Larger Nitrox tanks in Bonaire

[diversteve]

One of the operators on Bonaire has/can get AL100's. Not an AI resort IIRC. They list it on their rental page. If I remember who, I'll post it in this reply.

 

[herman]

Interesting, but ultimately meaningless piece of information. And corresponding faulty conclusion. The net buoyancy CHANGE is the important thing, not whether the tank ends negative or buoyant. Which tank has the greater buoyancy SHIFT?

An AL 80 goes from -1.4lbs when full to +4.4lbs when empty; a 5lb buoyancy shift
An HP100 goes from -8.5lbs when full to -1lb when empty; a 7.5lb shift

So all other things being equal, to offset the larger CHANGE in buoyancy from full to empty you will actually need 2.5 MORE pounds of ballast if you're diving the steel tank that ends the dive negatively buoyant than if you're diving the AL tank that ends the dive positively buoyant.

You may end up with "less lead" by diving the steel tank, but you've simply replaced it with an even greater amount of steel.

That said, I dive double 119's that I overfill...

Not only that but the extra weight shift is going to require more air in the BC at the beginning which will increase drag using more air.
Size is not the major factor in gas use, technique is. One of my regular dive buddies is 250+ and over 6 ft, he can easily hang with me. 75 to 90 minutes dives with an 80 on Bonaire is common for us.

One of the operators on Bonaire has/can get AL100's. Not an AI resort IIRC. They list it on their rental page. If I remember who, I'll post it in this reply.

Most likely Walt at RecTec.

 

[drrich2]

Herman:

Size is not the only factor, but it is a big factor. Yes, I've seen postings in 'air hog' threads where someone knows someone who's a big guy with a great SAC, but you'll notice these threads are often started by big guys.

How many skinny women under 5'9" gripe about how they can't get a long enough dive time on an 80 cf tank?

RJP:

Manipulating your breathing, is what you mean. You're not "optimizing" anything.

Since respiration is a function of "demand" rather than "supply" what you're doing really has no meaningful effect on how much oxygen your cells need or use. You can screw around with your inspiration rate (inspiration being different than respiration) but what you're doing is not "optimizing" anything. It may make a tank last a few moments longer, but you're screwing with your blood chemistry and other things. The known equations for how your body's cells utilize oxygen don't change based on what you do with your tongue or how many bursts of exhalation you take. This is as universally true as the Earth being round - disagreeing with it is really just sort of silly. What you're essentially saying is that, in an attempt to get better gas mileage, you only fill your gas tank half way rather than filling it up. That way you use less gas, right?

I would suggest that you'd see better improvement in SAC rate if you stopped thinking about how to "optimize" your breathing.

It gets me longer dive times with a better SAC and that's more optimal for what I'm trying to do, usually. I do need to be mindful there are potential complications, of course, such as the intense head ache one can suffer from skip breathing.

From what's been said in other threads, it's not so much oxygen consumption as carbon dioxide production & the need to expel it that drives respiration in most of us.

Simply 'not thinking about' breathing while diving doesn't yield the same respiratory pattern I have on land. Sitting here typing, I figure I very easily inhale, oh, it feels like maybe 1/3'rd (or less) lungs full of air, exhale, little movement involved. Air movement is slow, and I naturally pause before exhaling without trying.

Underwater, the reg. is delivering air (or nitrox) to me with some mild pressure. I start to inhale, and the reg. tends to 'fill me up' unless I cut the inhalation short. At least, that's my subjective experience. And I don't know why, but even trying to passively exhale, it seems more gas flows out of me if I just relax & let it flow.

From Wikipedia:

Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration when extra effort is not applied. In a healthy, young adult, tidal volume is approximately 500 ml per inspiration or 7 ml/kg of body weight.^[1]

What I'm saying is, if I don't make a conscious effort to control my breathing, my tidal volume tends to be greater and my 'gas in, gas out' rate somewhat faster, vs. sitting or walking calmly on land, even when I'm on a leisurely warm-water high-viz negligible-current dive.

So I can't 'just breathe normally' underwater, because the conditions are different than on land.

Richard.

P.S.: Note that in the definition supplied, tidal volume is impacted by body mass. Also, the larger the cross-sectional mass of diver & gear being shoved through the water, the greater the effort & so O2 consumption & CO2 production required, I'd think.

 

[Spitts6654]

Interesting, but ultimately meaningless piece of information. And corresponding faulty conclusion. The net buoyancy CHANGE is the important thing, not whether the tank ends negative or buoyant. Which tank has the greater buoyancy SHIFT?

An AL 80 goes from -1.4lbs when full to +4.4lbs when empty; a 5lb buoyancy shift
An HP100 goes from -8.5lbs when full to -1lb when empty; a 7.5lb shift

So all other things being equal, to offset the larger CHANGE in buoyancy from full to empty you will actually need 2.5 MORE pounds of ballast if you're diving the steel tank that ends the dive negatively buoyant than if you're diving the AL tank that ends the dive positively buoyant.

You may end up with "less lead" by diving the steel tank, but you've simply replaced it with an even greater amount of steel.

That said, I dive double 119's that I overfill...

If you are diving steels you should end up with less overall weight. You need more weight to offset the positive buoyancy of an aluminum tank when empty.

