Question Perdix Shearwater AI

[Belzelbub]

I agree that a computer that allows post-hoc adjustment of conservatism by reanalyzing old data and figuring out if there is a violation given the new conservatism setting would be best, but I imagine that's a lot of work and complexity (depending on the software architecture) to implement for the manufacturer, and that may be why they don't do it, given it would be a very niche feature, especially for recreational diving. Interesting concept though.

Well, at least one computer manufacturer does do this. The SurfGF feature I mentioned is one way. GF99 is another. Both can easily be displayed in real-time on my Perdix. I have SurfGF displayed on the main screen, so at any point of the dive I can get a sense of probable risk if I had to get out of the water immediately.

Should is a strong word... if the buffer is due to model uncertainty, how much of the buffer you should be allowed to cross really just depends on your risk tolerance.

I disagree. If the buffer is added by the user in the form of selecting higher conservatism, then a violation of that should not cause a lockout if a lower conservatism setting would not mean a violation. Most divers are not selecting conservatism factors based on any actual data.

 

[tursiops]

If they would resort to foolish tricks, why wouldn't they just dive on gauge mode?

That would require knowing how to use tables.....which are even easier to misuse than a computer.

 

[grassybreakfast]

Well, at least one computer manufacturer does do this. The SurfGF feature I mentioned is one way. GF99 is another. Both can easily be displayed in real-time on my Perdix. I have SurfGF displayed on the main screen, so at any point of the dive I can get a sense of probable risk if I had to get out of the water immediately.

That's cool. Sounds like a Perdix is a good choice if that feature is important to you.

I disagree. If the buffer is added by the user in the form of selecting higher conservatism, then a violation of that should not cause a lockout if a lower conservatism setting would not mean a violation. Most divers are not selecting conservatism factors based on any actual data.

I think it's probably more accurate to say the size of the buffer is selected by the user. There is no buffer size that is "safe" and anything above is extra. It's a sliding scale from 0 buffer (most probably not safe) to a large buffer (that is safer). "Violation" is defined relative to that buffer, so at high conservatism, a violation is still a violation based on that risk tolerance, and it's just as valid a violation as a violation at a different risk tolerance setting. I guess you can argue that lockout decision should always be made based on the lowest conservatism setting allowed by the computer, and that wouldn't be something I agree with, but I can see why someone would want that if they are pushing the limit.

Personally, if I get to deco in my NDL diving at my conservatism setting, something has already not gone to plan. And then skipping deco would be another thing that has gone wrong. At that point not being able to dive for 24h is not really something I worry about. That's why my recommendation for the Aqualung computer is qualified for being for rec diving. I think intentionally trying to cut deco short based on GF setting is probably beyond the definition of rec diving by most definitions, and cutting deco short accidentally because of ignorance we have already discussed as well.

 

[Blackcrusader]

You mean the recreational tables published by many dive training agencies? There’s a reason for that. Key word is recreational, as most training agencies do not train for deco procedures in the recreational world. Maybe light deco, but that’s it.

Most agencies such as PADI? SSI? Maybe in the USA but in the UK and Europe deco diving was pretty normal when I did my courses. I am not certain for today except that BSAC which teaches sports diving is deco dives. Deco is deco doesn't matter the bottom time. If we agree PADI is the largest agency which does not teach deco in recreational diving then yes that's true. I learned deco as a novice sports diver that's no different than a PADI OW. That's only because the country I was working in the dive center was run by British instructors who basically said forget your PADI OW and join the dive club and learn a broader range of skills. As there was no internet in the 1980's there really wasn't many ways to learn about agencies. Today people can search and find many agencies.

I do not see deco dives as not being recreational diving but others may claim it is technical diving. When I was learning mixed gas diving was technical diving and certainly not even nitrox was considered safe for "recreational divers" back then.

When I do my TDI advanced nitrox and deco course this year I will still consider that recreational diving. I guess I could claim I have a "technical diving certificate" For me Trimix and CCR diving is where technical diving is at.

Now back to the OP's question I think she should keep her Perdix AI as it is a great computer.

 

[Blackcrusader]

For the record, I’m not against justified lockouts, or dire warnings. However, this should be based on actual violations of the algorithm limits. Adding conservatism to keep away from those limits should not be the basis for a lockout. There are better ways to handle these violations of conservatism limits that don’t actually even violate NDL.

The point is they violate the NDL for that dive computer. It matters not what tables or other computers may read. Divers have to pay attention to the DC they are using. I owned a Suunto and yes it was conservative but I still dove to it's NDL limitations on NDL dives.

I was diving in a group and a young chap who just finished his AOW and Nitrox course was buddied with his father also newly certified AOW. He was diving on Nitrox 32% and following his guide. ( I was on the same dive boat but by then I had my Perdix AI ) Anyway his Suunto DC was on 21% and he missed that before the dive even with a dive check. So he exceeded his NDL as he just followed the guide and the computer locked him out as he missed clearing his deco obligation because he did not understand his computer fully even when it was beeping at him he thought it was someone else's computer beeping. All the divers were on nitrox. So anyway he was told that he could not dive for 2 days until his DC unlocked itself. He was of course disappointed as he was diving with his father and brother and sister but after a briefing we accepted the reason why. Justified to miss two days of diving? Maybe not but it was a good lesson for him. He asked could he use a different computer the next day and was told no and the reasons explained that none of his previous dives were logged which affects NDL times on repeat dives.

How would you have handled this diver?

 

[Belzelbub]

The point is they violate the NDL for that dive computer. It matters not what tables or other computers may read. Divers have to pay attention to the DC they are using. I owned a Suunto and yes it was conservative but I still dove to it's NDL limitations on NDL dives.

