Graph of Air vs Nitrox vs Tank Limit

[Stone]

If you use Microsoft Excel and are interested in seeing (or downloading) a graphical representation of NDL vs Depth for Air, EANx32, and EANx36, go to ( http://www.magnificentrelief.com ). I have just added a link (last dive flag on the home page) to a location where I will start putting dive-related down-loadable documents.

In addition to plotting the gasses, I plotted a line which represents a single 80 cf tank of breathing gas. The user can change a single number to make the line represent his or her gas consumption. For example, the number <1> represents "average" gas consumption. If your gas consumption is less than "average", use a number less than <1> like <.8> or <.9>. If your gas consumption is better than average, use a higher number (I use <1.2> ). Change the number to <2> and the line would represent an "average" person using doubles.

This is the first time I've put an Excel file on my website, but it worked O.K. when I tried it. Internet Explorer lets you "right click" on the file and save the document on your computer so you can open it later.

 

[bash]

I'd never bothered to set up something like that... but it's verrry intersting.

Thanks for posting it.
-bash

 

[Fishkiller]

Thanks for the timely post , I just returned from my class ans was wondering about the relation and

Thank you

 

[WetDane]

Interesting -
Could you define what you average DCR is based on?
Also - a question - how would a presumed DCR of 2 mirror doubles?

Big T

 

[Stone]

The red "Tank Limit" line is nothing more than a graphic representation of Boyle's Law (volume is inversly proportional to pressure). If you have a full 80 cf tank on the surface, you will breathe the tank dry in some number of minutes. All things being equal, at 33 fsw, you will breathe the tank dry in half the time.

I "normalized" the tank line on the graph by looking at my log book. I dive at 90 ft a lot, and I usually log 35 to 45 minutes of bottom time. If you look at the graph using the number <1> for "average" gas consumption, you'll see 35 minutes of bottom time at 90 fsw.

If you use the number <2>, you'll see about 70 minutes of bottom time at 90 fsw. So the number <2> can represent either half the gas consumption rate of an "average" diver, or double the gas supply (twin 80s) for an "average" diver.

The idea is to use the number <1> as a starting point to "tweak" the "Tank Limit" to fit a particular diver's actual gas consumption.

What if you sometimes use a 100 Cf tank? You can tweak the tank line to fit your "real" gas consumption for an 80 cf tank, then multiply that number by 1.25 (a full 100 cf tank can hold 25% more gas)

 

[WetDane]

ok, I follow you on that - this however indicates that you are not using a SCR to do your math, rather an average of your diving... Hmm - interesting.
If I was going to do anything to this I think that I would make it based on SCR for consumption input and I would set the sheet up to do the math for me on the size of tank, since most larger tanks are not 100 but rather 95 or 104, the math get a little harder...

Still a cool little thing.

Big T

 

[Stone]

I only bothered to plot the lines because the tables and computers give these huge NDL numbers for shallow diving, so I wanted to see the limiting factor (available gas) cut off the useless part of the graph.

If someone wanted to get elegant, they could even write macros to accomodate the variables (like tank size).

I basically plotted the lines, said "Yep, that's about what I thought", and forgot about it until I saw the Nitrox thread.

 

[WetDane]

Yeah - I kinda figured that - still cool.
nice car btw - can you fit all your tanks in that?


Big T