Depth averaging tables.

[tursiops]

Yes, worked rather hard at it. As tursiops said, it isn't linear with depth.

I came up with this for your first hard deco in minutes: divide depth squared (in feet) into 222,222. Compare that to Navy Air Tables.

Cutting to the chase, I came up with something for a multilevel dive that probably wouldn't kill me, but I wouldn't trust it either. The more I learn about deco, the less I know to be true.

Not sure what you mean by this.
By "first hard deco in minutes" do you mean an NDL time for some depth?
Do your really mean 222.222/D**2, or do you maybe mean D**2/222.222? the first one, which is what you wrote, would give 0.06 for 60 ft. What does this mean? At least the inverse gives 16.2, which might mean something....but what?
And you really mean 222.222, not just 222?

The old Depth (ft) plus Time (mins) = 120 is perfect for the (old) Navy tables, between 60 and 90 ft. Above 60 ft you get much more time than simply D+T=120, and below 90 ft you get less time than D+T=120.

 

[lowviz]

Type six 2's into a calculator. Divide by depth in feet and then divide by depth in feet again. The number that you get is an aggressive NDL for air for a square dive at that depth.

So now you can use this as an on-gassing "rule" to construct multilevel dives...

 

[Basking Ridge Diver]

Not averaging as others have said but using the tables for a multi level dive example - I am using the NAUI tables.
130 for 3 mins ascend to 80 feet for 14 mins ascend to 50 for 16 mins - Note as others have said this does not include time taking to get to each level.

1st Dive -
130 feet for 3 mins puts you at Letter C - Letter C for 10 min SIT - this is fictitious you are not going to the surface but this is how you use it.
Follow C to 80 feet (13 RNT and 22 AMDT)

2nd Dive - remember you are not going to the surface this is really an extension of the first dive but I am explaining how this works.
80 feet for 14 mins (14 + 13 = 27 RNT) you are now in Letter G - Letter G for 10 min SIT - this is fictitious you are not going to the surface but this is how you use it.

3rd Dive - remember you are not going to the surface this is an extension of the first dive...
50 feet for 16 mins
Follow G to 50 feet (16 + 56 = 72 RNT) you are now in Letter J.
So you began in Letter A and ended in Letter J - All within NDLs.

You could plan a second (real dive) but your SIT time is going to be elongated. And yes this works - would I do deep dives on this - hell no I would use my PDC.

 

[tursiops]

Type six 2's into a calculator. Divide by depth in feet and then divide by depth in feet again. The number that you get is an aggressive NDL for air for a square dive at that depth.

So now you can use this as an on-gassing "rule" to construct multilevel dives...

Got it. I had read 222.222, not 222,222. My bad.

 

[muddiver]

I guess if you really understand the physiology and physics behind decompression you could call the 50 foot portion of the presented (not proposed) dive profile as an extended deco stop or extended safety stop. At 50 to 60 feet you will eventually reach saturation from the nitrogen loading at 130 feet and the subsequent cruse at a shallower depth. Though you would run out of breathing has on open circuit first.


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[tursiops]

Not averaging as others have said but using the tables for a multi level dive example - I am using the NAUI tables.
130 for 3 mins ascend to 80 feet for 13 mins ascend to 50 for 16 mins - Note as others have said this does not include time taking to get to each level.

1st Dive -
130 feet for 3 mins puts you at Letter C - Letter C for 10 min SIT - this is fictitious you are not going to the surface but this is how you use it.
Follow C to 80 feet (13 RNT and 22 AMDT)
2nd Dive - remember you are not going to the surface this is really an extension of the first dive but I am explaining how this works.
80 feet for 14 mins (14 + 13 = 27 RNT) you are now in Letter G - Letter G for 10 min SIT - this is fictitious you are not going to the surface but this is how you use it.
3rd Dive - remember you are not going to the surface this is an extension of the first dive...
50 feet for 16 mins
Follow G to 50 feet (56 + 16 = 72 RNT) you are now in Letter J.
So you began in Letter A and ended in Letter J.

You could plan a second (real dive) but your SIT time is going to be elongated. And yes this works - would I do deep dives on this - hell no I would use my PDC.

Yes, you can do this on any set of tables. But you do not get an answer that you should use, unless you are very far away from any limits. That is why the Wheel was invented.

This paper explains how to validly use the RDP with multilevel dives. The same ideas will apply to all tables, but there is no way to test them because there is no equivalent to the Wheel for those other tables. Sorry, I cannot attach the paper (too large), but you can get it on Rubicon with this link.

 

[Eric Sedletzky]

I guess if you really understand the physiology and physics behind decompression you could call the 50 foot portion of the presented (not proposed) dive profile as an extended deco stop or extended safety stop. At 50 to 60 feet you will eventually reach saturation from the nitrogen loading at 130 feet and the subsequent cruse at a shallower depth. Though you would run out of breathing has on open circuit first.


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Or a penalized dive at 50'.
Truth is, no matter what you call it, the time spent at 50' would be less than if you were never to have gone past 50' to start with. The question is, has anybody played around with how much less time at 50' with out just winging it?

---------- Post added December 11th, 2015 at 05:13 PM ----------

The old Depth (ft) plus Time (mins) = 120 is perfect for the (old) Navy tables, between 60 and 90 ft. Above 60 ft you get much more time than simply D+T=120, and below 90 ft you get less time than D+T=120.

you meant 60 to 100 feet right? The USN tables show 20 mins max no deco at 100'.

 

[muddiver]

I ran your dive plan (130 for 1 and 50 for 50) through V-Planner. I got scolded for too little time to descend and ascend to 130. So changed to 6 min at 130 (130/75 fpm decent, 1 min bottom and 30 fpm ascent) and I got a 5 min stop at 10 feet. I guess it works.

It also shows 102 cu ft of gas consumption based on the settings I have for SAC.


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[DiveNav]

I am not sure if this is relevant .... but, few years ago we added to divePAL the Estimated Pressure Group feature.
EPG visualizes how a table Pressure Group progresses (changes) during a multilevel dive. (Please note that this tool should NOT be used for planning real dives as its main intent is for education)

Full post (the shape of a dive table) is HERE

 

[tursiops]

you meant 60 to 100 feet right? The USN tables show 20 mins max no deco at 100'.

Not sure what table you are looking at. The Navy Dive Manual, Rev 6, table 9-7, gives 25 minutes at 100 ft.

---------- Post added December 11th, 2015 at 05:31 PM ----------

I am not sure if this is relevant .... but, few years ago we added to divePAL the Estimated Pressure Group feature.
EPG visualizes how a table Pressure Group progresses (changes) during a multilevel dive. (Please note that this tool should NOT be used for planning real dives as its main intent is for education)

Full post (the shape of a dive table) is HERE

Which Pressure Groups did you use, RDP? USN? Other?