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

[KenGordon]

My BSAC tables came today. Page 9, level 1, greater than 984 millibar.

I had to sit down and take a breath. I get NDL's. FIVE sets of them depending on what I want my surfacing code to be!

So, an NDL is directly related to what you want to do later? (@boulderjohn alluded to this in an earlier post) For BSAC, NDL doesn't seem to have the least bit of "cross this line and die" flavor. I'm pretty sure of that, I read all the way to page 30. OMG, what a revolutionary concept! Now I want to compare the top-shelf sport NDL's to the supposedly aggressive BSAC's most aggressive NDL and the US Navy NDL's.

They are all copyrighted, but I can legally curve fit them to 0.99+ r^2. Did that. See pic.

View attachment 388676

Bottom line, BSAC is CONSERVATIVE on the first dive for depths above 130 feet. Show me where I'm wrong. My point is made. If you enter deco in a planned and light manner, you should be fine. Best post of this thread: "Riding your Computer Up" vs. "Lite Deco"

BSAC is truly ahead of the game. Pick an NDL that works for you and run with it all the way to level 4 altitude tables.

But then, altitude doesn't have any effect on dive planning. Does GUE/UTD still profess that???


OH, one last observation. IANTD RGBM and PADI RDP are both EXACTLY THE SAME. Other than lawyers, can anyone explain this?

Maybe you should say 'shallower than 130' rather than 'above 130' for the sake of the easily confused such as myself.

I think you should also look at stop times and multiple dive days before deciding whether the tables are conservative or not. Comparing against systems people commonly use might be good too.

The 88 tables came out about the time computers started to be widely available and affordable, so for most of their time they have not been the primary source of decompression profiles. This means we can't really claim a lack of bent people was ever due to them.

 

[DevonDiver]

Bottom line, BSAC is CONSERVATIVE on the first dive for depths above 130 feet. Show me where I'm wrong. My point is made.

What's mind blowing about a model that gives you ample bottom time in the expectation that you won't be doing further repetitive dives?

That's was the norm before PADI chopped things down to better suit the typical habits of recreational divers (vacation diving etc)....and meant a more conservative first dive was the trade-off for repetitive dives with short-moderate surface intervals.

That was a trend replicated by other subsequent recreational diving algorithms.

Obviously, if tech/deco diving... where dives ideally have a significantly longer surface interval and repetitive dives are limited (2 max per day?!), then longer half-times and a more permissive initial dive are preferable.

That also, incidentally, should better suit the diving habits of club-type, dive-at-home (non-vacation) divers.

Taking such tables/algorithms on a typical 5 dives-a-day liveaboard would be frustrating though..

 

[KenGordon]

Taking such tables/algorithms on a typical 5 dives-a-day liveaboard would be frustrating though..

This is a good point, especially since these particular tables only allow for three dives a day. Tables tend to be part of a system.

 

[dmaziuk]

Looks like the keyword here is system: the way many seem to see "lite deco", "NDL", "tables", etc. is that it's some number set in stone and if you exceed it YOUR GONNA DIE!!! Leading to all kinds of hilarity, like "buy a DSAT computer or you will have your dives cut short" for one example. Training programs that give you no hint that a systematic approach even exists are definitely not helping.

 

[lowviz]

Maybe you should say 'shallower than 130' rather than 'above 130' ...//...

Apologies, I see the confusion. Especially so when I start out with a reference to altitude.

Your suggestion is a great intro to what I have to say about how my thinking has changed in light of several posts in this thread. It is all about confusion, right?

What's mind blowing about a model that gives you ample bottom time in the expectation that you won't be doing further repetitive dives? ...//...

The presentation is the 'mind blowing' part if one comes from a PADI culture.

Look at your first PADI tables. Gray goes to black as one approaches the dreaded DECO cliff. Go further and you are off the charts, no lawyer can save you, you did it to yourself. Never, ever go there, we told you...

It is hard for PADI to get a full day's dives in with all that drama, so we'll just make an optional 'Safety Stop' a mandatory 'Safety Stop' Yeah, that's it. Fun with names. You aren't really in deco, you just have to do this because we say so...

... That's was the norm before PADI chopped things down to better suit the typical habits of recreational divers (vacation diving etc)....and meant a more conservative first dive was the trade-off for repetitive dives with short-moderate surface intervals. ...//... That also, incidentally, should better suit the diving habits of club-type, dive-at-home (non-vacation) divers.

Let's do this accurately. The casual reader can bail out here, this will run long...

I don't dive tables, I never will. However, I contend that they (as a collection) offer great insights. In addition, yes I can compare the 'conservatism' of a first N2 unloaded dive across various agencies. Why can't I? Doing so allows me to see the thinking behind their various approaches. What they are pushing and where they are sandbagging for subsequent dives.

