A question about NOAA air table chart 3

[nohappy]

When I look closely into PADI's RDP table, I noticed that Table 3 is actually Table 1 with a matrix rotate. And that makes sense. For example, if I made a dive at 35ft for 10min (Group A), and then take 10min S.I. (still Group A). Now if I look up table 3 at 35ft, my RNT is 10min (at 35ft) which is exact the same time as my first dive (of course, because that's what I just did).

However, when I look up NOAA's air table, Chart 1 (table 1) and Chart 3 (table 3) are not the same. If you checked them, they don't just make a matrix rotate, the number has add up around 1min in each cells. For example, if I made a dive at 12.2m for 12min (Group A), and then take 10min S.I. (Still Group A). Now if I look up RNT at Chart 3, my RNT will be 13min (at 12.2m). Well, I can understand if the RNT after S.I. at the same depth is the same or smaller, but I don't understand why it became 1min more than the original RNT. In other words, according to NOAA's air table, if I dive 12min at 12.2, then I would have 163-12=151min left before deco. However, if I surface and take 10min break and then start the next dive, my NDL now become 150min. And that don't make sense to me. I understood this is not a big issue and it might be a minor question. Most people probably don't care, but I want to know if there is any reasonable explanation for this.

 

[lowviz]

Wow, somebody is paying attention.

First, you are talking about a difference of one part in 150. That is nothing in the fuzzy world of decompression. If you really want to gain insight, get TableCurve2D and force an equation to those points. You will shortly see that the tables are approximations too.

 

[johndiver999]

Your question seems like: "how can I get a penalty greater than my actual bottom time when I come to the surface"?

One thing to think about is bottom time.. it is NOT the time underwater! It is the time when you start the descent until you start the ascent.. All the time you are coming up - doesn't "count" on the dive table - so if you start the ascent at the 10 minute mark, the dive duration is considered to be 10 minutes - but in actuality you are still absorbing nitrogen (in some tissues) on the way up.

So the amount of nitrogen you absorb in the first, 10 minute portion of a longer dive "on the bottom" is probably less than in the 12 minutes (total) it takes for you to come up - should you do just a 10 minute dive..

Thats my idea.. not sure if it is correct.

 

[NAM001]

When I look closely into PADI's RDP table, I noticed that Table 3 is actually Table 1 with a matrix rotate. And that makes sense. For example, if I made a dive at 35ft for 10min (Group A), and then take 10min S.I. (still Group A). Now if I look up table 3 at 35ft, my RNT is 10min (at 35ft) which is exact the same time as my first dive (of course, because that's what I just did).
View attachment 454172

However, when I look up NOAA's air table, Chart 1 (table 1) and Chart 3 (table 3) are not the same. If you checked them, they don't just make a matrix rotate, the number has add up around 1min in each cells. For example, if I made a dive at 12.2m for 12min (Group A), and then take 10min S.I. (Still Group A). Now if I look up RNT at Chart 3, my RNT will be 13min (at 12.2m). Well, I can understand if the RNT after S.I. at the same depth is the same or smaller, but I don't understand why it became 1min more than the original RNT. In other words, according to NOAA's air table, if I dive 12min at 12.2, then I would have 163-12=151min left before deco. However, if I surface and take 10min break and then start the next dive, my NDL now become 150min. And that don't make sense to me. I understood this is not a big issue and it might be a minor question. Most people probably don't care, but I want to know if there is any reasonable explanation for this.
View attachment 454173

Try t his using the noaa table 80 ft for 28 min. exit group g Si till you get to group d next depth is 60 ft if you use the loop yo have 24 rnt and 30+ remaining till ndl you make your second dive.

now go to the entry table like yo did for your first dive and make your second depth 60 ft and look at columd d and it says 22 (that would be where you start the second dive with 24 rnt or as the entry table shows table shows 22 adn the hext higher is 28 . The loop around is dong some minor corrections etc. Is there some error yes but your si is in time groups of hours. so by the tabl e 1.5 hour is the same as 2 hr. when you go left to the to exit group lettter it works best when you use your exit group add 1 and do it like above If you only use say 1/2 of a si window and the exit says group c for istance you did not do the full window so you are closer to d than you are c. so if a window says 3:21 to 2:28 then 2 hours and 30 minutes is treated the same 3 hours adn 25 minutes. If it were 2 hours and 25 min you would be in one group and if it were 2 hours adn 30 mnutes you would be in another. Other differences is that o entry chart is in distinct depths and times whre the SI in time locks that are way different than teh exposure section 6,7,9 minutes vs 1.5 hours sections.

One last thing you ca n most likely not have to do the exit group adn add one thing if your exposure depth you are using is the max depth as a dive from 60-80 ft was not all done at 80 ft for the full time. So much depends on how you use the tables and how you do your rounding of your depths and times. Computers make it so much easier but nothing beats playing with tables when it comes to learning how it works.

 

[Bob DBF]

One thing to think about is bottom time.. it is NOT the time underwater! It is the time when you start the descent until you start the ascent..

Actually it is the time you start the decent until you start your *direct* ascent to the surface. This means that if you do not ascend directly to the surface at the ascent rate prescribed by the tables you are off the tables, unless you count all the time on a multilevel dive until you make your direct ascent.

The Wheel, or recalculating your multilevel dive for each depth by calculating each level as a seperate dive with a zero surface interval can keep you on the tables. Both of these can fudge the tables, but a computer is easier, and made for the job.


Bob