Air in an AL80 swings about -3 to +3. Trimix with a high Helium content like the WKPP uses swings about -1 to +3. The full buoyancy endpoint changes, not the empty endpoint. Empty is empty
Roak
al double 80's , pst 104's ?
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Roak
roakey once bubbled...
Air in an AL80 swings about -3 to +3. Trimix with a high Helium content like the WKPP uses swings about -1 to +3. The full buoyancy endpoint changes, not the empty endpoint. Empty is empty
Roak
Thanks, that helped. But that would still apply to steel tanks as far as the swing goes. The He would make the more positive, (alum) less negative, which would be good for wetsuits. I think.
Bad day. Still don't see the relevance to the quote :upset:
MD
Youre right, the swing is the same, steel or AL. But note he says:
The buoyancy characteristics of aluminum, especially when using helium...
AL is the key point; the Helium is just an added bonus that makes ALs even better since you arent as negative at the start of the dive as youd be with air (or Nitrox). The problem with steels is that theyre intrinsically too negative to start with; so much so that even the He cant make up for it.
Roak
Okay, finally sunk in
ThanksMD
I have no problem with using high HE mixes in double 80s. I vastly prefer my 80s to my 104s.
WW
WW
and here's why.
GI3 is talking about LP104s!
Yes, two LP104s are a problem when wet. Why? Because you're so negative EMPTY in a wetsuit that you need buoyancy to stay up! If the BC fails...
Now let's look at this in detail.
As has been noted, air (or Nitrox) weighs about 1lb for every 13 cubes in the tank(s). No matter what the tanks are made of. So if you have 240 cubes of gas (dual HP120s) you have 18 lbs of GAS. With a single 120 you have 9 lbs of GAS.
The container is irrelavent to this discussion.
Now, let's look at the TOTAL diver package, because that is all that matters, and this is where GI3 steps off the deep end and into religion instead of fact!
Let's take me, for instance, diving wet.
I have a 3 mil wetsuit on and booties. I, personally, am about 3lbs positive in my birthday suit. My 3 mil wetsuit with the booties is about 9 more positive (its a bit "odd" in that it is more positive than I would expect, but there you have it - I think the booties are responsible for about 2 of that....)
An AL80, nearly-empty, is approximately +4. We use that for our weighting, because if you are low on gas you MUST be able to stay down without fighting - burning what little gas you have to stay underwater is VERY ungood if you have a mandatory obligation - or even just want to control your ascent rate.
Ok. We are now +16 in total, right? (All of this in salt water - a bit less in fresh)
I dive a steel BP (-6) with a STA (-4). To get neutral, I thus require 6lbs on my belt.
I am now neutral and can go diving. When I step off the boat I have 6lbs MORE negative buoyancy in the form of the gas in my tank.
When I get to the bottom at 110', my +9 wetsuit combination is now about +3. I am now -12. If my BC fails entirely, I must swim up 12 lbs until I regain some of that wetsuit buoyancy.
This is, by the way, a "worst case", since I probably will have breathed 1lb of gas by the time I get to the bottom, especially if I know there's a problem and/or have vented some of it in futility trying to inflate a holed BC....
AT NO TIME, OTHER THAN AS AN ABSOLUTE LAST DITCH NEED, CAN I DITCH WEIGHT UNDERWATER. IF I DO THEN I WILL BECOME A POLARIS, AS I CANNOT STOP MY ASCENT ONCE MY SUIT REGAINS SOME OF ITS BUOYANCY!
THAT is GI3s fatal flaw in his argument. He argues that it is "ok" to ditch for emergency buoyancy control. IT IS NOT WHEN DIVING WET, since the act of ditching weight will by definition make you positive as you approach the surface and that WILL injure you or worse.
Now let's substitute an HP120 for the AL80. The HP120 is -1 empty. I am still +3, and my suit combination is still +9. I am thus inherently +11. If I take the SS BP + STA, I am now +1, and need only ONE pound on my belt.
When I jump in the water, I am -9, because I am carrying 120 cubes of gas instead of 80. I get to the bottom and my wetsuit is now +3 instead of +9; the same 6lbs has been lost. I am now
-15 if the BC fails, and must swim that up. As I rise, I will get back not only the wetsuit's -6, but also the gas will be consumed as I breathe it, slowly returning the other -9.
Nothing material has changed; I removed weight from my kit in order to compensate for the inherent buoyancy difference of the tank.
If I need to ditch at the surface, by the way, I can ditch the KIT, immediately becoming +12! There is no way I can sink if I drop my kit; my wetsuit prevents that.
Now let's look at DOUBLE HP120s.
Now I am carrying EIGHTEEN pounds of gas, and need NO weight on my belt to be neutral at the surface. When I get to the bottom now I am -24! Oh oh.....
But with Double AL80s, I'm still carrying 12lbs of gas, and still lose 6lbs of buoyancy from my suit. I am STILL -18 at the bottom! I might not be able to swim up that -18.... I probably can't swim up the -24...
Note that the material of the tanks has changed, but the only real shift in the issue is that of the mass of the GAS IN THE TANKS. The tank material itself does NOT change the argument one bit! In fact, if I doubled HP80s instead of HP120s, I'd have EXACTLY the same -18 buoyancy as with the AL80s!
Further, it is idiotic to argue that you can do a ditch, either in whole or part, at depth to compensate for this. Why? Because as soon as you start up that suit buoyancy will return! Unfortunately, you have now dropped your ballast on the sea floor, so you are now inescapably positive - with nothing you can do about it. That's an absolutely fabulous recipe for an embolism or a SERIOUS DCS hit.
