Another Tables vs. Computers Thread

[TheRedHead]

There is, but you don't seem to want to average depths.

Are you talking about profiling?

 

[JeffG]

Are you talking about profiling?

Unsure. There are so many names for very similar things. Other people may call it min deco.

But it boils down to using your average depth and "shaping" your ascent.

 

[TheRedHead]

Unsure. There are so many names for very similar things. Other people may call it min deco.

But it boils down to using your average depth and "shaping" your ascent.

But that's a different thing than averaging your depths to plan a multilevel dive where the example would come out to 60 minutes at 60 feet (I'm not sure if I recall it exactly). That doesn't tell you anything useful and I think it would exceed the NDL for most tables.

You don't need tables to do what you are talking about. What I was referring to is using tables with depth averaging.

 

[JeffG]

But that's a different thing than averaging your depths to plan a multilevel dive where the example would come out to 60 minutes at 60 feet (I'm not sure if I recall it exactly). That doesn't tell you anything useful and I think it would exceed the NDL for most tables.

You don't need tables to do what you are talking about. What I was referring to is using tables with depth averaging.

Silly me. and here I thought this is what you were asking.

And my point was it is conceivable that it could be taught in open water if it were a reasonable way to plan multilevel dives.

There is and you don't need a computer.

 

[Charlie99]

I'm not even sure what you guys are trying to calculate?? What repetitive group you'll be in at the end of the dive?

The "zero SI" method of dive planning I described above both tells you whether a dive stays within NDL and also gives you a proper ending dive group for calculating repetitive dives.

You'll be in the repetitive group from the last level. In my example above, you would be in the PADI Pressure Group V. (This, btw, corresponds to the 60 minute ht compartment being loaded to 47fsw ppN2 or 83% of its M-value if you prefer those terms. )

The Pressure Groups (PADI RDP) or End-of-Dive Group, aka repetitive dive group (NOAA/USN) table are determined solely by the compartment upon which that table is based --- 60 min halftime for PADI RDP, 120 minute halftime for USN and all the various spinoffs such as YMCA and SSI tables. NDLs are calculated using all of the compartments, but the letter groups are based upon one and only one compartment. That's why the NDLs end up in different letter groups at different depths.

 

[TheRedHead]

Silly me. and here I thought this is what you were asking.

There is and you don't need a computer.

But we were talking about tables and multi-level and I was making a different point. :mooner:

Why don't you just make a post about ratio deco and be done with it instead of doing the Socratic method with me?

 

[TheRedHead]

You'll be in the repetitive group from the last level. In my example above, you would be in the PADI Pressure Group V. (This, btw, corresponds to the 60 minute ht compartment being loaded to 47fsw ppN2 or 83% of its M-value if you prefer those terms. )

Just use Jeff's method and you won't need to worry about repetitive groups because you'll come out clean.

 

[JeffG]

Why don't you just make a post about ratio deco and be done with it instead of doing the Socratic method with me?

I'm not talking about ratio deco. We are just talking about recreational dives here.

I just want to know where those funky compartments are that everyone is talking about.

 

[Charlie99]

You can't really do averaging because the tissue compartments won't average.

Actually, in most cases depth averaging works. Just like the simplistic zero SI method of using tables, there are some profiles that look ok when averaged but are a bit outside the model limits, but it is generally close enough to use.

There are a few restrictions on what is valid for averaging. Most are commonsense. For example, averaging 15 minutes at 100' followed by 15 minutes at 60 foot is OK to be the equivalent of 30 at 80' is OK, but the reverse isn't OK.

As for not being covered in OW water classes, I consider lack of discussion of reasonable planning tools for multilevel dives to be a significant omission. It is also indirectly a reason that many divers end up blindly following profiles given to the by DMs or blindly following their computers.

 

[Charlie99]

Just use Jeff's method and you won't need to worry about repetitive groups because you'll come out clean.

Only if I took the RIGHT DIR-F. Some DIR-F graduates learned that surface intervals are not needed because a minute pause every 10' during the ascent leaves them bubble free and without residual nitrogen, and get taught that time-to-fly delays are optional. Others are taught differently.