NAUI Dive Planning Table Soft Flexible material NAUI

Dive Table Terms

Different dive tables and dive computers might use terms different from the ones used in the NAUI Dive Tables (figure 5-5). Also, the same term might have a different meaning.

The following terms apply to the NAUI Dive Tables:

Dive Schedule

This is an abbreviated statement giving the depth and time of the dive. It is expressed as depth/time (for example, 21 meters/40 minutes or 70 feet/40 minutes). It is also called a dive profile, especially when it is one dive in a sequence of dives.

Maximum Dive Time (MDT)

This is the time you can spend at a given depth without having to do a required decompression stop during ascent. This time is also known as the Maximum Allowable Dive Time or no-decompression ddmit.

Decompression Stop

This is a point in a dive where you stop at a specified depth for a specified time during ascent to allow nitrogen offgassing before continuing your ascent or surfacing.

Precautionary Decompression Stop

This is a stop at five meters (15 feet) for three minutes as a safety precaution when you have not exceeded the Maximum Dive Time. You should perform such a stop at the end of every dive. It is also known as a Safety Stop.

Required Decompression Stop

This is the amount of time specified by the NAUI Dive Tables, that you must spend at five meters (15 feet) whenever you exceed the Maximum Dive Time. Other tables specify additional stop depths for deeper or longer dives.

Actual Dive Time (ADT)

This is the elapsed time from the moment you begin your descent from the surface until the time you return to the surface. Time spent at your Safety Stop does not need to be included in the Actual Dive Time when determining your Letter Group.

Residual Nitrogen

This is the excess nitrogen remaining in your body from any dive or dives made before you have completely offgassed.

Letter Group Designation

This letter symbol identifies the amount of residual nitrogen you have in your system. The closer the letter is to the beginning of the alphabet, the less residual nitrogen you have in your body.

Surface Interval Time (SIT)

This is the time spent on the surface between dives. During this time, your body is eddminating excess nitrogen. Your Letter Group will change and move closer to the beginning of the alphabet, depending on how long you are on the surface.

Repetitive Dive

This is any dive that you make before you have completely offgassed from any previous dive or dives.

Residual Nitrogen Time (RNT)

This is the amount of time you must consider as already having been spent at a given depth for a planned repetitive dive. This time is based on the residual nitrogen remaining in your body from a previous dive or dives.

Adjusted Maximum Dive Time (AMDT)

This is the Maximum Dive Time minus the Residual Nitrogen Time for a repetitive dive to a given depth.

Total Nitrogen Time (TNT)

This is the sum of your Residual Nitrogen Time and your Actual Dive Time following a repetitive dive. You use this total to obtain your new Letter Group at the end of the dive.

Dive Table Rules

You must understand the following NAUI Dive Table rules completely. Similar rules will apply to any new set of dive tables or dive computer that you might use to calculate your dive times.

• Ascend no faster than 9 meters (30 feet) per minute. This is 0.3 meters (1 foot) every two seconds. You need a timing device and a depth gauge (or a dive computer) to measure your rate of ascent. This rate will seem quite slow to you.
• Use the exact or the next greater number listed in the table for your depth. If you exceed a number in the table, use the next greater number. The depths in the table range from 12 meters (40 feet) to 40 meters (130 feet) and increase in increments of 3 meters (10 feet). For example, you round a dive to 13 meters (43 feet) up to a 15 meter (50 foot) dive.
• Use the exact or the next greater number listed in the table for your time. If you exceed a number in the table, use the next greater number. The times range from 5 minutes to 130 minutes. For example, you round a dive to 15 meters (50 feet) for 41 minutes up to 50 minutes.
• Use the deepest depth you reached during your dive to determine the dive schedule for your dive. For example, if you do a dive to 18 meters (60 feet), but spend most of the time at 12 meters (40 feet), you must consider the dive to be an 18 meter (60 foot) dive.
• Always make your deepest dive first when making a series of dives. Plan each of your repetitive dives to a shallower depth than your previous dive. This might allow you to offgas nitrogen on progressively shallower dives and prevents you from carrying progressively larger amount of residual nitrogen on deeper repetitive dives.
• Consider any dive shallower than 12 meters (40 feet) to be a 12-meter (40-foot) dive when planning your dives.
• Surface Interval Time (SIT) must be at least 10 minutes between dives. If your SIT is less than 10 minutes, you must consider your second dive as a continuation of the first dive. NAUI recommends a SIT of at least one hour between dives.
• Use the next greater dive time if your dive is particularly cold or strenuous. For example, if you do a dive to 18 meters (60 feet) for 22 minutes, the 22 minutes rounds to 25 minutes. However, if you become chilled during the dive, round the time again to 30 minutes.
• Avoid dives that take you right to the no-decompression limit for any given depth and time combination. If you accidentally overstay your bottom time or use an incorrect ascent rate on such a dive, you could be in a required decompression situation or suffer DCS. Always allow yourself enough time to make a slow, comfortable ascent with plenty of air