Air strategy for 4-5 tank dive days?

[northernone]

I think we're talking about Cozumel, not SE Florida, just sayin'.

Both 36 and 32 are common gasses in Cozumel as well.

Being able to adjust a computer between dives is pretty similar regardless of the location too.

At five tanks per day 21% will give you less time on the reef than a lower nitrogen blend gas if you're diving the wall and staying within NDL on a dive computer over many days diving.

 

[gopbroek]

So we keep getting conflicting advice and hopefully those here who dive with 3P can chime in. We just did the Spring Lake DAC/PADI course and dove with a DM who spent the last 3 months in Cozumel. He said he didn't think alternating air/36 was a good idea for Cozumel due to the depth on many of the dives, since our MOD with 36 is pretty shallow. He said he dove with air 100%.

So we're trying to choose between alternating air/32, or air/36 or one 32/36 tank out of 4. Or even all air. Thoughts?

Having dove a few times now with 3P I go with Jorge's advice of using 36 initially if the expected depth is going to be above MOD. His reasoning is to keep the N2 loading to a minimum from the start of the day to prevent carrying a high residual around through 1 to 3 subsequent dives in the day. A perfect example is Chuchakab with a floor around 90-95' which is basically a 80-85' dive for about 55 minutes. On air you will max out and possibly ride the NDL limit upwards and end up fighting NDL's for the rest of the day. On 36 it can be done comfortably with out exceeding a conservative 1.4 PPO2 MOD of 95'. The downside is O2 loading towards the end of the day which may be come a problem depending how your computer calculates offloading.

 

[scubadada]

I think we're talking about Cozumel, not SE Florida, just sayin'.

I think we were talking about switching back and forth between 32 and 36%

 

[ChuckP]

You could easily dive 36 all week in Cozumel, with a MOD of 95' @ 1.4, there's very little time your missing below that depth. It seems that 32 for first dive and 36 for second has become very common there..... Limit your N2, you won't get close to O2.....

There are dive masters that I know there that only dive 36.

 

[nodakdive]

So we keep getting conflicting advice and hopefully those here who dive with 3P can chime in. We just did the Spring Lake DAC/PADI course and dove with a DM who spent the last 3 months in Cozumel. He said he didn't think alternating air/36 was a good idea for Cozumel due to the depth on many of the dives, since our MOD with 36 is pretty shallow. He said he dove with air 100%.

So we're trying to choose between alternating air/32, or air/36 or one 32/36 tank out of 4. Or even all air. Thoughts?

The depth the DM may have been talking about was probably with regard to first dives. Second dives generally have a floor. There are exceptions, of course but for the most part, that's what happens. You'll likely be doing those 2nd and 4th tanks at reefs with a floor that's above the MOD. Was that DM doing 4 tanks per day? If a DM is doing a 4 tank day, the shop I use sends them out with 2 tanks of nitrox for the 2nd and 4th dives.

Let's assume you decide to dive nitrox one tank out of 4 and the shop knows this. When you ask for tanks of 32%, it may be suggested that you dive that tank on 36% as the cost is the same whether it's 32% or 36% and you'll get a little NDL benefit.

In a vacuum, one can plan just about any mix for any dive. Thing is, you're not diving in a vacuum. There are other divers on the boat. That said, it's not impossible to get on a boat and all the tanks on that boat are Nitrox. The dive plan would take that into consideration. i.e. you won't be diving Devil's Throat that trip.

Contact 3Ps and get their input. My understanding is that they're quick to respond.

 

[CajunDiva]

3P is recommending 36% Nitrox on two of the 4 dives each day. I believe someone said this in an earlier post but it seems like if the third dive was on 36% this would be enough to keep us in safe zone. I think 80% - 90% of our dives will probably be in 80 ft or less.

Already done...

 

[nodakdive]

Already done...

Right, and I'd be inclined to heed that advice. Maybe they weren't specific on which of those 4 dives to use nitrox? It's a guess, but I suspect they would suggest dives 2 and 4. Maybe they didn't ask the shop about diving just one tank of nitrox per 4 tank day? Another guess, but I suspect the shop would suggest diving the 2nd tank on nitrox as opposed to the 3rd.

