Big Mistake

[SeaJay]

chrispete once bubbled...
The first is that you did have an ascent rate violation on the second dive,

I didn't have an ascent rate violation on my second dive. If you're referring to the bookmark, that's the point at which my NDL became a mandatory deco dive. At that point in my dive, my 'puter sounded an alarm telling me that I'd exceeded my NDL.

There's also two tick marks during deco... On each of those I "bumped the ceiling"... I rose from say, ten feet of depth (where I was supposed to be) to like nine or even eight feet of depth by accident. That day had 6' seas, and so staying at ten feet wasn't easy, with all the wave action. You'll notice, too, that in order to compensate a little, I spent a good bit of my deco at 11 or 12 feet, just to resist that wave action.

the second is is reference to your pressure rating on your AL80 - I noticed that you have the 80's rated for 3300 PSI in your setup. What is/are your tank/tanks actually rated at?

Well, the field in my program calls it "working pressure," and since I regularly get a 10% overfill, I'd used 3300... And you're right... That's not what should be in there. My tanks are rated at 3000 psi.

I replaced the number with 3000 instead, and it recalculated my SAC... .59 for the first dive, and .63 on my second. Yeah, there's a 5/100ths of a liter per minute difference in SAC rate on the second dive... The first was hardly changed. I don't know that I'd call this a "wide margin," but you're right... I had not put the correct number in that field.

Sorry 'bout that!

 

[chrispete]

Not riding ya man, just bringing up a couple of things that had not been brought up that might help explain some of the issues. On your second dive, under the alarms section, it shows two alarms, NDL and ASC - ASC is an ascent rate violation. On the pressures question, it should have created about a 10% error in your SAC rate, I call that a wide margin of error, even though it may not affect the numbers by very much.

 

[Spectre]

SeaJay once bubbled...
I didn't have an ascent rate violation on my second dive.

Yes you did. That's why it says you had an ASC violation.

I'd be willing to guess that the ascent rate violation was from your stop to the surface. It looks to me like you blew from 12 feet or so to the surface within 20 seconds.

Your 8 fpm ascents are better served from your last stop to the surface.

Check the tissue loading charts. Does it theoretically have you at over 100% for one of the compartments at the end of the dive?

I'd be willing to bet that is due to the rapid ascent from your stop to the surface.

 

[Dryglove]

biscuit7 once bubbled...
this facinating discussion of SAC rate, but besides one minor mention I haven't seen anyone really nail the point that computer NDL limits are not meant to be pushed!! I dive a computer but 5 minutes to NDL for me is for emergencies only. I prefer to stay well above those times and give myself the extra time by going up and staying not pushing times at depth. I have an Aeris computer which I know is more liberal, but I have no intention of ever getting close to the edge of the envelope with it, therefore I have more time if something comes up. To whomever thinks that 0 NDL means it's time to end the dive, you're already at least 5 minutes too late in my book.

Rachel

The instruction booklet for my Vytec says this.......

Gray zone- as the bars reach the gray zone, your no decompression stop time is less than 5 or 10 min and you are getting very close to no-decompression limits. At this point, you should start your ascent towards the surface.

 

[MikeS]

Seajay,

This has been one of the few useful posts on Scuba board. The number of posters and posts shows that it has got people thinking.

Here’s my 2-cents for whatever it’s worth:

Based on the information you’ve provided I cannot see how your believing your computer got you into trouble.

SeaJay once bubbled...
At one point, I remember thinking, "I've been down here a while," and checking my computer. It still said I had 3 minutes of dive time left, so I began an ascent from 91 feet. That should have done me nicely. Unfortunately, two minutes later at 59 feet (I was a little slow to ascend), my computer went into deco.

We do not have enough information to know what happened here. You could have misread the computer, perhaps estimated airtime versus remaining NDL time, the computer could have malfunctioned, we’ll probably never know.

In your description you talk about “About five minutes into my dive, my computer was telling me that I still had some 16 minutes to dive,” and “At one point, I remember thinking, "I've been down here a while," and checking my computer.”

That is not how I dive with my computer. I always try to keep track of the remaining NDL time as well as depth and air pressure. I check it any time I significantly change depth, just as you should with a depth gauge diving tables.

This thread pointed out something I’ve been doing, if not wrong, at least not totally correct. That is diving based on two separate air mixes while relying on each others computers (or tables, depth gauge and bottom timer) for redundancy.

Still thinking about how to deal with this but the solution that comes to mind is for both divers to dive based on the mix with highest nitrogen content. A potential problem there is that you disable the O2 partial pressure alarm as well as the CNS% and OUT tracking so that’s not a perfect solution either.

Mike

P.S. Keep dogging them rocks!

 

[MikeS]

SeaJay once bubbled...


