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NAUI Scuba Diver 136 Decompression, Dive Tables, and Dive Computers 00 : 7. Add your ADT to your RNT to get your TNT. For example, your ADT is 27 minutes, plus an RNT of 24 minutes, gives you a TNT of 51 minutes. 8. Go back to Table 1 and find the row corresponding to your deepest depth. Follow the row across to the block containing the time corresponding to your TNT. For example, your depth was 16 meters (52.5 feet), which rounds up to 18 meters (60 feet) and your TNT was 51 minutes, which rounds up to the 55 minute block. 9. Look down the column containing the appropriate time until you reach a letter. This is your Letter Group. For example, for a dive to 18 meters (60 feet) for 55 minutes, your Letter Group is I. 10. Record the Letter Group on the line above the time you completed your second dive. This completes the dive profile for your second dive. Use the same steps to plan and perform a third dive. Do not rely on your memory to keep track of dive times, maximum depths, or surface intervals. You must record this information, and the NAUI Dive Planning Worksheet provides a convenient way to record your data. Get into the habit of recording your dives on the worksheet, and it will become easy to keep track of your diving. This will also make it easier to complete your logbook at the end of the day. MAXIMIZING YOUR UNDERWATER TIME There are times when you are making repetitive dives that you will either not be able to dive to the depth you would like or for the length of time you would like. You can maximize your underwater time and depth to which you want to dive by adjusting your SIT, your depth, or your ADT. In this section, you will see how the three factors interact and how working with them will get you the depth or time you want. Limiting Your Dive Time The first way to keep within the Maximum Dive Time is easy – limit your ADT. Your first dive of the day must not exceed the MDT for the depth of that dive, and your repetitive dives must not exceed the AMDT for your planned depth. This can be restrictive. Suppose you want to make three 25 minute dives to a depth of 18 meters (60 feet). You want to spend an hour on the surface between each dive. Your first dive is to 18 meters (60 feet) for 25 minutes so your Letter Group is E. After a SIT of 1 hour, your new Letter Group is D. With a Letter Group of D, your AMDT for a dive to 18 meters (60 feet) is 31 minutes. If your ADT for the second dive to 18 meters (60 feet) is 25 minutes, your RNT is 24, and your TNT is 49. Your Letter Group following this dive is H. After another hour of SIT, your new Letter Group is G. According to Table 3, the maximum time you can spend at 18 meters (60 feet) is 11 minutes. You can see that making three back-to-back dives to depths of 18 meters (60 feet) or more can be quite limiting if you want to spend the maximum amount of time in the water. 12:35 1:05 AMDT= 51 AMDT= 31 RNT = 24 ADT = 27 TNT = 51 15(50) 18(60) 16 (52.5) D I 3 FIGURE 5-16. THIS PROFILE IS COMPLETE FOR A REPETITIVE DIVE TO 16 METERS (52.5 FEET) FOR 30 MINUTES.


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