Big Mistake

[ibnygator]

Do you believe that the computer incorrectly showed the deco obligation? If not, why wouldn't it show it prior to your beginning your ascent?

I'm very curious because I use a Suunto Vyper...

 

[Dryglove]

Oh oh, am i smelling a solo dive here

 

[SeaJay]

Big-t-2538 once bubbled...


That sums it up nicely....BTW...dare I ask why your buddy didn't get a deco obligation, or convince you to thumb the dive earlier?

O-ring one bubbled...

What did your buddy's computer say?

Oh, man... Now I'm in REAL trouble.

My buddy wasn't wearing a computer. He had also come from out of state, and had brought a pair of steel 120's filled with EAN32. Thus, there was nothing wrong with HIS dive profile. Just mine. He did express concern towards the end of the dive about my profile, as his buddy awareness skills were excellent.

In short, my buddy planned his dive, and dove his plan. He had a better profile than I did because he used the right gas, too. And he stuck with me the whole time, surfacing because I needed to, even though he didn't.

Sure, he could have donated to me... And in fact, it would have been a good thing, since he was using EAN32. But given that he surfaced with just 500 psi, he wasn't really in a position to be donating.

...So yes, we had a couple of bailout options. But that's not the point. The point is that I did something really stupid when I believed that computer...

 

[Crispy]

SeaJay,

Is your computer air integrated?

-Crispy

 

[Big-t-2538]

SeaJay once bubbled...

He had also come from out of state, and had brought a pair of steel 120's filled with EAN32. Thus, there was nothing wrong with HIS dive profile.

<snip>

Sure, he could have donated to me... And in fact, it would have been a good thing, since he was using EAN32. But given that he surfaced with just 500 psi, he wasn't really in a position to be donating.

Just out of curiosity, was he diving the 120s as single tanks (1 dive for each tank?)....if so, good thing you 2 didn't have any emergnecies...especially with his gas...his consumption had to be higher than yours.

 

[SeaJay]

ibnygator once bubbled...
Do you believe that the computer incorrectly showed the deco obligation? If not, why wouldn't it show it prior to your beginning your ascent?

I'm very curious because I use a Suunto Vyper...

No, I don't think that it "incorrectly" showed my deco obligation. I think it did exactly what it was programmed to do. I think it showed exactly what it's alogarithm computed. Now, about that alogarithm... It does seem very conservative.

I think the reason why I suddenly went into a deco obligation was because I was making regular "dips" to about 90 feet from about 75 feet. I think was cruising along at 75 feet or so, then "dipped" to 91 feet, at which time I thought to myself subconsciously, "Hey, I'm getting deeper, and I've been down here a while, so let's check the gauges" and I looked, to see that I had 3 minutes of NDL. I turned the dive within 10 or 15 seconds or so, rising immediately to 75 feet, and then swimming for one minute or so to the anchor line. This whole time I was ongassing, which meant that I should have been using that 3 minutes... In fact, it should have immediately gone from 3 minutes of NDL left to maybe 4 of NDL left because of the fact that I rose from 91' to 75'. Unfortunately, because of the combination of the fact that I was still ongassing and that I took a minute to find my upline, I blew my NDL by the time I got to 60 feet. Mind you, though, I did not take but maybe 2 minutes to get to 60 feet... So I thought I was still fine. However, I believe that that point where 3 minutes was shown at 91 feet was a sort of "lag." I don't think that number was accurate... I think that it was showing 3 minutes at 75' or so, and that I'd outswum my computer and it had not yet calculated an NDL at 91 feet. I think that it would have put me into deco right then and there.

 

[raviepoo]

Suunto computers are conservative for the first few dives of a multiple dive series. If you compare a Suunto to a less conservative computer on the first (also the second i think) dive of a series you will see that the Suunto allows for less bottom time. After a few dives the difference evens out and both computers will show similar no deco times.

If Seajay had been using a different computer he might not have had a deco obligation. However, if he had blown off the deco obligation with the rationalle, "Hey, it's a conservative computer and my buddy doesn't have a deco obligation!" the computer would have locked him out.

I threw my Viper into deco once by diving with the computer set to the wrong 02 percentage. (Long story. Set the computer too long before the dive, the setting didn't hold, defaulted to 21% and shame on me for not checking before the dive.) I did the deco anyway, although I knew it wasn't necessary based on my dive plan. That is a mistake I will NEVER make again.

There's nothing wrong with the computer. Conservative is better than the alternative.

ibnygator once bubbled...
Do you believe that the computer incorrectly showed the deco obligation? If not, why wouldn't it show it prior to your beginning your ascent?

I'm very curious because I use a Suunto Vyper...

 

[Scubaroo]

SeaJay once bubbled...
something about 75 to 91 to 75 to 91 and then something about NDLs for 3 minutes blah blah blah

Suuntos are very conservative computers - see if you can track down Rodale's reviews on computers and conservatism, they're right down there at the "safe but short dive" end of the scale. My buddy's Cochran will often have NDLs of 10 or 15 minutes longer on the second dive, but we always surface according to the most conservative computer as a buddy team.

Good thing about the Suuntos though is that they really push you towards using them as a bottom timer instead to get around the conservatism :tease: Planning on taking that route.

 

[SeaJay]

Big-t-2538 once bubbled...


Just out of curiosity, was he diving the 120s as single tanks (1 dive for each tank?)....

Yes.

if so, good thing you 2 didn't have any emergnecies...especially with his gas...his consumption had to be higher than yours.

We DID have an emergency. I blew my NDL, which was a problem because I did plan on needing gas for deco. Effectively, I did not have enough gas, and knew it fifteen minutes ahead of time. Believe me, as I hung there at 10', checking my gauge every minute or so (what was I expecting, for it to INCREASE?) it felt like every bit of an emergency.

...But I understand what you are saying... What if HE'D had the emergency? We'd have been dangerously low on gas...

Don't forget that we were not diving overhead... No deco obligation (was the idea anyway) and no places to get ourselves in trouble on the wreck (no true penetration). My point is that we could have thumbed the dive at any point, since we had a straight shot to the surface... And thus, the rule of thirds wasn't necessary. Effectively, this was a true open water dive, and so the situation that you describe... The threat of not being able to support a buddy... Wasn't really realistically a threat.

That is, until the end of the dive.

And that WAS the emergency. That's what I got so freaked out about.

 

[Zagnut]

..and you can tell me if this is a dumb question or not.

Off gassing at your safety stop occurs during the process of breathing. If you slow your breathing down to conserve air on your safety stop, aren't you also slowing down the offgassing process? Wouldn't this increase the time required for the deco stop? It seems like conserving air at the safety stop would be detrimental to the whole deco stop process.

Your thoughts please...