Divecomputer NDL calculations

[Alekseolsen]

Had another great dive today, but was a bit puzzled by my computer.

At ~25m or so, I ran out of NDL, and as I've usually been doing, I went up a few meters.
Usually that gives me quite a bit of additional NDL-time, but not so today.

Although my "ceiling" never went below 0,2meters, it puzzles me as to why I did not "gain" any additional NDL-time. I went up to 18 meter and followed the bottom shallower, but I wasn't "rewarded" until I hit ~10 meters.

If it matters, I've been diving daily for a week (only 1 dive a day), on air, around 60 minute dives. My computer is a heinrich weikamp OSTC 2C.

Had I simply just been too deep for too long. (As in, my earlier experiences have been shallower/less time)?

I guess I shouldn't, but I'm quite happy it's finally NDL and not air supply that is the limiting factor

Buddy was diving twinset with Nitrox, so he had plenty of time on his computer.

 

[tursiops]

If you ran out of NDL, did your computer show a deco ceiling and time?
Diving until you hit NDL or until your air runs out is not a best practice....

 

[Alekseolsen]

It did show ceiling, at 0,2 meters. It cleared imideatley as I arrived at ~10 meter ish. Obviously I wouldn't want to run out of NDL, I've just been used to going a couple meters shallower-> "NDL-refill", but seems like that's not every time. (Or, 7meters wasn't enough). I'll get some Nitrox for next dive

As I read your comment, I realise it might seem like I usually run out of air, which wad not what I meant, just that earlier I've reached half tank (and returned) long before the NDL have been an issue.

 

[doctormike]

It did show ceiling, at 0,2 meters. It cleared imideatley as I arrived at ~10 meter ish. Obviously I wouldn't want to run out of NDL, I've just been used to going a couple meters shallower-> "NDL-refill", but seems like that's not every time. (Or, 7meters wasn't enough). I'll get some Nitrox for next dive.

Nitrox won't fix this problem, if your dive plan is to dive until you go into deco, and then hope that it clears on the way up.

As a practical matter, yes it might. But if you haven't trained for that, planned for that, calculated how much back gas you need to safely deco, etc... you could find yourself in trouble.

What would you have done if your LP hose had blown while you still had a ceiling?

 

[Alekseolsen]

At that specific dive, get gas from buddy.
Regardless, I did not intend to hit the NDL-limit, that was a ****up. The limit did not change as I've been used to, so curious as to what I made different this dive compared to others. Approaching NDL-> go shallower. Clearly, I failed to go shallow enough quick enough (no rushing, just slowly ascending).

For the future, I'll make sure there are more minutes available before going shallower.


Just to make it clear, I'm a couple hundreds dives from potentially considering getting training to do deco-dives, so that's by no means the plan.

 

[Fastmarc]

The behaviour this time is different because it seems you actually exceeded the NDL and went into deco. You would no longer be seeing NDL, so it won’t be showing NDL going back up. It would be showing your ceiling.

What others are saying is that running your NDL to 0, sometimes referred to as riding your NDL is not a good idea for a variety of reasons.

 

[Alekseolsen]

Correct that I did exceed the NDL, but that was at 18 meters, where I had expected the NDL limit to have increased. Guess it all comes down to simply me beeing to deep for too long.
I'll definitely ascend earlier from now on.

Thanks too all of you.

 

[doctormike]

At that specific dive, get gas from buddy.
Regardless, I did not intend to hit the NDL-limit, that was a ****up. The limit did not change as I've been used to, so curious as to what I made different this dive compared to others. Approaching NDL-> go shallower. Clearly, I failed to go shallow enough quick enough (no rushing, just slowly ascending).

For the future, I'll make sure there are more minutes available before going shallower.


Just to make it clear, I'm a couple hundreds dives from potentially considering getting training to do deco-dives, so that's by no means the plan.

Ok, that makes more sense. As long as you are aware that you shouldn’t deliberately run your NDL to zero with the expectation that your deco obligation will just go away on a normal ascent...

 

[Alekseolsen]

Oh, seems I've been explaining poorly then. Apologies for that.

It's the first time I've seen any other ceiling than 0.0 on my computer, and I do not intend to see it again for a couple hundred dives. (Computer displays Ceiling all the time, but with 0,0 meters.)

I'm not trying to dive "Cowboy-mode"

 

[Miyaru]

Can you download the dive profile and post it here?