Faith diving and magic?

[SailNaked]

How much do you count on your dive computer?

do you dive twice a day and it never really shows you near any limits so you feel safe?

Do you push every last second out of your computer and ride the thin line of NDL right to the boat?

Are you a thrill seeker and occasionally put your watch into Deco, but manage to clear it by the time you get on the boat?


Short story of a near miss, and maybe this will be moved there but it is in advanced diving now because it is not a technical or beginner discussion.

my wife and I were on our 4th dive of the day in Cozumel. Great diving and we had 3 computers between us. (stuff left out or this would be real long).

end of the 4th dive and my watch beeps so I look at it. 2 minutes to deco, oops we had been diving right up to the limits this trip, seems we did a lot of 80-120ft diving, the rays were about, and life is good. my wife and I usually can touch when we dive but the current and all the fun stuff to see and my interest in photography have kept us only nearby, and not hands length.

so 2 minutes, where is my wife. she has found one of her favorite sea creatures, a sting ray in the sand, so she is slowly swimming to it about 15ft down and 30 ft away heading down a sand slope. hmmm well my watch is bitching, so hers must be screaming..... I am the anal one, I am always pointing to my watch and she looks at hers sees that we have 5 minutes or whatever and gets mad at me for messing with her mojo. we have done this a lot so I know she is going to be pissed if i interrupt her time with her new friend to point to our watches. but no choice she is headed for trouble, and at that point I did not know how much.

I did some calculations, based on air, and predicted deco time, we would have enough air if we went into a small amount of deco at this point.***

So I swim after her, take one and a half minutes of video of her playing with the ray and then grab her arm and show her, her watch, and I get a look at it myself, 14 minutes of deco, OH ##$^^$*

we did an ascent to 20ft and started our stop, after a few minutes I realize that the computers are not giving us much credit on the obligation,** they wanted us at 10 ft, #$^#$ ok well we are too light to hang at 10ft, so clip off some of my weight to my wife and we go to 15ft, better but still not clearing her time fast enough, we are going to run out of air. I am working on slowing my breathing, better to get a head ache than to run out of air, she needed me because she does not usually think about this type of situation and I have.

Both of my watches clear (they did not show the same obligation despite being the same manufacturer). hers is at about 8 minutes*, I am thinking of the rouses and Ritchie Kohler, the seeker and other stories I have read, getting ready to call in the coast guard, (@%$# we are in Mexico) remembering first aid for DS. they have chambers in COZ so I was thinking about if we were within a 1/2 hour or not.

ok she is at about 5 minutes, i lost track but we are out of air time to face the music. we get out, I ask the DM for the O2 and put my wife on it for the trip back and apologize to the other divers for making them wait and scaring them.

No symptoms, no problems, bullet dodged.

*** My calculations were based on my computers not hers, mistake #1, #2 was not realizing the profile of the dives we had done, we did a lot of dives at 80-90ft with the average being about 60ft, we were at a limit that takes a long time to deco from not like single deep dives.

**With a shallow obligation you have to burn it shallow, ie at 10ft, we did not weight to be able to do a deco stop at 10ft, big mistake if you have a risk of needing it.

* we did a total of 21 minutes of deco, total dive time about an hour(58m) max depth about 80ft.

I will never do unplanned deco on the fly again, that was stupid and could have resulted in catastrophe.

If you are still with me, then here is the reason for the post, how much faith do you put in your computer? (I risked our lives on ours).
We do multi level diving these days, and as such we are a little off the reservation with the tables and the science and guesswork that went into them.

last story, I said I had 2 watches, one had the option for a different algorithm, and as a scientist of sorts, I put it on the other one for the first dive, it went to Deco when my original watch said I had 24 minutes. and on the second dive showed a deco obligation of 28 minutes at the safety stop when my other one showed nothing. so I had to switch it back to the same algorithm or else it would not be usable. what is that Alg. for? really old people with heart conditions? hypochondriacs? What science was used for that one that is so different from the other?

