Air strategy for 4-5 tank dive days?

[rsingler]

What I'm seeing is that the limit for 1.2 ppo2 diving is 210 minutes and that the limit for 1.4 ppo2 diving is 150 minutes.

You are perhaps forgetting that you are probably not doing square wave profile dives.
Here's the Hilma Hooker in Bonaire a few years back. The first dive of four that day. By your numbers, 40 min x 96 feet on EAN32. PPO2 of 1.28. Except it's not, except briefly. Average depth for a dive that went though one tank was only 54 feet. Total CNS: only 9%!

PPO2 of 1.4 x 150 minutes?
As others have said, it's just not reasonably possible in one day's diving without deco. Especially with a reasonable surface interval for lunch.

Over a couple week dive trip on Nitrox, we might need to invoke OTU's. But not acute Ox Tox, unless one exceeds MOD.

 

[nodakdive]

You are perhaps forgetting that you are probably not doing square wave profile dives.
Here's the Hilma Hooker in Bonaire a few years back. The first dive of four that day. By your numbers, 40 min x 96 feet on EAN32. PPO2 of 1.28. Except it's not, except briefly. Average depth for a dive that went though one tank was only 54 feet. Total CNS: only 9%!
View attachment 486588
PPO2 of 1.4 x 150 minutes?
As others have said, it's just not reasonably possible in one day's diving without deco. Especially with a reasonable surface interval for lunch.

Over a couple week dive trip on Nitrox, we might need to invoke OTU's. But not acute Ox Tox, unless one exceeds MOD.

Well, didn't actually forget the square profile, just treated it like a table dive, but didn't consider the NDL issue of a square profile table dive for that length of time, that depth and that mix.

 

[chillyinCanada]

Is it time to split this thread or is it merely time to remind the readers and posters of the OP's original question and concerns for diving 4-5 dives a day in Cozumel?

I doubt OP and buddy are interested in rebreathers, etc.

Further, I've noticed that some posters may be getting all up in arms with each other, when they should probably take more consideration of the possibility that another poster may not have English as a first language.

 

[The Chairman]

But recreational open circuit divers like myself really have not way to exceed the CNS clock.

At five dives a day over multiple days? Aggressive diving like this is exactly why the CNS clock exists. In addition, the OP doesn't specify only recreational diving. I've seen a lot of recreational divers do technical dives in Cozumel without any thought or preparation. Just because you don't treat a dive with the respect it deserves doesn't mean it won't turn around and bite you. There is no such thing as an "undeserved" hit. It might be unexplained or not fully understood, but you can bet that the individual brought it on themselves. While time/depth/gas are obvious limits, other factors like fatigue, dehydration, sickness, injuries, hangovers, previous exposure and more need to be factored in to keep a diver safe. Deco algorithms are based on you being well and reasonably fit. Push or otherwise operate out of the intended parameters and you just might be hit with DCS. Just because you don't understand it, doesn't mean you didn't bring it on yourself. Dive conservatively. Safety is no accident and it's all up to you. I'm on my fiftieth year of diving and have yet to be bent. As I age, I am getting even more conservative in how I dive.

 

[Colliam7]

There is no such thing as an "undeserved" hit. It might be unexplained or not fully understood, but you can bet that the individual brought it on themselves.

YES! (Yes, yes, yes, yes, yes.) Probably one of the most important comments in this thread, and one that needs to be given more attention across threads.

Thank you, Pete.

 

[horn34]

Thanks for the responses from the 3P veterans. I think we're going to alternate air/36 on the 5 days we have 4 tanks dives and just do air on the days with 2 tank dives.

 

[CajunDiva]

After the inquiries and extended discussion, I hope you will come back and let us know how your experience worked out

 

[Illini_Fan]

Thanks for the responses from the 3P veterans. I think we're going to alternate air/36 on the 5 days we have 4 tanks dives and just do air on the days with 2 tank dives.

That's what I did, so I'm a bit biased, but I think that is a great decision. Enjoy your trip!

 

[Streydog]

What did you end up doing and how did it work out?

 

[Scuba Scott]

My instructor took the liberty to explain that is was one of the ways to trick the dive computer or increase NDL conservatism.

I view this the same way I would view tricking your doctor into believing you don't have a broken leg to reduce your time spent in the hospital. There may be a very good reason for doing this but it is generally not the safest choice.