A little help with Nitrox, please...

[theskull]

You all are on the right track, but I must ask:

Considering the cost of getting there, why get cheap at the last minute and save $8 by not diving Nitrox on BOTH dives/ALL dives each day?

It was an interesting intellectual exercise, but why not use the best mix for every dive? (Assuming Nitrox availability for all dives.)

theskull

 

[DandyDon]

You all are on the right track, but I must ask:

Considering the cost of getting there, why get cheap at the last minute and save $8 by not diving Nitrox on BOTH dives/ALL dives each day?

It was an interesting intellectual exercise, but why not use the best mix for every dive? (Assuming Nitrox availability for all dives.)

theskull

$100 for all one wants at Fantasy Island Roatan was fine.

$8 a tank would be okay x 15 tanks = $120

They charge $14 each on Ambergris Caye Belize, more remote and all that x 15 = $210.

For 90 feet and more, certainly, but for 60-80 feet dives like I've told to expect, this exercise, and - buy one a day, unless we get deeper dives...

 

[theskull]

I certainly understand. And I would be in perfect agreement for 40-foot dives. But 60-80 feet is where Nitrox really pays off in bottom time if you have a decent consumption rate. And even more so considering the repetitive diving you have planned (am I right, or is that 15 tanks over 8 days?).

Not arguing here, really, because it is your money and there is nothing wrong with your plan. But I would return to the cost of the Nitrox fills in proportion to the cost of the TRIP, and you are already set on paying for 1 tank per day so you only have to justify the cost of the additional fills rather than all 15 tanks.

Enough from me. Enjoy your trip. You're heading for an excellent destination and sure to have a fabulous time. Wish I were coming!

theskull

 

[DandyDon]

I certainly understand. And I would be in perfect agreement for 40-foot dives. But 60-80 feet is where Nitrox really pays off in bottom time if you have a decent consumption rate. And even more so considering the repetitive diving you have planned (am I right, or is that 15 tanks over 8 days?).

Yeah, if they were going to be 60 feet or more Square Profiles, I'd agree, and I won't know until we start, but I'm expecting starting below 60 feet, but doing a gradual ascent over the whole dive - like in Roatan. That, combined with my no-great comsumption rate, I'm going to start with 1 tank a day.

Still, 3 a day for 5 days is a little aggressive. I could do what I think the dives will be with All Air and get back to the boat Not-Red on my Oceanic computers; however - safety requires getting back All-Green on Oceanics, well below Padi tables. I may well bump up my Nitrox orders after a day or two, depedning on how the dives actually go.

Not arguing here, really, because it is your money and there is nothing wrong with your plan. But I would return to the cost of the Nitrox fills in proportion to the cost of the TRIP, and you are already set on paying for 1 tank per day so you only have to justify the cost of the additional fills rather than all 15 tanks.

Huh? It's $14 per filled Nitrox tank.


Day five is the Blue Hole trip, and I understand that 28% is available for it. May do All Nitrox that day...?

No free diving until day six, then fly day seven...

 

[sharkmasterbc]

I dive Nitrox all the time...safety vs. $...for me there is no question. If you plan your dives then you can get whatever mix you need for that paticular depth. Even for deeper dives to max rec depth of 130 a 28% trox will do fine.
I still dive air tables while on nitrox for added safety...if one can eliminate some of that pesky N2 from entering their tissues then why wouldn't they ?
Just calculate MOD and track CNS manually and your good to go. just my opinion but if I was doing an 80 ft dive I would request a 40% (ppO2 is still only 1.34). Of course this is has a lot to do with availability of gas and if you know what kind of dives you will be doing.
Hey as soon as I have the cert I will be diving without N2 as much as possible, helium is your friend !

 

[Scuba_Vixen]

There's 2 other things about nitrox you may want to factor into your use plans.

1) While most basic nitrox courses teach that O2 is as narcotic as N2, so therefore trox is as narcotic as air, ... There is considerable research that suggests that it's more closely 1/3 to 1/5 as narcotic as air. Many divers who do nearly back to back nitrox/air dives to the same site generally agree that they see more details and recall more about the dive on trox than on air. On dives in the 80' range for most of the NDL time, I found significant advantage to trox. If half of what a dive vacation is for is the memories, then trox is your best friend.

2) Since Many divers who use trox when they dive with great frequency report feeling noticably better that they did on air for the same diving schedule ..... I'm thinking you may find that quite a nice benefit as you go into the second half of your dive week with as many dives in a few days as you've done in the last few weeks or months or so.

