PADI Deep Diver course- gas management

[boulderjohn]

Do you want to call it total ascent time instead?

You're doing a lot to dodge and weave vs just addressing why you think it's reasonable to not define a maximum exposure.

Your comments in this thread are moving step by step into the realm of the bizarre. Of course maximum exposure is defined. The biggest problem we are having is working our way through your verbiage, since you seem to be using words in a way only you can understand.

Maybe I am misunderstanding what you are writing, but you seem to be saying that the course should predefine the specific depths and bottom times of each dive rather than have the divers work those out with the instructor.

That reminds me of a problem I had when my former UTD/DIR dive buddies came to me for technical diving training, including trimix, and I had to determine at what point in the program I could cross them over. There is a chart for such cross overs for all the major agencies, but UTD was not on it because it was such a small agency with so few divers. I asked headquarters, and it took weeks of study before they got back to me. The answer was a crossover would be at a fairly low level, and the primary reason was that the UTD/DIR program dictated so much of this sort of thing, leaving little room for divers to work things out for themselves and make decisions.

I was immediately reminded of a case during that training when a diver was being reprimanded for a decision he made during a dive, and the diver started to explain, saying, "I was thinking that...." He was cut off by the instructor saying, "Dave, what I need you to do is stop thinking and just do exactly what I tell you to do."

 

[grantmac]

This is actually a relevant discussion since many dive computers when used in recreational mode take into account the safety stop when calculating NDL even though it's not strictly required.
Example is when using a Shearwater the SurfGF will go past the set GFHi without indicating that you have a required decompression stop. Chances are it would clear before you hit 3-5m but it might not (I don't dive it in Rec mode).
Since I don't use the RDP (I use military 1S tables if I go old school or min-deco GUE style) the question I have is whether the RDP also bases it's SurfGF on a stop at 3-5m.

 

[tursiops]

the question I have is whether the RDP also bases it's SurfGF on a stop at 3-5m

SurfGF had not been invented yet when the RDP was developed, but the RDP has mandatory safety stops if you pass 30m or are within 3 pressure groups of your NDL for any depth. See Info - The DSAT Recreational Dive Planner (RDP), 1994

 

[boulderjohn]

This is actually a relevant discussion since many dive computers when used in recreational mode take into account the safety stop when calculating NDL even though it's not strictly required.
Example is when using a Shearwater the SurfGF will go past the set GFHi without indicating that you have a required decompression stop. Chances are it would clear before you hit 3-5m but it might not (I don't dive it in Rec mode).
Since I don't use the RDP (I use military 1S tables if I go old school or min-deco GUE style) the question I have is whether the RDP also bases it's SurfGF on a stop at 3-5m.

All NDL algorithms assume that the diver will make a safe ascent, and that is included in the NDL. I have never heard that any computer changes the NDL with the assumption that a safety stop will be part of the ascent. I would welcome documentation showing that.

The RDP is based upon extensive research done about 40 years ago. The algorithm that research led to was designed by the team that did that research, Diving Science and Training, and it is called the DSAT algorithm.

The Buhlmann algorithm was created based upon the research led by Albert Buhlmann from 1959-1983.

A couple decades later, Erick Baker created the idea of Gradient Factors, a system for adding conservancy to the Buhlmann algorithm. It cannot be applied to the DSAT algorithm.

The SurfGF is a modern computer-based concept that did not exist in the past. It is a calculation of what your surface gradient factor would be if you were instantly taken to the surface--neither a safe ascent rate nor a safety stop included. It only applies to the Buhlmann algorithm.

 

[boulderjohn]

but the RDP has mandatory safety stops if you pass 30m or are within 3 pressure groups of your NDL for any depth

Just an added comment....

When the RDP was created, the use of safety stops was really not common. PADI's use of them was really the start of that trend. What they decided (in MY wording) was that for most dives done by what they called recreational divers, no safety stop was needed, for some deeper, longer dives, a safety stop was a very good idea, and for stops getting close to required decompression, it was a really, really good idea. That's my wording. They worked harder at their wording, and created endless confusion with the idea that some optional safety stops were mandatory.

If you go back 10-15 years ago, ScubaBoard probably had 1.3 zillion threads per year on "mandatory optional stops." Thankfully, the fact that almost everyone uses computers today has those debates much more rare.

