Feedback on recent two-tank and dive limits

[rongoodman]

If someone doing an NDL dive on air/nitrox and „slips into deco“ their computer will for sure prioritize RBT (remanning bottom/gas time) over deco optimization (GFs or MB levels are to be escalated to the next level all the way to the least conservatism)

I've never heard of any computer or algorithm which would attempt this. Unless the computer had air integration and a working transmitter it would have no way of even knowing how much gas was available.

 

[Belzelbub]

Apologies for the headache. But GFs can be a headache for the recreational diver. I agree that if you are using a GF on your computer for NDL dives you need to monitor the duration of your bottom time. When you select a particular GF, it will reduce your bottom time not only on your first dive but even further on your second dive and even further on your third dive (common on dive resorts and liveaboards).

The same can be said for other algorithms that offer differing levels of conservatism. I really don't think you understand how GFs work. At least with Buhlmann with GFs should a diver choose, they can use a variety of planning tools to understand how subsequent dives will act. You really can't do that with proprietary algorithms.

If not monitoring your computer (on the subsequent dives), your computer may direct you to complete a multi-stop ascent with the first stop at 21 metres. This surprise may be very challenging for an inexperienced recreational diver.

If a diver is using a dive computer and not monitoring it, then why are they even using the computer? If doing multiple dives a day, the diver needs to ensure they can do all the dives. If they are surprised to find their computer in deco, that's not the fault of the computer, algorithm, or conservatism settings/GFs. That's their own fault.

I'll never understand divers who choose to get a computer then never look at it.

In reality you may not need to do the multi-stop ascent. However, you selected the GF and now you have to decide to either follow the computer on a long multi-stop ascent or just do a 5 min safety stop at 5 metres. What would you do?

Again, you keep using GF as if that's the problem and it's unique to computers that use GFs. It's simply a conservatism setting. If you set a higher conservatism setting, then you will have reduced NDLs compared to the more liberal settings. That's true for Buhlmann, RGBM, DSAT, or whatever. If you choose a particular setting, I'm going to assume you did so for a reason. Therefore, you follow it. It's really not that hard, and has everything to do with conservatism settings, not just those that are adjusted by GFs.

Computers with customizable GFs really only offer the diver to fine tune the conservatism to what they need. Before that diver does that, they really should understand what that means and what the implications of those settings are.

A more conservative GF only reduces NDL time for a NDL dive. It does not, as you stated, automatically turn that dive into a multi-stop deco dive.

 

[inquis]

I am not saying that they are going into decompression. The Low GF they select (which sets the first stop), that programs the computer may tell them they are going into decompression, as opposed to a safety stop. In reality they may be well within the NDL.

This makes no sense. If they are "well within NDL", as you say, they can directly surface. The very concept of a "first stop" requires that you cannot directly surface, which is why GFLow is ignored until tissues are above GFHigh. As stated several times above, GFHigh determines the NDL.

 

[Mobulai]

I've never heard of any computer or algorithm which would do this. Unless the computer had air integration and a working transmitter it would have no way of knowing how much gas was available.

That’s true, my bad — slipped my mind since that’s how I dive

But even without AI, if the „planned“ stop isn’t at the ceiling, it can be skipped if a look at the spg suggests the current depth and gas reserves aren’t sustainable (if the user had the knowledge to actually support this decision)
That’s the essence of what I was getting at

Thanks @Blackcrusader and @rongoodman for pointing it out

 

[Belzelbub]

I've never heard of any computer or algorithm which would do this. Unless the computer had air integration and a working transmitter it would have no way of knowing how much gas was available.

Yes. Air integration would be required. My Oceanic had a Dive Time Remaining optional display, but I don't think it functioned as was described. It was simply a calculation. It would use both NDL and GTR and just display whichever was lowest. I didn't really care for that as there you couldn't really tell which was controlling. I much prefer the display on my Shearwater ( Sarcasm: Even with those dangerous GFs /Sarcasm) which allows me to show both.

 

[Blackcrusader]

That’s true — slipped my mind since that’s how I dive

But even without AI, if the „planned“ stop isn’t at the ceiling, it can be skipped if a look at the spg suggests the current depth and gas reserves aren’t sustainable
That’s the essence of what I was getting at

Yeah see my Deco dive log and the fact I do not use AI. So I asked how so to your post

Now I do have a Cressi Digital display but it only shows the range / time of dive remaining left to 50 bar.
After that you just get a flashing display.

 

[34109411]

Are you not all working this morning ??? (like me ).

So much time debating this.

 

[boulderjohn]

I am not saying that they are going into decompression. The Low GF they select (which sets the first stop), that programs the computer may tell them they are going into decompression, as opposed to a safety stop. In reality they may be well within the NDL.

No. The GF low setting only comes into play if you go into decompression.

 

[Belzelbub]

I am not saying that they are going into decompression. The Low GF they select (which sets the first stop), that programs the computer may tell them they are going into decompression, as opposed to a safety stop. In reality they may be well within the NDL.

This is completely wrong. Again, I'm saying you don't understand how GFs work.

The GF that sets the first stop is GFLo (The first number). For an NDL dive, this simply doesn't matter.
GFHi (second number) is what will tell the diver that they are going into decompression. Only if this is exceeded, will GFLo actually come into play.

And, if they accidentally exceed the NDL, the ascent decompression profile calculated by the computer, may increase exponentially in a short time. Hence the 21m or perhaps 15m first stop.

That's not actually how it works. As a few others have posted, a minor breach of NDL will possibly clear on the way up. It will show a stop is required, but depending on the ascent, when the diver reaches that depth, they may find that it is no longer required.

One could argue that it is not probable, but it may be possible. We are talking about recreational divers who may not have much experience.

You keep vilifying GFs. What is the difference with a diver using another computer and setting a higher conservatism? If they exceed the NDL, they exceed the NDL. They should have been watching their computer better. Can't blame the tool in this case.

 

[34109411]

This is completely wrong. Again, I'm saying you don't understand how GFs work.

The GF that sets the first stop is GFLo (The first number). For an NDL dive, this simply doesn't matter.
GFHi (second number) is what will tell the diver that they are going into decompression. Only if this is exceeded, will GFLo actually come into play.

That's not actually how it works. As a few others have posted, a minor breach of NDL will possibly clear on the way up. It will show a stop is required, but depending on the ascent, when the diver reaches that depth, they may find that it is no longer required.

You keep vilifying GFs. What is the difference with a diver using another computer and setting a higher conservatism. If they exceed the NDL, they exceed the NDL. They should have been watching their computer better. Can't blame the tool in this case.

thank you for that ! you explain my taught better than me !