Past NDL. And then this???

[stepfen]

Hello, I am a beginner with AOW certificate and about 50 dives.

During the 3rd (and last) dive of that day on a multi-day diving vacation trip the following incident happened. The max depth of the dive was at 27meters and I was getting pretty close to my NDL. We had already started our (slow) ascent being now somewhere near 20meters 26 mins into the dive.

I knew from previous dives that my computer (Cressi Leonardo) was quite conservative (compared to my fellow divers’ computers - mostly suuntos zoop, d4 etc) so I didn't worry too much about diving very near my NDL .

Well, something came to my attention few meters below me and I descended 1-2 meters to have a look and that was it. My computer went to DECO “mode”.

I remained calm knowing that that it was not the end of the world (eg my fellow divers had several minutes NDL left, I had plenty of gas etc) and continued a slow but now steady ascent (no more looking around for fish etc – just focusing on the ascent, my gas, the computer and the group).

My question is about the behaviour of my computer. I know Leonardo is not a Deco computer and that it should not be used that way, but still it has made me very confused. It directly gave me 7 minutes total deco time (4 mins deco + 3mins safety) at 3 meters – fair enough. But then, every second I was below 4 meters or so it kept adding (a lot of) deco stop time.

I was hopping that by slowly assenting, deco time would decrease or at least stop increasing. It took me 20 minutes to reach 4 meters - now 45 minutes into the dive. The main reason being I didn’t want to separate too much from the rest of the team (they continued their pre-decided dive profile). By the time I reached 4 meters my computer was asking me to have 35 mins deco plus 3 mins safety!

I remained at about 3-4m for 35 more minutes. Then my air was getting low and I decided to surface (boat was next to me most of this time). By that time the computer was still asking 5 mins deco (I don’t know why). The dive guide took my computer and stayed in the water for another 10 mins or so to make it happy.

Needless to say that everybody else in the group was within their NDL at the end of their dive (70 mins duration) and look at me like an alien or something trying to figure out how the heck I managed something like this. At least they were nice enough not to show even the slightest frustration to me delaying their going back to base for these 20-30 extra mins or so.

Following this I did investigate the dive with Subsurface and I saw that indeed I was outside my NDL time (I know I shouldn’t have been there to begin with). But Subsurface (with the default algorithm/settings) by the time I reached 4m gave me 0 calculated deco time while my computer was giving me 35 + mins deco time! Is such difference normal?

I also investigated SB and I fount out that it is well documented in SB and elsewhere that Leonardo becomes very conservative (compared to other computers) from the 3rd daily dive onward! But such differences?

Please keep in mind that the purpose of this post is to learn. I think I understand the risk and what I did wrong from my side. Please don’t focus too much on blaming/punishing me for my mistake. I could just forget about all these, keep quiet and just keep diving like it never happened. But I don't because I want to know what is going on.

What I am querying about in this post is the behaviour of my dive computer past the NDL. Is that behaviour the right one? Am I asking too much from my computer? And of course the next question is: are the other computers that liberal? Why? Is that ok?

Another less important question: I did check later my computer and “Deep Stop” option was enabled but I don’t know why my computer choose not to suggest a deep stop either.

Thanks a lot for any insight and sorry for the long post. I just wanted to have everything as clear as possible.
Cheers

 

[Edward3c]

Hi,

First, have you read the computer manual and what the algorithm will do if you don't follow its rules?

Deep Stops will increase your gas loading of slow tissues, and are now not recommended.

All the time you spent slowly ascending may have been adding more slow tissue deco time (read the manual), whereas if you'd gone straight to you stop depth you wouldn't have had such a penalty.

If you're going to do dives involving deco stops my suggestion is get some training on them, their not difficult.

 

[stepfen]

Hi,

First, have you read the computer manual and what the algorithm will do if you don't follow its rules?

Deep Stops will increase your gas loading of slow tissues, and are now not recommended.

All the time you spent slowly ascending may have been adding more slow tissue deco time (read the manual), whereas if you'd gone straight to you stop depth you wouldn't have had such a penalty.

If you're going to do dives involving deco stops my suggestion is get some training on them, their not difficult.

Thanks for the quick reply Edward3c.

I have read the manual before that dive (several times), and I re-read it after the dive. But all the manual is saying about deco is basically:
A. Don’t go to deco
B. If you do, the computer will help you to ascent as safe as possible by setting ceiling/deco times. Just follow the instructions and it will hopefully be ok.

No other details are given and big part of my frustration is this too. Maybe I am asking too much?

Thanks for the advice concerning deco dives too, but I don't plan to make planed deco dives (at least for now). The reason I want to know about these is that I want to know what happens in a case of an unexpected deco dive (due to eg an emergency or a similar mistake like mine). Yes, it shouldn't happen. But in case it will happen in the future I would like to know how to best handle it. And to me simply following my computer doesn't seem to be the best option.

Thanks again

 

[KenGordon]

As Edward says, you ascended far too slowly. For part of that time you were still ongassimg. If you are not deco trained then I suppose you should try to abort an accidental deco dive asap. You did not do that as you were trying to keep the rest oyour 'team' in sight. Really you should have shown them an up signal and all ascended together.

Alternatively, train to do the dive, and get comfortable with a deco ascent. You should learn what is vaguely normal, how Nitrox helps and how surface intervals are important.

