Is nitrox worth it for deeper rec dives?

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Marie13

Great Lakes Mermaid
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I've going to have some deeper dives (110-130ft) this coming season. I'm wondering if nitrox is worth the cost for the wee bit of extra bottom time! I ran the numbers on my Perdix (medium conservatism). At 130ft with 28%, you only get 3 more minutes of NDL time than on air.

At my shop, I'd pay $14/tank (up to 100cft tank) for custom mix (you can get banked 32% for $12/tank). In addition, I'd have to have a pair of tanks O2 cleaned ($50/tank, so $100).

Most of my diving is only 2 dives a day. Occasionally I'll do 2 Lake Michigan charters in 1 day (4 dives), but most of those are shallower (less than 90ft, most under 70ft). I have a trip to the Straits of Mackinac in June (3 days of 2 dives each) and Toby in July (1 day of 4 dives 1 day of 2 dives). I'll be taking my own tanks on the Straits trip, and am up in the air about the Toby trip (Divers Den only has 6 HP100 tanks for rent) - I refuse to dive aluminums now. Screws with my weighting.

I got a pair of tanks O2 cleaned last summer, but I really only used the O2 cleaning when I was on my Alpena, MI trip. I could have easily done those dives on air.

I've debated this with several friends and they all just do deeper rec dives on air. I didn't get my new doubles setup (tanks I already had) O2 cleaned, either.
 
In my opinion Nitrox is always good to have, whether you're planning to go to 70 ft or 130ft .
The main benefit is like you said the NDL , at shallower depths it can add a significant amount considering you dont use up all your air before reaching the NDL.
Shorter intervals can also be a benefit if you are planning to do multiple dives per day.
And last but not least the slightly controversial "you absorb less nitrogen in your blood stream which is healthier " - im not sure if medically accurate but cant hurt.

If i have the option i would normally go for Nitrox over air, the mix depending on the type of dive.
 
Good question. I think you will get differing views.

My best reference is probably diving Scapa Flow in the UK. Dives from 12m (36ft) to 42m (126ft). Battleships, Cruisers and blockships.
My first time we took O2 clean stages and breathed air for the dive, then 50% to flush out Nitrogen on the stops (in the days that we used air computers).
The second time I had my twins cleaned for the trip.

The normal form is big ship (deep 30-42m (90-126ft)), in the morning (many of these sit 25m off the seabed some upside down, some on there side), then a shallower site 12-20m in the afternoon. What we started doing was diving a 32% or 36% mix in the afternoon on the shallow site. Then blowing air onto it for a lean nitrox to suit the max depth of the morning dive. (We still carried decompression gas on the deep dives to accelerate the stops).

Many still only use air. Others go for a Specific mix every dive. We saved a bit of money by only having the 'Nitrox' fill for the afternoon, then cheated by adding air for the second.

I'm not saying its THE way to do it, its an approach!
 
Another consideration is that most of the people I buddy with do NOT dive nitrox on a regular basis. What's the point in paying for O2 cleaning and the additional cost of nitrox if your buddy has to ascend earlier than you do?
 
Good question. I think you will get differing views.

My best reference is probably diving Scapa Flow in the UK. Dives from 12m (36ft) to 42m (126ft). Battleships, Cruisers and blockships.
My first time we took O2 clean stages and breathed air for the dive, then 50% to flush out Nitrogen on the stops (in the days that we used air computers).
The second time I had my twins cleaned for the trip.

The normal form is big ship (deep 30-42m (90-126ft)), in the morning (many of these sit 25m off the seabed some upside down, some on there side), then a shallower site 12-20m in the afternoon. What we started doing was diving a 32% or 36% mix in the afternoon on the shallow site. Then blowing air onto it for a lean nitrox to suit the max depth of the morning dive. (We still carried decompression gas on the deep dives to accelerate the stops).

Many still only use air. Others go for a Specific mix every dive. We saved a bit of money by only having the 'Nitrox' fill for the afternoon, then cheated by adding air for the second.

I'm not saying its THE way to do it, its an approach!

Your dives were deco dives, from the looks of it. Mine are not (not for a couple more years, at least).
 
And last but not least the slightly controversial "you absorb less nitrogen in your blood stream which is healthier " - im not sure if medically accurate but cant hurt.

Correct me if I'm wrong, but this is only correct if you dive nitrox, but 'trick' your computer by still running it on air? When doing so, keep that MOD in mind too...
 
Your shop is pretty expensive. My local dive shop banks EAN40, and partial pressure mixes anything else using the banked mixed. But the cost is the same, and O2 cleaning isn't required. Cost is $10 a tank or $7.50 on an air card. Also O2 cleaning is $30 if it needs it only.

For me at only $2.50 a tank more expensive it is a pretty easy choice. Particularly since I often stay around 100ft where EAN32 provides quite a bit more no stop time. But for deeper dives I still feel that it is a good choice, as those extra 3 minutes is 3 more minutes you didn't have (since no stop time is often my limit).

Now if your buddy (and you are required to stay with) is the issue, diving different mixes makes no sense.
 
Correct me if I'm wrong, but this is only correct if you dive nitrox, but 'trick' your computer by still running it on air? When doing so, keep that MOD in mind too...

EDIT - Think i misunderstood you so ill re phrase
the assumption is that because you inhale more oxygen with each breath there is less nitrogen that's being absorbed into your blood stream, again im not sure if this is medically accurate .
 
@Manatee Diver

My shop is DRIS and their nitrox rates are on the cheaper end I've experienced in the Midwest.
 
@Marie13...
What limits your bottom time?? Your available gas, or your NDL? I know that when I dive deep on AL80's my NDL time doesn't really matter, as I'm limited by my air consumption. You may be diving bigger tanks, or have a better SAC rate then me... if NDL was a factor (with bigger tanks, or a lower SAC rate) I'd dive nitrox and not mind the added expense...

As a side note, if diving a mix with less Oxygen then the banked 32%, couldn't you start with a 'regular' 32% fill, and 'water it down with ambient air' to get to your desired mix (no O2 cleaning needed)?? You'd only have to O2 clean if you wanted to shoot pure O2 into your tank, no??
 
https://www.shearwater.com/products/perdix-ai/

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