same as it does. You want to be neutrally buoyant throughout your dive (figure 4-9). Negative If an object displaces an amount of water that weighs less than the object does, it sinks. Because the object is denser than the water, the water does not provide sufficient buoyancy to make it hover or float. You want to overcome any buoyancy you have when you begin your dive to be able to get beneath the surface. Factors Affecting Buoyancy Your weight and your volume affect your buoyancy. Your weight includes the weight of your body and the weight of your gear (diving suit, weight belt, and scuba unit). Your volume depends on your body size, the thickness of your diving suit, and your gear. Remember, density is mass per unit volume. Wetsuits are much less dense than water because of the thousands of nitrogen gas bubbles trapped in the neoprene material. If you wear a full 6 mm thick wetsuit and jump in the water without any other gear, it will be impossible for you to sink below the surface. You cannot dive with a heavy wetsuit and a standard 12-liter or 80 cubic foot aluminum cylinder without wearing additional weights. If you can imagine making a dive in a wetsuit, you can begin to understand how your buoyancy changes over the course of a dive. As you descend, the pressure of the water increases and compresses the gas bubbles in your wetsuit. As the bubbles compress, the wetsuit displaces less water and therefore, loses some of its buoyancy (figure 4-10). You will notice that you are sinking faster and faster the deeper you go. To compensate for the loss of buoyancy, you must add air to your BC, which increases your volume to regain the lost buoyancy. As you ascend at the end of your dive, the bubbles in your wetsuit and the air in your BC will expand because the pressure of the water is reduced. You will notice that you are rising faster and faster. To compensate for the additional buoyancy, you must vent air from your BC to control your ascent. Uncontrolled ascents are extremely dangerous. Chapter 4- Diving Science The density of the water in which you dive also affects your buoyancy. Salt water is about 2.5% denser than fresh water because of the weight of the minerals dissolved in it. Therefore, you displace more weight in salt water than in fresh water, so you have greater buoyancy in salt water. If you are weighted to be neutral in salt water and you dive in fresh water with the same amount of weight, you will sink. You must recheck your buoyancy if you change from diving in salt water to fresh water and vice versa. As a diver, you usually want to avoid having so little buoyancy that you must work to maintain your depth or to keep from sinking (figure 4-11). Neutral buoyancy beneath the surface is your constant goal, and it is important to help protect marine life. Divers who land, Diving Science 99 FIGURE 4-10. AS YOU DIVE, THE PRESSURE COMPRESSES YOUR WETSUIT AND MAKES YOU LESS BUOYANT.
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