Big Mistake

[Spectre]

I'm not really sure how this has anything to do with the computer, other than it got SeaJay out of the water after a royal CF.

His plan was 12 minutes. Looking at the simulation after his first dive, the Suunto computer would have told him his NDL for 100 was 12 minutes.

At 12 minutes he began his ascent. He screwed up in that he wasn't back at the anchor line, but whatever...

So he got to the anchor... Instead of continuing to ascend, he rode his computer down to 98 feet for 4+ minutes...

I ran the simulation out with that 4 minute CF removed... as if he ascended to 72 feet, swam to the anchor, and proceeded with his ascent from that point. In water time: 30 minutes. No deco ceiling.

So if your plan was 12, and the computer algorithm told you 12, why did you think that being at 98 16 minutes into your dive was "believing the computer"?

IMHO the computer got your ass out of the fire.

Tell me this. what would you have done if you happened to find yourself at 98 feet 4 minutes past your planned time if you didn't have the computer to walk you through your deco?

Actually, I guess what I really want to ask is what the hell were you thinking when you decided to blow plan?

 

[SeaJay]

Well, I did screw up. That's all there is to it. And no, it's not appropriate to blame it on my computer. However, it did add to the problem.

If I wasn't using the computer at all, I'd have done my second dive at 12 minutes... Plain and simple. Instead, at the point where I turned the dive, my computer was reading "3 minutes," not "1 minute." I know the log doesn't show that, but perhaps I looked at the 'puter a few seconds before actual rock bottom. However it happened, I understood three minutes, not one.

Nonetheless, computers don't do square profiles... In other words, as I ascend, the NDL display INCREASES. My key was to never hit zero, but I did. That's what put me into deco. I saw three minutes and turned the dive, but it wasn't enough. I was already too close. I wasn't but maybe 20 feet or so from the anchor line... But getting to it, communicating with my buddy, thumbing the dive, and beginning the ascent apparently took more than a minute. Also, I was still ongassing for many feet... Which also took me past zero in my NDL.

So, mistake number one was cutting it that close. Again, that's something that I would not have done had I been diving my plan, which was 12 minutes surface-to-surface. Instead, I thought, "I'll ascend when this thing tells me it's okay and that way get a few more minutes out of my dive."

Mistake number two, which wasn't obvious until I posted that profile, was taking a whopping 10 minutes to ascend to my "safety stop." I'm not sure why I did this... I don't remember consciously thinking to slow my ascent so much. I was aiming for 30 ft/min, not 8! This second mistake was the real reason why I went into deco, I think.

So if your plan was 12, and the computer algorithm told you 12, why did you think that being at 98 16 minutes into your dive was "believing the computer"?

Well, because I wasn't 12 minutes at 100'... It was a multilevel dive. And my dumbass thought that perhaps the computer, which had been with me the entire dive, was more accurate, since it had real data to go on instead of "the plan." When it said "three minutes," and I took two, I thought I was fine. Unfortunately, that was not correct. I should have stuck to the plan.

The fact that the plan - both with and without the computer - was the same, only proves the validity of the plan, which I ignored. Instead, I went by the "real data" that was on my wrist, which promptly put me into deco.

The lesson isn't to avoid computers, IMHO... It's to dive the plan. The fact that I can create an accurate plan with or without the computer makes me wonder why I spent $400 on a computer.

And frankly, if I hadn't had the "false security" of that thing on my wrist, I'd have never tried to push it. I'd have simply been back on the surface at 12 minutes... Or I probably would have made sure I had a rock bottom of 80 feet at 20 minutes total dive time instead, or something equivalent.

IMHO the computer got your ass out of the fire.

Hm. Well, I can certainly see that point of view, but I believe that the best way to have avoided this whole shebang would have been to dive my plan.

Tell me this. what would you have done if you happened to find yourself at 98 feet 4 minutes past your planned time if you didn't have the computer to walk you through your deco?

1. I should have taken better care not to get myself into that situation.

2. Assuming the above situation, I'd have done the following: In my PADI OW class, I was taught that if I blow my tables for no more than five minutes, then I'm to ascent to 15 feet and do a deco stop for no less than 8 minutes. If I added a normal 3 minute "safety stop" of 3 minutes to the mix, then I'd have decoed for a total of 11 minutes at 15 feet... Very similar to the 12 minutes at 10 feet that my computer mandated. There's more, too... No flying for 24 hours... No diving for 6... You know, standard stuff. This is all printed right on the PADI OW tables.

That's the extent of my training. I have not been taught decompression technique yet... Another reason why I should not have blown my tables like I did. Instead, I made decisions based on the information that was given to me which was a mistake... I should have stuck to my plan.