That's interesting. Are you talking about the fact that the AL cylinder that I'm using holds only 77.4 cuft?

I'm not using a compact AL80... I'm using a Luxfer S080... Which is standard, and holds 77.4 cuft of air at 3000 psi...

Seajay,

Based on your logs, the cylinder size is set to 77.4 cu ft. with a working pressure of 3300 psi. It shows that your starting pressure is 3100 psi. The computer would interpret this as you only had 72.7 cu ft. (3100 psi in a tank that holds 77.4 cu ft when filled to 3300). This will result in artificially low (6%)SAC rates.

Mike

 

[Nanook]

you swimming against that 6 kt current? You are superman.

There's also two tick marks during deco... On each of those I "bumped the ceiling"... I rose from say, ten feet of depth (where I was supposed to be) to like nine or even eight feet of depth by accident. That day had 6' seas, and so staying at ten feet wasn't easy, with all the wave action. You'll notice, too, that in order to compensate a little, I spent a good bit of my deco at 11 or 12 feet, just to resist that wave action.

You don't just bump the ceiling. You either do your stop correctly or you don't.


For every post you make, continuing to try and justify your errors, instead of just admitting to the mistake (yes, I realize you have said that it's your fault, and then you go on a 33 page rambling attempt at justifying your actions), I revert to one of my original statements:

Get more training.

 

[Spectre]

SeaJay once bubbled...
We were centered around the upline, and about a minute later we began our ascent anyway... So the plan wasn't deviated far. Really, my only deviation from the plan was a hesitation of about a minute.

Now that I see the true graph of the dive, I'd like to revisit this one.

Do you truely believe you only blew your plan by a couple minutes?

Look at your depth vs. time chart. This is what it looks like in my eyes.

You ended your dive at the deepest portion at your planned time, 12 minutes. You began your ascent. About a minute or so into your ascent you stopped at 70. You then blew off your ascent, and dropped back down to 98. By the time you returned to the point in your ascent where you went back down [70 feet] you were over 10 minutes off schedule.

For a planned 12 minute dive, 10 minutes off schedule is very deviated in my eyes.

In case you're still thinking the computer was overly conservative due to being a couple minutes beyond plan... it wasn't. It's right. You blew your plan by almost double.

 

[SeaJay]

chrispete once bubbled...
On your second dive, under the alarms section, it shows two alarms, NDL and ASC - ASC is an ascent rate violation.

Not necessarily.

According to Suunto, an ASC alarm also sounds when the computer switches from NDL time to ASC time (effectively, deco time).

I didn't realize that the printed graphs did not show the alarms. There's three on the second dive... One "yellow triangle" at 22 minutes into the dive, at 85 feet of depth. According to the Suunto help file, a yellow triangle means, "A decompression ceiling first appeared during this interval. The dive computer's ASC indicator appeared." That's what gave the ASC alarm.

There's also two upside-down pink triangles on my graph... One at 32 minutes and the other at 38 minutes. According to the Suunto help file, an upside-down, pink triangle means, "The dive ascended above the decompression ceiling during this interval."

Thus, there is an ASC alarm and a Ceiling alarm in the logbook.

Spectre once bubbled...

Yes you did. That's why it says you had an ASC violation.

Nope. I rose too slowly during this dive. I never exceeded my recommended ascent rate. Heck, I never even got to my recommended ascent rate... Something that I didn't think could really be a problem until now.

I feel like I got pulled over by the police for going too slow.

Spectre once bubbled...

I'd be willing to guess that the ascent rate violation was from your stop to the surface. It looks to me like you blew from 12 feet or so to the surface within 20 seconds.

Yeah, it appears on the graph that this might be so, but I didn't. There was no ASC violation at that time.

Spectre once bubbled...

Check the tissue loading charts. Does it theoretically have you at over 100% for one of the compartments at the end of the dive?

I have the highest compartment at exactly 100% when I hit the surface. No doubt I was anxious to get topside the moment my deco ended.

MikeS once bubbled...

Based on the information you’ve provided I cannot see how your believing your computer got you into trouble.

Well, let me be clear on this... This was my fault. We've figured out that there were four possible solutions to this problem of overstaying my NDL. So no, I don't blame this on my computer.

But when I was at 98 feet, and it told me that I still had three minutes, I comprehended that I was golden for three minutes... Which wasn't correct. When I turned the dive, it was less than a minute from the point when I said, "Hey, I've still got three minutes."

And yet I went into deco.

It's not the computer's fault... But it's something to be aware of. "Three minutes" means, "Three minutes to be above the floor," not "three minutes to turn." There is a huge difference, and one that was not made clear in the manual.

 

[ericfine50]

I can't believe I am going to do this, but - SJ _ don't dive the computer, dive your plan. Going from 70 to 98 back to 70 is a continuation of the dive.

Eric