Deco dive plan sheet

[Rick Murchison]

It is worthwhile to me to keep those "antiquated" (the latest update/mod, found in the US Navy diving manual rev 6, is all of three years old, an antique for sure!) navy tables in my back pocket. They can keep me alive if I have to blow off all those fancy deep stops. I cannot overemphasize the peace of mind gained by doing the manual plan with the navy tables and having that fall-back position on hand for a reasonably safe deco should I need to get shallower quicker than my computer generated plan.
A little gas goes a very long way indeed at 30' and shallower... and it's a whole lot easier to get more gas delivered there, too.
I just don't see any down side to doing that bit of extra planning.

Rick

 

[Cave Diver]

Just imagine what will happen when I finally take a trimix class.

 

[Rick Murchison]

...I don't think flying a computer blindly is a bad idea...

Really?
I don't think you think you don't think flying a computer blindly is a bad idea, no, I think you think you do think it *is*... don't you?

Rick

 

[ucfdiver]

Really?
I don't think you think you don't think flying a computer blindly is a bad idea, no, I think you think you do think it *is*... don't you?

Rick

Yeah, my bad.

Being a poor/starving recent college graduate, I don't even OWN a computer, let alone fly one blindly

 

[HowardE]

I always dive my computer (Shearwater) when I do deco dives (does that make me blindly follow it??). I look at a dive plan on vPlanner or MV Plan, but save that in my pocket in case my computer fails, which is unlikely. Why would I dive a table vs a computer? Tables are limiting.

 

[ucfdiver]

I always dive my computer (Shearwater) when I do deco dives (does that make me blindly follow it??). I look at a dive plan on vPlanner or MV Plan, but save that in my pocket in case my computer fails, which is unlikely. Why would I dive a table vs a computer? Tables are limiting.

What dives are you limited by tables?

Our LDS owner is doing dives to depths of 300ft with run times in excess of 30 hours and using tables, so I've got a ways to go.

 

[HowardE]

Dive times are limiting using tables... do the math.

Sure... you can plan a dive to 500 feet using dive tables... but how's the runtime compared to using a computer? Did you descend at the exact rate on the table? Because if not... then you're off the table. right?

Then you don't have to cheat your deco by choosing the algorithm that gives you the shortest deco time, but rather, you can use a gradient factor that you've determined is good for your body, and optimize your decompression based on actual dive time, and not some theoretical time at some averaged depth.

 

[rx7diver]

Once at a technical level, you need to know the following-

• How much gas do I need to complete my objective (20min @ 150ft, 3000ft swim into a 90ft deep cave @ 50fpm, etc)?
• How much deco gas do I need?
• How much gas do I need to get an OOA buddy to his first gas switch?
• How much gas (and what type) do I need to cover a failed deco bottle?
• Where should I place this gas for maximum safety?

Tables really don't teach you this. Vplanner/Decoplanner and similar software is a way to start these conversations with current deco theory as your starting point. Further to the point, these software even show graphs of tissue loading over time to show students all 16 compartments, the falloff of tissue loading as you near saturation, the exponential off gassing at gas switches, etc. This helps you visualize the mathematical model representing your body. Exporting to excel, you can witness how models cross each other (switch which has longer deco) as you add helium or bottom time.

Ucfdiver,

I agree that software is very convenient for planning tech dives. But tech dives can be planned very thoroughly using pencil and calculator, too (though not nearly as effortlessly). I'm sure you know this.

And I personally would prefer a set of empirically derived and empirically verified tables to plan my dives with, than software which uses algorithms based mostly on the most modern/advanced decompression theory! BTW, I never found much use for those pretty graphs which display simulated inert gas loadings in theoretical compartments.

Safe Diving,

Ronald

 

[ucfdiver]

Ucfdiver,

I agree that software is very convenient for planning tech dives. But tech dives can be planned very thoroughly using pencil and calculator, too (though not nearly as effortlessly). I'm sure you know this.

I've calculated profiles by hand to help think my way through how to program the algorithms. Nearly every time I made a mathematical error somewhere along the way. Hopefully no one does this outside of academic exercise for that reason.

 

[rx7diver]

I've calculated profiles by hand to help think my way through how to program the algorithms. Nearly every time I made a mathematical error somewhere along the way. Hopefully no one does this outside of academic exercise for that reason.

Back when I was doing "modest" deco dives (say, for 200 ffw, plus-or-minus, with 20-25 minute bottom tmes), I would always plan these by hand. I would check my hand solutions by doing my calculations a second, different way. And then check again by comparing my solutions to my buddy's hand-calculated solution.

Whenever I would check my solution against a software-computed solution, I would sometimes observe significant differences. Closer inspection invariably revealed that the software made some assumption here or there that my hand solution did not make. Being a former computer programmer (my first degree and my first job), I *know* there are hidden assumptions coded into computer programs. When I generated my solutions by hand, I was more confident about the presence or absence of hidden assumptions.

I continue to believe there is a great deal of value in planning tech dives by hand.

Ronald