NAUI Master Scuba Diver 240 Diving Techniques and Deeper Diving PLANNING A DEEP DIVE PROFILE Planning your dive profile should involve a little more thinking than just choosing a time and depth. Here are some guidelines: • Plan the dive not to exceed the Maximum No-decompression Dive Time limits of the NAUI Dive Tables. These time limits are more conservative than the U.S. Navy no-decompression limits. If you are using a dive computer, you may be able to make a multi-level dive that is longer than the square-wave time limits. Check the dive planning mode of your dive computer. • Make sure the profile is realistically tailored to the underwater terrain and depth (figure 10-4). • Select a profile that is feasible, considering the air supply and air consumption rate for both you and your buddy. • Take an underwater slate with you, with your primary and contingency profiles written out. • Dive your plan. • Do the deepest part of your dive first, and move progressively shallower as the dive continues. • Allow both time and sufficient air to make a slow, controlled ascent with safety stops. A good practice is to plan your turn-around and return to your ascent point at one-half your starting cylinder pressure plus 20 bar (300 psi). • Perform a safety stop at a depth of 5 m (15 ft) for 3 to 5 minutes at the end of every dive. • If you and your buddy are not using identical models of dive computers or tables, the dive must follow the more conservative of the two computers or tables. • Plan for a minimum gas reserve for you and your buddy, to include all required stops. GAS MANAGEMENT It is important for divers to be able to estimate how long their air supply will last at a given depth. Air consumption may be expressed in terms of pressure or psig per minute. Many divers prefer to use this method because they feel it is easier to relate to pressure, since air supply is commonly reported by gauge in terms of pressure rather than volume. However, the use of pressure values can be somewhat misleading. For example, which diver has more air, one with 150 bar (2200 psi) in a steel 2000 L (70 cf) cylinder or one with 150 bar (2200 psi) in an aluminum 2300 L (80 cf) capacity cylinder? The diver with the steel “70” has only approximately 1800 L (64 cubic feet) of air, whereas the diver with the “80” has only 1600 L (57 cubic feet). So if you use different sized cylinders, you must determine your air consumption rate and remaining volume for each independently. Metric Example Let’s assume that a diver swimming at a depth of 10 meters for 20 minutes uses 100 bar of air from a 12 FIGURE 10-4. DEEP DIVES ARE OFTEN CONDUCTED ON DROP-OFFS AND WALLS
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