Need help with RDP calculation

[s.s.seafan]

Hi,

Here is a likely 3-dive/day scenario for my upcoming trip next week:

1st dive - 20' deep, round up to 35', for 60 min, makes it group L
SI is 2 hours (11:30am-1:30pm), makes it group B
2nd dive is 60', RNT=11, ABT=44. dive for 40 min, makes it group Q (do I need to add the 11 min of RNT to the actual bottom time of 40 here?)
SI is 45 min, makes it group H
3rd dive is 45' (round up to 50), RNT=28, ABT=52. dive for 50 min.

Did I do that right? Given the fact that 1st dive is shallower than the 2nd, 3rd, am I still well within NDL based on the above?

Thanks,

-Jason

 

[boulderjohn]

You do add the RNT to the actual bottom time.

There is no concern about the first dive being shallower, no matter what it may say on the fine print of your RDP. If you have sufficient surface intervals to do the dive you want to do, then everything is hunky dory.

EDIT: Misinformation in original.

 

[bygolly]

I get Group U after the second dive and 3 minutes over after the third when RNT's are added to actuals.

 

[boulderjohn]

I get Group U after the second dive and 3 minutes over after the third when RNT's are added to actuals.

That is correct--I probably made the same simple arithmetic error as the OP when I checked.

 

[bygolly]

That is correct--I probably made the same simple arithmetic error as the OP when I checked.

Thanks John....for a while there I was checking and re-checking to see where MY problem was. I love these question when they come up as I get to drag out my tables and re-learn how to use them.

For a pure square profile Jason's dives push the limits but in reality the dives will likely be multi-level with many credits and the profiles will likely be fine. Maybe increase the second SI a touch.

 

[boulderjohn]

As an experienced instructor, I can do the tables in my sleep. I also scored in the 93rd percentile on my math Graduate Record Exam (GRE) when I graduated from college. Yet, I was felled by a very simple arithmetic error. I see that a lot in students. The most common mistake in using the tables, though, is simply pulling the number or letter from the wrong line. It is easy to do, very similar to the mistake I make when I screw up a Sudoku puzzle by putting a number in the wrong square after I have correctly identified it.

It is for this reason that I chuckle when people say they prefer tables over computers because they don't trust the computer to do the calculations correctly.

 

[s.s.seafan]

Just got update email from the dive shop, their schedule is the following:

boat leaves dock at 10:30am, 1st dive at 20' for 50 min, return to dock at 11:30am
SI 2 hours, 2nd dive leaves dock at 1:30pm, dive 60' for 40 min
SI 40 min, 3rd dive at 40' for 40 min

so, now the calculation i have is -

1st dive 50 min, makes it group J
SI 2hrs, makes it group A (RNT=6, ABT=49 at 60')
2nd dive at 60' for 40 min, 40+6=46, makes it group S
SI 40 min, makes it group J (RNT=44, ABT=96 at 40')
3rd dive at 40' for 40 min, 40+46=86, makes it group T

now I can't remember what that ABT is used for?

 

[bygolly]

Just got update email from the dive shop, their schedule is the following:

boat leaves dock at 10:30am, 1st dive at 20' for 50 min, return to dock at 11:30am
SI 2 hours, 2nd dive leaves dock at 1:30pm, dive 60' for 40 min
SI 40 min, 3rd dive at 40' for 40 min

so, now the calculation i have is -

1st dive 50 min, makes it group J
SI 2hrs, makes it group A (RNT=6, ABT=49 at 60')
2nd dive at 60' for 40 min, 40+6=46, makes it group S
SI 40 min, makes it group J (RNT=44, ABT=96 at 40')
3rd dive at 40' for 40 min, 40+46=86, makes it group T

now I can't remember what that ABT is used for?

Those calcs work. ABT is actual bottom time of the dive ie your third dive ABT is 40 min.

 

[oreocookie]

Just got update email from the dive shop, their schedule is the following:

boat leaves dock at 10:30am, 1st dive at 20' for 50 min, return to dock at 11:30am
SI 2 hours, 2nd dive leaves dock at 1:30pm, dive 60' for 40 min
SI 40 min, 3rd dive at 40' for 40 min

so, now the calculation i have is -

1st dive 50 min, makes it group J
SI 2hrs, makes it group A (RNT=6, ABT=49 at 60')
2nd dive at 60' for 40 min, 40+6=46, makes it group S
SI 40 min, makes it group J (RNT=44, ABT=96 at 40')
3rd dive at 40' for 40 min, 40+46=86, makes it group T

now I can't remember what that ABT is used for?

You've done it right, except for dive 3, you added 46 instead of the RNT of 44 to your bottom time, giving you a Total Bottom Time of 84 putting you in group S instead of T.

What you're listing as ABT, though, is actually the adjusted NDL (ANDL). Your Actual Bottom Time should not be greater than the ANDL, just like you don't plan your first dive to be longer than the NDL for that depth, but otherwise you don't use that number (the ANDL) for anything else.

 

[DiveNav]

......boat leaves dock at 10:30am, 1st dive at 20' for 50 min, return to dock at 11:30am
SI 2 hours, 2nd dive leaves dock at 1:30pm, dive 60' for 40 min
SI 40 min, 3rd dive at 40' for 40 min....

I did enter your dives in divePAL and using a moderate setting I get 78% nitrogen loading at the end of dive 3.

​

Alberto (aka eDiver)