of visible light. And as these colors are separated by raindrops to form rainbows, so does water filter out the colors at different depths. Red is the first to go, followed by orange, then yellow, then green. Blue stays until the end and colors everything.
If you want to take underwater photographs and capture the subject’s true colors, you’ll need to bring your own “sunlight,” in the form of a strobe, even in the brightest conditions. One of the reasons that night diving is so different and vivid, especially on the ocean reef, is because your handheld lights show nature’s true colors, colors that are painted with filtered light during daylight dives.
Although water is relatively colorless liquid, there are times when you can see it. When swimming in a thermo cline, that “line” which separates warm and cold water can look like clear jelly and becomes strikingly visible. You can see this at home, too. Put some ice cubes in a glass of cool water and stir gently.
Naturally there are water conditions that don’t allow you to see much of anything. Divers always want visibility of 150 feet (or more), but water clarity depends on where and when you are diving. Recent storms, constant winds, and a variety of other forces can shake and stir the water and its sediment to the point where you won’t see much. Still these conditions offer the chance to concentrate on closer and smaller pieces of the underwater environment, and they can be as interesting as the bigger picture.
Water absorbs heat perhaps even better than it absorbs different colors of light. Unlike air, which is a poor heat conductor and a good insulator, water can quickly steal your body heat. This is why your living room is comfortable at 72 F while the same temperature water is not only chilly, it requires some kind of exposure suit to make diving comfortable, and even safe.
Although water temperatures below 98. 6 F will lead to hypothermia, the lowering of your body’s core temperature, you’d have to be in this water for about a month for the effects to be noticed.
This process is accelerated, however, when the water is below 75 F, which is why it’s recommended that you wear an exposure suit when the water is at this Relax | DIVE | Chill Call us at 649-432-2782 email@example.com | www.aquatci.com Out of Harbour Club Villas & Marina temperature or below. Using alcohol further aids hypothermia by dilating your blood vessels, which pumps more heat to your skin, which means the cooler water can steal it more quickly.
To a diver, one of water’s most important attributes is weight. Water is heavy; about 8 pounds per gallon, or 64 pounds per cubic foot. (Salt water is heavier than fresh water.) On the surface, although we don’t notice it, we’re always under pressure from the air above us. (Air has weight too, a little over one once per cubic foot.)
Aptly called “one atmosphere,” this pressure refers to the 14.7 pounds that bears down on every square inch of Earth. In other words, if you measured the pressure exerted by a one-squareinch column of air that rises from the surface to the edge of space (that’s the thermosphere, about 52 miles high), that pressure would equal 14.7 psi (pounds per square inch). To double that pressure, all a diver needs to do is descend 33 feet. Every additional 33 feet adds another atmosphere of pressure, so if you are at 66 feet, you have three atmospheres of pressure to contend with (one from the thermosphere to the surface, another for the first 33 feet, and the third for the second 33 feet).
We don’t notice this one atmosphere of pressure on land because we’re designed for it. We do notice it when flying. As the airplane climbs, there is less “atmosphere” above, which means less “weight,” or pressure (the atmospheric pressure is halved at 18,000 feet). As the plane descends, the pressure increases. It works the same way underwater.
Because the majority of our body is comprised of incompressible water, whether we’re flying or diving, we feel these pressure changes only in our natural air spaces, our ears and sinuses. These air-filled cavities are most comfortable at ambient pressures, or when the pressure inside equals the pressure outside.
Although divers can be surrounded by pressure that would crush a sealed, airfilled can, you really don’t notice it just as long as the pressure in your airspaces – ears, sinuses, and mask – are equal to the pressure surrounding you.
Even though you don’t necessarily feel the pressure, you certainly have to understand and respect it. It’s the pressure of water that determines how long you can remain at given depths.
How your body deals with gases, such as nitrogen, under pressure, is the reason you should religiously adhere to your dive tables, safety stops, and rate of ascent. Pressure is the reason we don’t hold our breath underwater. It all has to do with the weight of water. Much of your training is devoted to the physics of pressure and how it relates to diving. And as a new diver it’s important to study it well.
Water affects the diving experience in many ways. Tides, currents, wave actions, temperature and salinity all play a role, and we’ll be discussing these interesting topics in future issues of Dive Training
Issues to Consider – Captive Dolphins in Sea Pens
Although better than artificial concrete pools, sea pens used to house captive dolphins still have a number of issues.
• Are they exposed to run-off from roads, parking lots and waste facilities?
• Are they exposed to oil and other pollutants from heavy boat traffic and/or marinas?
• Are they exposed to high levels of ambient noise (music, boat traffic, industry, etc.), which can cause stress in the animals?
• Is there adequate sun protection, since dolphins can be sunburned?
• Is there adequate isolation space for sick animals and to quarantine new arrivals so as not to expose indigenous animals to foreign diseases?
• Is there adequate water flow to maintain healthy water quality by eliminating uneaten food and the waste generated by the dolphins in the facility? An adult dolphin produces about a gallon of urine and about 3 pounds of feces each day.
• Is the waste from the facility endangering any coral reef system from high levels of nutrients that will cause algae to overtake the reef?
• Is there a safe place for the animals to be held in the case of a major storm or hurricane?
• Where will the animals come from and, if they are coming from another facility, how will they be replaced in that facility?
• Are there regulations in place to govern the facilities’ structure, activities, operations and safety of both the public and the animals, and who will ensure compliance with these regulations?
• What impact will constructing the facility have on the existing marine environment?
• What is the total economic benefit to be gained by the Government from such a facility, including not just the number of potential jobs created, but also the potential negative impact on tourism to the islands?
Read the full article at http://onlineissues.wherewhenhow.com/article/Water/2721373/387443/article.html.
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