2 Tank Dive, Nitrox for Both?

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

1967Goat

Contributor
Messages
134
Reaction score
166
Location
Conifer, CO
# of dives
50 - 99
I'm heading to Coz on Thursday for 9 days. While there I am going to complete my AOW (I have about 35 dives total so far). I was Nitrox certified last November. Dive shop asked if I want to use Nitrox for this trip.

For this example, let's assume for each 2 tank dive the first will be deep (max 90') and the second will be shallow (25' - 40' or so). The Nitrox has the advantage of allowing longer bottom times at deep depths. Shallow, not so much (run our of air first).

Nitrox is an additional $8 per tank. Not a huge price difference, but money is money!

Do folks use Nitrox on the first dive, then switch to air for the shallow dive? Is it better to just use Nitrox for both, even if there's a not a benefit for shallow dives? I plan on diving 6 - 7 days.

I realize I would have to change the setting on my brand new Deep6 Excursion I received over the weekend. :D Maybe @cerich or @LandonL have an opinion on how swapping mixture settings between dives effects the Excursion? (Can't wait to get it wet!!!)
 
With those depths and only 2 dives per day, especially as a new-ish diver, you might be limited by your air consumption rather than NDLs. The question then is how much the extra safety margin is worth to you. For me, at home, Nitrox is only an extra $5 per tank and I rarely use it, but I'm sometimes willing to spend more on safety when I'm far from home.
 
with those I'd be tempted for nitrox on dive 1, but certainly not on dive 2.

The excursion won't care about gas switches between dives. You have to change the mixes, but the computer doesn't really care what you set it to.
 
I generally just do Nitrox for both. As they said above...you don’t “need” to do Nitrox for the second one, but I tend to do so just for the extra safety cushion (my computer is set to conservative, as well).

It’s not a big deal to swap the gas type or oxygen percentage on your computer (mine has air and Nitrox mode and then I select the O2 percentage for the Nitrox), so I wouldn’t let that be the determining factor for you.
 
Are you sure you'll be at 90' max on the first dives? We seem to often be between 100' and 115' on the first dives (Columbia Deep), which is near the M.O.D., and makes me nervous using EANx -- so we often dive air for the first dive and 36% for the 2nd, shallower dive to have extra cushion (as sometimes surface intervals seem to get cut a little short).
 
Not that it would make that much difference but usually the second dives in Coz are deeper than that. Looking at the second dives on my last couple trips my average depths were in the 40-55' range. You could always start out using nitrox for dive 1 and air on dive 2 and see monitor your NDL's, if you get close to your comfort levels change your plan. I don't know about your computer but changing the nitrox settings between dives is not a big deal, just make sure you learn how to do it before your trip. I would ask your dive op what they suggest as well.
 
@1967Goat : As you still have some time, why not reach out to the dive shop to get a bit more info on dives you are likely to be doing. Setting alarms on your Deep6 and paying close attention to depth is good discipline for safe and enjoyable diving. Personally, I would be diving nitrox for a 9 day trip and switching to air only if there was something special to see at a greater depth.
 
Great points everyone, thanks! This is my first trip to Cozumel and my first time with the dive op. We usually stay in Playa del Carmen and the Dive Op I use there makes 2 - 3 trips per week to Coz in their fast boat, so I have dived 4 sites in Cozumel....That's why I wanted to stay in Cozumel this time, rather than paying extra to take the boat from Playa to Coz.

Since I'll have 9 days on site, I'll have plenty of time to ask questions and go over everything! This is also my first time using my own dive computer.
 
Do folks use Nitrox on the first dive, then switch to air for the shallow dive?

Not normally no. It's either one or the other. And if you are only doing 2 dives a day, honestly it really doesn't matter. Unless you have a good breathing rate or large tanks, you probably aren't going to get longer bottom times on the first dive anyway.
 
Depends a lot on your SAC rate and average rather than max depth (while respecting MOD). I always use nitrox on both dives as I was continually running up against my NDL on the second (shallow) dive. And while that had not happened since switching to Nitrox 200 dives ago, just yesterday we ended up hanging out deep longer than planned on our first dive (hunting lionfish), and on the second dive I ran up against NDL and had to shallow up - but at least got a full dive in. Would have been a very short second dive if on air.

also the ops I dive with almost never set a time limit, so for me it’s worth the cost of the nitrox to get another 15 min of bottom time per dive. If you are going to be time limited it may make less of a difference.
 

Back
Top Bottom