first deco dive

[tracydr]

How much planning would have been adequate for a 2 minute deco obligation? Glancing at your gauge and relizing you have over half a tank left, coupled with knowledge of past dives, was likely enough of a plan. Planning in the water is just as valid as plans done before hand. For "big dives" having more of a plan becomes essential, but I would be hard pressed to call running 2 minutes over NDL a big dive.

Operators in some areas (e.g. Cozumel) routinely run single tank divers well into deco. Essentially none of those divers have a gas or deco plan. I'm not comfortable with that approach but the high sucess rate of those dives makes me question the frothing at the mouth condemnations you see on threads like this.

I thought it was 2 minutes past NDL, not two minutes of deco. I've had that give me as much as 20-30 minutes of deco time when nitrogen saturated in Bonaire.
Mine was planned for though and I was diving with my instructor/husband who is also a computer engineer. He understands his computer pretty well, I'd say.and, he's helped me understand mine, too.

 

[TSandM]

I think most recreational computers don't use algorithms that are tested or sometimes even reasonable for staged decompression diving. I do know that my Suunto computer specifically stated that it was NOT to be used for decompression diving. On the other hand, my Liquivision is specifically made for staged decompression diving, as are the Shearwater and VR3 computers. So to say that computers are not useful for staged decompression diving is an overstatement. Computers like the ones I mention will not produce nonsense profiles like giving someone 20 minutes of deco at 10 feet for overstaying by 2 minutes at depth, though.

 

[Tortuga68]

to say that computers are not useful for staged decompression diving is an overstatement

I didn't see anyone say that; maybe I missed it

 

[TSandM]

I was responding to Blackwood's statement:

They may be functional for dives where you mostly clear the deco by the time you reach the ceiling (divers who break NDL and ascend at 30fpm on a 60fpm model have likely experienced that), but for anything beyond NDL computers are clearly not the proper tool.

He and I both dive in a system that doesn't USE computers to determine deco. But there are a lot of people who do use such computers for that purpose, and so long as they are purpose-built computers, they seem to work. Recreational dive computers are not designed to handle staged decompression diving.

 

[Blackwood]

Is this some DIR brain wash material or what? I've done hundreds and hundreds of deco dives using a computer and many were for more than a few minutes of deco?

I had my computer to 225 pretty many times, 240 once and 287 ft (all on air) and the computers never gave me a question mark.

No, it's an assumption by a non-computer diver based on generic LDS talk (sales driven, no doubt) and post I read around the time I responded (actually it was an exclamation point, not a question mark).

In any case, I've always been lead to believe that NDL computers have a tendency to lock you out when you exceed their target range (depth/time) by more than a little. As a non-computer diver, I've never had reason to follow up on or verify that understanding.

I think most recreational computers don't use algorithms that are tested or sometimes even reasonable for staged decompression diving. I do know that my Suunto computer specifically stated that it was NOT to be used for decompression diving. On the other hand, my Liquivision is specifically made for staged decompression diving, as are the Shearwater and VR3 computers. So to say that computers are not useful for staged decompression diving is an overstatement. Computers like the ones I mention will not produce nonsense profiles like giving someone 20 minutes of deco at 10 feet for overstaying by 2 minutes at depth, though.

By "NDL computer" I was disregarding units like the X1, Shearwater, etc.. They are as you say 'purpose built' to give you a detailed comprehensive profile, not just a "don't go past this ceiling for a while."

Let me clarify my statement: "single gas recreational computers are the wrong tool for big staged decompression dives." And per DumpsterDiver, that may not even be true (though I don't know what computer he's using, and even if it is a 'rec' computer, I'm not sure using someone with his experience to determine the efficacy of Joe Diver using tools beyond their design limit).

 

[dumpsterDiver]

No, it's an assumption by a non-computer diver based on generic LDS talk (sales driven, no doubt) and post I read around the time I responded (actually it was an exclamation point, not a question mark).

In any case, I've always been lead to believe that NDL computers have a tendency to lock you out when you exceed their target range (depth/time) by more than a little. As a non-computer diver, I've never had reason to follow up on or verify that understanding.



By "NDL computer" I was disregarding units like the X1, Shearwater, etc.. They are as you say 'purpose built' to give you a detailed comprehensive profile, not just a "don't go past this ceiling for a while."

Let me clarify my statement: "single gas recreational computers are the wrong tool for big staged decompression dives." And per DumpsterDiver, that may not even be true (though I don't know what computer he's using).

Thanks for telling us the source of the information. I think it helps other people to understand context of comments better when someone prefaces their comments with: I heard at the dive shop that.....

However, I suppose if you read the manual of the hockey puck computers they will say NOT to use them for staged decpmpression. Also, most people who are doing "big staged decompression dives" are NOT using a single gas, so if the compter is not using multiple gases, then i would agree that these are obvioulsy not the best tool.

I don't do big deco dives because I use a single tank, have a simple nitrox computer and keep my deco under 25 minutes or so. If I use oxygen, my computer has no way of knowing the gas change. Plus i have zero techincal dive training. I just read stuff on the internet.

The original topic of this thread was about going a little into deco and using the computer to get you out of trouble. It is my contention that all the recreational computers that I have used, do a pretty good job of handling this task safely.

For years I used the Skinny diper computer, a very aggressive air only computer that would allow us to do 4 dives per day to 180-190 feet. I got bent on it once, but it was unique in that it never displayed the ascent time or deco stops, it just gave you a ceiling depth and would let you know when the ceiling rose or cleared, but as you were hanging, you never knew how much more deco time you had. It kinda trained you to have a working knowledge of the tables or past profiles.

Of course just because a computer can do the dive doesn't mean the average recreational diver should be causually experimenting with going into deco without understanding a lot of factors.

 

[LanceLisenby]

Is that a "freak out limit" where you fry the algorithm, or is that just the depth that the case is rated for and they don't recommend you exceed due to increasing chance of flooding the computer?

If I recalll correctly the manual said it switches to gauge mode. I didn't store the exact nature of the computers freak out at 330' to memory since I probably wouldn't care at that depth or get a chance to tell the story!

 

[Rhone Man]

My Suunto D9 says that it is designed for decompression diving, and allows multiple gas switches.

But once you go into deco, all it wants to tell you is to ascend to 10 feet (or lower, as things progress). Switching to your first deco mix at the lowest stop doesn't curb its enthusiasm for getting you up and out.

I understand that this irritable foible has even carried through into the Helo2

 

[Cave Diver]

If I recalll correctly the manual said it switches to gauge mode. I didn't store the exact nature of the computers freak out at 330' to memory since I probably wouldn't care at that depth or get a chance to tell the story!

What model Oceanic? I'd like to see if I can find an online manual to take a look at.

 

[Garth]

My Suunto D9 says that it is designed for decompression diving, and allows multiple gas switches.

But once you go into deco, all it wants to tell you is to ascend to 10 feet (or lower, as things progress). Switching to your first deco mix at the lowest stop doesn't curb its enthusiasm for getting you up and out.

I understand that this irritable foible has even carried through into the Helo2

Sure your using it right????