 

[tursiops]

All NDL algorithms assume that the diver will make a safe ascent, and that is included in the NDL. I have never heard that any computer changes the NDL with the assumption that a safety stop will be part of the ascent. I would welcome documentation showing that.

The RDP is based upon extensive research done about 40 years ago. The algorithm that research led to was designed by the team that did that research, Diving Science and Training, and it is called the DSAT algorithm.

The Buhlmann algorithm was created based upon the research led by Albert Buhlmann from 1959-1983.

A couple decades later, Erick Baker created the idea of Gradient Factors, a system for adding conservancy to the Buhlmann algorithm. It cannot be applied to the DSAT algorithm.

The SurfGF is a modern computer-based concept that did not exist in the past. It is a calculation of what your surface gradient factor would be if you were instantly taken to the surface. It only applies to the Buhlmann algorithm.

Funny, but some of these posts are almost asking if the RDP is consistent with modern ideas and calculations. The question is almost backwards! Given that the RDP has been tested probably millions of times by people who mostly never heard of GF but were able to dive without problems, perhaps the question ought to be if the modern calculations agree with the RDP!

 

[inquis]

many dive computers when used in recreational mode take into account the safety stop when calculating NDL even though it's not strictly required.
Example is when using a Shearwater the SurfGF will go past the set GFHi without indicating that you have a required decompression stop. Chances are it would clear before you hit 3-5m but it might not

I'm not aware of any computers that assume/consider a safety stop in their NDL calculation. All Shearwaters, for example, do not. Yes, surfGF can slightly exceed GFHigh without displaying a mandatory deco stop, since an ascent at 30 fpm is assumed.

 

[crofrog]

SurfGF had not been invented yet when the RDP was developed, but the RDP has mandatory safety stops if you pass 30m or are within 3 pressure groups of your NDL for any depth. See Info - The DSAT Recreational Dive Planner (RDP), 1994

Ok, so to back our way into the original topic of this post.

With RDP procedurally requiring stops on some dives, is there gas planning as part of the course that takes into account the need to make these stops?

Your comments in this thread are moving step by step into the realm of the bizarre. Of course maximum exposure is defined. The biggest problem we are having is working our way through your verbiage, since you seem to be using words in a way only you can understand.

Maybe I am misunderstanding what you are writing, but you seem to be saying that the course should predefine the specific depths and bottom times of each dive rather than have the divers work those out with the instructor.

If you're not defining as part of the course standards Maximum Depth AND Maximum Time at that depth then you are not defining the maximum exposure. I do not think the specifics should be defined per dive, but I think course limits should be in place.

Saying "follow the computer" leaves a lot up to individual computer setup and algorithm selection. Unless you define allowable algorithms and computers.

 

[tursiops]

With RDP procedurally requiring stops on some dives, is there gas planning as part of the course that takes into account the need to make these stops?

If you're not defining as part of the course standards Maximum Depth AND Maximum Time at that depth then you are not defining the maximum exposure. I do not think the specifics should be defined per dive, but I think course limits should be in place.

Saying "follow the computer" leaves a lot up to individual computer setup and algorithm selection. Unless you define allowable algorithms and computers.

You can't a priori state the limits because it depends on the students, the gas, the site, the conditions. All you can say a priori is you can't exceed 130 ft/40m, nor NDL, nor 60 f/min or what your computer's ascent rate is. The students are likely to have different computers; maybe different gases. So you find out what the limiting case is. that is, whose NDL is the shortest, whose ascent rate is the slowest, and that becomes the limit for all in the class. Then you discuss gas usage. Again, the person with the highest SAC becomes the limiting case for the class; if they don't know their SAC (and they should by this class) call it 0.7 cu/ft/min to cover most people. You work out gas usage, with a comfortable reserve (please, let's not dwell on that!), and then maybe have to back off further on the max depth or the max time to meet the gas usage requirements. The point is to have the students learn how to do this, NOT to predesign a perfect dive and have them execute it; they learn nothing from that.
Now, perhap all instructors don't do it that way; all I can say is how it is intended to be done and how I did it as an instructor.

 

[Sebs]

I did my deep diver in Dahab with a Tech Instructor and specifically told him I wanted to do a lot of gas planning because that's what I was interested in. So we did that and I went away feeling like it was the best course I've ever done.

So I would say: Find an instructor who will teach the course how you want it to be taught. Especially with something like Deep you really need to be on top of gas requirements. Who gives a **** if the color red disappears as you go deeper when you're sucking down a tank in 5 minutes.