Best Nitrox Mix/ Profile at 100'

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I agree with the "get better training" part. This is basic stuff that you
should be able to figure out on your own.

In the meantime, take a look at the intro article

How To Scuba Dive | Scuba Diving Training & Certification | Scuba Diving

under the section "Staying Longer". You'll find that decreasing your depth slightly,
say to 60 feet, is likely to extend your NDL and leave less "excess" air in the tank
(while sticking to the rule of thirds).

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
 
Why would anyone follow the rule of thirds on an OW dive? I have never understood that.

Copying the answer from someone else's test but not understanding the question?
 
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.

and what if he's not lucky?
 
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

Perhaps a more liberal computer would help if that's within your risk tolerance. I dive an Oceanic computer using the DSAT algorithm. NDL at 100 feet is 30 minutes and at 110 feet (nearly the MOD) the NDL is 25 minutes. I often dive deeper wrecks such as the Speigel Grove, the Duane, and the Castor on 32% and with a little multilevel diving, get in a total dive time of 45-50+ minutes. It's often a head to head race between available gas supply and NDL. At times, I end up diving a slightly richer mix and limit my time and effort below the MOD. Seems like you should be able to do a bit better than 22-25 minutes.
 
All this talk about LUCK and when we are doing longer deeper dives.
Makes me feel warm and fuzzy like when I was training for Adv. Nitrox and Deco.
I love my instructor and appreciate his training more and more especially when I read threads like this.
Seek out the training for goodness sake you will not be sorry and then we all can sleep better knowing you are aware of the risks and planning for them.
Just know that death favors the unprepared and sometimes there is not a second chance!

Enough doom and gloom, train well, have fun!

CamG
 
ianr33:
Why would anyone follow the rule of thirds on an OW dive? I have never understood that.

Some instructors, rather than go through the whole "rock bottom" or "minimum gas" concept, simply get around it by teaching their students to dive thirds. It's not conservative enough for some dives, and wildly overconservative for others, but it is simple.

There ARE open water dives that are more appropriately done on thirds. Anyplace where surfacing is a really bad option -- because of surface currents, surface conditions, boats, or the fact that the boat you got off of is anchored and CANNOT come and pick you up -- may require that kind of gas planning. Most of those dives are walking the blurry line between recreational and technical diving.
 
If you are feeling lucky and are willing to push your ppo2 then you might be willing to push your NDL. Just skip that pesky 20ft stop, lots of people skip deco and are fine.

****Disclaimer****. I take no responsibility for anyone following this bad advice.
 
Thanks for the responses. Certianly more training and more gear is an answer in a longer term scenario. Shott term I think a slight change in mix and dive profile will get us where we want to be. The Oriskany doesnt have alot to see, IMHO, until you get below 100' so multi level doesnt offer much. The Duane or Spiegel Grove on the other hand offer more to see up and down the water column so multilevel is better. I "parked" the CCR when I moved from CA to the gulf coast. None of my current dive buddies have mire than 2 years diving exp and the dive shops and boats here kinda shy away from rebreathers. I've only seen one since being on the gulf coast. Anyway, thanks for the advice.
 
Not sure if this is the caution zone you are referring to, but some computers have a little yellow area that the nitrogen loading bar graph ticks through before going into deco mode. The NDL time left is the most important thing to pay attention to. Quite a few years ago my wife and I had two different puck computers that ran the same algorithm. One computer took much longer to turn red from the yellow zone and the other would hold off entering the yellow zone, but blow through it quickly even though both had basically the same NDL time left. I ended up switching computers with her because she got nervous watching her computer enter the yellow area.
 
https://www.shearwater.com/products/teric/

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