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

[uncfnp]

With most computers, it is impossible to carry enough gas to make it to the surface. You will always run out around 20 ft. But you wll be able to immediately surface when that happens.

In fact once the safety stop "ceiling" has cleared you could either stay there indefinitely or even return to depth? I would imagine though that the NDL at that point would be extemely short since the surface interval is essentially zero.

 

[boulderjohn]

With most computers, it is impossible to carry enough gas to make it to the surface. You will always run out around 20 ft. But you wll be able to immediately surface when that happens.

In my experience with recreational dives, if you are near NDL during the bottom portion of the dive and head for shallower depths, your NDL will often go to triple digits when you get much above 30 feet. If you watch the numbers change as you ascend, you will usually see a leap when you get above 2 ATA. When I used a Suunto, the NDL would change from numbers to two horizontal lines (- -). With other computers, it would show its maximum number of 99. I have completed a number of recreational dives in which my maximum depth was around 100 feet and my total dive time was more than 80 minutes, all because most of the dive was done in shallow water.

In fact once the safety stop "ceiling" has cleared you could either stay there indefinitely or even return to depth? I would imagine though that the NDL at that point would be extemely short since the surface interval is essentially zero.

Your NDL for a second dive with no surface interval would depend, as always, on the depths and times of the two dives. In the PADI table version of the OW course, students had to do a number of dive planning calculations using the tables. In one of the problems, they had to calculate the minimum surface interval required to do pretty reasonable dives. In the imperial version of the question, the correct answer is 4 minutes. In the metric version, the correct answer is 0 minutes.

 

[Bob DBF]

What constitutes recreational versus heavy drug use?

Can 'lite' heroin use be considered recreational?

Is 'lite' crystal-meth preferable to 'heavy' cannabis use?

Interesting turn, I didn't see that one coming.


Bob
---------------------
...missed the Summer of Love.

 

[lowviz]

Sidemount is not tech. It is permissible under PADI standards to do your OW training in sidemount. ...

Things were getting pretty loose back when I posted that. It was a one-liner that attempted to get the ball back somewhere near the playing field. Sidemount is not inherently tech, but it certainly allows one to do technical dives.

... [Sigh.] I don't know how many times I have had to tell you this. The PADI tables are not an adjustment of the U.S. Navy tables. ...

OK, how about we agree on what you wrote. I'll refrain from any further suggestions that PADI did anything to the navy tables: (Please expand boulderjohn's quote below)

... PADI Tables: Before PADI created its tables in the early 1980s, recreational diving was done almost exclusively using the U.S. Navy tables. Bühlmann's research had not yet been published, and the first Bühlmann-based tables were years away. The U.S. Navy tables were quite unsatisfactory for recreational diving because they used the 120 minute compartment to guide surface intervals, which meant that divers had to spend a very long time out of the water between dives. The Navy's decision to do that was made without any real testing, and it did not matter to the Navy since their divers rarely did more than one dive in a day. PADI's primary goal in creating their tables was to find a way to make recreational dive schedules more doable.

To this end they did extensive original research using hundreds of divers doing thousands of dives. As scubadada wrote in post #413 quoting Mark Powell's fine book, "The M-values used for the RDP were adopted from the Doppler bubble testing and tested by Dr Merrill Spencer and tested by Dr Raymond E Rogers, Dr Michael R Powell, and the colleagues with Diving Science and Technology Corp, a corporate affiliate of PADI. The DSAT M-values were empirically verified with extensive hyperbaric chamber and in water diver testing and Doppler monitoring." Their research was published in peer reviewed journals. The work was both extensive and expensive. Dr. Michael Powell is Dr. Decompression on ScubaBoard, and if you do a search through that forum you will find many threads in which he talked about the work they did. The PADI tables were thus based primarily on original research. They did not ignore previous studies, but they did far more than just adjust an existing table. When they were done, they were fully invested in the results and made them the basis for their open water instruction.

I bolded the part of your quote that seems to highlight the source of your consternation with me. Apologies to PADI if it appears that I'm not giving them full credit for their efforts and results.

... Yes, the DSAT algorithm used in many recreational dive computers is based on the original PADI research, but that research is now nearly 40 years old, and many of the other algorithms being used are based at least in part on newer research. PADI does not endorse any one computer algorithm, and it would be a mistake to do so since there is not anything close to universal agreement on which is best.

"Which is best" is the key phrase, here. How about: Which is most appropriate? (as the algorithm in a standardized diveable DC that is only intended for training OW/AOW students in the proper use of a DC)

... What if I do a dive to 90 fsw or so. I hit my NDL and come up to 75 fsw. My dc gives me some more time so I stay there until I again hit my NDL and come up to 60 fsw where I get more time. At some point I will be gas limited so tissue loading may not be that great but what if I strap on a set of doubles. Now I can really ride the NDL.

And that behavior would be in the realm of recreational NDL diving. DC's easily allow for these excesses, the same dive would be an awful lot of work using tables.

So it appears to me that we all pretty much agree that different DC's behave differently.

Which is another way of saying DC's handle tissue loading differently. So, for a series of repetitive NDL dives, one would expect that there exists one particular series of dives that leaves the diver with the worst tissue loading possible while still remaining within that DC's NDL rules. It would be interesting to both know what this series is (something to avoid) and just as interesting to compare various DC's based on each DC's worst repetitive dive sequence.

