Article: THE FIVE WAYPOINTS AND SIMPLE ASCENT BEHAVIOR

[gcarter]

Steve-

Interesting read. I LOL's when I saw this, as I read your book over Christmas *, but hadn't yet bothered with the last chapter - I don't ever expect to do any deco diving. I actually read it just last night. Timing, as they say, is everything.





* Highly recommend. Even as a new diver, not a tech diver, I got a lot out of it. My son is reading it now, and when he is done I will be giving it a re-read before getting back in the water this spring. Godd job!

 

[DiveNav]

-click on Thread View link below and then scroll down to my post for pdf attachments.....

Thank you.
I actually took the RD class some time ago and I had already Baker's article on Deep Stops .... basically he is saying "use Gradient Factors" ..... and we do have GF implemented in divePAL

Still, I can't find the magic wand .... but I have a feeling I am getting closer

In re-reading Baker's article this passage stood out:

Within the context of the dissolved gas model, the deepest possible decompression stop for a given profile can be defined as the next standard stop depth above the point where the gas loading for the leading compartment crosses the ambient pressure line.
​

But, where is this magic deep stop?
And, is GF really the best way to find it?

Yesterday my team gave me a nice addition to divePAL that I think will come handy in my quest.

My first test was to analyze a reference dive with ZH-L16C and GF 100/100 and .... surprise .... surprise .... the resulting graph is a clear visual demonstration that deeper stops are a good idea.
Why? Just look at the image below.
At my first stop (12m) there is a wopping 2.81atm overpressure gradient in C2 (that is still sitting at 40.1m). That seems a lot to me.
The other interesting factor in this graph is the almost artistical efficiency of the ZH-L16C algorithm; do you see how the leading compartments change in progression as the diver is ascending?

​

So, ascending too shallow it seems to be not a good idea.
Where do we stop then?
Are the stops provided by GF the best one? Let's find out.

In the next test I will analyze the same reference dive with GF 15/85.

I will be back.

Alberto (aka eDiver)

 

[Doppler]

Steve,

Great article, but incredibly conservative. I have made in excess of 15,000 dives now. Most of those dives were made with a rigorously controlled ascent rate of 60 fpm and no "safety" stop, with no ill effects. All of your concepts aid in understanding what is going on, but I really question the need for either slowing one's ascent rate to 10 fpm or making a "safety stop." The only change that I made (until the new revision of the Navy tables) was being an early adopter of deep stops and faster (120 fpm) ascents to my deep stop.

BTW: the initial purpose of "safety stops," as explained to me by Pilmanis, was to slow recreational divers down (according to Egstrom, they were ascending in pre-computer/ascent meter days at 100 to 150 fpm) and to assure that they did the last ten feet with a higher degree of control, instead of accelerating through those last few feet and popping to the surface.

Thanks a bunch... no argument at all about the level of conservatism... although I must admit that as time passes it becomes more and more obvious to me that it's a good idea to modify my personal dive agenda.

Also concur on the original purpose of safety stops, but forgive me for injecting a little poetic license... cheating a little but the intent behind it is much the same. Recently watched a boat-load of divers doing bounce dives to about 130 and their average ascent rate was far from optimal... not saying they are typical but I have learned to tune-out the distant sound of PDC ascent alarms!

Stay well.

 

[Kevrumbo]

Thank you.
I actually took the RD class some time ago and I had already Baker's article on Deep Stops .... basically he is saying "use Gradient Factors" ..... and we do have GF implemented in divePAL

Still, I can't find the magic wand .... but I have a feeling I am getting closer

In re-reading Baker's article this passage stood out:

Within the context of the dissolved gas model, the deepest possible decompression stop for a given profile can be defined as the next standard stop depth above the point where the gas loading for the leading compartment crosses the ambient pressure line.
​

But, where is this magic deep stop?
And, is GF really the best way to find it?

Yesterday my team gave me a nice addition to divePAL that I think will come handy in my quest.

My first test was to analyze a reference dive with ZH-L16C and GF 100/100 and .... surprise .... surprise .... the resulting graph is a clear visual demonstration that deeper stops are a good idea.
Why? Just look at the image below.
At my first stop (12m) there is a wopping 2.81atm overpressure gradient in C2 (that is still sitting at 40.1m). That seems a lot to me.
The other interesting factor in this graph is the almost artistical efficiency of the ZH-L16C algorithm; do you see how the leading compartments change in progression as the diver is ascending?

View attachment 118601
​

So, ascending too shallow it seems to be not a good idea.
Where do we stop then?
Are the stops provided by GF the best one? Let's find out.

In the next test I will analyze the same reference dive with GF 15/85.

I will be back.

Alberto (aka eDiver)

Here's your theoretical basis for a complete and comprehensive dissolved & free phase bubble mechanics model: an early 1990 article by Bruce Weinke on the RGBM (http://www.divetable.de/skripte/rgbm_params.pdf).

Actually, the applied empirical & practical methods described here and elsewhere (Ratio Deco) are adequate, easier to understand and implement. . .

 

[faze]

The only problem with articles like this is not enough sport divers think they are relevant! Great article and very easy to digest.

Thank you