Two gas vs Three gas computer

[DA Aquamaster]

+1 on the 1 deco gas for nitrox bottom gas comment. I'd say that is the case 95% of the time.

In N FL cave diving, 100% is a very common deco gas and a lower epercentage gas is not normally used with nitrox for a bottom mix.

Even in OW deco diving with nitrox, the run times have to get pretty long before a second deco gas becomes worth the extra logisitcal effort.

For example using DPlan with GFs of 30-85, a 110' dive for 60 min with 32% back gas and 100% for deco requires 25 minutes of deco. The same dive with both 50% and 100% for deco will still require 23 minutes of deco, providing very little benefit in return for carrying a second deco bottle. The same dive with a "backgas only" deco requires 50 minutes for deco but unless the SAC rate is high, it is still easily managed by 200 cu ft of gas. In this case a second deco gas makes zero sense.

Add 15 more minutes on the bottom and the picture changes, but only slightly. The deco is now 35 minutes with 100% and 31 minutes with 50% and 100% but rises to 72 minutes with the "backgas only" lost gas deco scenario and (with a SAC of .6 on the bottom and .4 on deco) that scenario requires 243 cu ft of gas - probably farther than you want to push it on 260 cu ft of backgas. Adding a second deco gas now makes some sense in terms of reducing the deco time with a single lost gas to 35 minutes with 100% only or 48 minutes with 50%. But obviously, two separate bottles of 100% to provide some insurance against losing access to one or the other makes almost as much sense and would still do the job with a 2 gas computer.

So in effect, there is very little need for 3 gasses until you actually get to depths where trimix is needed, and once there, a two gas computer will still make an excellent bottom timer in gauge mode.

 

[AbyssalPlains]

I like my Nitek Duo, which I bought before the Trio came out, however, I have to admit that people ain't lyin' when they say this computer is the most conservative one you can get. Whenever I dive with a group, I'm always - and I mean ALWAYS - the first one to get close to or into deco. Even though we've all been to the same depth most of the time, everybody else is happily paddling about at depth when my computer threatens to throw me into deco if I don't go up ASAP. It's not a big deal since I'm deco-trained and used to the computer's level of conservatism, but it can be annoying at times. I don't know how much the Duo and the Trio differ in terms of algorithm. Probably it's the same. If the Trio is even only slightly less conservative, that would kill any considerations about the Duo right there in my book.

 

[battles2a5]

The Duo should give you everything you need for nitrox + deco. I really don't see the need for the third gas since you will most likely be diving trimix once you introduce the third gas. The Duo also makes a great bottom timer so once you get a trimix computer you can always use the Duo in guage mode as a back-up. I agree with others that the Duo is conservative, but not exceedingly so. I really only use mine for cave diving now and I never mind spending a few more minutes chilling at 20', shutting off my light, enjoying the cool clear water, and reflecting on the dive. There are worst ways to spend your time

 

[Wayne at DiveSeekers]

For entry level Tec (longer time/swallower than 130') a 2 gas computer is sufficient although when I teach Tec we do dives with a Stage & Deco gas so that you start building the skill sets up for the next level (Trimix). In this teaching environment my students already have the computers they need so that they go through the proper gas changing procedures as a team and get familiar with their computer at the same time. In this case, the 3 gas computer comes in handy. If you buy a multi-gas computer now, you do have to realize that if you go this route (Tec), you will still need redundancy to your computer. Redundancy is in Depth/Time/Ascent Rate (ScubaPro Bottom Timer) for software we run V-Planner. We actually do it the other way around and use V-Planner w/Bottom Timer (Schedule) as our main tool and the computer (Liquivision X1) as our redundancy (many different beliefs on this topic). This combination Software (tables)/Computer are right in sync with one another and our dives run flawlessly.
I don't know if this helped you in any way but if the Tec is a ways off than I would go with a 3 gas computer (Trio). The Duo is a better price point but are now too hard to get and if you were to have a warranty issue it would be better to go with the current model. Overall, the DiveRite computers have been super reliable for us. If you are going into Tec sooner than later then my recommendation is Bottom Timer/Liquivision combination and don't waist the money on the 3 gas computer.

We offer FREE DS&S boots with purchase of the Trio or Liquivision Computers, let me know if I can help you out with this.

 

[wedivebc]

Thanks folks. This is exactly the type of info I was looking for. I am interested in "tec" diving but the realities of my personal life will take priority from getting real seriously into "tec" for the forseable future. Sounds to me like the Duo will serve me well. Thanks again

Just so you know TUSA sells an exact duplicate of the DUO I believe is called the IQ 700 and may be cheaper than the DUO