23 replies to this topic

[peterbj7]

I'm tempted to start a new thread with this, but here goes. Can anyone think of any dive which would employ three nitrox mixes? I can't see any application for the third mix that some computers provide.

[MODERATOR NOTE: good idea - it's a new topic!]

[Dive_Girl]

Yes. For those wanting to do those kinds of dives on computer (I'd personally use tables) A dive with one mix as your back gas, a deco bottle with 50% for a 70fsw switch, and a second deco bottle at 80-100% for a 20fsw switch.

[6Gill]

I'm tempted to start a new thread with this, but here goes. Can anyone think of any dive which would employ three nitrox mixes? I can't see any application for the third mix that some computers provide.

[MODERATOR NOTE: good idea - it's a new topic!]

talk about opening a can of worms....
next you'll question the logic of manufacturing vehicals that exceed the speed limit or the supersize option when ordering junk food and so on which in turn leads to the spirialing decline of life as we know it.
That and what DiveGirl says....I'm guessing this computer will do a trimix gas along with up to two deco gases

[Lubold8431]

Yes. For those wanting to do those kinds of dives on computer (I'd personally use tables) A dive with one mix as your back gas, a deco bottle with 50% for a 70fsw switch, and a second deco bottle at 80-100% for a 20fsw switch.

Exactly. 'Nuff said.

[peterbj7]

An air dive with two deco mixes? Certainly possible, but I've never done it. Can't see the point. Now, if one of those gases were trimix then that would be a different story.

[PerroneFord]

Sure, seen it done. Try bikini pre-trimix.

45 minute BT on air at 180ft, switch to 50% at 70ft, switch to oxygen at 20ft. you could ride the 50% bottle all the way shallow, but you might need to carry more than 40cuft of it per dive, which would suck.

In places where tri-mix is hard or impossible to get, I could easily see doing a 3-gas dive.

[cdtgray]

Although I am sure that someone my flame me for admitting so, during the course of my technical training I did a number of deep air deco dives. It is exactly this type of diving that a computer capable of calculating three different nitrox mixes would be used for.

The Nitek3 is set up exactly that way, allowing the user to program up to three nitrox mixes between 21 and 99 percent O2 (it does not register helium mixes). Of course Dive Rite stopped producing the Nitek3 and started making the NitekHe - no doubt due to helium use becoming more common iand deep air diving becoming taboo.

Edited by cdtgray, 17 July 2006 - 06:41 PM.

[Geek]

In essence a rebreather is giving you a continuously changing mix, constantly optimizing for the current depth. In theory, the more gasses you carry, the more you could optimize on Open Circuit. As a practical matter, who wants to carry a zillion little tanks? As a result, I think if you are considering such dives, it is time to seriously look at rebreathers.

[PerroneFord]

As a result, I think if you are considering such dives, it is time to seriously look at rebreathers.

Rebreathers constitue a miniscule part of the technical diving world. Thousands of technical dives happen each year without their use. I don't think doing a 3 mix dive (backgas, and 2 deco tanks) is outside the realm of open circuit. In fact, with the short time you're probably going to be underwater, the rebreather is likely going to be more trouble than it's worth.

Now if you tell me you've got some work to do, or you need a 4hr exposure at 200+ feet, then a rebreather starts to look very attractive.

[Geek]

As a result, I think if you are considering such dives, it is time to seriously look at rebreathers.

Rebreathers constitue a miniscule part of the technical diving world. Thousands of technical dives happen each year without their use. I don't think doing a 3 mix dive (backgas, and 2 deco tanks) is outside the realm of open circuit. In fact, with the short time you're probably going to be underwater, the rebreather is likely going to be more trouble than it's worth.

Now if you tell me you've got some work to do, or you need a 4hr exposure at 200+ feet, then a rebreather starts to look very attractive.

A 3 mix dive is certainly within the realm of open circuit. I did not say you had to use a rebreather. I said if you are considering such dives, it is time to seriously look at rebreathers. You can look at them and then decide to remain open circuit. It is a personal decision.

[ScubaDadMiami]

In essence a rebreather is giving you a continuously changing mix, constantly optimizing for the current depth. In theory, the more gasses you carry, the more you could optimize on Open Circuit. As a practical matter, who wants to carry a zillion little tanks? As a result, I think if you are considering such dives, it is time to seriously look at rebreathers.

O2 + Optimize = O2ptima. That is where the name comes from since it does exactly what you say in your post.

[BradfordNC]

Sure, seen it done. Try bikini pre-trimix.

45 minute BT on air at 180ft, switch to 50% at 70ft, switch to oxygen at 20ft. you could ride the 50% bottle all the way shallow, but you might need to carry more than 40cuft of it per dive, which would suck.

In places where tri-mix is hard or impossible to get, I could easily see doing a 3-gas dive.

bikini pre-trimix???

hate to tell ya, but bikini is now post-trimix.

they stopped using it because it is not necessary and was extremely expensive to get on the island, especialy since so few divers showing up were qualified to use it, and most who were chose not to use it.

all dives are done on Nitrox 21 and deco is done on Nitrox 75


but the need for a computer with 3 nitrox mixes? yeah, mine does that, and i use it all the time.
Nitrox 32 as a travel gas to get into the system
Nitrox 21 as a backgas for the portion of the dive dropping down into the deeper section
Nitrox 32 as a travel gas back out of the system
100% O2 for deco

Edited by BradfordNC, 17 July 2006 - 07:16 PM.

[Diverbrian]

If it is below the 150-160 ft. range, I don't care how much mix costs. That is what I will be on. If it is unavailable, I guess that I won't be doing the dive. I prefer mix below 100 ft. but will live with nitrox mixes down to the range mentioned. I am typically comfortable with an END of 130 in cold water.

Anyways, I was doing these types of dives at the quarry this weekend. EAN28 or Air to 135 ft./ EAN50 at 70 ft. (or EAN36 for practice with that stage at 110 ft.)/ O2 at 20 ft. They were work-up dives for the Daniel J. Morrell which is in 200 ft. of water and will be a mix dive. I didn't want to spend the money on the mix in this case as I pratically lived in the quarry for my early tech training and know it like the back of my hand. Getting narced there is really not a huge deal and there is nothing to see worth remembering. As well, my END would likely be the about the same as it will be on the Morrell.

On wrecks in the 100-150 ft., I actually tend to use tri-mix and one deco gas (typically O2 or EAN50 depending what I have the most of in my tanks at the time) as I have enough backgas to do a backgas deco if necessary from the dives that I plan to those depths. However, I could easily see the Air/EAN50/O2 model working out quite well for those dives too . For those that like really deep air, I could see three mix model working out even better . Some of the divers in my regular dive group do prefer deep air, so I am familar with this profile.

There is the reason that the VyTec has three nitrox mixes instead of two . Oh, and I will do about anything safe and possible to accelerate deco in these cold Great Lakes. Deco is boring.

[BradfordNC]

For those that like really deep air, I could see three mix model working out even better . Some of the divers in my regular dive group do prefer deep air, so I am familar with this profile.

There is the reason that the VyTec has three nitrox mixes instead of two .

yup, works great with deep air.

[Dive_Girl]

Although I am sure that someone my flame me for admitting so, during the course of my technical training I did a number of deep air deco dives. It is exactly this type of diving that a computer capable of calculating three different nitrox mixes would be used for.

Well you don't stand alone, cdtgray...