Actually, it could be that they violate the NDL for that computer at the user selected conservatism. If that were to be a violation of the base algorithm on that computer, that’s a different discussion.

How would you have handled this diver?

That was a good example. 48 hours does seem to be pretty severe, especially when the dive itself was actually within the NDL. That is a good lesson for him to learn. Missing two days of diving for an error is definitely a lesson. But, there was more than one mistake there. First was not setting the correct mix. Next was just following the dive guide, and not paying attention to/understanding the computer.

Not sure there is a real good solution that would be commonly accepted today. One option would be to dive tables, assuming the diver is familiar with their use. Depending on the dives, that may not be ideal and could limit the other divers unfairly.

If he had a computer that wouldn’t lock out, there could have been another option. He may have had to sit out the next dive until that computer would allow for a dive of the planned duration. That sounds better than sitting out for two days.

 

[Blackcrusader]

Actually, it could be that they violate the NDL for that computer at the user selected conservatism. If that were to be a violation of the base algorithm on that computer, that’s a different discussion.

That was a good example. 48 hours does seem to be pretty severe, especially when the dive itself was actually within the NDL. That is a good lesson for him to learn. Missing two days of diving for an error is definitely a lesson. But, there was more than one mistake there. First was not setting the correct mix. Next was just following the dive guide, and not paying attention to/understanding the computer.

Not sure there is a real good solution that would be commonly accepted today. One option would be to dive tables, assuming the diver is familiar with their use. Depending on the dives, that may not be ideal and could limit the other divers unfairly.

If he had a computer that wouldn’t lock out, there could have been another option. He may have had to sit out the next dive until that computer would allow for a dive of the planned duration. That sounds better than sitting out for two days.

Yes he was actually within NDL limits as he was on nitrox 32% but the DC on 21%. But the lockout was a combination of your points, he did not check his DC on the dive, he had an incorrect setting. The other thing was that he didn't know that he may have even violated the 32% NDL limit either. We don't think he did but who can be totally sure you cannot download the log when the DC locks you out. So there is an uncertainty factor.

Also back to points made, it would be bad diving practice to have a DC lock out then allow the diver to just continue diving as if nothing was wrong and let him dive on RDP tables as he could not know his previous dive profiles either. Btw I have dived with him after that and he now checks his DC before every dive and one time found he was setup for 32% on his DC on a normal 21% tank. He had forgotten to change from the previous days diving. So he did learn from being locked out. Those 2 days he remembers for the rest of his life and it has impacted his attitude towards his diving. Those two days of sitting out let him reflect on making mistakes on not properly checking his and his buddies diving DC's setup.

He also understands he has to dive to his own DC even though his buddy may have a DC showing more time to NDL due to variance in settings. He learned his DC has 3 settings that he did not know about when he bought his DC. Like many divers with a new DC they really do not know fully know it works. He also learned my Perdix does not have audio alarms so when diving with me and he hears beeping he checks his DC not mine lol

 

[Belzelbub]

We don't think he did but who can be totally sure you cannot download the log when the DC locks you out. So there is an uncertainty factor.

I was not aware that you couldn’t download the log in that case. Yes, that would make things more difficult if you can’t even access max depth and dive time, where reverting to tables might be possible.

He also understands he has to dive to his own DC even though his buddy may have a DC showing more time to NDL due to variance in settings. He learned his DC has 3 settings that he did not know about when he bought his DC. Like many divers with a new DC they really do not know fully know it works. He also learned my Perdix does not have audio alarms so when diving with me and he hears beeping he checks his DC not mine lol

Sounds like he’s more aware today, so I guess that’s a benefit. I wonder, though. If he were to be buying a computer today, would he make the same choice?

I’d hope he’d at least do a bit more research and get familiar with the functions and settings of his computer.

 

[Blackcrusader]

I was not aware that you couldn’t download the log in that case. Yes, that would make things more difficult if you can’t even access max depth and dive time, where reverting to tables might be possible.

Sounds like he’s more aware today, so I guess that’s a benefit. I wonder, though. If he were to be buying a computer today, would he make the same choice? I’d hope he’d at least do a bit more research and get familiar with the functions and settings of his computer.

He was a young man who asked the dive center what DC would be good. The dive center was telling divers to buy the Suunto Vyper or Zoop as they were good for recreational divers with limited experience. So you get this quite often dive centers promoting cheaper DC's for newly certified divers. I meet many OW AOW certified Suunto owners who have never dived in anything other than the default setting the Suunto came with. They are unaware of different settings being available apart from 21 % air and Nitrox 32%. Very common with PADI vacation divers. Nothing really wrong with that if they don't exceed NDL lol

They do not know gas planning or understand what software the DC uses. They don't know RMV or SAC they don't know how many liters of air an AL80 holds at 210 bar or 50 bar. GF and surf GF, Deco, CNS, PPO2 all these things are alien to them. Some barely understand TTS. They certainly do not understand how some fat fella like me comes back from a dive with 120 bar and they only have 40 bar. It's not right. They were told large people use more air than others. They get told nitrox gives them longer dive times only to find out they stayed deeper and had a shorter dive time and this does not compute lol

 

[grassybreakfast]

Sounds like he’s more aware today, so I guess that’s a benefit. I wonder, though. If he were to be buying a computer today, would he make the same choice?

I’d hope he’d at least do a bit more research and get familiar with the functions and settings of his computer.

It sounds like now that he knows how computers work and won't be blowing through deco stops, it shouldn't really be a factor anymore anyways?