How long of SI after the computer dies?

[--tom--]

I was reading a local dive magazine’s guest editorial that talks about his computer failure. This was his second day of diving, to be first dive of the day, to be the fourth dive of the trip. When he found his computer had failed and wiped out the previous day’s dive profiles his comment was he was not diving for 24 hours. His comment was “because that is what you do when your computer fails and you didn’t bring a backup”. He then went on a diatribe that said in effect that if you deviated from this, you taking unnecessary risks, breaking the rules, not fit to dive and stupid/suicidal (yes, I am embellishing, but you get the point).

Now let me say that I am fairly open-minded when it comes to styles of diving. The DIR/non-DIR, MOF/no MOF and Back plate vs. Jacket BCD discussions are great entertainment and I am willing to dive with any of the above parties and would probably have a great time doing it. I also do not have a death wish. But there is a point in which there is a trade off between risk and reward. For example, you want a Zero chance of DCS? Easy, never go deeper than your shower and don’t dig tunnels under rivers (obscure, I know).

My premise is that his rule is too conservative. For me it is pointlessly conservative. Here is my train of thinking. (Since I am certified through PADI these are the standards I know best, hence I am using PADI standards as a benchmark, YMMV). The only reason to have a 24-hour SI, according to tables is by grossly violating the NDL. Something I have never done. I don’t play there. While I am not religious on my logbook, on my trips I note bottom time, max depth, average depth and dive site (so I can fill in my computer log later). I know whether I am within recreational standards or not, every single dive, every single day. The problem becomes: how can I change to tables safely, reasonably?

If I have done repetitive days of NDL dives, I can fly in 18 hours. That should be a complete start over point, not 24 hours, 18 hours. But, for me, all I want is a point where I can switch to a table accurately. I can plan and dive repetitive dives off of a table if I am starting from a sure point. If I dive the PADI RDP for something like 40’ and 180 minutes (or the equivalent) I am a “Z” diver, worst in class for NDL diving. However, after a 6 hour SI I am an “A” diver, and after 12 hours I am off of the charts. That should be an indicator where I could safely begin to use tables as a replacement to my computer.

So here is my thought, I finished a day of dives, always completing my safety stop; never violating NDLs and the next morning my computer has wiped out the history or died. I do not brainlessly throw out a day of diving, I go to a guaranteed fixed point and dive tables, namely: I start the repetitive dive program as an “A” diver on tables (provided it has been at least 6 hours SI) and enjoy my vacation, well within the proscribed safety limits I was trained with.

Am I wrong?

Let the flames begin.

 

[turtle_guy]

No i think you are just right, though I would take my last dives max depth and work out the tables for my repetitive dive off of that one.

 

[ctref4]

Well, 24 hrs is what SSI teaches and is probably a good bet to follow these rules. But, I understand the whole NDL'S and SI of 6 to 8 hours. Those are good guide lines, But its not the end of the world, Just go buy another computer. Diving tables limits your bottom time especially if your diving nitrox. You will not get the credit of such and will be tied to tables. happy talking and this is just an opinion.............Maybe someone else can provide a little more info. I am curious as well

 

[bmcsteve]

I dont have a ton of experience but I tend to agree with you here. I think that the author of that article was being overly conservative. If you work it out on the tables, as you have demostrated for us, there is no reason to scrap a days diving if you have had the (I'm guessing) 12 hr SI. I sure wouldnt waste my vacation time or dive dollars that way.

 

[rigdiver]

24 hours is what NAUI teaches also. I always dive with 2 computers.

 

[Rick Inman]

Let me suggest a different twist on this. Forget the computer for a minute. There are two places for a diver to off-gas nitrogen: Underwater and on the surface. The "Surface Interval" is the time a diver is off gassing on the surface. As to underwater off-gassing, there are alternatives to the popular 3 minutes at 15' that can effect how much N2 you surface with, and therefore effect the amount of surface off-gassing one needs to be concerned about.

Say for example that you do a dive to 100', but instead of going straight up to 15' for 3 minutes, you do a deep stop, and then some stops at 10' intervals along the way up. And then, say you take 6 minutes to get from 20' to the surface. Would you come out "cleaner" than someone who just does a 3 minute stop at 15'? Would this then effect the amount of surface-off gassing you would need to take into account on the next dive?

Well, sure it would.

What I am suggesting here is that the amount of time on the surface between dives is really less important than the amount of time spent cleaning up before you get out. Blindly following some agency "rule" that is so general that it's rarely applicable to any specific diver isn't how I would suggest approaching it. I would prefer to think it through.

 

[bmcsteve]

Nicely put Rick.... Imagine that... divers thinking for themselves.

 

[jeckyll]

I think much of this would depend on the diver, their comfort level with diving tables vs computers and also their familiarity with the dive profiles they had been diving.

There are spots that I dive often, that I would be quite comfortable diving without a computer and could probably dive quite safely without a watch (by PSI used alone ...).

If doing new dives it would depend quite a bit on the profiles. Square profile dives I plan on tables anyways. For people wo do tons of multi level stuff, on a vacation with 3 dives a day where you're pushing the limits? Well, that type of diving would be tough if you're relying on a computer and it dies (especially if the user isn't well educated on table use).

Still, waiting 24 hours before getting back in the water seems pretty extreme. I'd estimate where I would have been and simply dive more conservative profiles the next day and extend the shallow stops. If day was supposed to be a 3 dive day, perhaps I would have sat out dive #3 to be on the safe side.

Just my $0.02.

 

[Thalassamania]

If all previous dives are no-D dives, AAUS recommends 18 hours, for a variety of reasons.

If you want to shift to USN tables, 12 hours works.

 

[jeckyll]

...
Say for example that you do a dive to 100', but instead of going straight up to 15' for 3 minutes, you do a deep stop, and then some stops at 10' intervals along the way up. And then, say you take 6 minutes to get from 20' to the surface. Would you come out "cleaner" than someone who just does a 3 minute stop at 15'? Would this then effect the amount of surface-off gassing you would need to take into account on the next dive?

Well, sure it would.

What I am suggesting here is that the amount of time on the surface between dives is really less important than the amount of time spent cleaning up before you get out. Blindly following some agency "rule" that is so general that it's rarely applicable to any specific diver isn't how I would suggest approaching it. I would prefer to think it through.

Crazytalk!

Seriously, I do like Steinhoff's tables though and use them for dive planning. But I remember getting quite a bit of attitude about it from some divers.
"Why would you make such a fuss over an NDL dive etc"

I have a feeling that most(?) vacation divers would not be disciplined enough to hold stops in that manner, nor would they want to dive that way if it involved extra time hanging on the line (still talking about square profile here). But I'm just guessing ...