Dive Computer No Deco Computations Question

[Bento.Box]

So, if you are slightly above the stop for more than 3 minutes, the computer locks you out DURING THE DIVE.

but then you're outside your operating envelope, not anymore in a normal dive.

how should the algorithm continue?

 

[beldridg]

but then you're outside your operating envelope, not anymore in a normal dive.

how should the algorithm continue?

Without putting a ton of thought into it, I would probably calculate your tissue off-gasing based upon your actual depth (even if that means you are above your stop) and continue to calculate the stops based on your gradient factors and tissue loading.

Pretty much anything is better than going into VIOL mode during a dive.

In fact, at least on Shearwater, you can see your theoretical ceiling (CEIL) which is generally above your stop depth because of the stop intervals at 3m/10' increments. E.g., when you are at your 30' stop, your CEIL could very well be 21' before it switches to your 20' stop. If you go above your stop but below your CEIL, you get a "Yellow" warning. If you go above the CEIL, you get a "Red" warning.

If I am on a 30' stop and my CEIL is 23', and I go to 29' for 3 minutes, should the computer just shut down and not show me any of the remaining stops?

Regards,

- brett

 

[Bento.Box]

If I am on a 30' stop and my CEIL is 23', and I go to 29' for 3 minutes, should the computer just shut down and not show me any of the remaining stops?

But the remaining stops are calculated under the premise that you are able follow the decompression plan.
Hence the data becomes invalid. Question is also, would you be able to follow the remaining stops?

I honestly don't know what the best practice is for resolving decompression violation - what does the theory say?

As an NDL diver I wouldn't expect my computer to automagically offer a resolution to this issue. If that happens, I probably have a lot worse problems to deal with at that moment as I've already failed to follow both floor and ceiling restrictions for an extended time.

 

[tursiops]

But the remaining stops are calculated under the premise that you are able follow the decompression plan.

Nope. On the Shearwater they are calculated based on what you are doing, not on what you should have done.

 

[Bento.Box]

Nope. On the Shearwater they are calculated based on what you are doing, not on what you should have done.

but is this copium or sound medical advice?

 

[tursiops]

but is this copium or sound medical advice?

It is the best you can do under the circumstances. Far better than just being locked out and told to go spend the rest of your gas at a safety stop. The Suunto approach is outdated. It is the same advice given if you overstay your NDL while using tables.

 

[Belzelbub]

A couple I met this trip just a few days ago who were diving Nitrox 32% with air set in their computers and got locked out in the water. I tried to explain to them the illogical concept of tricking your computer as a safety pad but it went in one ear and out the other. So they just continued to dive with nothing.

Sheesh. Well, at least you tried to help. Some people just can't be helped.

Really makes me wonder, though. Why did they buy the computers if they aren't actually going to use them? While I'm not a fan of lying to your computer by setting to Air when diving NX32, I understand why some do. However, if you then just ignore the warnings and guidance of the computer, what good is it. I just can't understand the reasoning there.

 

[boulderjohn]

Sheesh. Well, at least you tried to help. Some people just can't be helped.

Really makes me wonder, though. Why did they buy the computers if they aren't actually going to use them? While I'm not a fan of lying to your computer by setting to Air when diving NX32, I understand why some do. However, if you then just ignore the warnings and guidance of the computer, what good is it. I just can't understand the reasoning there.

It was once a very common practice. People with the necessary credentials to be published in scuba magazines recommended diving with nitrox but using air tables/computer settings for many, many years. It never made sense to me, but they were the respected scuba authorities. Go back through enough ScubaBoard discussions and you will see it argued many times.

 

[dmaziuk]

but then you're outside your operating envelope, not anymore in a normal dive.

how should the algorithm continue?

There is nothing stopping it from tracking gas loading above the ceiling. What it can't do is recalculate you a different ceiling -- not until you off-gas enough to have one above your current depth.

Edit: speaking straight-Haldanean model like ZH-L. Bubble voodoo can be somewhat more complicated.

 

[David Carron]

It is the best you can do under the circumstances. Far better than just being locked out and told to go spend the rest of your gas at a safety stop. The Suunto approach is outdated. It is the same advice given if you overstay your NDL while using tables.

You certainly might think so, but consider this case:

GF 50/80 you descend to 50m and stay there for 20 minutes resulting in 45 minutes of decompression starting at 18 metres.

Same GFs, your buddy executes the same dive but at 15 minutes, he ascends rapidly and directly to the surface in 1 minute where he remains for 2 minutes before redescending to 50 metres in 2 minutes. At the 20th minute of the dive, your buddy will be told by his shearwater that despite the suicidally dangerous profile the recommended ascent is only 35 minutes of decompression starting at 9m.

Whilst this is clearly an extreme case, actively reducing the decompression obligation doesn't really seem to be "the best you can do under the circumstances".