My number one suggestion is to always have a buddy, only have a true team if so trained, and stick with your buddy and have them stick with you. It sounds like your 'team' was just a bunch of people diving from the same boat really.

 

[tilikum]

Or get a more liberal computer.

 

[tursiops]

What was your actual dive profile? Can you post a graph from your computer download?

It sounds like you essentially ignored the deco warning and kept diving....20 mins to get to your deco stop is almost ten times as long as it should have taken. You kept doing a "deep" dive, so your computer kept accumulating additional deco time. No surprise.

 

[azstinger11]

Thanks for the quick reply Edward3c.

I have read the manual before that dive (several times), and I re-read it after the dive. But all the manual is saying about deco is basically:
A. Don’t go to deco
B. If you do, the computer will help you to ascent as safe as possible by setting ceiling/deco times. Just follow the instructions and it will hopefully be ok.

No other details are given and big part of my frustration is this too. Maybe I am asking too much?

Thanks for the advice concerning deco dives too, but I don't plan to make planed deco dives (at least for now). The reason I want to know about these is that I want to know what happens in a case of an unexpected deco dive (due to eg an emergency or a similar mistake like mine). Yes, it shouldn't happen. But in case it will happen in the future I would like to know how to best handle it. And to me simply following my computer doesn't seem to be the best option.

Thanks again

It told you exactly what to do, you just didn't do what it told you.

Page 50, cressi Leanardo owner's manual
1) Stop icon with the writing DECO, showing that the no decompression limits have been violated and that decompression stops must be performed. The arrow indicating UP flashes.

2) Depth of first decompression stage (the deepest), given in meters (m) or feet (ft.). It may vary from a maximum of 78 ft. to a minimum of 10 ft., by steps of 10 ft..

3) Time in minutes for the first decompression stage (the deepest).

4) TOTAL icon, indicating the total ascent time, that is the time required to ascend to the deepest stage, respecting the ascent rate, PLUS the stop time at that depth and at any other subsequent stop (including the deep stop if necessary), PLUS the safety stop time, PLUS the time required to reach the surface after completing the decompression stages.

So it gives you a depth, time to get there, and a time to stop at that depth. When you willfully ignore that and don't ascend on schedule, you get more deco obligation.

You want to dive deco? Great, there are courses and computers for that.

You aren't "asking too much" out of your dive computer. It's doing exactly what is suppose to, trying to stop you from getting bent. You busted your NDL and then you didn't honor the deco schedule thus you got hit with a long deco once you finally got near the surface.

Your DM taking it to make it happy bothers me a lot. You busted deco, simple as that, no more diving for a while.

 

[Diver0001]

My question is about the behaviour of my computer. I know Leonardo is not a Deco computer and that it should not be used that way, but still it has made me very confused. It directly gave me 7 minutes total deco time (4 mins deco + 3mins safety) at 3 meters – fair enough. But then, every second I was below 4 meters or so it kept adding (a lot of) deco stop time.

This is normal behaviour for a computer running a Buhlmann algorithm. Deco will usually start with 7 min "time to surface" and the ceiling will be 3m to start. The reason it didn't give you a deep stop is probably also related to the algorithm you had selected. I believe you can choose between two different algorithms with that computer.

It took me 20 minutes to reach 4 meters - now 45 minutes into the dive.

This was a mistake. Once the computer was in deco mode you should have signaled your buddy to end the dive. Your ascent should be at LEAST 3 meters/min and at MOST 10m / min. From 26 to 4 meters it should have taken you 3 minutes or so. The reason it kept adding deco time is because you were not actually ascending even though you had convinced yourself that you were.

R..

 

[stepfen]

As Edward says, you ascended far too slowly. For part of that time you were still ongassimg. If you are not deco trained then I suppose you should try to abort an accidental deco dive asap. You did not do that as you were trying to keep the rest oyour 'team' in sight. Really you should have shown them an up signal and all ascended together.

Alternatively, train to do the dive, and get comfortable with a deco ascent. You should learn what is vaguely normal, how Nitrox helps and how surface intervals are important.

My number one suggestion is to always have a buddy, only have a true team if so trained, and stick with your buddy and have them stick with you. It sounds like your 'team' was just a bunch of people diving from the same boat really.

My (obviously naive/newbie) understanding is that once past the NDL there is already more than the safe amount of gas in my tissues. Don’t I risk turning that gas to bubbles by going up “fast” ??? And obviously by fast I don’t mean faster than 30 feet-10m/min.

Obviously I was slow, but subsurface’s algorithm was happy with it (0 deco once I reached 4m). Of course that was much later, being totally dry in the comfort of my desk.

I will try to upload the profile once I find out how (I am new to the forum).

Thanks a lot

 

[stepfen]

It told you exactly what to do, you just didn't do what it told you.

3) Time in minutes for the first decompression stage (the deepest).

Ok. Now I see. English is not my native language. Hence I interpreted no 3) as time to spend on the next deco stop and not time to reach the next deco!!!

I thought the computer was telling me: Look, you will have to spend 4 mins deco at 3 meters while it was telling me, within 4 minutes you have to be at 3 meters ! It makes a lot much more sense to me now.

Thanks a million to help me see that