Why would you need to switch gases?

[clownfishsydney]

Of course you may need to switch gases.

What if you are using nitrox but for some reason, you need to use your buddy's tank which contains air? If your computer stays on nitrox setting while you are breathing air, then your no deco time will not be correct. If you are close to deco, then this may mean you actually go into deco while your computer shows you are not.

If you are in deco, then it certainly will cause problems as your computer set to nitrox will require less deco stop time than if it was set to air (which is what you are using).

 

[Dhboner]

skankpile, that's not true at all. Certain gas switching computers don't, hell the Shearwaters don't actually have the ability to beep or vibrate or anything like that.

For me, there are a few criteria that are very important when purchasing a computer
MUST have gauge mode, this is not optional. If it doesn't, you have a useless paperweight if you ever go into technical diving

MUST have at least 2 gasses. It doesn't actually cost the manufacturers any more to make these, they already have algorithms made with multi gas and it is all of like 10 lines of programming to program the gas switch. Same reason as above, 2 gas computers with gauge mode are the sweet spot, allows you to "ride the computer" for light technical diving, i.e. extended bottom time at 100ish feet with relatively short O2 decompression, and has gauge mode if you get into more gasses or want to dive tables

Preferably have user replaceable battery. None of this have to take it to a dive shop to change the battery bs.

Preferably has avg. depth function. My primary dive buddy disagrees on the importance of this, but I track my SAC rate for every dive as it is a very good indicator of how I was feeling on said dive. Without avg depth it is pretty much impossible.

Preferably have easy log uploads to computer without stupid $100+ proprietary cable. This is the least important, but if shopping for a long term computer it is nice if it has BT upload capability or some other easy and cheap upload capability.

Mmmmm...you just described a Petrel!!!!!

 

[tbone1004]

Mmmmm...you just described a Petrel!!!!!

probably why I own one....

I still maintain the used Nitek Duo's/Cressi Archimede II's are the best bang for buck if you're cash strapped, they offer all of the above except easy computer integration, but for $150 max you can't really argue too much

 

[Diver0001]

Hi all,

I'm looking at buying a dive computer but I don't understand why the average person would need to switch gases during a dive. So for example, I'm looking at the Suunto D6i which can do air and nitrox and can switch between two gases. Is the only reason for this if you were to put two tanks on your back? Or is it just for ease between repetetive dives so that you can set everything in the morning and be good for your two dive boat trip? I don't understand why non-technical divers would need this feature.

Any input appreciated, Thanks!

The ability to switch between different gasses during the dive means that you must be carrying different gasses during the dive. For the vast majority of divers this is not the case. Technical divers, however, routinely do this. It's not uncommon for some divers to carry 2 or even 3 different gasses during a single dive. Most of the time they will also have 3 or 4 tanks. 2 on their back (a double set), and the others under the arms.



Therefore the "gas switch" functionality has infiltrated mainstream computers. For 99% of divers it's useless functionality. For a small group, they can't live without it.

R..

 

[drbill]

Had a dive computer once that actually switched gasses on me without any intervention on my own. Unfortunately it switched from air (all I ever breathe) to 50% Nitrox spontaneously several times and according to the computer I died at 80 feet. Fortunately someone stole that computer a few years back. I hope they "die" a thousand deaths. None of my current dive computers have spontaneously changed the dive gas on me... yet.

 

[dmaziuk]

My suspicion as to why seemingly every computer available today now has gas switching is that it is largely marketing hype.

Once you wrote the gas-switching code it costs you nothing to install it. As far as the actual hardware goes, it usually costs more to source and maintain several different production lines than to just stick better hardware in the entry-level product. The sale price markup was 20-30% last I looked (e.g. leonardo vs giotto), so little to no extra cost sells for 25% more.

That is not the case with "heavy tech" computers like petrel, of course, just the "rec with light tech features" models.

 

[Scared Silly]

Many divers will carry a pony bottle that may have a different mix in it. I.e. air instead of nitrox to avoid any MOD issues at depth, or nitrox instead of air ... It's more accurate to have that put in there.

Of course you may need to switch gases.

What if you are using nitrox but for some reason, you need to use your buddy's tank which contains air? If your computer stays on nitrox setting while you are breathing air, then your no deco time will not be correct. If you are close to deco, then this may mean you actually go into deco while your computer shows you are not.

If you are in deco, then it certainly will cause problems as your computer set to nitrox will require less deco stop time than if it was set to air (which is what you are using).

The above are two very reasonable reasons. A third is along those same lines. You did two morning dives on nitrox but the afternoon dive is on air and you splashed and forgot to switch. One can switch underwater and continue the dive and not worry (been there done that).

As such, I recommend that folks set one gas to what they are diving and the other to what might end up diving (air). Then your bases are covered. Anything more on why having multiple gasses for recreational diving is marketing.

 

[RonR]

I can say something about the rationale in giving the Cobalt gas switching ability.
1) There are regional variations in styles of diving. Some areas it would be quite normal to have a tank with say, 50% O2 hanging off the boat at 20’. Other areas, as was mentioned above, carrying a pony with a richer mix for the end of the dive might be fairly normal, in that fuzzy area between tech and rec diving. Gas switching ability means the computer can track these changes.
2) Having the ability to store different tank and gas configurations, if there are several you use frequently, makes switching between air and nitrox, or between different tank sizes, a one button press operation.
3) This reflects the same underlying code being used in both recreational and tech products, which simplifies code maintenance.


In the Cobalt, we lock out gas switching ability unless the diver has specifically turned it on for a particular dive. This is to prevent confusion or the possibility of inadvertently switching mixes for the vast majority of divers who won’t use this function. So while the ability to switch mixes while diving is technically there, it’s inaccessible unless the diver looks for it and enables it.

Ron