new neutral 80

[newdiverAZ]

dove my new neutral al 80 today, and man did it screw me up. The first dive I dove a regular al80, then the second dive switched to the neutral 80 and dropped 3# of weight. My trim and bouyancy went nuts.It amazed me the difference in the bouyancy characteristics between the 2 tanks. Once I get the weighting worked out I think I'll really like it. I also think I will be able to drop more weight than the 4# difference in the tank as dropping the 3# didn't even seem to be close. I'm gonna work on it in the next few days and see how much it lets me drop

 

[mddolson]

newdiverAZ, could you elaberate a little.
was this in salt water?

I normally consider a standard 80 cuft aluminum to be neutral in fresh water. It's about 2 lbs negative full and about 1 lb possitve empty (500 psi)

Mike D

 

[newdiverAZ]

It was in fresh water. the new tank is supposed to be .05# positive in salt water. whereas the regular tank is supposes tp be 4.4# positive in salt water. I had the weighting right with the other tank so was assuming that the bouyancy swing would still be 4#. I think I was wrong both numbers are with an empty tank

 

[roakey]

Air weighs about 1 pound for every 13 CF. Therefore an 80, ANY 80, be it steel, AL, high pressure, low pressure, a "neutral" (talk about misleading marketing) AL80, a standard AL80, whatever, will swing about six pounds from full to empty. Really empty.

So an AL80 from full to 500 PSI will swing about 5 pounds.

A long as your cylinder isn't blowing up like a baloon when you fill it (trust me, it isn't) there's no ifs, ands or buts about this: 1 pound of swing for every 13 cf of air.

What's different between cylinder materials and designs is only the endpoint buoyancy of the swing.

Roak

 

[CuriousMe]

I was taught that in salt water an AL80 was 4 lbs negative full and two pounds positive empty...

Peace,
Cathie

 

[newdiverAZ]

well this tank is definitely heavier than a normal 80. The outside size is the same, the internal size has been reduced(thicker walls, and the fill has to be 3300 to get the same amount of air as a standard 80. The problem I had was not the bouyancy swing. It was the placement of more weight. I think the stated difference of 4# effects me as a diver as if it were wore weight. In conclusion. what I'm trying to say is I believe the tank which is 4# heavier(full or empty) will allow me to take more than 4# of lead off

 

[newdiverAZ]

Roakey, how is the term neutral misleading? This AL80 is alot closer to neutral empty than a regular 80. .02 positive compared to 4.4 positive in salt water. From what I've read this is the advantage of steel tanks, and sounds to be almost the same bouyancy characteristics.

 

[roakey]

CuriousMe once bubbled...
I was taught that in salt water an AL80 was 4 lbs negative full and two pounds positive empty...

Note the 6 pound swing. I think it's closer to -3 to +3, either set of numbers is close enough to make a good, educated guess. In any case you've always got to get a nearly empty cylinder and work out your weight in the water in order to be spot on.

newdiverAZ,

You're right, the characteristics are closer to steels; one thing this does is move more weight up over your lungs than a standard AL80 which forces you to put more weight around your waist. So technically you're weighted the same, you just moved where that weight was and this effects your trim (for the better, BTW).

If it looks like you can drop more than the delta in empty buoyancy between the cylinders, you're probably over weighted with the normal AL80s. It's fairly common that people get used to diving with X amount of weight and when they do something to perturb the system they go back to the basics and get properly weighted again, but never challenge the original, "standard" system.

"Neutral" is misleading because by omission Lufxer implies, but of course never states that it's neutral from full to empty (A physical impossibility). Some shops, who as a whole I find very cylinder naive, fall for this and actually tell customers that they don't swing at all from full to empty. Luxfer, of course, stands mute on this in order to sell more cylinders.

The fact that a neutral costs a bundle more than a standard AL80 and you can make a standard AL80 have *exactly* the same buoyancy characteristics by strapping a three pound weight onto the tank strap for 2-3% of the price of a new "Neutral" AL80 makes the neutral a solution in search of a problem.

Roak

 

[newdiverAZ]

but wouldn't strapping the weight to the tank also negate one of the arguments for steel tanks?

 

[newdiverAZ]

and my tank was only 180$ considerably less than a steel tank