[TABLE="width: 264"]
[TR]
[TD][/TD]
[TD]Tank Weight
[/TD]
[TD]Full Weight
(Wet)[/TD]
[TD]Empty Weight (Wet)
[/TD]
[/TR]
[TR]
[TD]AL 80
[/TD]
[TD="align: right"]31.3
[/TD]
[TD="align: right"]-1.6[/TD]
[TD="align: right"]4.4
[/TD]
[/TR]
[TR]
[TD]Steel 100
[/TD]
[TD="align: right"]34.3
[/TD]
[TD="align: right"]-8.4[/TD]
[TD="align: right"]-1
[/TD]
[/TR]
[TR]
[TD]Delta
[/TD]
[TD="align: right"]3
[/TD]
[TD="align: right"]-6.8[/TD]
[TD="align: right"]-5.4
[/TD]
[/TR]
[/TABLE]

Based on this I can reduce my lead by 5.4 lbs and still end up 2.4 lbs lighter overall.

The buoyancy swing comes from the increased wet weight of the tank, which will require you to use more air in your BCD to compensate, but you are still lighter overall.

 

[KeithG]

I will echo the suggestions to consider altering your dive behavior as opposed to your tank.

if you go deep, stay deep and swim hard you will drain any size of tank that you are capable of carrying.

Attempts to increase dive time via bigger tank will not yield much improvement.

You can easily get a major improvement in bottom time by limiting your depth and cutting the amount of swimming.

My Bonaire al80 normally has 1500 psi in it after a 75 minute dive. I do not stay deep and do not swim much. I do notice a significant increase in consumption from as little as 10 minutes a 70 feet.

Stay shallow, stop kicking.

 

[Tunaman68]

You may end up with "less lead" by diving the steel tank, but you've simply replaced it with an even greater amount of steel.

I stand corrected for my meaningless and faulty offer of information

I just know that I can wear 5lbs +/- less lead with my steel tank in CA being a fat guy wearing a thick wetsuit. It 'seems' like less weight (perhaps because it's been shifted to a better place) going up and down the stairs in Laguna to dive sites. In addition, moving the weight helped my trim in the water and even if I have to have some extra in air the bc, the trim is better, the body is more streamlined and I can work less and use less air. Just my experience, not science.....

I make my 18yo daughter dive buddy use a 60 and that solves it for us!!

Have Fun!!

 

[RJP]

From what's been said in other threads, it's not so much oxygen consumption as carbon dioxide production & the need to expel it that drives respiration in most of us.

You're confusing "respiration" with "inspiration." Like a hand and a glove, they are closely related, but completely different.

 

[Hintermann]

I am not an air hog but like the 15-litre steel tank because I find that maintaining buoyancy and comfort with it, particularly towards the end of a dive. Therefore, I request it on all my trips even if it means a small additional charge. But if they cannot supply it - Cayman Aggressor for example - no big deal. I just make a slight adjustment to the weight carried.

Incidentally, during my queries with The Habitat, they said that 15-litre (100 cu ft) steel tanks would be no problem.

 

[jimw]

I am not an air hog but like the 15-litre steel tank because I find that maintaining buoyancy and comfort with it, particularly towards the end of a dive. Therefore, I request it on all my trips even if it means a small additional charge. But if they cannot supply it - Cayman Aggressor for example - no big deal. I just make a slight adjustment to the weight carried.

Incidentally, during my queries with The Habitat, they said that 15-litre (100 cu ft) steel tanks would be no problem.

I am no air hog either--225lbs and an al67 is my usual tank. At Habitat, the tanks out for use are aluminum 50 to 80 cu ft. They seem to have a bunch of 63's, so that's what we use mostly. I did not see a steel in use there during our April trip. So, I would guess that will mean some toting for you up and down the steps or ramp................

 

[RJP]

Incidentally, during my queries with The Habitat, they said that 15-litre (100 cu ft) steel tanks would be no problem.

No problem for THEM is what they mean. Do you think "no problem" for you means you'll be able to get 4-5 of them to throw in your truck in the morning and spend all day out and about... or do you think that "no problem" means you can get one and will need to bring it back to their fill station between every dive?

---------- Post added May 31st, 2013 at 08:39 AM ----------

Attempts to increase dive time via bigger tank will not yield much improvement.

Of course, that's just not true. Why does ANYONE carry bigger tanks? Why does anyone dive doubles? Are you suggesting that when I dive double HP 119's filled to 4,000psi I won't get "much improvement" over a single AL80?

Bringing 25% more gas (going from 80cf to 100cf) will pretty much allow for 25% longer dives.

---------- Post added May 31st, 2013 at 08:42 AM ----------

I stand corrected for my meaningless and faulty offer of information

I just know that I can wear 5lbs +/- less lead with my steel tank in CA being a fat guy wearing a thick wetsuit. It 'seems' like less weight (perhaps because it's been shifted to a better place) going up and down the stairs in Laguna to dive sites. In addition, moving the weight helped my trim in the water and even if I have to have some extra in air the bc, the trim is better, the body is more streamlined and I can work less and use less air. Just my experience, not science.....

I make my 18yo daughter dive buddy use a 60 and that solves it for us!!

Have Fun!!

Helps trim for sure, so not suggesting its not a good idea - it is, in fact, for all the reasons you mentioned. Just pointing out that while it's 5lbs less lead, it's (at least) 7.5lbs MORE steel.