Nitrox and computers

[tbone1004]

I've send Deepblue a few emails saying that I don't think they have created a safe computer and have expressed my concerns about how what they think are "safety factors" are actually incredibly dangerous to the point that I would not be able to use one as a primary computer in a teaching environment and because of that, despite being an ambassador, won't promote it yet. Thankfully it is all programming things that they can update whenever they want, but I'm trying desperately to get them to do it.

I basically said this
Read Shearwater Recreational Nitrox mode
write code that makes your computer do what it can: 3 options for gradient factors, 3 gas mixes with decompression, and NEVER locks you out, for any reason. Continuously tracking your tissue loading regardless of what's going on. Any computer that doesn't do that is dangerous to me because if you HAVE to descent again for some reason, the computer just shuts down and that's a deal breaker for me.

regarding VPM, the reason you have to pay for the upgrade is because Shearwater has to pay royalties for the VPM algorithm, so it is there to cover their fees. Super annoying, but I don't have any faith in that algorithm anyway.

 

[EFX]

It appears from the OP first post shown below that DeepBlue has created the COSMIQ for recreational use. Yet, you want 3 deco gasses which is not needed for rec divers. I agree that no computer should ever lock you out. Just when you need the computer the most (i.e. missed deco stop, NDL) you can't use it. Three conservative settings is good. My Perdix in rec mode has three conservative settings. The Lo-Hi GF, although not settable, is grayed out but visible. The setting for medium conservatism is 40/85. I think the settings for low and high conservatism respectively are: 50/95 and 30/70.

I am looking at that new Deepblu computer and it states:

"Multi-Gas: COSMIQ does not offer a multi-gas function. Only one type of gas may be set (oxy-
gen 21%-40%). If you are planning a multi-gas dive, DO NOT use COSMIQ as your primary
device."

 

[kelemvor]

It appears from the OP first post shown below that DeepBlue has created the COSMIQ for recreational use. Yet, you want 3 deco gasses which is not needed for rec divers. I agree that no computer should ever lock you out. Just when you need the computer the most (i.e. missed deco stop, NDL) you can't use it. Three conservative settings is good. My Perdix in rec mode has three conservative settings. The Lo-Hi GF, although not settable, is grayed out but visible. The setting for medium conservatism is 40/85. From memory the settings for low and high conservatism respectively are: 50/95 and 30/70.

My understanding was that computers that lock out did it after the dive (and any necessary deco stops). I don't thin they lock out during the dive, preventing you from doing a mandatory stop. They prevent you from doing a repetitive dive after doing unplanned deco. They also may prevent you from doing a repetitive dive after skipping a stop. Not that I think lockouts are a good thing, but they're only a safety concern if you dive a computer and then decide you're going to ignore it for subsequent dives.

 

[tbone1004]

which is the big safety concern especially in a teaching environment because you can't afford to have the computer lock you out for any reason. For recreational divers it's one thing, but the way they implemented it makes the decompression "taboo" and that's just not good

 

[EFX]

My understanding was that computers that lock out did it after the dive (and any necessary deco stops). I don't thin they lock out during the dive, preventing you from doing a mandatory stop. They prevent you from doing a repetitive dive after doing unplanned deco. They also may prevent you from doing a repetitive dive after skipping a stop. Not that I think lockouts are a good thing, but they're only a safety concern if you dive a computer and then decide you're going to ignore it for subsequent dives.

Yes, you're right. However, there is one scenario I can think of where it would be useful not to lock it out. There may be others. What if you didn't have enough gas to complete deco? You could surface, quickly change tanks, reenter the water and complete the deco.

 

[kelemvor]

As I said, I prefer no lockouts. One of the reasons I bought two shearwater computers is that. I just think most people make a bigger deal than necessary out of the lockout issue. I've only ever done one decompression dive. It was planned, and I had 02 for accelerated deco. it was at the end of a day of repetitive dives on doubles. I'd never have been able to get into deco on single tank dives in a day. Some gas sippers can, I guess. I'd bet most new divers (especially males) are gas limited on their dives.

