Question: SCUBA dive tables help please...?

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Answer #1:

You need to be specific about what kind of tables you are trying to use (ie PADI RDP, NAUI, NOAA, Navy, etc etc). From your terminology you appear to be interested in PADI RDP, but you need to confirm that.

EDIT: if you are trying to understand either the PADI or NAUI dive tables, try this web site Click Here

EDIT: OK, if you think you have a NAUI table I can certainly help you with that.

So in your example you have completed Table 1 (End-of-Dive Letter Group) as a G diver. However, you are skipping a step and trying to find residual nitrogen time without accounting for a surface interval.

Upon leaving Table 1 as a G diver, you first would move on to Table 2 (Surface Interval Time). Continuing with your example, let's say you spent 1 hour 15 minutes on the surface before starting another dive. Starting at the bottom of the G column on Table 2, you would search for a cell where the bottom interval is less than or equal to 1:15, and the top interval is greater than or equal to 1:15. Using the current version of the dive tables (which can be found online at Click Here ), you will see that your surface interval of 1:15 puts you in the 2nd row from the bottom of column G (lower interval of 0:41 & upper interval of 1:15). Following the arrow to the left of that row, then, shows that at you would now have a new letter group of F at the beginning of the next dive.

You are now ready to move on to Table 3, which is the Repetitive Dive Timetable. Continuing on with the example, let's say you are planning for the next dive to again be a max depth of 50 feet. You would then go to the cell at the intersection of the 50 ft column and the F row on Table 3, which like Table 2 has an upper and lower number. The upper number (in light-faced, blue colored text) is the residual nitrogen time (RNT) for that dive. The lower number (in bold-faced, red colored text) is the Adjusted Maximum Dive Time (AMDT) for that dive. For this example (50 ft max as an F diver), the RNT is 47 minutes and the AMDT is 33 minutes...so this repetitive dive planned to 50 feet could not exceed 33 minutes without exceeding no-decompression limits.

Let's assume (of course) that you adhere to this dive plan for the next dive, and make this dive to 48 feet for 30 minutes. This dive remains a 50 foot dive, so your RNT would still be 47 minutes and you now have an Actual Dive Time (ADT) of 30 minutes. Adding the two together gives you a Total Nitrogen Time (TNT) of 77 minutes, which you then take back to Table 1 to determine a new end-of-dive letter group...which in the case of 50 feet for 77 minutes would be J.

This process would then repeat for as long as you are making repetitive dives (ie dives within 24 hours of each other)...the surface interval table credits your off-gassing with a (probably) reduced letter group, and the repetitive dive timetable provides you with AMDT (for dive planning before the dive) and RNT (for dive recording after the dive). After the dive, RNT + ADT gives you TNT, which is then used back on Table 1 to provide you with another end-of-dive letter group. And round & round we go....

Hope this helps. You can also take a look at the link I posted on my first edit for a more basic explanation of table usage and terminology, this answer skips the stuff normally explained in lecture on this topic.

FINAL EDIT: It looks like you may be trying to use the US Navy tables upon which the NAUI tables were based. The operation is similar to the NAUI tables but the format is slightly different and the numbers are more liberal than the NAUI tables. The concepts remain the same, but on the Navy tables the Surface Interval Time table is layed out horizontally instead of vertically as on the NAUI tables. To find a new letter group following a surface interval on the US Navy tables, you would start at the leftmost cell for the end of dive letter group (say, G) and continue to the right until you find your new letter group. Additionally,Table 3 on the Navy tables only gives you the RNT for the new letter group so you have to calculate AMDT yourself (AMDT = MDT - RNT, where MDT is the maximum dive time/NDL limit for that depth).

Here is a link to a document explaining how to use the US Navy tables in detail: Click Here

FINAL FINAL EDIT: OK, so SSI has their own version of the dive tables, again appearing to be based on the US Navy tables and looking quite similar in format. The big difference is that Table 2 (which they confusingly call the Reptitive Nitrogen Timetable instead of the Surface Interval Table) reads from right to left instead of left to right. Table 3 is similar to the US Navy table in layout but contains both RNT and AMDT (ANDL) numbers like the NAUI tables.

Here is a site which describes usage of the SSI tables: Click Here

I'm hopefully done updating this answer. Good luck!





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