I hope this will stimulate some adult conversation and not a bunch of pointing out my mistakes.

 

[nolatom]

Excellent topic, thanks.

I pretty much do count on my computer, and sometimes push the limits, but almost always stay in the yellow. But you've really pointed out that while this may work out for solo or when you're the "deeper" buddy, it may lead you into trouble if you aren't the "deeper" buddy but are trying to stay in touch with one.

And I don't really know if my computer is conservative or liberal (I don't discuss politics with it). I just know it has worked for me so far. Do I overdepend on it, without a ready backup? Probably.

 

[Rhone Man]

As we all know, deco is an inexact science. That is usually used as a warning, but it cuts both ways. If you surface with the computer showing you in deco, if it is not much deco, then there is a good chance you will still remain asymptomatic, or possibly only have minor discomfort or a skin bend.

Two anecdotes that may be relevant, but probably are not:

• a couple of years ago, British diving magazines reported an incident where a British diver had about a 20 minute deco obligation, had a drysuit malfunction, and shot straight to the surface. No O2 on the boat, so they made the long ride back into town. No DCS symptoms at all.
• when J. Scott Haldane was busy torturing goats to develop the first set of diving tables, on one occasion he sent 5 goats to a notional pressure of 180 fsw in a chamber and brought them all to the surface rapidly. Two died immediately. Two writhed in agony and died later. One displayed no symptoms at all.

Computers are usually pretty conservative. Just because they think you are bent doesn't mean it is so.

Converse of the above anecdotes: I just came back from a week of doing 4-5 dives a day, most of which were below 100 feet. I was with my 73 year old Dad, so I was keeping us well clear of deco, and we were doing 6 minute safety stops. However, by the end of the week we were still both complaining about minor joint pains during evening time. Maybe we are just getting old, but I have my suspicions.

 

[Warmwater Wank]

I count on my dive computer a lot. I count on my training and common sense even more. You asked for adult conversation, not "a bunch of pointing out my mistakes" but I'll ask you this. As an instructor, if a student were telling you this exact same story, what would your response be? Hopefully not "Do as I say, not as I do".

I think my wife dives a lot like yours ("I am Woman, I am invincible...") but you know what? I love her too much not to be "messing with her mojo" if need be. Sorry, but to me what you relate isn't so much about dive computers as it is about common sense, based on training and understanding.

Thankfully you acknowledged it was "stupid" to do unplanned deco and I applaud your honesty and willingness to take the hits this thread will probably generate. I'm not trying to guilt trip you, there are many good lessons to be gained from your post. Thanks for your candor. // ww

 

[scubadiver888]

I typically dive twice a day and rely on my computer to tell me where I'm at. I find I'm approaching NDL on pretty much every dive unless my buddy hits NDL before me. I have an understanding with my buddy that if he/she is approaching NDL he/she will let me know and if I'm approaching NDL I'll let him/her know. Because I'm not doing liveaboards and diving 3 to 5 times a day for a week solid, I tend to feel safe pushing myself to the NDL. I have NEVER gone into deco on my computer.

Now that I'm a DM I'm starting to think more about things like this. More time in the water means more money but I have to balance that with more time in the water means higher risk of DCS. All the stories I hear about people getting bent tends to be people who did something totally dumb or they were diving 4+ dives a day for a week straight.

As I start to do 4+ dives a day or if I join the shop on a dive vacation/liveaboard I'll start looking to using Nitrox (highest mix recommended and available for the profile), not pushing it right to the NDL and spending a little more time at 15 feet.

My other plan is to get technically trained so I can safely go into deco.

 

[JahJahwarrior]

Seems to me that your wife is not a safe scuba diver. She's demonstrated a complete lack of awareness, as well as deficient knowledge of basic math and simple decompression theory. She should probably take a certification course again, for her own safety.

You demonstrated poor gas planning. You should study how to calculate a safe turn pressure.