 

[tursiops]

My Perdix in rec mode has three conservative settings. The Lo-Hi GF, although not settable, is grayed out but visible. The setting for medium conservatism is 40/85. I think the settings for low and high conservatism respectively are: 50/95 and 30/70.

My Petrel 2 in Rec Mode uses Low, Medium, High GFs of 45/95, 40/85, and 35/75. What is interesting is if I set the computer in Tec Mode, at 35/75, I do NOT get the same NDLs, by 1-2f minutes (more) at 6-=110 ft.

 

[EFX]

Lockout may not be a big deal for some. The real ball buster is missing one minute of deco and getting locked out for 24 hours. Missing one minute of deco is not going to matter over the course of many dives but locking you out for a full day is a real inconvenience. At least the computer should unlock when the controlling compartment has cleared sufficiently during the locked out SI.

 

[stuartv]

Yes, you're right. However, there is one scenario I can think of where it would be useful not to lock it out. There may be others. What if you didn't have enough gas to complete deco? You could surface, quickly change tanks, reenter the water and complete the deco.

My Atom and the other rec computers whose manuals I have read, give you a few minutes (5?) at the surface before they go into Violation mode and lock you out, I believe.

As I said, I prefer no lockouts. One of the reasons I bought two shearwater computers is that. I just think most people make a bigger deal than necessary out of the lockout issue. I've only ever done one decompression dive. It was planned, and I had 02 for accelerated deco. it was at the end of a day of repetitive dives on doubles. I'd never have been able to get into deco on single tank dives in a day. Some gas sippers can, I guess. I'd bet most new divers (especially males) are gas limited on their dives.

I was hitting my NDLs (on Nitrox) while I still had plenty of gas left in my tank on a regular basis, by the time I had somewhere around 35 dives. And I'm no gas sipper. And that's with a very liberal computer. But, it did take using a 100 or larger. I probably would have been hitting my NDLs even sooner if I had just gone to North Carolina to dive the Outer Banks sooner. Dives to 100+ feet have pretty short NDLs, even when using Best Mix. Shallower dives have longer NDLs and I do think it would be hard to hit my NDL before running out of gas, if say, the bottom was only 60 - 70 feet.

However, I do agree that the lockout issue seems way overblown. I wouldn't necessarily call someone dumb for exceeding the NDL on their rec computer. But, if they do that and then get out without doing the stops their computer is telling them to do (the only way you're going to get locked out), THEN I would call them dumb and say that I don't see anything at all wrong with their computer locking them out of Dive mode. I just don't see where there would ever be any good reason for having required stops and skipping them. It would only be a result of diving stupidly. If you're not diving stupidly, but shtuff happens that results in getting locked out - say you were out of gas, hit the surface, switched tanks and went back down for in-water recompression, but weren't quick enough on the turnaround to avoid getting locked out - well, then, one, you shouldn't be getting back in the water. But, two, if getting back in really is your best option, you oughta spend 2 brain cells to remember what the required decompression was that your computer was asking for, get back in, do at least double what the computer wanted (which you can do with your computer in Gauge mode - which it should do even when locked out), and then still get out and stay out for at least 24 hours.

People who get locked out, quote "for no good reason", and want to keep diving anyway are being, well, I'll be generous and say they are being unsafe. I wouldn't want to dive with them, and I have no sympathy for their complaint of their computer locking them out. If they think they know better than their computer and want to ignore what it says, they should check their tables and dive their computer in gauge mode.

If I had a computer that was shortening my dives so much that I decided to stay longer than it allows because "my buddy's computer gave a much longer NDL, so I was following that", then I would get a more liberal computer. Except that several people on here have ASSURED me that no Rec computer gives so much shorter NDLs than any other that it would ever make any significant difference in the real world. So, that should never happen....

 

[stuartv]

Lockout may not be a big deal for some. The real ball buster is missing one minute of deco and getting locked out for 24 hours..

So don't skip that 1 minute of deco. How hard is that??