15L vs 12L for beginner

[babycover]

Hi all,
I a beginner at diving and on my way to assembly my first set of gear.
I'm looking at the option of :
- 12L tank
- 15L tank
which one would you recommend.

I'm fully aware the heavy of the 15, i dont mind that at all.
with the 15 i can reduce my ballast weight, plus i usually do 2 shore dives ( <15m). i would try to do it without going to refill the tank.

Any advice, experience dive with their own opinions would welcome to share.

Also, what your experience / opinion about purchasing tank still in test?

thank you in advance.

 

[AJ]

If weight is no problem, go for the 15L. A 15L has more reserve than a 12L for two shore dives.

 

[Nasser]

I really like 15L steel tanks. Not only do they provide you with more gas, but they don't have that excessive floaty buoyancy shift that AL tanks have as the tank starts to empty. Keep in mind that the cylinders come in a variety of shapes... some are short and wider while others taller and slimmer. Try them out if you can as they can ride differently on your back and the weight distribution varies depending on the shape - go with what is most comfortable for you.

 

[DA Aquamaster]

It depends on the tank in question and there is more involved that just internal volume.

15 liter tanks

A Faber LP95 is a 15 liter tank with a 2640 PSI / 182 BAR service pressure, and it's about 7 pounds negative when full (with valve, in seawater).

On the other hand a Faber FX117 is also a 15 liter tank, but with 3442 PSI / 237 BAR service pressure, and it's almost 11 pounds negative when full (with valve in seawater).

12-13 liter tanks

If you're looking at Faber tanks the only 12 liter volume tank they have is the M100, and it has a 3498 PSI / 241 BAR service pressure but it's an awe inspiring -15.5 lbs negative when full (with valve in sea water).

The Faber FX100 is a 12.9 liter tank with a 3442 PSI / 237 BAR service pressure, and it's about 10 pounds negative when full (with valve in seawater).

The Faber LP85 is a 13.0 liter tank with a 2640 PSI / 182 BAR service pressure, and it's only about 5 pounds negative when full (with valve, in seawater).

The tank as part of the overall diving equipment system.

Your tank needs to be part of your entire diving system including the size and capacity of the BCD and the type of exposure protection needed to accommodate the water temperatures.

For example, if you dive with a 2mm or 3mm wet suit or a shorty, the FX100, FX117 and M100 are all progressively worse choices. Their progressively greater negative buoyancy will require more gas in the wing to get you neutral, that larger volume will need more adjustment with depth changes to keep you neutral. In turn, the greater volume in the wing will result in more drag, which requires more energy and more gas consumption to move through the water. Many divers have found that they actually get shorter dive times when using larger, more negative tanks. Many cave divers for example have found they have lower RMVs and longer penetrations with cave filled LP 95s than they do with cave filled LP 104s.

In addition, if the heavier tank leaves you overweighted, you're at elevated risk in the event of a BCD failure as you may not be able to swim yourself to the surface with the heavier tank.

In the case of a warm water diver with minimal exposure protection the LP85 is a much better choice in a steel tank. It's only 5 pounds negative when full and won't overweight the diver. It's also a 7" diameter tank and the low profile reduces drag. Those traits offset the "loss" of 10 or 15 cubic feet (283 L to 424 L) of gas capacity relative to a FX 100 or LP 95.

The LP95 is the next best choice for a wet suit diver, due to only being 7 pounds negatively buoyant when full.

If on the other hand you are a cold water diver using a drysuit or a heavy wet suit where you need a lot of lead weight to achieve neutral buoyancy, then the more negative steel tanks makes sense as you're just trading lead weight for the more negative, but larger capacity tank and it doesn't have the downsides of forcing you to carry more gas in the wing than you would otherwise with a smaller, less negative tank.

----

If you live or dive someplace where the shops will over fill a 3AA steel tank, the LP85 and LP95 have the additional bonus of holding 115 cu ft and 129 cu ft of gas respectively at 3600 psi. They will be more negative when full, they compare extremely well to higher pressure steel tanks in terms of overall capacity and buoyancy traits.

 

[babycover]

thank you for your advice.

i forgot to mention that i am in Melbourne so a cold water diver with 7mm wetsuit or dry suit all the time.
a Faber steel tank is a must have. if it a 15L would a 300bar much better than the 232bar or it is not worth it?

