Is a super computer needed for gas switching?

[rongoodman]

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".

And don't forget, if they've been shot, stabbed, or otherwise assaulted, they "were just minding their own business, and these two dudes walked up"...

 

[waterpirate]

Not yet. I'm a wuss when it comes to cold.

Why, have you dived Ocean City?

I do aprox. 50 dives a year out of o.c. md weather gods permitting. From the lunch box in 40fsw to the big boy dives off shore. Dry suit highly reccomended for anything over 30 minutes.
Eric

 

[FPDocMatt]

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.

I can only imagine, having had difficulty just being on the surface by myself (keeping from inhaling water from the swells, getting water in my snorkel, trying to put on or take off fins on the surface of the water, etc).

I'd like to at least know what needs to be done in a rescue situation. Being able to actually do it is another thing altogether.

 

[waterpirate]

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.

I respectfully disagree. The ability for your computer to switch automatically negates the human factor of forgetting to do it. My duo is still pissed I forgot to "push it's button". As for lost gas, that is why we carry tables with lost gas plans cut as part of the back up. The argument is valid for both sides so it is prefrance, and I prefer auto switches.
Eric

 

[FPDocMatt]

And don't forget, if they've been shot, stabbed, or otherwise assaulted, they "were just minding their own business, and these two dudes walked up"...

Exactly!

There's a standard aphorism among emergency doctors, that the biggest risk factor for non-accidental trauma is having a couple of beers and minding your own business.

 

[FPDocMatt]

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.

Interesting! Do you use a computer to calculate the decompression stops you're going to need? The only non-computer planning I'm familiar with is the RDP, which I don't imagine would be useful for decompression stop diving.

 

[Saxatilis]

Wow! Slot of really long answers for a pretty standard question. Yes, any multi-gas computer must allow you to switch gasses while diving. Hopefully this is accomplished as simply as possible, it depends on the computer.

 

[Doc Harry]

Do you use a computer to calculate the decompression stops you're going to need?

V-Planner

I don't even use a dive computer for a back-up during deco. The only tme I use a dive computer is for recreational diving (live-aboards and drift diving).

 

[Dive Bug Bit Me]

Interesting! Do you use a computer to calculate the decompression stops you're going to need? The only non-computer planning I'm familiar with is the RDP, which I don't imagine would be useful for decompression stop diving.

A big difference between technical decompression diving and recreational diving is the amount of planning for a technical dive. Before I get wet on a decompression dive I will know my planed descent time, bottom time and decompression stages potentially with different gasses. I will know to within a minute what time I should be on the surface again and when I will send up my SMB (again to within a minute). I should know how much of each gas I will use and can predict my remaining tank pressure after the dive to within 300 psi for each tank. (If I am out by more than this I actually sit and check why my planning might have been out).

In terms of how to actually plan these, we use specialized computer software. The VPM seems to have become the dominant tool, though I also like the Buhlmann algorithms available from iDeco for minor deco dives. Before the dive we will use this software to cut a decompression plan specific to the dive. This sounds pretty complex, but in reality the software has become pretty user friendly and creating a deco profile on it is straight forward.

Much of the technical diving training is about dealing with unforeseen problems. (e.g. what do you do if your regulator fails, if your deco regulator fails, etc). One of these is what do you do if your computer fails underwater. Consensus is that you dive two computers. If I am diving a self cut plan, I only need a recreational computer that can be put into gauge mode to provide me with depth and time. So I dive one recreational computer in gauge mode and one tech computer that could provide me with options if something unforeseen happens.

I do know some guys who plan and dive with two tech computers. These guys are doing some unbelievable deep cave exploration diving. They are using VPM and then diving with two VR computers. They will clear the deco off both computers their computers on the way back. (interestingly their deco obligations on the two computers can differ by up to 10 minutes).

 

[BabyDuck]

I respectfully disagree. The ability for your computer to switch automatically negates the human factor of forgetting to do it. My duo is still pissed I forgot to "push it's button". As for lost gas, that is why we carry tables with lost gas plans cut as part of the back up. The argument is valid for both sides so it is prefrance, and I prefer auto switches.
Eric

and i'll respectfully disagree with you!

off topic of the original question, and what you like is wonderful for you if it works - but *i* want to do the button pushing to switch gasses. my dive buddy used to have a computer that switched for him (a cochran). it would switch swimming over the gap at olsen since that's shallow and not let him put it back to backgas once we were over and back on the line and at 60ft. so it thought he was dead from oxtox after about 40min into the dive. that kind of rigidity is not what i want. *however*, for strictly 'open water' deco (ocean or what have you), i agree it would not be that unhelpful and i can see why someone might like the idea. i just don't.