Deco dive plan sheet

[netmage]

Tim, using V-planner is just as easy as using a spreadsheet.

Even with the formulas - Not if you start w/ a blank one.....

 

[Jax]

I admit, I have a spreadsheet for dissimilar tank gas matching on my phone.

:ssst:

 

[Randy43068]

I admit, I have a spreadsheet for dissimilar tank gas matching on my phone.

:ssst:

I suppose it's an Iphone no less.

 

[Jax]

HTC, thank you!

 

[netmage]

I admit, I have a spreadsheet for dissimilar tank gas matching on my phone.

:ssst:

Is it that hard to remember 6/7/8....?

 

[rongoodman]

So is plugging and chugging numbers into Vplanner (or whatever) what passes for teaching technical dive planning....?

While I certainly appreciate the ease of these tools, there is something about doing it the hard way during class and struggling over understanding the concepts you gain in doing the work long hand.....

-Tim

I can do all the various calculations by hand, and Dayo knows it. When it comes to actually planning a deco schedule to get my old body out of the water, I'm more interested in current thinking, not the Navy tables.

 

[Randy43068]

I can do all the various calculations by hand, and Dayo knows it. When it comes to actually planning a deco schedule to get my old body out of the water, I'm more interested in current thinking, not the Navy tables.

I'd think most people would agree with that.

 

[netmage]

I'd think most people would agree with that.

Cept Jax.....

 

[Jax]

Cept Jax.....

Now why do you say that . . . ?

 

[lowviz]

..............C'mon, guys, he's teaching it all - he wants a thorough understanding of the eaches and the processes, ...................

Noticed that.

Can't add much to what has been said other than this:
The way that we are taught to calculate EAD is one of my pet peeves. Look at that formula, is there anything in it that would cause you to remember it accurately? Same with the diagram. -Lose the Pt, lose the diagram. Both complicate one’s ability to see what is actually going on.


Below is copied something I made up when I had to explain EAD to someone really struggling with the concept. This post is very long but I remain hopeful that it is also very easy to follow and comprehend.


Another way to look at EAD:
ATA is everything, know it. ATA is all of the pressures that you experience at your given depth. ATA is pressure.

ATA = (D/33) + 1

“D” is the true depth from the surface in feet.
Rounding down to the nearest foot is close enough.

“33” converts “D” (in feet) to atmospheres.
Don’t take my word for it, you can calculate a better number if you are really, really, really bored:
http://unesdoc.unesco.org/images/0004/000461/046148eb.pdf
http://www.srh.noaa.gov/jetstream//ocean/images/avg_salinity.pdf
However, 33 for seawater or 34 for fresh water will be close enough.

“1” is the pressure supplied by the air above us
1 is close enough.
​

Second concept:
In a mixture of gasses under pressure, each gas acts just like it would if pure and at a pressure that is lowered so that it corresponds to its fraction of the mix. So if I’m breathing 30/70 (O2:N2) at 60 psi absolute, the nitrogen is acting like it is pure and at 70% of 60 psi or 42 psi absolute. So the nitrogen partial pressure (at the depth in question) is 42 psi absolute. We just need this concept, won’t ever solve for partial pressures either. Just remember that the partial pressure for a gas in the mix is the total pressure times the gas’s fraction.

One last concept:
EAD is about nitrogen, not oxygen, so we use 0.78 for nitrogen’s fraction in air. (Could also use the less correct 0.79 if you want to include all the trace junk other than oxygen and nitrogen. )


Don’t need anything else so let’s do an EAD calculation using what we know:

EAD calculation, state the problem:
I’m breathing something other than air at a given depth and getting a nitrogen effect. If I was breathing air, what depth would I have to be at to get the same nitrogen effect? Let’s call this ‘theoretical’ depth the equivalent air depth, or EAD.

EAD calculation, state the solution:
For nitrogen to act the same on us in either case, its partial pressure has to be the same in either case. We don’t even need to know what the partial pressure is. All we have to do is to make the partial pressure equations equal to each other. We already know that partial pressure is pressure times gas fraction.

EAD calculation:
PressureAtDepth * FN2 = PressureAtEquivalentAirDepth * 0.78

PressureAtDepth is ATA. ATA = [(D/33) + 1] This is the very first thing we did. ATA, you know that.

PressureAtEquivalentAirDepth should now make sense, it is [(EAD/33) + 1]

Just plug these two pressures in and you get:
[(D/33) + 1] * FN2 = [(EAD/33) + 1] * 0.78

Done. Don’t rearrange anything. Plug in the values for “D” and “FN2”. Do the easy math first then solve for EAD.



Jax:
If you first do the algebra and solve the equation for EAD, you will get the equation at the top of your page. (Note that Pt = D/33, but never needed Pt)

The real value in understanding something well is that you can often use it in other ways. I dive EAN28 a lot. I want to know how I will feel on air at a depth that I normally use 28. Simple, put air into the left side of the equation, and on the right side replace EAD with E28D and replace 0.78 with 0.72. That gives the depth on EAN28 where I will feel the same as the depth that I'm planning to use air.

EAD calc, no prob. You own that puppy.