 

[Storker]

If you want to reduce the amount of lead on your belt, by all means get a 15x300. It's a beast, some 10kg heavier than a normal tank. And it holds enough gas for two short dives, not for two good dives.

If you want to reduce the total weight of your gear, get a smaller tank. I've more or less standardised on the 10x300, but I have one 15x200 and I had a 15x300. Good riddance to the 300, it was a beast to lift and handle, about 10kg heavier than the other tanks. But my gear with belt weighed about the same with either 15, and some 3-4kg less with a 10.

A 10x300, 12x232 or 15x200 holds some 3000 surface liters and is pretty much the sensible choice for most divers. If you use a lot of gas, consider a 12x300 or 15x232. Neither will have enough gas for two good dives, though.

 

[Peter69_56]

thank you for your advice.

i forgot to mention that i am in Melbourne so a cold water diver with 7mm wetsuit or dry suit all the time.
a Faber steel tank is a must have. if it a 15L would a 300bar much better than the 232bar or it is not worth it?

You might find that some LDS wont fill them to 300 BAR or if they do they charge more. Most don't like them, on that basis I suggest 232 BAR. Where were you thinking of getting them from? I can recommend a place which is cheapest I think in OZ and post to your door post free.

By the way if you are looking for dive buddies, drop me a message as I dive portsea/Queenscliff too.

 

[Storker]

You might find that some LDS wont fill them to 300 BAR or if they do they charge more. Most don't like them, on that basis I suggest 232 BAR.

That of course depends totally on common practice in your area of the world. I've never had any issues with filling to 300 bar, but I understand that it may be different in other parts of the world. The only downsides I see with 300 bar tanks are:

1: You lose some 10% of nominal capacity due to compressibility
2: The tank gets rather warm when you fill to 300, so it's a good idea to let it cool a bit and top it up if you want a good fill.
3: You can't use a yoke reg. You need DIN. This isn't an issue for me, though, since I live in DIN country.

The good thing about 300 bar tanks is that the physical volume of your tank is smaller for the same gas capacity, so you need less total weight compared to 200 or 232 bar tanks.

 

[Patoux01]

That of course depends totally on common practice in your area of the world. I've never had any issues with filling to 300 bar, but I understand that it may be different in other parts of the world. The only downsides I see with 300 bar tanks are:

I have yet to see anyone fill at more than 250b. I haven't been in many countries yet, but 300b is not very usual in most places I've been to (which includes Australia, though I haven't dived in Melbourne). Personally, I wouldn't use a 300b tank except carbon tanks... They're too heavy, both out of the water and underwater.


Most of my buddies simply used 2 12l tanks (232b from faber, one each dive). Sure, it's more expensive. But the amount of air in a 15l tank would not be enough for 2 dives (at least, not in the way we did them), even from shore.


I'm not sure how a 15l tank would have "less buoyancy shift than an Al80 tank", it simply doesn't seem possible to me (the shift is due to the amount of gas in it).


Also, the heavier the tank (in water), the more it will affect you when "playing" (being upside down etc). The bigger the tank (diameter), the more its center of mass will be away from yours, hence it will "roll" more, and will have more influence on you.

To each their own, but I'd go for the 12l tank, or if you want a higher volume, using a small twinset (but be careful about their height, or they might be backbreakers).

 

[Storker]

Personally, I wouldn't use a 300b tank except carbon tanks... They're too heavy, both out of the water and underwater.

Since I dive dry, I see no reason whatsoever to use a carbon tank. Any weight I save on my tank has to be added to my BP or my belt. And my Faber 10x300s weighs more or less the same as an old 15x200 or a compact 12x232 (they're all some 14-15kg empty without the valve), so for smaller tanks the weight out of the water isn't an issue. A Faber 12x300 is only about two-three kilos heavier than their compact 12x232, so that difference isn't too big either

To each their own, but I'd go for the 12l tank, or if you want a higher volume, using a small twinset (but be careful about their height, or they might be backbreakers).

I agree with that. A monster single is seldom a good idea, a small rec twinset would usually be better. A D8.5x232 holds some 4000 surface liters, which may be good for two shallower dives of your SAC is half decent. A 12L filled to 232 bar will give you about 2800 surface liters, about the same as my 10x300s and a little less than the old 15x200s. Good for one nice dive, and if you're on air you'll probably be nitrogen limited anyway unless you're a hoover.