Insights gained:

The US Navy Air Tables rev 7 (US NAT-7) will not allow for a 'simple' curve fit. Restating this, there isn't a simple mathematical equation that 'nails it'. I can only believe that this is due to adding slower tissue loading along with the fast. If it were only all about fast tissues (one tissue compartment), it would look like PADI's curve. You can see this in the graph below. I made a best 'simple equation' fit to US NAT-7 and other than being more aggressive, it nails PADI's curve. I know what they did.


Enter BSAC.

The 'given' here seems to be that their local diving is rather deeper as set by local conditions. The BSAC curve is most interesting. It seems to be saying to keep well away from the slower compartments, notice the nearly identical start to their curve. But, and it is a big 'but', they reclaim all that conservatism at depth.

So back to 'mind blowing'. Table A, Level 1 page 9 (BSAC 88) teaches mandatory decompression stops at 6 and 9 meters. Up to 20 minutes. In addition, you have a choice of NDLs that you can pick from to suit your days diving. From one and done to as many as possible. No scare tactics. 'This is what you have to do to return safely'.

So now back to my premise.

If I directly surface at the worst point in my dive using US NAT-7 and a proper ascent rate, I'll probably be OK. So now I have a limit on my bottom time. Next, I poke that limit into my overly conservative DC and just follow my DC's recommended deco schedule to return from that bottom time.

I don't need or want an aggressive DC to keep me down with the pack. Just know your limits, plan your gas, and do your stops. It isn't the end of the world if you can't do/complete your stops. I suppose that this all comes down to the deco scare tactics that I was taught early on.

...Taking such tables/algorithms on a typical 5 dives-a-day liveaboard would be frustrating though..

I could well imagine. I don't dive tables, never intend to. They don't even work as a back-up to a DC.

They DO allow you to pick an intelligent limit to 'lite deco'.

 

[KenGordon]

Apologies, I see the confusion. Especially so when I start out with a reference to altitude.

Your suggestion is a great intro to what I have to say about how my thinking has changed in light of several posts in this thread. It is all about confusion, right?
The presentation is the 'mind blowing' part if one comes from a PADI culture.

Look at your first PADI tables. Gray goes to black as one approaches the dreaded DECO cliff. Go further and you are off the charts, no lawyer can save you, you did it to yourself. Never, ever go there, we told you...

It is hard for PADI to get a full day's dives in with all that drama, so we'll just make an optional 'Safety Stop' a mandatory 'Safety Stop' Yeah, that's it. Fun with names. You aren't really in deco, you just have to do this because we say so...

Let's do this accurately. The casual reader can bail out here, this will run long...

I don't dive tables, I never will. However, I contend that they (as a collection) offer great insights. In addition, yes I can compare the 'conservatism' of a first N2 unloaded dive across various agencies. Why can't I? Doing so allows me to see the thinking behind their various approaches. What they are pushing and where they are sandbagging for subsequent dives.

Insights gained:

The US Navy Air Tables rev 7 (US NAT-7) will not allow for a 'simple' curve fit. Restating this, there isn't a simple mathematical equation that 'nails it'. I can only believe that this is due to adding slower tissue loading along with the fast. If it were only all about fast tissues (one tissue compartment), it would look like PADI's curve. You can see this in the graph below. I made a best 'simple equation' fit to US NAT-7 and other than being more aggressive, it nails PADI's curve. I know what they did.

View attachment 388686
Enter BSAC.

The 'given' here seems to be that their local diving is rather deeper as set by local conditions. The BSAC curve is most interesting. It seems to be saying to keep well away from the slower compartments, notice the nearly identical start to their curve. But, and it is a big 'but', they reclaim all that conservatism at depth.

So back to 'mind blowing'. Table A, Level 1 page 9 (BSAC 88) teaches mandatory decompression stops at 6 and 9 meters. Up to 20 minutes. In addition, you have a choice of NDLs that you can pick from to suit your days diving. From one and done to as many as possible. No scare tactics. 'This is what you have to do to return safely'.

So now back to my premise.

If I directly surface at the worst point in my dive using US NAT-7 and a proper ascent rate, I'll probably be OK. So now I have a limit on my bottom time. Next, I poke that limit into my overly conservative DC and just follow my DC's recommended deco schedule to return from that bottom time.

I don't need or want an aggressive DC to keep me down with the pack. Just know your limits, plan your gas, and do your stops. It isn't the end of the world if you can't do/complete your stops. I suppose that this all comes down to the deco scare tactics that I was taught early on.

I could well imagine. I don't dive tables, never intend to. They don't even work as a back-up to a DC.

They DO allow you to pick an intelligent limit to 'lite deco'.

I think you ought to completely explain what you mean about a choice of NDL. I think I know what you mean - being which tissue code you come out at, but you might mean which table you start with.

