Is a super computer needed for gas switching?

[IanBrit]

I'm amazed that my beginner-level dive computer (Mares Puck) actually has nitrox capability. The instructions talk about MOD, which I didn't understand when I first read it. Of course, this basic computer wouldn't be able to handle a gas change during the dive, I bet. On the other hand, it'll be a good long while before I'll be even considering technical diving.

Note: After practicing medicine here in rural Maryland for 13 years, asking patients how long they've had symptoms, I finally learned what these terms mean:

• Awhile: 2 months
• A good while: 6 months
• A good long while: 1 year

:shades:

I'd be more amazed if a computer these days *didn't* have nitrox already baked in, at least as a single gas (don't confuse nitrox ready with multi-gas ready). It's a very small step from OW to nitrox since there are few new skills involved and the benefits are extensive.

A 'good long while' to Tec maybe... figure 'a while' before you feel the need to breath nitrox , especially at the rate you're broadening your question base - this indicates a true dedication to the hobby.

 

[FPDocMatt]

Do you do any ocean diving in Ocean City?

Not yet. I'm a wuss when it comes to cold, and really didn't enjoy the added weight and bulk of a thick wetsuit/hood/gloves/extra weights attire. At some point I'll invest in a dry suit and start diving in colder water, but for now I'm sticking to plane trips to warm water locales.

My LDS operator said he'll let me try out one of their drysuits in a local pool, which is good because I'm afraid I might find a dry suit to be unpleasantly bulky too. But I don't want to take him up on the offer until it's in my budget, because he'll have to pay for the pool time and it's not fair to him for me to just try it out without at least the possibility of a purchase.

Why, have you dived Ocean City?

 

[kundalinichi]

As many have already said, you will be pre-entering the gas mix(es) into your computer before the dive, with some computers having the option of entering a mix on the go (shearwater predator, liquivision x1). The way we learned it in our class, was plan the dive and dive the plan, the computer you paid 1k+ for being a simple gauge until you lose your dive plan on wetnotes So, if you have good attentiveness to buoyancy and awareness of your surroundings, a bottom timer like the Liquivision Xen would almost be as beneficial, and cheaper.

I dive an Oceanic OC1 in gauge mode and Liquivision X1, and the point of the gas switch is it should be asap when you do the actual switch, so the computer calculates new ascent profile\stops. all the OC1 takes is 1 long press on top left button, and then your at the gas select menu - one more press and your 'switched'. The X1 is similar, 3 taps to get into menu from dive mode, one tap to get into Deco Mix list, and one more to select and 1 more to confirm.

 

[FPDocMatt]

A 'good long while' to Tec maybe... figure 'a while' before you feel the need to breath nitrox , especially at the rate you're broadening your question base - this indicates a true dedication to the hobby.

My understanding is that Nitrox allows you to stay down longer (for no-stop diving) or decompress more quickly (for technical diving). Is that right? Now that I have my AOW certification, I'll probably be amazed at how soon I have to surface from a deeper dive. I imagine I'll want to get nitrox certified in order to be able to stay down longer. The weird thing is that, even though you use nitrox to stay longer at depth, nitrox limits your depth! It's counter-intuitive. But anyway, I'm about halfway through Deco For Divers, and thoroughly enjoying these concepts.

On my upcoming trip to Grand Cayman, I'll get the Rescue Diver certification. (Even though many SB-ers think this is too soon, after only having logged 14 dives, being a physician makes me want to have the knowledge for rescuing people. After all, it's part of my role in this world.) The next logical course to take is the Nitrox course. If I am able to fit in another dive trip in late May to Florida, I'll do the Nitrox certification then, and have it under my belt before we invade Cozumel. But if not, perhaps I'd do it in Cozumel.

 

[IanBrit]

Correct. Nitrox is used to either extend the NDL or increase the safety margin by diving it as air (having burned the MOD into your brain, or set the depth warning on the computer). It is also used to accelerate decompression by switching to it at the correct depth. Being a cold water diver, I use to reduce those pesky hangs and when I'm warm water diving, I use it for a safety margin for the flight home.

On the point of placing the rescue course ahead of any others, I'm not commenting other than do not underestimate the dangers involved in rescuing a panicking diver. Solid buoyancy skills, a cool head and confidence in your own skills are critical.

 

[rongoodman]

Most agencies let you do a Nitrox course with no dives involved, so you might be able to do the class at home and not take up time with it on a dive trip. It should be very easy for you with your background in the sciences, and it's good to have even if you're not doing a lot of dives using Nitrox. I'd recommend the TDI course if you can find one locally--it has a little more about how the math works, rather than just looking things up in a table. The concepts you'll get will be a foundation for a lot of future learning, especially becoming comfortable with thinking about partial pressures.

 

[Dirty-Dog]

I'm amazed that my beginner-level dive computer (Mares Puck) actually has nitrox capability. The instructions talk about MOD, which I didn't understand when I first read it. Of course, this basic computer wouldn't be able to handle a gas change during the dive, I bet. On the other hand, it'll be a good long while before I'll be even considering technical diving.

Note: After practicing medicine here in rural Maryland for 13 years, asking patients how long they've had symptoms, I finally learned what these terms mean:

• Awhile: 2 months
• A good while: 6 months
• A good long while: 1 year

:shades:

LOL I know the feeling. I've always just said "I don't know how long 'a while' is." In the ER, when you ask how much people drink, "a little" is pretty much the standard answer. Turns out that can mean anything from a glass of wine on your anniversary to a quart of whisky every day.

And if they've been in a fight or a crash, then the answer is "2-3 times whatever they say they had".

 

[Doc Harry]

Am I the only one who doesn't use a computer for deco diving?

 

[BabyDuck]

yes.

hee hee - no, not really.

matt, my response is that, yes, there are computers you use when you have more than one gas per dive. a simple one like the old nitek plus or duo or a clone will go a very long way with you, up to the point you want to use more than two gasses (obvy) or use trimix (obvy, since they are nitrox computers). i love frank (love you, frank!), but also disagree with getting a big kid computer now - by the time you need it, you'll want the latest & greatest. my plus took me through full cave and advanced nitrox/deco procedures.

have you had some pm conversations with lynne? (tsandm) she's your questioning twin, and also a physician, so would be a great resource. y'all seem to think a lot alike.

 

[TSandM]

Doc Harry, that was my feeling as I read all these answers . . .

Matt, one of the things that makes staged decompression diving different from recreational diving is that it has to be planned. You can't just hop in the water and hope you have enough gas to do the deco you are going to end up needing to do, so you plan your bottom time, calculate the deco you are going to need to do, and then calculate the gas you will need to do it (with contingencies for lost bottom mix and lost deco gases). As a result, a computer is really just a backstop and not a primary instrument for doing this kind of diving (for most people, anyway). A lot of technical diving is done with just a bottom timer, which does no decompression calculations at all.

For those who DO use a computer for tech diving, a "supercomputer" eventually ends up being necessary, in part because most recreational computers, even those which permit the use of multiple gases, do not have programming to handle helium mixes.

And as you have already heard, most computers require that you manually gas switch, which makes sense, since, if for any reason you don't HAVE your deco gas and have to deco out on backgas, you don't want the computer assuming you're on the rich mix.