Question Why own an aluminum tank?

[ginti]

The Al tanks typically go from slightly negative to slightly positive, but that is not perceptible in the water, only on land where you have to add ballast to account for it. Steel just has that ballast built in.

I don't think the shift itself is crucial since it depends on the gas inside the bottle. It's just that it goes from slightly negative to slightly positive -> so they are almost neutral, and no additional weights are necessary. Or not?

However, I don't understand very much why so many of my friends diving side mount like aluminium tanks. When I said "I believe it is for their buoyancy properties" I meant that, in case one needs to disconnect the tank for whatever reason, the diver's buoyancy would not be affected that much. But it's just a guess... do you have any idea?

 

[ScuberDuber]

Why own aluminum tanks? To practice one's diving using equipment similar to what will be provided when diving in Mexico.

 

[Cheizz]

Why own aluminum tanks? To practice one's diving using equipment similar to what will be provided when diving in Mexico.

For practice, fine. But for day-to-day local, personal use? Unless you only dive locally to practice for the tropics...
And would you want to buy/own an alu tank for that? Or just try to use them a few times to practice? There's a difference in that, too.

 

[Cheizz]

I don't think the shift itself is crucial since it depends on the gas inside the bottle. It's just that it goes from slightly negative to slightly positive -> so they are almost neutral, and no additional weights are necessary. Or not?

However, I don't understand very much why so many of my friends diving side mount like aluminium tanks. When I said "I believe it is for their buoyancy properties" I meant that, in case one needs to disconnect the tank for whatever reason, the diver's buoyancy would not be affected that much. But it's just a guess... do you have any idea?

Exactly. Alu: from negative to slightly positive; steel: from negative to less negative (but still negative and not more or less positive/neutral buoyancy).

 

[Damselfish]

For practice, fine. But for day-to-day local, personal use? Unless you only dive locally to practice for the tropics...
And would you want to buy/own an alu tank for that? Or just try to use them a few times to practice? There's a difference in that, too.

I think @ScuberDuber post may have been a joke? A play on the common phrase.

But yeah - they're cheap and less prone to corrosion in salt water. Just one of those is enough for some people No need to overthink it. (And those of us that would be overweighted with steel in the tropics are good with that, and may not even own a wetsuit to help float steel tanks, never mind want to wear one.)

When we dove locally, we learned with steel tanks Then bought AL tanks because they were cheap. No one explained the differences to us, and that was pre-internet so not as easy to pick that up. We wore more weight and lived. All that practice with 1/4" farmer john and AL tanks probably did wonders for my bouyancy control.

 

[boulderjohn]

I think the buoyancy change of an aluminum tank during the dive would be a disadvantage over steel tanks.

Exactly. Alu: from negative to slightly positive; steel: from negative to less negative (but still negative and not more or less positive/neutral buoyancy).

As Tom said above, the buoyancy swing during a dive is 100% determined by the loss of the weight of the gas you consumed. The composition of the tank is not a factor.

This is a very common misunderstanding in scuba. The evidence people cite is the fact that an aluminum tank goes from negatively buoyant to positively buoyant as it loses air, whereas most steel tanks will stay negatively buoyant throughout the dive. Although that is true, it doesn't matter.

What matters for a diver's buoyancy is the total weight and volume of the diver and the gear combined. With any tank, the total weight will shift by the loss of air during the dive, and the volume will remain about the same. The total weight of the diver and gear will include the extra weight needed because the aluminum tank is lighter than steel. To make a fair comparison, you need to add that extra weight in lead to the weight of the tank, in which case it is the same as a steel tank in terms of buoyancy.

 

[ScuberDuber]

I was not joking. I have a manifolded set of Aluminum 80 tanks to practice cave diving how it is done in Mexico so when I go to Mexico it is not a shock. I switch back and forth between Aluminum doubles vs Steel doubles. It makes me a better diver because I am always adjusting to different gear with different characteristics and confusing my brain and body which leads to greater resilience and confidence.

 

[Cheizz]

I was not joking. I have a manifolded set of Aluminum 80 tanks to practice cave diving how it is done in Mexico so when I go to Mexico it is not a shock. I switch back and forth between Aluminum doubles vs Steel doubles. It makes me a better diver because I am always adjusting to different gear with different characteristics and confusing my brain and body which leads to greater resilience and confidence.

I was not at all ridiculing you. I was just wondering if that warrants owning alu tanks. In your case it obviously does.

 

[Marie13]

I always scratch my head when I see local drysuit divers with AL80s - tanks they own. Their weight pockets just bulge with all the weight needed to sink a drysuit with an AL80. Some didn’t want to spent the extra for steels and others are just so used to diving AL80s they can’t conceive of diving anything else. These are the responses I get when I’ve asked if they have considered steels. Then there are the short women who struggle with an AL80 hanging down their butt. Back when I had steel HP80s, I offered my tanks so they could try them on dives. Just had to cover the cost of a fill. Nope. Wouldn’t even try, even after putting a HP80 next to an AL80. The HP80s are so much shorter and more comfortable for short people to dive.

I consider AL80s a very poor choice for cold water divers, especially people who own their tanks. I refuse to dive aluminums now unless they’re a deco or stage bottle.

 

[Angelo Farina]

For personal use exclusively, why would one want to own an aluminum tank?

It is not lighter than a similarly sized steel tank to carry on dry land, it doesn't carry a hugely different amount of gas. The main difference, as far as I can tell, is the buoyancy properties. And steel tanks seem to be much more consistent in that respect and need less lead weight to compensate. A steel tank, on the other hand, is more prone to corrosion, especially in saltwater. Am I missing something?

For my personal local dives (90% of which are freshwater dives), there would be no reason to buy my own aluminum tanks, it seems. If I just take proper care of my own steel tanks (as I would with all my equipment), there is no disadvantage over aluminum tanks, is there? The other way around - I think the buoyancy change of an aluminum tank during the dive would be a disadvantage over steel tanks.

The buoyancy changd is given just by the weight of air you consume. So there is absolutely no difference between aluminium and steel.
Of course most aluminium are small, typically around 11 liters, while steel can be larger: my Faber steel is 15 liters, so it contains much more air than an AL80.
If I use it entirely, I get more buoyancy variation than emptying entirely an AL80.
But steel has many more advantages: more resilient to shocks, more compact for the same internal volume, less buoyant (so requiring less weights), no problem of corrosion in the area of contact between brass (valve) and aluminium (cylinder).
So many years ago (in 1989) I swapped my old aluminium twin tank (two Luxfer of 9.5 liters each) with my current 15-liters Faber (with Cressi double valve plus reserve). Almost the same capacity, less weights, more practical.
So yes, a steel is highly recommended for personal property. And it lasts decades if properly used.