 

[boulderjohn]

Things were getting pretty loose back when I posted that. It was a one-liner that attempted to get the ball back somewhere near the playing field. Sidemount is not inherently tech, but it certainly allows one to do technical dives.

OK, how about we agree on what you wrote. I'll refrain from any further suggestions that PADI did anything to the navy tables: (Please expand boulderjohn's quote below)

I bolded the part of your quote that seems to highlight the source of your consternation with me. Apologies to PADI if it appears that I'm not giving them full credit for their efforts and results.

The part you bolded is: They did not ignore previous studies, but they did far more than just adjust an existing table.

You seem to think that means "PADI adjusted the Navy tables and then did a little more." That's not what it means at all. It means they did something very different and much more involved than merely adjusting an existing table. Let's put it in context. I was responding to your previous statement that said that all PADI did was make some adjustments to the Navy tables. In the full context of what I wrote, you will see that I described a full-length study of their own leading to new tables, not merely an adjustment of what went before. Of course they did not start from scratch, ignoring all research that was done in the roughly 80 years since Haldane, and that is what I said as well.

I really hate having to respond to everything you write this way. I know nothing will change your thinking. I am just afraid some readers with lesser experience will be misled by what you are saying in this thread..

 

[Basking Ridge Diver]

Which is another way of saying DC's handle tissue loading differently. So, for a series of repetitive NDL dives, one would expect that there exists one particular series of dives that leaves the diver with the worst tissue loading possible while still remaining within that DC's NDL rules. It would be interesting to both know what this series is (something to avoid) and just as interesting to compare various DC's based on each DC's worst repetitive dive sequence.

If I understand where you are headed and all the previous comments combined...

It seems more important to know your specific "limitation" or "physiological weakness" on that day that you use that specific DC.

So I still go back to - I want the longest NDL that I can pay for in a DC. Then I will dive the DC and determine if I need to add conservatism. Remember I am still in the recreational realm and wish to maximize my bottom time - that to me is the end game.

If and when I get the "niggles" or skin bends I may back off that setting on the DC. Until then I will stay hydrated as best I can and continue to stay in shape and when I am not feeling well - I just back off the NDLs shown.

 

[lowviz]

...//... I really hate having to respond to everything you write this way. I know nothing will change your thinking. I am just afraid some readers with lesser experience will be misled by what you are saying in this thread..

If you read my posts carefully, you will see that they are mostly observations and questions.

This is a social diving site, you won't find me on RBW, DS, or any of the like. Here, the intent is discussion.

I'm not spewing misinformation, however, you as a mod make that call. Now I'm taking up too much of your time. All set-up for a ban. I'll save you the trouble and mostly lurk for a while.

 

[RayfromTX]

If you read my posts carefully, you will see that they are mostly observations and questions.

This is a social diving site, you won't find me on RBW, DS, or any of the like. Here, the intent is discussion.

I'm not spewing misinformation, however, you as a mod make that call. Now I'm taking up too much of your time. All set-up for a ban. I'll save you the trouble and mostly lurk for a while.

As a scuba diver I am new but as a forum participant I have lots of experience and what I see in this thread is that there are those including you that push the discussion to the extreme to expand it and feel about for push back. This demands a response from those that feel it has strayed from the "truth". It can create fatigue among those that feel responsible for accuracy. More troubling are the instances in which a poster's comments are stretched or twisted to portray an unintended meaning. This is even more demanding of a response. I don't perceive John as angry or vindictive but he does seem to be more patient than most. Hundreds of posts back he stated that as a moderator he was recusing himself from that role because he had become a participant in the thread. Excuse me if I am intruding through ignorance into a place I don't belong and thank you for what has been, so far, quite informative on many levels.

 

[boulderjohn]

'm not spewing misinformation, however, you as a mod make that call. Now I'm taking up too much of your time. All set-up for a ban.

No, I don't make the call. In general, the SB staff does not vet the facts in a thread like this. We leave it up to people participating in the discussions to call people when they misstate the truth. Furthermore, when a moderator (like me) participates in a discussion, we miraculously lose all moderator powers for that thread. We do not moderate threads in which we participate, except for obvious and uncontroversial acts like removing SPAM or duplicate posts.

Dealing with misstatements can become an issue for staff, though. We do not allow "trolling." Here is the Wikipedia definition of a troll:

In Internet slang, a troll (/ˈtroʊl/, /ˈtrɒl/) is a person who sows discord on the Internet by starting arguments or upsetting people, by posting inflammatory,[1]extraneous, or off-topic messages in an online community (such as a newsgroup, forum, chat room, or blog) with the intent of provoking readers into an emotional response[2] or of otherwise disrupting normal, on-topic discussion,[3] often for the troll's amusement.​

If the staff were to get the idea that a person who persistently posts false information is indeed doing so intentionally for the purposes described in that definition, then some sort of moderation would be called for. Simply making repeated inaccurate statements, even the same ones over and over again, is not in itself grounds for any moderation, let alone a ban. If someone intentionally repeats false information for the purpose of provoking an emotional response, that would be different.

 

[Storker]

Now I'm taking up too much of your time. All set-up for a ban.

Don't be silly.

ETA: Or what @boulderjohn said.