Best Nitrox Mix/ Profile at 100'

DiveLvr · Sep 15, 2013

When diving a 32% mix using a AL 80 @ 3100 psi diving between 85-115' I get about 22-25 min before I start getting into caution zone on my computer. With a 3 min safety stop I surface with about 1200 -1400 psi.My dive partner usually does a little better than me.we're leaving a good bit of gas in our tanks.

Since running out of gas isn't the problem, how can we increase our bottom time? We would like to increase our depth too, 122-130'.

Any pointers?

Doug

Captain Bil · Sep 15, 2013

Without knowing you at all, I suggest the following:

Regarding getting better bottom time, how's your trim and attitude in the water? Is your rig balanced? Are you and your gear streamlined? Are you relaxed and breathing controlled? Experience and attention to those points should in time yield you a better SAC rate, thereby extending your bottom time.

Regarding the depth increase, two points: first, the deeper you go, the faster you use up your gas. Boyle's Law. Second, 32% is a little rich for your proposed new depth. Do a best mix calculation for a PO2 of no more than 1.4 for that depth.

I'm sure lots more advice is coming your way, hope this helps

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chrpai · Sep 15, 2013

Captain Bil:
Regarding getting better bottom time, how's your trim and attitude in the water? Is your rig balanced? Are you and your gear streamlined? Are you relaxed and breathing controlled? Experience and attention to those points should in time yield you a better SAC rate, thereby extending your bottom time.

While this is always good diving advice, I'm not sure how it's relevant since he says he's coming back up with 1400 psi. He seems to be constrained by NDL not available gas.

@DiveLvr:

You throw out some numbers regarding EANx and FO2 choices and max depths that exceed MOD for that mix. You need to make sure that you really understand the math and that you are selecting a mix that is appropriate for your max planned depth.

There's no magic bullet here. Nitrox has diminishing returns the deeper you go. You either need to come up with multilevel dive plans that give you more time at shallower depths after your deeper depths or you need to get into technical diving and learn how to do decompression dives.

Nwcid · Sep 15, 2013

Here is a link to different calculators, Technical Diving and Recreational - Nitrox Calculator The last one is for "best" mix based on depth.

As the previous poster stated you need to really make sure you understand what you are doing and why. On 32% your MOD is 110' for a PO2 of 1.4. With that mix at 110' your get a bottom time of 25 min, and at 100' 30 min.

From your description it sounds like you are doing square profile dives, doing contour dives would give you more time.....

ianr33 · Sep 15, 2013

DiveLvr:
Since running out of gas isn't the problem, how can we increase our bottom time? We would like to increase our depth too, 122-130'.
Any pointers?
Doug

Training,doubles and deco?

halocline · Sep 15, 2013

DiveLvr:
When diving a 32% mix using a AL 80 @ 3100 psi diving between 85-115' I get about 22-25 min before I start getting into caution zone on my computer. With a 3 min safety stop I surface with about 1200 -1400 psi.My dive partner usually does a little better than me.we're leaving a good bit of gas in our tanks.

Since running out of gas isn't the problem, how can we increase our bottom time? We would like to increase our depth too, 122-130'.

Any pointers?

Doug

What exactly do you mean by 'caution zone'? Do you mean NDL is near zero? Or are you just getting close enough to get nervous? About the only thing you can do to extend your NDL is use a higher O2 blend; 36% is pretty popular, but you're limited to 95 feet at 1.4 ppO2.

So if you want to increase your depth AND your bottom time, that's deco diving and you'd want to train for it. But even within recreational, no stop diving, it seems that doing some homework and planning would be beneficial for you if you want to dive more aggressive profiles. You really don't want to rely on discussion board advice for this sort of thing. Get some deco planning software, read a bit about deco theory, and you could plan dives that are aggressive but stay within limits, and stick closely to that plan, and do an extended safety stop. I always do one, sometimes 10 minutes, if I've been pushing NDL. It really lowers N2 loading efficiently.

Jim Lapenta · Sep 15, 2013

Get some adv nitrox and deco training and put the computer in guage mode. Figure your best mix for your desired depth and bottom times. This used to be covered in Nitrox classes. I know it still is in the SEI and the TDI Nitrox classes. That's why those are the only ones I offer.

bamafan · Sep 15, 2013

If you feel lucky go to a higher o2 mix. 40 percent at 100' you can do over 40 minutes of bottom time before going into deco per vplanner with a 0 conservative factor. You will slightly exceed 1.6 ppO2 but if you are lucky it just might work. Personally I would recommend a deco procedure / advanced nitrox class. With that you will learn that you can do a 2-3 hour bottom time in that depth range and luck will not have anything to do with it. In fact you will have a plan in case the stuff hits the fan.

Kevrumbo · Sep 15, 2013

That's roughly a Truk Lagoon wreck profile for the recreational range wrecks 18 to 33 meters deep, with O2 deco if you plan going over Eanx32 NDL"s (double 11L/AL80 cylinders with a 5.5L/AL40 O2 deco tank). Typically the customary "recreational" nitrox for the Truk Odyssey Liveaboard during a week charter with 3 to 4 max dives for most days is Eanx30 (slightly deeper MOD advantage for approx the same week's CNS O2 exposure as Eanx32). For the wrecks at 30 to 39 meters, I just use deep air or 20/20 bottom mix and O2 deco.

Captain Bil · Sep 15, 2013

OP, I told you - plenty of good advice would come your way. Listen to these guys' most important point - seek training. And in the meantime, dive safe.

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Best Nitrox Mix/ Profile at 100'

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