Deep Dive Strategy

[-hh]

Wow. Thanks for all the info.

-hh, I think your discussion can be summarized in the bar graphs of the changing compartment saturations, no?

Yes, it can be displayed as a series of bars in a graph (one bar per compartment in the model), and since each compartment has a different M-value limit, you can plot a curve of these M-value limits, which is shown the display of this photo of an old ORCA EDGE dive computer:

http://www.divetable.de/bilder/Museum/edge1.jpg

Unfortunately, that illustration doesn't have any N2 loadings on it, so there's no black pixel bars that illustrate each compartment. Anyway, the way that this graphical interface works is that you'll have a bunch of bars and you watch ALL of the bars and make sure that they ALL stay "beneath the curve" to keep it a no-stop (no-deco) dive profile.

FWIW, several dive computers these days have a single graphical depiction of your overall N2 loading. The problem is that you can't obviously tell which compartment this bar represents, for what it is is the "worst compartment at that moment", or your controlling compartment.

That's why I personally think the simulation software is so much better to learn from than just the tables. You can get a better sense of some very complex interactions. But again I'm just guessing.

I think you're spot-on. Youre conciously choosing to make the effort to understand the complexities inherent to the model, rather than to blindly rely on the "magic" of a Table or Electronic Black Box.

Anyway, I'm still not clear on the practicality of managing those dives where NDL, not SAC rate is a controlling factor.

its two things.

First, it comes with the territory: if you want to dive deeper, it becomes a factor to manage, just like Narcosis and the Oxygen Clock.

Second, it is because of the complexity of the interaction that we've developed tools to help simplify this management task.

For example, the simplest tool is a Dive Table. It has boiled the many variables down into needing to only track your maximum depth and total dive time. Its not necessarily efficient, but it is simple to use.

A dive computer is a step up in complexity - its essentially a real-time Table calculator, and better resolution of your dive profile translates into more allowed overall dive time (at least for multi-level dives), and we can say that bottom time is a measure of efficiency.

When you drop down to 90ft. for 10 or 15 minutes, and your NDL is down to 5-10 minutes, and you're trying to figure out how to maintain a no decompression dive, you need to have some sense of how to gain NDL time while at the same time not ascending too quickly, and not ultimately running out of air, etc.

The simple answer you're probably looking for here is that anytime that your NDL gets too low, you're going to ascend to a shallower depth in order to "gain back" (in a manner of speaking) more dive time, until you're either low on gas or you're back at the surface.

The more complex answer is that this practice is known as being "chased up" by your NDL, and it is often considered to be a bad dive practice, because it tends to cause several compartments to be loaded up to close to their NDL instead of just one or two compartments, which represents a higher DCS risk exposure. Hence, we have a trade-off to contemplate.


-hh