Tank bouyancy, help in comprehending

[BigTuna]

http://www.njscuba.net/gear/eqpt_05_tanks.html
Scroll down to the section titled "Scuba Cylinder Specifications." It echoes what Spectrum and others said.

It the rest of it offers lots of insights on tanks.

 

[tbeindit]

for recreational diving i believe steels are a much better all around tank, you just have to have the extra money to get them.

 

[The Kraken]

http://www.njscuba.net/gear/eqpt_05_tanks.html
Scroll down to the section titled "Scuba Cylinder Specifications." It echoes what Spectrum and others said.

It the rest of it offers lots of insights on tanks.

There is no "equation" . . . it's all variables !!!

the K-onstant (Not)

 

[Nemrod]

If you dive warm water were no exposure protection is required then aluminum 80s do just fine. I need no weight with an aluminum backplate on an aluminum 80 in seawater but then I am wearing only a swimsuit and T shirt or a thin neoprene shortie type suit. This allows me to either dive with no BC or with my wing totally empty. If I had a negatively bouyant steel cyclinder then I would have to put air in the BC to compensate which then increases drag and potentially upsets trim which then requires a weight shift or other weight etc and on and on. In simple terms, for everything there is the correct tool and the much maligned aluminum 80 has it's place. For those who enjoy complicating everything then by all means. For diving with a 5/4 or my old sharskin 1/4 inch suit I like my LP Faber 85s. They add enough negative bouyancy to reduce my weight belt obligations or I often use a old camband with 2 pound weights on it and strap it to the rear of the aluminum cylinder--a tank weight belt. BTW, aluminum 19s, 40s and 80s are superb when slung, I would hate to have to try and sling negative steels for my pony or stages or deco bottles etc. N

 

[reo]

It answered it, but incorrectly. Empty weight is not used in figuring the change in lead when changing tanks. The only thing "empty weight" affects is how much total dry land weight you have to haul down to the beach, or up the ladder of a boat.

For comparing how much lead one has to wear, the only spec that counts is "EMPTY BUOYANCY". The change in lead when going from one tank to another is simply the algebraic difference in EMPTY BUOYANCY.

Using the original poster's numbers of +4.1 for the AL80 and -7.3 for that particular steel 80, you can see that the difference is 11.4 pounds. So going one way, drop 11 pounds, going the other way add 12.

A simple way to visualize or comprehend this calculation is to realize that if you have 11.4 pounds of lead strapped onto an empty +4.1 pound buoyant AL80, the tank + the lead will have the same 7.3 pounds of negative buoyancy as the empty steel tank without any lead.

Charlie Allen

Thanks Charlie for the correction. Its easy to get lost in the numbers.

Ron

 

[Central Fla]

I just looked at XS scuba tanks and the X-series 80 specs would knock a huge amount of weight off my existing gear

X-80 80cf, 3442 psi, weight 27.7, full bouy -9, empty bouy -3, and the length is only 19.7 inches.

that should knock off 16 or 17 pounds from my gear!!!! is that possible??

and yes I have that much, my integrated pouches are full, my two non removables are 4+4, and I even have some in my BC pockets so I can move them around for trim. I am a short guy with small feet and have avoided shore entries because I sink in the sand.

 

[The Kraken]

Well, the difference in required weight will be in difference of the buoyancy factors of an Aluminum 80, I suppose, and the steel 80.

It takes you X amount of weight to be neutral at the end of the dive with an Al 80. Empty, the Al 80 is about 4 pounds positive. The steel 80 is 3 pounds negative.

So you will be able to drop approximately 7 pounds from your basic weight requirement, that is, assuming you're diving a single tank.

the K

 

[D_B]

I just looked at XS scuba tanks and the X-series 80 specs would knock a huge amount of weight off my existing gear

X-80 80cf, 3442 psi, weight 27.7, full bouy -9, empty bouy -3, and the length is only 19.7 inches.

that should knock off 16 or 17 pounds from my gear!!!! is that possible??

and yes I have that much, my integrated pouches are full, my two non removables are 4+4, and I even have some in my BC pockets so I can move them around for trim. I am a short guy with small feet and have avoided shore entries because I sink in the sand.

-3lbs empty buoyancy ... plus the 4lbs lead you don't need any more to counter the empty +4lbs al80 = 7lbs your not going to need if you switch to that tank .. your center of buoyancy will change as well, you've removed weight from your belt, and put some on your back .. it can be noticed, but is easily learned

 

[Central Fla]

plus the 5.9 tank weight ??

 

[The Kraken]

Nope, has only to do with buoyancy of the tank.

the K