Computers and Tables

[Minipinny]

After filling out the blanks on m tables in my log book I noticed that the group designations didn't add up here and there. I called Oceanic and talked to the techy and he said that once you dive with computers, the tables become obsolete. That part I know is true. My question is, Do I just fill in parts of my table info just for reference purpose only ie. the depth, bottom time, Total Time, RT Time, SI Time and juist forget about the group designation all together? Or do I just get GDs for the first dive and the beginning of the 2nd dive?

 

[H2Andy]

well, once you start using a computer, your ending group after a dive will not jive with the information stored in your computer (mostly because of multi-level calculations which your computer tracks)

you can still track your ending group AS IF you had done a square profile, which will result in a much more conservative ending group.

why? so that if your computer goes bonkers, you can still switch to tables and make the next dive.

do i do that? no. i find it too cumbersome. in the odd chance that my computer fritzes between dives, i will simply re-calculate my dives assuming a square profile for the first dive, and then go from there. it will cost me some bottom time, but that's ok.

 

[Mauifish]

After filling out the blanks on m tables in my log book I noticed that the group designations didn't add up here and there. I called Oceanic and talked to the techy and he said that once you dive with computers, the tables become obsolete. That part I know is true. My question is, Do I just fill in parts of my table info just for reference purpose only ie. the depth, bottom time, Total Time, RT Time, SI Time and juist forget about the group designation all together? Or do I just get GDs for the first dive and the beginning of the 2nd dive?

The M factors for most dive computers are different from the table, the RDP "table" is more conservative and does not compute multiple level diving which most computers do thereby giving you more bottom time and shorter surface intervals.
My logbook has a shaded section exclusively for computer dives, you need only fill in those portions as you have mentioned in your OP

 

[do it easy]

I usually just record the depth, time, and surface interval. You can get off the tables pretty quickly with a computer, especially when you have a multi-level profile.

You should do a reality check for dive planning purposes so that you have an idea of what kind of surface interval/bottom time you can safely expect for the next dive.

 

[H2Andy]

You should do a reality check for dive planning purposes so that you have an idea of what kind of surface interval/bottom time you can safely expect for the next dive.

yeah ... i usually do this by using the 120 rule:

dive time + max depth = 120

for example, if my next dive is going to be to 70 feet, i expect my bottom time to be around 50 minutes for the first dive

for the second dive, i have to take into account residual nitrogen, so after a minimum of one hour surface interval, i half my bottom time available (in the above case, to 25 minutes)

again, this is worst-case scenario, just so i can dive if my computer fails

 

[Crowley]

generally agree - always try and check against the tables where possible however it's not always practical to do so - there's a wreck here which has a bottom at 29metres and the railing's about 20 so of course as per the PADI RDP - max bottom time 20min (for a 30 metre dive), however it's quite possible to get 45 mins on a computer if you're good with your air and profile it properly - well over double the table time but still well within No Decompression Limits as calculated by my dive computer (Suunto Vyper).

When I log my dives (and I still log most of them), I log them with depth, bottom time and all the details but where it say's Pressure Group I just write "CAD" - for "Computer Aided Dive"...

Small but significant details!

 

[Marek K]

And I concur. I log start/end time, max depth, and bottom time; omitting any pressure-group entries. That data is useful for things other than determining pressure groups.

If I ever need to (like if computer goes out), I can go back and calculate pressure groups.

--Marek

 

[serambin]

If you're lucky enough to own 2 computers, I can't see keeping a written 'dive log' at all. Instead, I keep a journal of dives focused more on the activities and conditions on the dive. In short, what I liked and what I didn't on each dive. My computer logs are printed and serve as a far better stat. record than any of my dive logs.

Stan

 

[do it easy]

yeah ... i usually do this by using the 120 rule:

dive time + max depth = 120

I was thinking something like depth averaging... But your "reality check" would be more conservative on multi-level dives since it uses max depth.

 

[Buoyant1]

I log the time, depth, surface interval etc...just in case the computer gives it up in between dives, but I only mess with the tables for the giggles of it (as well as check the air tables while diving Nitrox just to see the benefits in real time!) and to keep the tables in practice.

If you are bored, and your computer has a printout of your depths at any given time, you can try to figure out multi level dives on your tables also...(haven't been THAT bored yet!)

No other reason than that!