I wish you both the best of luck as you educate yourself on how to enjoy the underwater world. It sounds as if both of you have skills to brush up on, and recognize that. It also sounds as if you enjoy diving enough to learn instead of quitting.

As for your plea to have a conversation about this... The algorithm difference is a conversation topic. The "my wife had no clue she had 14 minutes of deco, I ignored my deco to play with her, neither of us had enough gas to get the pair back to the surface safely let alone get ourselves up including a deco stop" bit is where all one can say is you got lucky but you need to face the fact that you could have died for stupid reasons (lack of planning and poor situational awareness and perhaps a trust me dive on got wife's part) and take steps to fix that. Failing to plan is planning to fail. Not trying to be rude here, I just don't want to see you ending up a statistic.

 

[TSandM]

Well, this is one of the reasons that people who do planned staged decompression diving don't do it with recreational dive computers. Planned staged decompression diving is begun by considering the profile you want to do, and using some kind of tool to know how much decompression you will require and where you will need to do it. Recreational computers can get extremely irritated by deco violations, and as they are generally using some kind of pure dissolved gas model to decide the deco, it's long and has to be done very shallow (which is not how much of anybody does staged decompression nowadays).

But the very biggest lesson from this dive is one that my Rec 2 instructor pointed out to us. Our class had two teams, and he had been diving with both of them. At one point, the boat captain looked at him and asked, "Are you okay on deco?" And Joe looked at us, and asked, "Do you realize that he is asking the wrong question?" His point was that the captain should have been concerned about whether Joe had enough GAS to continue diving. In a macabre sentiment, you can fix bent, but you can't fix dead.

Technical divers spend a tremendous amount of time and effort learning to plan the gas requirements for their dives, and contingency supplies for all kinds of unlikely scenarios, simply because being trapped underwater by a deco obligation when you are running out of gas is a horrible place to be.

The point that was made that, especially when different algorithms differ so extremely in figuring how much deco you have to do, and where you have to do it, you are probably going to be okay blowing off small obligations if you have to for gas reasons, is quite valid. But nobody is going to tell you it's okay to ignore a decompression obligation. It's not okay, but it's preferable to drowning.

And the final lesson here is that weighting yourself to be neutral at 15 feet with 500 psi means you will be light shallower than that, or with less gas; one or two extra pounds is not perfect weighting but makes stressful situations a lot easier to manage.

 

[GrumpyOldGuy]

I count on my computer to run the calculations for NDL and occasional small amounts of DECO. I have complete confidence that is will run the numbers without error, with more precision and reliability than I can run hard copy tables.

What I don't do is count on it to plan my dive, calculate proper air reserves, factor in mitigating circumstances or think for me. The DC is like an idiot savant, it does one thing, does it well and performs poorly at most other task.

 

[Blackwood]

Stuff happens. Don't beat yourself up; rather learn from it.

At the risk of appearing to have ignored your hope...

Going deeper to get your wife knowing you had already hit unplanned deco is arguably a reasonable action; I'd do it for my buddy. Staying deeper to film her for another minute and a half while simultaneously burning gas and accumulating more deco... not so much. That's not a planning mistake or an algorithm issue, it's a red flag decision-making mistake. Is seeing that stingray worth bagging the rest of your trip? Worth drowning? Probably not, if you can't see that one, you can see the next.

I'm glad no one got hurt, and i f this incident improves your future dive planning, execution, and problem solving, awesome.

 

[Rhone Man]

Thankfully you acknowledged it was "stupid" to do unplanned deco and I applaud your honesty and willingness to take the hits this thread will probably generate.

Let he who is without sin cast the first stone. Most people, if they dive long enough, will make this mistake eventually. Some of us more than once.

I made a similar, albeit potentially more catastrophic error recently on a planned decompression dive, overstaying my planned bottom time by just over a minute - thereby turning a planned 34 minute deco into a 46 minute deco. Once you are into deco, remember that it works on a geometric progression (despite whatever ratio deco fans might say...).