As to your premise... you are essentially diving the navy tables but usually taking a longer ascent by your computer. Now, that is fair enough as a bail out plan but keep in mind that the navy tables are really for the fit and young so if that is not you and you have any of the other compounding risk factors you might want to back off from them a bit. Also I am not sure off the top of my head as to the impact of a slow ascent rate on those but it maybe that running up to those navy NDLs and then doing a slowish ascent results in actual (navy) deco.

Another, rather easier to justify in my opinion, way to the same thing is to have two plans with MultiDeco. One is the bail out no stop plan, the other the plan to actually dive. This way you can set likely ascent rates. If your bail out assumes an AS ascent with a buddy it is unlikely to be as per the specified navy rate.

The trouble with all of this is that you cannot really know ahead of time what your body is going to do with that bail out ascent. Compared to just diving within the NDL of your computer that is higher risk.

BTW, the tables do not teach how to do these dives. The lectures and open water lessons do that. The tables do have the information about how to drive the tables though. It is moderately complicated so the tables contain instructions. I would be genuinely interested to know if you can figure out how to do the altitude planning, and especially travel after diving, from the instructions.

Of course if you want to have proper fun you should order the Nitrox tables and the Ox-Stop (accelerated deco) tables. The latter are particularly entertaining.

 

[boulderjohn]

The presentation is the 'mind blowing' part if one comes from a PADI culture.

Look at your first PADI tables. Gray goes to black as one approaches the dreaded DECO cliff. Go further and you are off the charts, no lawyer can save you, you did it to yourself. Never, ever go there, we told you...

It is hard for PADI to get a full day's dives in with all that drama, so we'll just make an optional 'Safety Stop' a mandatory 'Safety Stop' Yeah, that's it. Fun with names. You aren't really in deco, you just have to do this because we say so...

It is really hard to know what you are actually saying here with the combination of sarcasm, hyperbole, misinformation and pure nonsense.

 

[lowviz]

...//... if you want to have proper fun you should order the Nitrox tables and the Ox-Stop (accelerated deco) tables. The latter are particularly entertaining.

Sincere thanks for your post, Ken.

There is a lot subtext in there. I'll need to assimilate it before I attempt an answer.

It is really hard to know what you are actually saying here with the combination of sarcasm, hyperbole, misinformation and pure nonsense.

Well, you picked the one little part of my post that did contain a bit of intended sarcasm. Nice to know that I'm being so closely monitored. I believe that it remained within the TOS.

The intent, in an attempt at a more British style of humor, was to highlight the differing cultures behind PADI and BSAC. Nothing more. I'm neither a POV nor an agency warrior, I love choices. I'll pick what works for me and hold no hard feelings toward what remains.

Competition keeps everyone honest. One of my core skills is the ability to type faster than I can think. I'll strive to keep this in check as I know that you are watching...

 

[stuartv]

Looks like the keyword here is system: the way many seem to see "lite deco", "NDL", "tables", etc. is that it's some number set in stone and if you exceed it YOUR GONNA DIE!!! Leading to all kinds of hilarity, like "buy a DSAT computer or you will have your dives cut short" for one example. Training programs that give you no hint that a systematic approach even exists are definitely not helping.

Seeing as how this is the Advanced forum, not the Technical, I think this modification to your statement actually makes it correct and appropriate:

NDL is a number that is set in stone by whatever computer or tables YOU choose to use and if you exceed it you will be in violation of your training (presuming we're addressing someone who has no deco training, of course - and we ARE in the Advanced forum, here). So, buy a DSAT computer if you don't want your dives cut shorter than they have to be, while staying with the bounds of your training.

It seems to me that the existing PADI, SDI, SSI, et al, OW training programs are providing a very systematic approach. One with very clear, black and white lines. One that is, apparently, producing a lot of divers who are diving with very very few cases of getting DCS. It's just not very flexible. Though modern computers have certainly made it a lot more flexible than it was before.

The (presumably) quite rare cases of a diver getting hurt because they got too close to their NDL and freaked out don't seem (in my relatively uneducated on the statistics mind) to merit making any changes to the way things are done. People are not getting hurt because of that particular issue in any remotely meaningful numbers (I don't think).

 

[lowviz]

...//... NDL is a number that is set in stone by whatever computer or tables YOU choose to use and if you exceed it you will be in violation of ...

In violation of what YOU initially chose before the splash. Well stated, NDL is a limit. It has to be a hard, exact, and well-defined limit or we can blow it off and continue to rationalize further and further unsanctioned forays into deco land.

...//... So, buy a DSAT computer if you don't want your dives cut shorter than they have to be, while staying with the bounds of your training.

That position statement has the taste and feel of a 'cheat'. Is that how the agencies train these days?