Dive Tables vs Dive Computers

[Winston1951]

I recently took part in the PADI Advanced Open Water course and did my dives with an instructor who relied on his dive computer. Our deep dive was the first dive of a two tank dive and we were told we were going to do a 100' dive and it would be a 30 minute dive. The dive actually lasted only 27 minutes and we were at depth no more than 5 minutes. We also did the safety stop at 15' on our ascent. After a 40 minute SI, we did a drift dive to 65 ' and total dive time was 40 minutes. The third dive being my navigation dive occurred after a 2 hour SI and it was to a depth of 20-25' for a total of 55 minutes. When I got back to my room, and finished completing my dive log, I discovered that my first dive of the day (according to the dive tables) put me me over the No Decompression limit and it compounded with the second dive. I know it's my responsibility to question if I'm unsure about instructions or how the dive will take place but I didn't think about it at the time. I asked the instructor about it on day two of the course and he explained it as the dive tables looking at it as a "bucket" and I wasn't really at 100' for the full 27 minutes but only for 5 and that the dive computer he relied on compensated for the actual time at depth. This goes against what I learned in the basic class and was wondering if the computer is really that reliable and you can get more dive time by using one instead of relying only on the dive tables.
Since I suffered no ill effects, I have to think everything was ok, but not having a lot of experience (25-30 total dives) and always using the tables I was concerned. And, if computers do grant you more dive time, I may well make that my next purchase.
Thanks for any help you can provide.

 

[Travis*N]

Yes, a dive computer will grant you alot more bottom time, as it "credits" you for the off-gassing that happens as you ascend during your dive. I believe, though, that even with a computer you should always descend to the deepest part of your dive first and then work your way up. As for your instructor relying on his computer for both your dive profiles and from what I remember from my AOW, this is not recommended in the training manual, as a dive computer is very specific to each divers profile. You should have been given your own computer to use during the dive.

 

[ScubaK-Dawg]

Yes, a computer would grant you more dive time in the profiles that you descibed. However, if you are diving tables you need to follow the tables. You never share a computer with anyone else during a dive. Therefore, although you were within the no decompression limits when using a computer, you did no have one and should have followed the tables.

 

[Scubakevdm]

I recently took part in the PADI Advanced Open Water course and did my dives with an instructor who relied on his dive computer. Our deep dive was the first dive of a two tank dive and we were told we were going to do a 100' dive and it would be a 30 minute dive. The dive actually lasted only 27 minutes and we were at depth no more than 5 minutes. We also did the safety stop at 15' on our ascent. After a 40 minute SI, we did a drift dive to 65 ' and total dive time was 40 minutes. The third dive being my navigation dive occurred after a 2 hour SI and it was to a depth of 20-25' for a total of 55 minutes. When I got back to my room, and finished completing my dive log, I discovered that my first dive of the day (according to the dive tables) put me me over the No Decompression limit and it compounded with the second dive. I know it's my responsibility to question if I'm unsure about instructions or how the dive will take place but I didn't think about it at the time. I asked the instructor about it on day two of the course and he explained it as the dive tables looking at it as a "bucket" and I wasn't really at 100' for the full 27 minutes but only for 5 and that the dive computer he relied on compensated for the actual time at depth. This goes against what I learned in the basic class and was wondering if the computer is really that reliable and you can get more dive time by using one instead of relying only on the dive tables.
Since I suffered no ill effects, I have to think everything was ok, but not having a lot of experience (25-30 total dives) and always using the tables I was concerned. And, if computers do grant you more dive time, I may well make that my next purchase.
Thanks for any help you can provide.

Well! You certainly did start off with a bang for your first ever post. This topic can become volitile. There are some who believe that the tables grant you more time, or as much time as a computer, and that computers are a big waste of money. I'm not one of those people. I'm a computer person. I believe that in practice, computers give one much more time, and are easier, and make diving more fun, for me. I dive quite a bit... like 600 dives a year, often one day's de-saturation will spill over into the next days dives, things get messy, and I'm not really a big math guy. I mostly just like swimming with the fish. Hopefully, someone who is a table type person will come along and read this, and offer you some insight from where they stand. No matter what, you are about to bear witness to a civil and free exchange of preferences and perspectives that will ultimately be beneficial to the scuba diving community as a whole.

 

[Arnaud]

Winston, tables only covers square profiles. If you don't dive a square profile, then you'll be penalized if you follow the tables.

 

[scubaroyster]

Yes, don't share a computer. And don't do a "trust me dive" even if it is with an instructor.

 

[rjens]

If you want to see an alternative way to dive tables check out this thread

 

[DandyDon]

Our deep dive was the first dive of a two tank dive and we were told we were going to do a 100' dive and it would be a 30 minute dive. The dive actually lasted only 27 minutes and we were at depth no more than 5 minutes. We also did the safety stop at 15' on our ascent.

Welcome to SB. You can also go to http://www.scubaboard.com/f19.html to post an Intro, where we can welcome you properly...

Yes, a dive computer will give you more time on a multi-level dive like this, as it tracks the reduced loading of the shallower depths. The Wheel will do about the same, if you can keep up with how much time you spend at each depth on a dive. A multi-level can even be tracked with a RDP designed to do square profiles, but that's really frowned on. How complicated would you like this...?

don

 

[Don Burke]

Winston,

Your bottom time on that first dive was five minutes, well within any no-stop limit I am aware of.

Stops are not part of your bottom time. If they were, you would never end a dive requiring staged decompression.

My trusty Navy tables show five minutes at one hundred feet makes you a "B" diver.

A forty minute surface interval means you are still a "B" diver, with nine minutes of RNT if you are going to seventy feet.

I don't know how much of that forty minutes of total dive time was actually bottom time. If it all was (which I doubt), you have forty-nine minutes of TBT, which makes you a "J" diver.

Two hours of surface interval makes you a "G" diver with seventy-three minutes of RNT. On a third dive I like to back off one pressure group, making you an "H" diver with eighty-seven minutes of RNT.

That means you could go to forty feet for over one hundred minutes without exceeding the tables.

That fifty-five minutes at twenty-five feet wouldn't be a problem.

I recently took part in the PADI Advanced Open Water course and did my dives with an instructor who relied on his dive computer. Our deep dive was the first dive of a two tank dive and we were told we were going to do a 100' dive and it would be a 30 minute dive. The dive actually lasted only 27 minutes and we were at depth no more than 5 minutes. We also did the safety stop at 15' on our ascent. After a 40 minute SI, we did a drift dive to 65 ' and total dive time was 40 minutes. The third dive being my navigation dive occurred after a 2 hour SI and it was to a depth of 20-25' for a total of 55 minutes. When I got back to my room, and finished completing my dive log, I discovered that my first dive of the day (according to the dive tables) put me me over the No Decompression limit and it compounded with the second dive. I know it's my responsibility to question if I'm unsure about instructions or how the dive will take place but I didn't think about it at the time. I asked the instructor about it on day two of the course and he explained it as the dive tables looking at it as a "bucket" and I wasn't really at 100' for the full 27 minutes but only for 5 and that the dive computer he relied on compensated for the actual time at depth. This goes against what I learned in the basic class and was wondering if the computer is really that reliable and you can get more dive time by using one instead of relying only on the dive tables.
Since I suffered no ill effects, I have to think everything was ok, but not having a lot of experience (25-30 total dives) and always using the tables I was concerned. And, if computers do grant you more dive time, I may well make that my next purchase.
Thanks for any help you can provide.

 

[clockradio]

you might want to take a multi-level dive course. it will show you how to use the wheel.i use a computer and have been very happy with it. remember one computer,one diver.