Yet another question on air consumption...

[Fish_Whisperer]

Last week in Cozumel, I dove 100's all week, and at the end of each dive, I generally had 8-900psi left over. Am I ready to drop the 100's and begin using 80's, or should I stick with 100's a little longer? Many of the dives were 45-60 minutes, by the way. The lowest pressure I ever ended with, was in the 700's.

Thanks.

 

[Meng_Tze]

Not sure what you are asking for here.

Tanks hold gas, you breath the gas. More gas = more breaths = longer BT. With 80's you will have less gas than in the 100's.

If you want less potential BT, go with smaller tanks. If you want more BT go with more/larger tanks.

 

[Fish_Whisperer]

Well, it's just that 100's tend to be a PITA, and I was the only one using them. Life would be a lot easier if I could switch to an 80 and not have my dive end earlier than everyone else's.

 

[TSandM]

FW, what depths were you diving? Remember that the rock bottom for an 80 cu ft tank at 100 fsw is half the tank . . . If you weren't getting to 1500 psi at depth, you could be okay, but if you were, you need to stick with the 100 or accept ascending before the rest of the group (at least if you want to reserve gas for a buddy).

I dove steel 100s in Cozumel, but that was because the dive op provided them, and I like long dives. I don't think I ever came up with less than 900 psi, but I don't mind gas left over. Much better that than wishing there were more there!

 

[Charlie99]

If I understand your question correctly, the answer is that you still need to use the 100's.

On the dives where you had 900 psi left on an AL100, if you were on an AL80 you would less than 200psi left.

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You didn't say what type of 100 you had. If it is 100 cu ft at 3300 psi, then the 77.4cu ft of a standard AL80 is equivalent to about 2500psi in the AL100.

 

[Fish_Whisperer]

Thank you, TSandM and Charlie. Much appreciated. And yeah, more bottom time is always a good thing!

 

[Meng_Tze]

Well, it's just that 100's tend to be a PITA, and I was the only one using them. Life would be a lot easier if I could switch to an 80 and not have my dive end earlier than everyone else's.

You were ending your dives earlier than others while on 100's? Sounds to me you need bigger tanks and/or better sac rate.

This comes in time and with comfort/experience. Why were you ending dives earlier?

 

[The Kraken]

Hey, Fran-N-Stein,

Were those HP or LP 100's?

Were the other divers diving 80's?

 

[Fish_Whisperer]

Meng, this time, I finished every dive with everyone. No problems. My SAC rate IS improving, and I'm vastly more relaxed and comfortable in the water, now.

Everyone else was diving 80's, K. I don't know the difference between HP and LP. (Also, as I look at my computer now, I see that it was set up for 80's, even though I was diving 100's... How does that affect things, I wonder?)

Yes, I am a dunce. (shaking my head....)

 

[Charlie99]

Everyone else was diving 80's, K. I don't know the difference between HP and LP.

There is more than one type of 100cu ft tank. What was the pressure for a full fill? How much lead did you remove compared to an AL80?

The Alumin 100's are fat (8" instead of the 7.25" of an AL80), long, heavy and awkward. Full fill is 3300psi. You use either 1 pound less or 3 pounds less lead than AL80, depending upon whether it is Luxfer or Catalina.

The newest steel 100's are 3442 fill pressure, 7.25", short, and light. You about 5 pounds less lead. Another similar tank is the older 3500psi HP100.

Their are also a variety of LP (low pressure) steel tanks in the 95 to 104 cu ft range that are 8" in diameter and a full fill is 2640psi.

http://www.huronscuba.com/equipment/scubaCylinderSpecification.html