Actually, I guess what I really want to ask is what the hell were you thinking when you decided to blow plan?

Lol... Great question. Maybe others can learn from my mistake if they just understand what I was thinking at the time. Maybe then they can recognize it and avoid it like I should have.

I was thinking, "Hey, cool... This gizmo on my wrist says that it's okay to be down here another three minutes... Maybe I can get just a couple more bubbles in. I love diving!"

 

[Spectre]

SeaJay once bubbled...
Mistake number two, which wasn't obvious until I posted that profile, was taking a whopping 10 minutes to ascend to my "safety stop." I'm not sure why I did this... I don't remember consciously thinking to slow my ascent so much. I was aiming for 30 ft/min, not 8! This second mistake was the real reason why I went into deco, I think.

Bingo. That's where your real problem was. The biggest lesson here is that the bottom time clock doesn't stop when you begin your ascent. If that was the case we could drop to 120 and spend a day ascending... 'cause we're ascending.

What you did was you dove the computer, and then ignored it for your ascent. There _is_ such a thing as too slow.

In your Dive Manager, go into the profile stuff for those dives. Scribble down all the numbers. Then go into the simulator and re-create the dives.

Now start playing around.

What you are going to find is that when you were sitting at 98 ft @ around 18 minutes, if you ascended at 30 ft/min; you would have hit 15 without incurring any deco obligation.

Even a 20 ft/min ascent wouldn't have caused a deco obligation.

Your minor mistake was changing the dive plan. Your major mistake was switching to a new dive plan [your computer] and then throwing that out when you started your ascent.

 

[SeaJay]

Spectre once bubbled...


Bingo. That's where your real problem was. The biggest lesson here is that the bottom time clock doesn't stop when you begin your ascent. If that was the case we could drop to 120 and spend a day ascending... 'cause we're ascending.

What you did was you dove the computer, and then ignored it for your ascent. There _is_ such a thing as too slow.

Yep, that's exactly what happened. I began my ascent, but continued to ongas past my NDL. By the time I got to a depth where I was offgassing, I'd already earned a good bit of deco. 18 minutes of it. By the time I got to my ceiling, that had fallen to 12 minutes.

...Which is what I have grown accustomed to with this computer. As I rise, I get more NDL time, or in this case, a shorter deco time... Which is what I expected, and did not get, when I began my ascent from 98'. Instead, I ongassed past my NDL. Now that I think about it, perhaps that's why I was so slow to ascend... I was wondering, "WTF??"

I believe that the major problem was that I ascended too slowly. But that in itself would not have created the problem... It was combined with the fact that I was already too close to the edge of my NDL and I went over the edge.

...Which wouldn't have been a big deal, really... Except that I did not have enough gas to do so.

...So three solutions, then, are the result of our discussion:

1. Shorter bottom time.

2. Quicker ascent rate.

3. Be prepared for deco or don't deco.

Any one of those three would have solved the problem. Of course, any one of these three would have been the result of sticking to my dive plan, too, doncha think?

 

[MikeFerrara]

Well, I'm not going to say much here except that I think everyone is missing the real lesson.

 

[SeaJay]

What's the "real lesson" here?

 

[MASS-Diver]

(Aside from diving your plan) to write down in advance your deco times (from a table or program) in case you overstay your bottom time or exceed you depth (for a multi-level you could figure it on the fly using the UP method of time below 3 atms + time above

. Either way, the point would be not rely on your computer to take you through deco, since it will probably give you way overly conservative times that your gas supply may not allow.

 

[Pez de Diablo]

MASS-Diver once bubbled...
[BSnip..
. Either way, the point would be not rely on your computer to take you through deco, since it will probably give you way overly conservative times that your gas supply may not allow. [/B]

I disagree, my Oceanic is so liberal I would want to stay in the water for every single minute that it specified if it gave me a deco obligation.

 

[navy85]

SeaJay once bubbled...
...Maybe others can learn from my mistake if they just understand what I was thinking at the time. Maybe then they can recognize it and avoid it like I should have.

SeaJay - as a relatively new, inexperienced diver, thanks for having the guts to share your experience and endure a few pokes. I am gaining a better understanding of dive computers, their limitations, NDLs and of course the reasons for diving your plan as a result of this thread.

BTW, my parents live in Summerville (and I am an SHS alumni - Go Greenwave). If I have time to dive next time I'm there, I'll look you up - I've never been diving in the area.

 

[jiveturkey]

You have some pretty serious peaks and valleys in your profile. I wonder if this has anything to do with the long deco time. I don't know exactly how much movement it takes for nitrogen to come out of solution but I wouldn't be comfortable yo-yoing more than a meter or 2. Your Suunto probably doesn't like it either.