Backup Computer went into Deco

[boulderjohn]

I tend to trust my computer between my ears.

All my initial tech training followed that theory--computers make mistakes; the human mind doesn't.

Two of my friends did a deco dive using that theory, as they always did. They kept track of their average depth, calculated their deco based on their time at that average depth, ascended to their first deep stop at a standard rate of speed, and followed the plan they had calculated for their ascent. Instead of a bottom timer, one of them had a computer in gauge mode. and when they looked at its logbook, they discovered that they had badly underestimated their average depth, they had badly underestimated the amount of time it took them to reach their first deep stop and begin their calculated ascent profile, and they miscounted the number of minutes in their final deco stop. Those three mistakes were almost certainly why they got bent.

Not being as smart as they, I now use a computer to make those calculations. Incredible as it may seem, over my lifetime the computer between my ears has made more than a couple mathematical errors. I suppose that is not true of you, I guess you have never made a mistake of your own, but I think it is possible that someday, somehow, you might just make a mistake of the kind my friends did.

 

[oldschoolto]

All my initial tech training followed that theory--computers make mistakes; the human mind doesn't.

Two of my friends did a deco dive using that theory, as they always did. They kept track of their average depth, calculated their deco based on their time at that average depth, ascended to their first deep stop at a standard rate of speed, and followed the plan they had calculated for their ascent. Instead of a bottom timer, one of them had a computer in gauge mode. and when they looked at its logbook, they discovered that they had badly underestimated their average depth, they had badly underestimated the amount of time it took them to reach their first deep stop and begin their calculated ascent profile, and they miscounted the number of minutes in their final deco stop. Those three mistakes were almost certainly why they got bent.

Not being as smart as they, I now use a computer to make those calculations. Incredible as it may seem, over my lifetime the computer between my ears has made more than a couple mathematical errors. I suppose that is not true of you, I guess you have never made a mistake of your own, but I think it is possible that someday, somehow, you might just make a mistake of the kind my friends did.

This is the problem with the internet... Lost in typing is the human part of a discussion.. I think it may even be like two guys drinking at the bar and hearing half of what the other guy said.. I "NEVER" said I don't make mistakes, Nor do I think I'm perfect... What I have said is I have many years of diving Navy Tables with a watch and depth gauge. Because that's all we had.. As a northeast wreck diver, The profile was drop to the wreck and come up to the drop line and do your DECO.. Other wise it was playing around in 30' - 50' of water grabbing lobsters and stabbing flat fish.. Two or three dives on the weekend.. Not really a need for a computer anyway..

Did you miss the part were I said I did a few lionfish dives down to 160' in Bonaire last month and used my computer because I had done a crap load of diving and it was "MUCH" easier(safer) to use the computer than do it with tables.. But I still knew about what it was going to look like and how to do it if the computer $hit the bed..

This thread is about a guy doing a 45 minute dive and having a computer tell him he's got to do 40 minutes of DECO.. A diver should in my mind be able to do the simple math in his head to say.. THAT"S F@#K'N WRONG !!!!

Jim....

 

[AdivingBel]

This thread is about a guy doing a 45 minute dive and having a computer tell him he's got to do 40 minutes of DECO.. A diver should in my mind be able to do the simple math in his head to say.. THAT"S F@#K'N WRONG !!!!

Yeah, given the dive profile/circumstances and at least 6 other computers saying no deco (OPs primary, his 5 buddies, maybe more if they were carrying more than one and assuming they dived similar profiles) hanging for 44 min was like turning left on the railroad tracks 'cause the GPS told me to. I give the OP props in that it was at least a conservative choice (tho' I wouldn't have wanted to be his buddy hanging with him) as opposed to some of the cowboy sh** that gets posted on here. Also given the very personal nature of risk associated with diving, I can see the reluctance of other divers to take the OP to task for his choices and that is not my intention either. It just kind of leaves a big elephant in the room.

A bigger concern, IMHO, is the justification of "following my training." I get clearing the most conservative computer if you're diving a backup, but this was so obviously malfunctioning that it would make me wonder about the OPs understanding of the WHY of the training. Training, experience, and computers all provide information for making reasoned, rational decisions to help you dive safely. IMHO, you can't just turn off your brain and follow "the book" or the "electronics" in the real world. We've probably all seen it. I had it happen with a diver that insisted on calling a 30 ft. reef dive 20 min into the dive when their rented computer acted wonky. Since I was the only other diver (other than their buddy and the DM) we all surfaced and got back on the boat. The diver adamantly refused to do the second dive (also a shallow reef dive) without a functioning computer even after the DM suggested an extended surface interval "just to be safe." Rather than make the diver & buddy sit on the boat (and make the captain & DM eat the rash of c**p the diver doled out), I agreed to call it a bust and go back to the dock as it wasn't much fun anymore. The shop was very apologetic, comped me another boat dive and shore dive tanks for the rest of the week. So, it wasn't a total loss. I could hear the diver barking at the shop folks all the way in the parking lot as I was leaving.

 

[DevonDiver]

Yeah, given the dive profile/circumstances and at least 6 other computers saying no deco (OPs primary, his 5 buddies, maybe more if they were carrying more than one and assuming they dived similar profiles) hanging for 44 min was like turning left on the railroad tracks 'cause the GPS told me to...

There's nowhere near enough info posted in this thread to determine a second opinion of the deco situation.

44 minutes of deco presumes that some relatively slow tissue compartments were stacked up to control the ascent. That could result from multi-day diving (which other divers may not have done). There's a LOT of things that diver A could have done to provoke severe deco obligations, that divers B and C hadn't done.