I'd go for a few less T-shirts and trinkets, and maybe pass on the fancy dinners and take home all the best memories I can.

I'd be looking for 30/30, but I'd settle for nitrox.

Darlene

 

[rjchandler]

Your analysis assumes square profiles and tables. It seems fine but...

I expect you won't be doing square profiles and i expect your bottom time will be greater than you project. Your Oceanic is going to have its own ideas about your profiles and may accumulate a gas load over the course of your trip.

I also suspect that you will be "led" on a series of dives that are all do-able on air. But if the operator and your air consumption will let you do 3-a -day dives to 70 ft where you stay at that depth for the times you are talking about, you might find you want to use more Nitrox than you have planned.

 

[DandyDon]

Your analysis assumes square profiles and tables. It seems fine but...

I expect you won't be doing square profiles and i expect your bottom time will be greater than you project. Your Oceanic is going to have its own ideas about your profiles and may accumulate a gas load over the course of your trip.

I also suspect that you will be "led" on a series of dives that are all do-able on air. But if the operator and your air consumption will let you do 3-a -day dives to 70 ft where you stay at that depth for the times you are talking about, you might find you want to use more Nitrox than you have planned.

Yeah, Oceanics are considered "liberal," some say too liberal - usually becasue they didn't read the service manual paragraph that instructs to finish a dive "in the green," rather than yellow/not-red.

And you're right about the multi-level expectations. I did the study with 70 squares, but if one does 10 minutes at 80, then 15 minutes at 60, then 15 minutes at 40, one would be an O diver on the Padi chart before moving to 20 feet for a cruising Safety Stop. Even better than the T diver in the initial example. So while many divers will be okay on air for all 3 dives a day, I think I'm going to go for the Nitrox on the 2nd at least.

Of course, the diving may play differently, and there's other reasons that my Oceanic may be slow to move to Green. I'm playing with possibilities now, knowing that finaly decisions will be made there. Yet, I want to have a good working knowledge, and not just buy on emotion.

I have no interest in diving Nitrox on Air tables or puter settings! DCS is so very rare overall, I'd see that as a relative waste.

 

[DandyDon]

Okay, here is one more comparison. Again, rather than working with multi-level plans at this point, I'm working using 70 foot sqaure profiles for this. Actual multi-level dives starting 10 feet deeper would be less aggressive, as illustrated in post above...

If 32% and 36% Nitrox are both $14 upgrades:

a: 2 Air dives: First to 35 min = Q, 81 min SI = C, only 28 min left for second = T, after 63 total min at 70 feet - the most I can do on 70 feet with a 81 min SI;

b: 2 Nitrox 36% dives: First to 44 min = N, with only 69 min SI = C, 46 min = T, after 90 total min at 70 feet - however - as much as they charge for Nitrox, do I really want to do both?


1: First on 36% Nitrox to 41 min = M, 86 min SI = B, then Air on the second to 31 min = T, after 72 total min at 70 feet; or

2: First on Air to 40 min = T, 83 min SI = D, then 36% Nitrox on the second to 40 min = S, after 80 total min at 70 feet.

Again, 2 - 40 min dives at 70 feet is about all I can hope far if I breath with both lungs, and the 36% tank on the second dive gets me back to S. With multi-level, I'll be in better shape.

Okay, if I end up at S after 2 dives, then take a 1 hr 50 min SI for lunch, I'll be down to a B, with 31 min possible on another 70 foot dive. 2 hr 39 min SI is more likely, bringing me back to A, with 35 min left to 70 feet.

Or, if I were to add a second Nitrox tank per day, add a 36% tank on the third dive, make another 40 min dive, and end up at Q.

Or, if we were to use EADs, then again - Air first, Nitrox second and third.

However, on Blue Hole Day, I'll run 28% on the Hole, 32% on the second if we expect more depth below 90 feet, 36% on the last dive.

 

[sharpenu]

First, I have been diving the Oceanic and Aeris computers for 3 years now, without a problem. Too liberal for some, but they work for me. I have even been into deco territory a couple of times.

Second, I look at paying for nitrox like this:

I pay $1200 to go on a trip. We are there for 4 diving days and do 15 dives of an average 40 mins each. That is 600 minutes of diving time, or $2 per minute. Even if I only add 6 minutes to the average bottom time by diving nitrox for $8 each day. That adds $32 to the trip. Now I dive 690 minutes for $1232 or $1.78 per minute. Just made each dive cheaper, didn't I?