Using Nitrox...

[halocline]

I don't think anyone has yet brought up how nitrox lets you dive a different profile than air, even if the dive length/depth is the same. For most single tank divers, the dive ends due to gas, but the profile is often set by NDL. Using nitrox can let you dive the deeper portion of a wall for a higher percentage of the dive, for example, and in a place like the flower gardens, where the topography necessitates deep profiles for the entire dive, nitrox could be very useful.

 

[NudeDiver]

I don't think anyone has yet brought up how nitrox lets you dive a different profile than air, even if the dive length/depth is the same. For most single tank divers, the dive ends due to gas, but the profile is often set by NDL. Using nitrox can let you dive the deeper portion of a wall for a higher percentage of the dive, for example, and in a place like the flower gardens, where the topography necessitates deep profiles for the entire dive, nitrox could be very useful.

But is this (significantly) true even if you're an air gulper - and consuming even MORE air simply because you're at depth?

For example - suppose you've got a 35m dive. And suppose your air consumption rate at 35m is such that you've got, oh, 15 minutes of time down there. Now, suppose, just for the sake of argument, the NDL is ALSO 15 minutes. In this case, both air consumption and NDL are limiting you to 15 minutes at 35m.

Now - again, your air consumption rate at 35m is such that you've got, oh, 15 minutes of time down there. But this time, you're on Nitrox. We know that Nitrox does not affect your consumption rate, but it does increase your NDL. Just for the sake of argument, suppose that it doubles your NDL from 15 minutes to 30 minutes, at 35m (keep in mind, I am making these numbers up). So, the NDL limits you to 30 minutes, but your personal air consumption rate is still limiting you to 15 minutes. So, in this case, Nitrox is not really buying you any more time at the bottom.

Am I thinking about this correctly?

 

[Charlie99]

The first part of Mattboy's post is in regards to multilevel diving on a wall or a reef that goes from your max depth back up close to the surface. You can adjust your profile to match the available air and your SAC. I often do dives of 60 to 70 minutes with maximum depth of 120'. Since I'm using a single AL80 for the gas, it's pretty clear that not all of the time is at 120'. I'll spend a few minutes at 120', then up to 80' for 10 or 15 minutes, then up to 40 or 50 for a while, and then spend the last part of the dive up around 30'. Mattboy's point is that nitrox will let you spend more of the dive deeper -- "lets you dive a different profile than air, even if the dive length/depth is the same".

Personally I find that shifting the average depth shallower by spending less time deep and more time shallow isn't a big penalty and so therefore usually dive air on very multilevel dives.

As I noted in http://www.scubaboard.com/forums/3841217-post8.html , I usually dive air in Maui and nitrox is SE Florida, even though the Maui dives have max depth the same or deeper than my SE Florida dives. The difference is that the SE Florida reefs and wrecks are relatively low profile, so nearly all of the dive is down near the max depth. Nitrox really helps in those cases. For the multilevel dive, the profile difference isn't enough to overcome the hassle of getting nitrox on Maui.

 

[CoralSeaMan]

But is this (significantly) true even if you're an air gulper - and consuming even MORE air simply because you're at depth?

For example - suppose you've got a 35m dive. And suppose your air consumption rate at 35m is such that you've got, oh, 15 minutes of time down there. Now, suppose, just for the sake of argument, the NDL is ALSO 15 minutes. In this case, both air consumption and NDL are limiting you to 15 minutes at 35m.

Now - again, your air consumption rate at 35m is such that you've got, oh, 15 minutes of time down there. But this time, you're on Nitrox. We know that Nitrox does not affect your consumption rate, but it does increase your NDL. Just for the sake of argument, suppose that it doubles your NDL from 15 minutes to 30 minutes, at 35m (keep in mind, I am making these numbers up). So, the NDL limits you to 30 minutes, but your personal air consumption rate is still limiting you to 15 minutes. So, in this case, Nitrox is not really buying you any more time at the bottom.

Am I thinking about this correctly?

Your understanding is correct. Any advantage comes from the fact that you have less nitrogen exposure and therefore less DCS risk.

 

[NudeDiver]

OK.

I've got it now. My suspicions have been confirmed.

Thanks all

 

[emttim]

Bravo to the shop that used that sales pitch to get you to buy an expensive reg. I guess even the old faithful "isn't your life worth it?" line needs a break now and then.

Your top-of-the-line SP reg is very nice and will serve you well for as long as you want it, but it will not lower air consumption. What do you think, less expensive regs are like sucking molasses through a straw?

My air consumption on one of my last dives was 0.37 cubic feet per minute and I'm using an Aqua Lung Titan that cost me 150 bucks. And like the ScubaPro Mk25 or whatever it was, I can adjust breathing resistance....the only difference is my reg was a lot cheaper.

I don't think anyone has yet brought up how nitrox lets you dive a different profile than air, even if the dive length/depth is the same. For most single tank divers, the dive ends due to gas, but the profile is often set by NDL. Using nitrox can let you dive the deeper portion of a wall for a higher percentage of the dive, for example, and in a place like the flower gardens, where the topography necessitates deep profiles for the entire dive, nitrox could be very useful.

Right, the benefits are a lot more clear cut at deeper depths, hence the misconception that nitrox is for deep diving. Several of the deep dive profiles I did recently I could not have done on air, even using the wheel to get a more accurate pressure group, it was just an impossible dive. However, even for shallower dives, it does reduce your surface interval time so it gives you the freedom to make more dives if you choose to.

And as far as being tired goes, I'm falling asleep at the end of a day of diving either on nitrox or air, so can't say I feel any difference.

 

[Blackwood]

...I'm using an Aqua Lung Titan that cost me 150 bucks. And like the ScubaPro Mk25 or whatever it was, I can adjust breathing resistance....the only difference is my reg was a lot cheaper.

The AquaLung is a diaphragm, the ScubaPro is a piston.

 

[emttim]

The AquaLung is a diaphragm, the ScubaPro is a piston.

And ultimately, whether the reg is a diaphragm or piston makes little difference in breathing performance, they're both proven designs. Hence why they're both still used. So there really was no reason to even bother pointing that out since it doesn't matter.

 

[Blackwood]

And ultimately, whether the reg is a diaphragm or piston makes little difference in breathing performance, they're both proven designs. Hence why they're both still used. So there really was no reason to even bother pointing that out since it doesn't matter.

There are pros and cons to each design, particularly felt when it comes to cost (both initial and recurring). Generally speaking, diaphragms are cheaper to buy and more expensive to maintain.