Also, and with all due respect, it's impossible to discount human error/misunderstanding/loss of awareness; when the scenario itself involves a diver who accumulated 44 minutes of deco without noticing it.

If the OP is absolutely convinced that this was a software issue, they should send their logged profiles to the computer manufacturer and demand an explanation (and post that here). A glitch of that magnitude would definitely constitute a severe safety risk... and demand a firmware update on all effected computers.

 

[AdivingBel]

He can do whatever to get his malfunctioning computer straightened out after the fact, but if the info provided about the dive is accurate and my five other buddies diving similar profiles all showed no deco, I wouldn't have seen anything wrong with discounting the obviously malfunctioning computer (44 min vs no deco on multiple units) and surfacing as prescribed by my primary computer. You can assume anything. I'm going by what the OP posted. We'll just have to agree to disagree.

 

[oldschoolto]

There's nowhere near enough info posted in this thread to determine a second opinion of the deco situation.

44 minutes of deco presumes that some relatively slow tissue compartments were stacked up to control the ascent. That could result from multi-day diving (which other divers may not have done). There's a LOT of things that diver A could have done to provoke severe deco obligations, that divers B and C hadn't done.

Also, and with all due respect, it's impossible to discount human error/misunderstanding/loss of awareness; when the scenario itself involves a diver who accumulated 44 minutes of deco without noticing it.

If the OP is absolutely convinced that this was a software issue, they should send their logged profiles to the computer manufacturer and demand an explanation (and post that here). A glitch of that magnitude would definitely constitute a severe safety risk... and demand a firmware update on all effected computers.[/QUOT

Here is the facts;

I went on a dive with 5 other divers - all friends in a fresh water lake. I had two dive computers, my backup was a Cressi Leonardo and the other was a air integrated Mares Icon HD Net Ready with 4.1 firmware, not sure on the Cressi. I paid complete attention to the Icon throughout the dive. What happened was that on my return at 45 feet I glanced at the Cressi and found it had me in deco, the Mares did not. I was diving a HP120 on Air. I decided to follow the Cressi mainly as practice. Note none of the other divers went into deco, they also all had AI Computers. In any case the Leonardo directed me at a 44 minute decompression. I followed through with it and after the Cressi cleared me I surfaced with no signs of DCI. Dive time before deco was 45 minutes, total time underwater was 89 minutes. Average SAC rate according to the Icon was .3

We have 6 divers making one dive in a freshwater lake. I take it's the first and only dive because the OP does not talk about any other dives..

We did go deep, max depth was 118fsw for 3 minutes, then 60 feet for the majority from there. Average depth 34 minutes (remember 44 minutes at 15 feet reduced that average depth

Facts... Max depth was 118' for 3 minutes than moving up to 60' total dive time before DECO time was 45 minutes.. So they drop down to 118' at lets say 25' a minute for about 4 minutes down and then 3 minutes at 118' then moving up at lets say 20' a minute to 60' is 3 more minutes... leaving 34 minutes at 60' or higher.. Now simple 60/60-120/140 rule will tell you he's fine.. And he has a second computer that said he was fine and we have 5 other divers diving the same profile and their computer say it fine...

Bottom line.... The Cressi computer was so wrong that's it's not even close....

Jim....

 

[Storker]

They might still give slightly different reading eg depth.
My two identical Uwatec Bottom timers rarely give identical reading on depth.

Yep. My primary computer is a hose AI Suunto Cobra. When I found a used Stinger at a good price, I bought it. I wear it on my wrist when diving, because that way I don't have to find a place to stow my watch. It's primary purpose is to be a really waterproof watch, its secondary purpose is to be my backup PDC. For me, it was important that my primary and my "backup" used roughly the same algorithm.

They always show slightly different max depths, since one is on my wrist and the other is clipped to my left hip D-ring. And their pressure sensors probably aren't calibrated identically. They might even disagree ever so slightly on my run time.

 

[DevonDiver]

Jim, with all due respect... You've completely missed the points I made. We don't know the full facts. Not talking about other dives doesn't mean they weren't done... it'd go some way to potentially explaining his deco... and, if so, he wouldn't be the first diver to absolutely discount the impact of a multi-day schedule.

If there were no subsequent dives... no residual nitrogen from previous days... then, I agree, 44 mins deco for the given profile seems impossible.

But if diving multiple days, some of the recreational algorithms can get very protective when the slower tissues get loaded and become controlling... it's unrefined shallow deco... so that means it's long deco.

The OP didn't have awareness of the Cressi. That's decreased situational awareness in effect. So we don't know how, when and where it arose.

 

[stuartv]

The OP didn't have awareness of the Cressi. That's decreased situational awareness in effect. So we don't know how, when and where it arose.

Is it really correct to say that a conscious decision to ignore something constitutes lack of situational awareness? IIRC, the OP said he made a decision to ignore the Cressi during the dive (unless his primary died). If he had put it in a pocket until near the end, then pulled it out to look at it, would that constitute a lack of situational awareness?

 

[DevonDiver]

If his plan was to keep within the no-stop of both units and/or honor any deco obligation demanded from both units (which he did), then it's a situational awareness deficit.

Fact is, he did the deco the Cressi demanded. If it was in his pocket, then it'd have been a pretty foolish call.

A good lesson is that a backup unit shouldn't just be stuffed into a pocket and forgotten about (or otherwise not checked) until the s__t hits the fan with your primary unit.

And, yeah, I'd say that bad situational awareness can result from flawed decision making. i.e. If I choose to do a dive with no mask on... I'd still be suffering low situational awareness LOL