Best way to calculate dive tables from a dive computer?

Scubaru_Steve · Oct 13, 2011

So I bought a Suunto Cobra 3 a few months ago, absolutely love this computer.

Well I am updating my paper dive logs and am not sure what is the best way to approach this.

On some of my dives (just the ocean dives) my depth is consistant for the most part of the entire dive as the ocean floor is pretty flat.

However when I dive Dutch Springs (Quarry in Pa for those unsure), I find I have a lot of ups and downs based on the location of each point of interest.

So the Cobra 3 gives me both a max depth and an average depth. I wasn't sure if I should utilize the average depth to calculate my dive profile on my dive logs. Sure the Cobra 3 keeps track of all of this and is digitally loaded on my computer, but I like having a hard copy of everything for safe keeping and signatures to allow me to advance.

Hatul · Oct 13, 2011

Personally I copy this info, including the max and ave depth into my paper logbook. With the Cobra you should also be able to get the SAC and ave psi/min. The graphs of the profile are available on the PC and I don't bother attaching to my paper logbook.

Adam

Mr Carcharodon · Oct 14, 2011

Take a look at your average depth and the NDL you get from the computer and tables and see if they agree. I think you will find they do at least if you do a check shaped dive profile. Depending which tables you use you may find an offset of 5 or 10 minutes. Collecting this sort of data lets you run your dive rather than letting you computer take you on a trust me dive.

Scubaru_Steve · Oct 14, 2011

Mr Carcharodon:
Take a look at your average depth and the NDL you get from the computer and tables and see if they agree. I think you will find they do at least if you do a check shaped dive profile. Depending which tables you use you may find an offset of 5 or 10 minutes. Collecting this sort of data lets you run your dive rather than letting you computer take you on a trust me dive.

See I realize the dive computer is giving me more time since its adjusting all my times depending on depth, bottom time, etc. Doing a one size fits all profile calculation turns my 23 minute dive into what should of been a 12 min dive. I just want to have some numbers to log to match up to the dive profile. If only the dive computer manager could spit out more useable numbers.

Scubaru_Steve · Oct 14, 2011

Now I just used my dive manager to find my NDL for the 2 dives. Then used my Padi eRDP to pull out some numbers. the eRDP gives me NDL based on the max depth within about 5 minutes of what the Cobra 3 gave me. However when I go to put in my ABT for the 2nd dive which was to 90' it alarms since my bottom time was 23 minutes and the the eRDP is telling me not to exceed 18 minutes.

How can I go around this for logging purposes?

fisheater · Oct 14, 2011

It's a fun and educational (but ultimately useless) exercise to compute your table pressure group from your computer data.

If you want to log the pressure group, go for it. But, we aware that you're likely to be bent (but only on paper).

DiveNav · Oct 14, 2011

The issue you are facing is due to the fact that tables were designed for square profile diving while dive computers do track your exact dive profile and produce a continuos estimate of your nitrogen loading.

I might be mistaken, but I am not sure how useful wil be to reconduce a continuos N2 loading profile generated by a decompression algorithm to a discrete set of "pressure groups" used by tables.

What is important is to understand the benefits / and limitation of both tools (tables and computers); and you are moving in the right direction.

Scubaru_Steve · Oct 14, 2011

DiveNav:
The issue you are facing is due to the fact that tables were designed for square profile diving while dive computers do track your exact dive profile and produce a continuos estimate of your nitrogen loading.

I might be mistaken, but I think it would be quite difficult, if not impossible, to reconduce an continuos N2 loading profile generated by a decompression algorithm to a discrete set of "pressure groups" used by tables.

What is important is to understand the benefits / and limitation of both tools (tables and computers); and you are moving in the right direction.

View attachment 105615

I mostly just want to have some form of calculation put into that profile at the top of each page, haha. But I do understand the tables, and part of it too is to keep up with understanding the Nitrox tables. Sure the dive computer does it all but having a basic understanding of my time and depth limits is key. Since I don't dive much Nitrox I figure I'll use the air tables to keep my brain active in the basic use and function of the table system.

BTW, that screen shot is really sweet, I finally have a PC (primarily use a Macbook) so I can finally buy the simulation to practice on. Thanks for the responce!

eponym · Oct 14, 2011

Steve,

As noted in other replies, and as you're already aware, the advantages of diving with a computer (longer bottom times and/or shorter surface intervals) means that at some point in the dive day you'll be breaking the table NDLs because they have to assume max depth for the whole dive.

I've dived computers for years and I still keep paper dive logs. But I don't know anyone who tries to convert computer dives back to table values. I'd advise you to ignore the repetetive group fields on the profiles in your dive log pages and just record the relevant data. Bottom time, max depth, avg. depth if you like, beginning and ending pressure since you have that from the Cobra, even SCR.

On the other hand (and as you pointed out in your last post above), staying fluent with the tables is good too. Never know when you might have a dive day without the computer, or try to help a non-computer buddy log his or her dives.

Hope this helps,
Bryan

DiveNav · Oct 14, 2011

Scubaru_Steve:
..... Sure the dive computer does it all but having a basic understanding of my time and depth limits is key. ...

I agree 100%

Scubaru_Steve:
.....BTW, that screen shot is really sweet ....

Thank you

Scubaru_Steve:
.....I finally have a PC (primarily use a Macbook) so I can finally buy the simulation to practice on. .....

eDiving and divePAL Basic are both free.... and soon divePAL will run on a Mac too

Best way to calculate dive tables from a dive computer?

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