What's the point of these 3 gas computers?

[gumbo717]

What is the point of having a 3 gas computer that is not intended for Adv Nitrox/Deco Diving?

Reason I am asking: I am practicing to take the Adv Nitrox/Deco procedures classes in the near future and I have an Oceanic VT3 which is a 3 gas computer with mixes from 21% to 99%. When bought from the LDS I was told that it would be a "good computer" to have for taking my tech classes. Should have asked the tech instructor and not the shop owner - I'll leave that for another topic and get back to my point.
After talking to several tech instructors the VT3 is not considered a tech diving computer even though you are able to switch to a higger (deco) mix while diving. It does however make a great bottom timer in guage mode and will be used with tables for classes and diving. Should I have purchased a bottom timer for a quarter of the cost of the VT3 then saved my pennies for a more standard tech computer?

Now, I could plan the dive on tables (with no result of deco stops below 60 ft), carry a set of tables cut for the accidental too deep or too long situation, compare that to the dive the profile the computer comes up with, carry a backup bottom timer and dive with the computer in normal mode.

I am trying to understand how this or any of the other three 3 gas computers, that are not your standard tech models, is able to be sold and not have somone try to use it for deco diving.

Thanks.

jt

 

[DevonDiver]

Exactly why did your instructor say it was not a tech computer?

 

[DA Aquamaster]

"Technical diving" is not universally defined and I could envison an instructor who feels a computer that is not trimix capable is not a "tech" computer, but associating technical diving with trimix would be a mistake. The odds of a non trimix trained cave diver surviving an open ocean trimix dive are a lot higher than a non cave trained trimix diver suviving a cave dive even at depths less than 100 feet.

In general, if it involves diving in a soft or hard overhead environment where by definition you have no direct access to the surface, it is, or should be, a technical dive. The major difference in mindset that then pervades equipment and training requirements is that in technical diving, any problemss that arise must be addressed underwater as immediate surfacing is not an option.

----

Most computers have allowed at least some degree of staged decompression diving since they were first invented. Back in the day it was common for them to lock divers out if certain parameters were met such as required stop depths deeper than 40' (based on US navy tables) or total deco more than X minutes, but that is generally not the case today. In any event the "risk" has always been there that a diver would buy a computer with deco capability and then go dive with no formal training in deco procedures. Its just a case of adding some chlorine to the gene pool and if a diver is dumb enough to do it, they are probably dumb enough to get them selves killed in all kinds of other endeavors in life.

A computer that allows the use of a second or third gas for accellerated deco is by definition a technical diving computer regardless of whether or not it has trimix capability.

It gets fuzzy as some agencies and divers insist that no dive should be done with an END greater than 100' while other agencies and divers will move the END down to 130', 150' or even 180'. If you draw the max END line at 100' then the opportunites to take full advantage of a technical computer that does not work with He are going to be limited (and the main agencies that promote a 100' END do not, for the most part, promote computer use at all.)

 

[RJP]

The odds of a non tri-mix trained cave diver surviving an open ocena trimix dive are a lot higher than a non cave trained trimix diver suviving a cave dive even at depths less than 100 feet.

Wow, suddenly I had an "SAT flashback"

:shocked2:

 

[ianr33]

What is the point of having a 3 gas computer that is not intended for Adv Nitrox/Deco Diving?

I am trying to understand how this or any of the other three 3 gas computers, that are not your standard tech models, is able to be sold and not have somone try to use it for deco diving.

jt

If divers insist on buying them then manufacturers will be happy to supply them.

IMHO "recreational" 3 gas computers are just marketing.

 

[Cave Bum]

What is the point of having a 3 gas computer that is not intended for Adv Nitrox/Deco Diving?

After talking to several tech instructors the VT3 is not considered a tech diving computer even though you are able to switch to a higger (deco) mix while diving.

Technical diving was defined at the first AquaCorp conference as diving which 'required you to switch gas supplies'. I think that's still a pretty good definition.

I'm not sure why the 'several tech instructors' you talked to think this computer isn't appropriate for technical diving (unless, of course, it's because they want to sell you one from their shop that they'll get a commision on, not that that would happen in the scuba industry ). One thing I do notice is that it is a wireless air integrated computer. If that is what they are complaining about, that's different from it's 3 gas ablity but, so long as you have a backup standard SPG, that shouldn't be a problem.

I use a Dive Rite Nitek Plus, a 2 gas 21%-99% computer, for all my cave and technical diving with a Casio DEP-610 Bottom Timer and tables as backup. I don't do enough trimix diving (usually just once or twice a year) to justify buying a helium computer and I usually just use tables for my deep dives (although, more often then not, one of my friends will lend me their backup Nitek He to wear for the dive).

Bottom line: I think the 'tech instructors' you talked to are mistaken and I would recommend questioning them more about their knowledge of tech diving before signing up for a class with them...

Be safe and have fun in the water! Bruce

 

[ianr33]

What algorithm does the VT3 run ? Do its profiles match up to dives planned on a laptop? Can conservatism be set in a "recognized" way such as Buhlman Gradient Factors ?

Bottom line is if you did a dive to ,say,150 feet for 35 minutes with 2 deco gasses do you know what the computer is going to do?

 

[DevonDiver]

If divers insist on buying them then manufacturers will be happy to supply them.

IMHO "recreational" 3 gas computers are just marketing.

Can you explain why you think this??

I've found my Suunto D9 perfectly acceptable.

 

[gumbo717]

Exactly why did your instructor say it was not a tech computer?

I may have misinterpreted what he was saying but that if I was considering a computer for tech diving then other things to take into account were the ability to use He, different algorithm, and are able to switch more than 3 gases. Also that some models are upgradable for CCR, not in the near future for me but never say never.

The LDS where I purchased the VT3 did not carry or even mention - VR3, X1, Nitek, or Shearwater even though those were out there but did not think about that two years ago when I purchased the VT3. They did just pick up Suunto and have some literature on the HelO2.

The instructor where I am thinking of taking the class (not the LDS) is of the mindset that we are using tables and bottom timers regardless of what computer we had. If we wanted we could bring a computer to compare dive profiles and since I have the VT3 I was checking into using it but it has limited capabilities.

 

[DevonDiver]

Well, given that Tech consists of many aspects and the use of He is only one of them. So, it is incorrect to state that a 3 gas, non-He, computer is not valid.

However, if you had expressed a desire to progress onto Trimix diving and wanted to buy a suitable computer to run those dives, then it would be fair advice to counsel you towards a more capable and 'future proof' computer.

For me, I just don't have enough regular access to depths that require Trimix, but my bottom times do require accelerated deco. That could change in the future... but today's market choices of He computers could also be redundant by the time that does....so I am not rushing out to buy something that may be antiquated before I can make the best use out of it.