How does the table math work?

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tesnusxenos

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I can use the tables. I have no problem using them or teaching them, I pester my sisters to calculate their dives. I calculate my dives even though I have a computer.

My question is about table three why does the amount of residual nitrogen change with depth?
for example I finish my first dive in pressure group N
if I want to dive to 50 feet there is 44 minutes worth of residual nitrogen left in my body
but if I want to dive to 90 feet there are only 22 minutes of residual nitrogen left in my body

why does it change? I would think that the amount left would remain constant. does the deeper pressure change it and in what way?
 
I asked exactly the same question in my OW class!

There's a reason it's called residual nitrogen TIME. It corresponds to the amount of time you'd spend at that depth to accumulate that amount of nitrogen in the chosen compartment (each table uses one compartment for figuring this, but they vary in which one they use). So at 60 feet, you might need to spend 18 minutes to get that much nitrogen in your bloodstream, but at 90, you might need only 12 minutes, because of the higher nitrogen tensions under 4 ATA of pressure.

Make sense?
 
thanks that makes sense to me
 
Look at it this way. You want to make a dive to 50 feet, the NDL for 50 feet is 100 minutes, your residual nitrogen time is 44 minutes. In order to stay within the NDL you need the sum of the residual nitrogen time and the actual dive time to not exceed 100 minutes.
If you want to dive to 90 feet and the NDL for 90 feet is 30 minutes. In this case the sum of the residual nitrogen time and the actual dive time can not exceed 30 minutes to remain in the NDL so your residual nitrogen time must be less than the NDL time or you can not do the dive.
What table are you using.
In the case of the Navy tables if I am in group F after my surface interval and want to dive to 50 feet my residual nitrogen time is 47 minutes. The 50 foot NDL is 100 minutes so 100 minus 47 leaves me a dive time of 53 minutes, 47+53=100.
If instead I want to dive to 90 feet the NDL is 30 minutes and my residual nitrogen time is 24 minutes so my actual dive time is 6 minutes, 6+24=30
The key to understanding it is the residual nitrogen time and the actual dive time can not exceed the NDL for a particular depth.
 
This thread is more evidence that teaching tables by NAUI, SSI, PADI, etc is not working.

Relying on dive computers like SDI is more safe and therefore makes more sense, rather than tables.

Dive computers have planning features as well, therefore tables are totally archaic in the 21st century. For the first dive, the computer in planning mode will give a regular NDL time. For residual dives thereafter, the computer will give adjusted NDLs with RNT taken into account, as well as surface interval time so far.

The key is to have a quality, reliable computer, like a SUUNTO, for example, rather than another brand that has a history of defects and recalls.
 
This thread is more evidence that teaching tables by NAUI, SSI, PADI, etc is not working.

Relying on dive computers like SDI is more safe and therefore makes more sense, rather than tables.

I agree that a computer combined with diving experience helps you understand this aspect of repetitive diving better, but I'm not sure you can eliminate tables from a dive class and still explain a lot of concepts to students. How does SDI demonstrate how you have less bottom time on a repetitive dive if you don't have tables to work through? An instructor can just say it but the only way to show it to those visual learners if you have only a computer to work with would be to go on a dive to a nontrivial depth.
 
This thread is more evidence that teaching tables by NAUI, SSI, PADI, etc is not working.

Relying on dive computers like SDI is more safe and therefore makes more sense, rather than tables.

Dive computers have planning features as well, therefore tables are totally archaic in the 21st century. For the first dive, the computer in planning mode will give a regular NDL time. For residual dives thereafter, the computer will give adjusted NDLs with RNT taken into account, as well as surface interval time so far.

The key is to have a quality, reliable computer, like a SUUNTO, for example, rather than another brand that has a history of defects and recalls.


Thanksgiving has come a little late to SB this year. We can always count on you for a larf. :D
 
This thread is more evidence that teaching tables by NAUI, SSI, PADI, etc is not working.

Relying on dive computers like SDI is more safe and therefore makes more sense, rather than tables.

I believe that while your first sentence may be true, the second does not follow logically from the first. It may be that neither teaching tables by NAUI/PADI works nor does relying on dive computers. There are other possibilities, including:
  • Some people may not be ready or motivated to learn what they need to know to be safe divers regardless of who teaches them.
  • There may be a better way to teach tables than NAUI/PADI use. For example, it may be that the curriculum is sufficient but their selection of instructors is poor or their business model pressures instructors to push people through the system as quickly as possible.
  • There may be a better way to determine safe dive profiles than tables that makes a diver safer.
I personally think all of the above are true for some segment of the diving population. A small number of people just want their certification so they can have fun on their vacation. Giving them a computer doesn't make them any safer because they will either do whatever their DM tells them to do, ignoring the computer, or do whatever they want to do, ignoring the computer.

I have witnesses the certification mill at work, it is not pretty. There is good information in the OW process, but some instructors don't want to answer your questions, they just want to push you through the system because they make money of trips and equipment sales, the instruction is a loss leader to get you in the door.

And while I am not a computer hater, I believe my study of the models behind the computers and planning programs makes me a safer diver.

Not trying to pick a fight here, just pointing out that it isn't a simple Door Number One or Door Number Two. take me for instance. If I am not a safe diver with tables, I would not assume that strapping a computer on my arm will fix the issue...
 
The most recent incantation of PADI OW essentially replaces the tables with the eRDP; they don't even include the table in the Crew Pack, just the calculator. The calculator is a lot easier to use and will give the Adjusted NDL (ANDL) for the next dive given the parameters of the previous dive(s) and the SIT. It's pretty slick! There is even a multilevel version for those that are interested.

That said, eliminating the tables or limiting the discussion isn't a good thing from my point of view. I like to see the context of being a 'K' diver and the alternatives for SIT and ANDL for the next dive. But that's just me! I started using NAUI tables back in '88 and I'm still comfortable with them today.

The PADI Nitrox course uses tables extensively so if the OW student didn't use them earlier, they will use them in this class.

But, when you add the complication of O2 loading and MOD limits to N2 loading, perhaps a computer is something to consider. I bought the Dive Rite Nitek Duo for that very purpose. But I will always have the tables for backup.

Richard
 
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https://www.shearwater.com/products/peregrine/

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