Regarding Coz 4 tanking. Those afternoon boats can be a hodge podge. It's not uncommon to have mainland day trippers. You may have divers diving with the shop all week, but only diving afternoons. That 3rd dive is likely going to be a deeper dive, like Santa Rosa or Palancar. Since those divers are doing their 1st dive on your tank 3, they don't have an NDL consideration that a 4 tank per day diver does. What if everyone is advanced and the shop knows the divers? Punta Sur? Colombia?

Itching to put a tank of nitrox to great use? Chunchakaab.

 

[AZTinman]

Here's a thought. How about asking the dive op what they recommend and going with it? When I'm diving Cozumel, I use Tres Pelicanos exclusively. The operation is very professional and the DM's are quite competent. Dive profiles are multi level and surface intervals are routinely an hour or longer. You're diving with a DM/Guide and their lead DM really does the dive planning. I've never had problems diving 32 with Tres Pelicanos.

I did have a DECO issue last December, but that wasn't at Cozumel with Tres Pelicanos. I had crossed the channel for a day to do some diving with bull sharks. Depth to get into bull sharks was 110' and the DM only allowed a 15 minute surface interval. Our second dive was only 17 minutes long and we spent the remainder of the dive doing safety stops. The second dive was something of a disappointment due to limited bottom time, but my computer took me through the DECO process really easy. It was nice to rejoin the Tres Pelicanos crew and not have to worry about dealing with extended safety stops.

-AZTinman

 

[Efka76]

My thinking is that the gas mix doesn't make much of a difference if you're still diving to within the same margin of the NDL. EANx will give you longer NDL's but if you're not using that to create a bigger buffer then there is really no safety benefit.

One thing that I think *might* help is what a buddy of mine used to do. He would dive 32% and put his computer in Air Mode to create a bigger buffer. he had a policy to never dive deeper than 100ft and was fully aware of what he was doing but chose to do so anyway in order to create the buffer he wanted.

That said, he did this quite a while ago. These days some computers use GF so you can adjust the gradient factors in order to achieve the same goal and with more control and precision.

All of this is to say that just diving Nitrox isn't the answer. There's more to managing your tissue loading than that.

R..

This is extremely bad idea to dive on Nitrox but set computer on "Air". In this case your computer shows incorrect NDL, does not alarm you when you actually exceed you Nitrox MOD. People die when they make stupid decisions. This is one of such decision, which even should not be discussed.

There is another advantage of diving with nitrox - you feel less tired after any repetitive dives. Almost everybody uses nitrox during repetitive dives in liveaboard.

 

[Strategist.]

My thinking is that the gas mix doesn't make much of a difference if you're still diving to within the same margin of the NDL. EANx will give you longer NDL's but if you're not using that to create a bigger buffer then there is really no safety benefit.

One thing that I think *might* help is what a buddy of mine used to do. He would dive 32% and put his computer in Air Mode to create a bigger buffer. he had a policy to never dive deeper than 100ft and was fully aware of what he was doing but chose to do so anyway in order to create the buffer he wanted.

That said, he did this quite a while ago. These days some computers use GF so you can adjust the gradient factors in order to achieve the same goal and with more control and precision.

All of this is to say that just diving Nitrox isn't the answer. There's more to managing your tissue loading than that.

R..

This is extremely bad idea to dive on Nitrox but set computer on "Air". In this case your computer shows incorrect NDL, does not alarm you when you actually exceed you Nitrox MOD. People die when they make stupid decisions. This is one of such decision, which even should not be discussed.

There is another advantage of diving with nitrox - you feel less tired after any repetitive dives. Almost everybody uses nitrox during repetitive dives in liveaboard.

1) The NDL may be incorrect but you cannot deny that it is a more conservative NDL as compared to setting the computer to diving EAN32.
2) @Diver0001 also provided the context that his buddy did not dive deeper than 100ft which demonstrates that his buddy has a dive plan, and he sticks to his dive plan. When diving EANx, is it not a policy to check your depth as you're diving to make sure you're staying within limits? Your critique make it seems as if people are solely dependent on the MOD alarm to highlight the fact that there are near MOD.