"Riding your Computer Up" vs. "Lite Deco"

[shoredivr]

What a common-sense approach BSAC has!

Except for how they approach the long hose, I agree with you ;-)

 

[KevinNM]

Yes, I can compare them for a single tank dive.

I'll point out that USN divers are normally diving supported by a chamber and medical team on site and their profiles allow for a several percent probability of bending a young, incredibly fit diver. Which is OK, because they will be in their chamber in a few minutes.

Are you still young and incredibly fit? Do you usually have a chamber and medical team on scene? If both of them are not true you should be careful trying to use navy tables for your diving.

 

[DevonDiver]

You cannot compare the PADI and Navy tables by simply looking at the first dive NDLs.

Absolutely. And those that want to crank up Multideco etc all... comparing only solitary dive parameters... need to get a better grip on how tables/algorithms work.

 

[scubadada]

Absolutely. And those that want to crank up Multideco etc all... comparing only solitary dive parameters... need to get a better grip on how tables/algorithms work.

Yes, it's really too bad more dive computer testing does not use a standard, multi-dive protocol
http://ads.bonniercorp.com/scuba/PDF/ScubaLab-Computer-Test-September-2014-data.pdf

 

[lowviz]

I'll point out that USN divers are normally diving supported by a chamber and medical team on site and their profiles allow for a several percent probability of bending a young, incredibly fit diver. Which is OK, because they will be in their chamber in a few minutes. ...//...

I totally get all that. And all that you posted only reinforces that I don't want to dive their NDL's. I use those NDL's for my final limit of bottom-time when planning an ascent using a very conservative algorithm. Anything past that is done by the books. I don't do much real deco anymore, having most of my fun in shallower settings now.

@boulderjohn Thank you for the Navy/PADI insight on the slower compartments. The PADI medium/deep sections look more evenly balanced (to me) in terms of loading as it appears PADI has nipped back on most of the first dive's longer exposures and had no need to do same in the deeper sections.

@DevonDiver I am trying to get a better grasp on the inner workings. Been doing so for years. And remember, I dive a DC with a very conservative setting. If I want to do a second or third dive that is over the top, I'll get called on it.

 

[Basking Ridge Diver]

I use those NDL's for my final limit of bottom-time when planning an ascent using a very conservative algorithm.

The Navy tables I believe use the time from descent from the surface to ascent when you are leaving the bottom - so in essence you are using a fraction of those bottom times. You may want to subtract the descent time (60fpm) from the bottom time at depth - (120 feet would take 2 mins...) and so on...
Reminder only but you may have taken that into consideration.

 

[Lorenzoid]

I'll point out that USN divers are normally diving supported by a chamber and medical team on site and their profiles allow for a several percent probability of bending a young, incredibly fit diver. Which is OK, because they will be in their chamber in a few minutes.

"Several percent"? Is that true? So you mean more than one out of a hundred typical USN dives is probably going to involve DCS? I vaguely recall once reading something to that effect about the pure Buhlmann algorithm, i.e., with 100/100 GF.

 

[dumpsterDiver]

The Navy tables I believe use the time from descent from the surface to ascent when you are leaving the bottom - so in essence you are using a fraction of those bottom times. You may want to subtract the descent time (60fpm) from the bottom time at depth - (120 feet would take 2 mins...) and so on...
Reminder only but you may have taken that into consideration.

The tables, as far as I know, use the same definition for bottom time.. from the time you leave the surface to start the ascent. I know if you come up slower than 60 fps (on the old navy tables) you were supposed to add that time to your dive, but my recollection is a little fuzzy on the recommended handling of very fast descents.

For diving 60 or 110 feet a fast descent, it is not going to amount to much time difference. I can descend at 160 fpm, if I really want to, but my computer knows that.

 

[scubadada]

The Navy tables I believe use the time from descent from the surface to ascent when you are leaving the bottom - so in essence you are using a fraction of those bottom times. You may want to subtract the descent time (60fpm) from the bottom time at depth - (120 feet would take 2 mins...) and so on...
Reminder only but you may have taken that into consideration.

No, USN tables use bottom time. BSAC '88 uses time until reaching the 6m or the 9m decompression stop, ascent time must be added to the bottom time.

"Several percent"? Is that true? So you mean more than one out of a hundred typical USN dives is probably going to involve DCS? I vaguely recall once reading something to that effect about the pure Buhlmann algorithm, i.e., with 100/100 GF.

For all of you whose curiosity regarding the history and derivation of dive tables has been piqued, I would recommend reading Deeper into Diving, Lippmann and Mitchell, 2nd edition, 2005. It covers tables by the USN, Buhlmann, DCIEM, BSAC, and DSAT/PADI. There is a short section on bubble models and tables including NAUI RGBM. The section on dive computers is way out of date. It would be great if this book was updated @Simon Mitchell

@Lorenzoid the USN tables were introduced to the Navy in 1955 and tested in 1956. Of the initial 564 dives, there were 26 cases of DCS, 4.6%. The tables were recalculated and then tested for repetitive dives in 1957. There were 61 profiles with 122 dives and 3 cases of DCS for a rate 4.9% of profiles and 2.5% of dives. The USN tables were published in the USN Diving Manual in 1957. DAN stats for 1988 indicate about 72% of recreational divers in the US treated for DCS were diving the USN tables within limits. In the 2008 USN Diving Manual, the USN tables were slightly modified with a decrease in the NDL at 70 and 80 feet.

The Naval Medical Research Institute pubished reports in 1985 (1% and 5%) and in 1997 (2.3%) on equal risk no decompression limits. I have reproduced some of the results along with USN and DSAT air NDLs

I have about 1200 dives using DSAT since 2002, many near NDL, about 5% light deco. I have had no suggestion of DCS, so far, so good

 

[scubadada]

I should have included Buhlmann ZH-L16C for @Lorenzoid