The correct soution to carrying too much weight in GAS, and/or too much exposure protection buoyancy shift due to depth, is to have a redundant means of lift to protect against your primary means becoming compromised.
This means either some sort of lift device that you can use to make it possible to swim up against your negative buoyancy, OR an inherently-usable secondary lift device (e.g. a drysuit)
If you have a bag, for example, you could clip it off on your left shoulder D-ring. Put some gas in it - not a lot - just enough so you can swim up against it. You now have +5 or +10 worth of lift. You can now swim up the kit. As you rise, and your suit buoyancy returns, you dump the bag to avoid a runaway ascent.
If you have a drysuit, then you can use it for emergency lift in the same fashion. Just crank down the exhaust and add air.....
The error in GI3s argument is in thinking that the problem is due to the tank material and that compensating for it by ditching things (like a canister) is an acceptable alternative at depth. It most certainly is not an acceptable alternative, because it leaves you unable to stop the ascent you initiate once you perform the ditch.
The problem is, in fact, that the shift in buoyancy that you are taking with you is too large to permit you to swim against it. This is a combination of the gas you have on your back and the exposure protection you are wearing.
The container the gas is in has zero bearing on either the problem or its solution!
Why GI3 and the DIR folks continue to spout this nonsense in the face of the inarguable facts of the matter is beyond me.
GI3 is talking about LP104s!
Yes, two LP104s are a problem when wet. Why? Because you're so negative EMPTY in a wetsuit that you need buoyancy to stay up! If the BC fails...
Now let's look at this in detail.
As has been noted, air (or Nitrox) weighs about 1lb for every 13 cubes in the tank(s). No matter what the tanks are made of. So if you have 240 cubes of gas (dual HP120s) you have 18 lbs of GAS. With a single 120 you have 9 lbs of GAS.
The container is irrelavent to this discussion.
Now, let's look at the TOTAL diver package, because that is all that matters, and this is where GI3 steps off the deep end and into religion instead of fact!
Let's take me, for instance, diving wet.
I have a 3 mil wetsuit on and booties. I, personally, am about 3lbs positive in my birthday suit. My 3 mil wetsuit with the booties is about 9 more positive (its a bit "odd" in that it is more positive than I would expect, but there you have it - I think the booties are responsible for about 2 of that....)
An AL80, nearly-empty, is approximately +4. We use that for our weighting, because if you are low on gas you MUST be able to stay down without fighting - burning what little gas you have to stay underwater is VERY ungood if you have a mandatory obligation - or even just want to control your ascent rate.
Ok. We are now +16 in total, right? (All of this in salt water - a bit less in fresh)
I dive a steel BP (-6) with a STA (-4). To get neutral, I thus require 6lbs on my belt.
I am now neutral and can go diving. When I step off the boat I have 6lbs MORE negative buoyancy in the form of the gas in my tank.
When I get to the bottom at 110', my +9 wetsuit combination is now about +3. I am now -12. If my BC fails entirely, I must swim up 12 lbs until I regain some of that wetsuit buoyancy.
This is, by the way, a "worst case", since I probably will have breathed 1lb of gas by the time I get to the bottom, especially if I know there's a problem and/or have vented some of it in futility trying to inflate a holed BC....
AT NO TIME, OTHER THAN AS AN ABSOLUTE LAST DITCH NEED, CAN I DITCH WEIGHT UNDERWATER. IF I DO THEN I WILL BECOME A POLARIS, AS I CANNOT STOP MY ASCENT ONCE MY SUIT REGAINS SOME OF ITS BUOYANCY!
THAT is GI3s fatal flaw in his argument. He argues that it is "ok" to ditch for emergency buoyancy control. IT IS NOT WHEN DIVING WET, since the act of ditching weight will by definition make you positive as you approach the surface and that WILL injure you or worse.
Now let's substitute an HP120 for the AL80. The HP120 is -1 empty. I am still +3, and my suit combination is still +9. I am thus inherently +11. If I take the SS BP + STA, I am now +1, and need only ONE pound on my belt.
When I jump in the water, I am -9, because I am carrying 120 cubes of gas instead of 80. I get to the bottom and my wetsuit is now +3 instead of +9; the same 6lbs has been lost. I am now
-15 if the BC fails, and must swim that up. As I rise, I will get back not only the wetsuit's -6, but also the gas will be consumed as I breathe it, slowly returning the other -9.
Nothing material has changed; I removed weight from my kit in order to compensate for the inherent buoyancy difference of the tank.
If I need to ditch at the surface, by the way, I can ditch the KIT, immediately becoming +12! There is no way I can sink if I drop my kit; my wetsuit prevents that.
Now let's look at DOUBLE HP120s.
Now I am carrying EIGHTEEN pounds of gas, and need NO weight on my belt to be neutral at the surface. When I get to the bottom now I am -24! Oh oh.....
But with Double AL80s, I'm still carrying 12lbs of gas, and still lose 6lbs of buoyancy from my suit. I am STILL -18 at the bottom! I might not be able to swim up that -18.... I probably can't swim up the -24...
Note that the material of the tanks has changed, but the only real shift in the issue is that of the mass of the GAS IN THE TANKS. The tank material itself does NOT change the argument one bit! In fact, if I doubled HP80s instead of HP120s, I'd have EXACTLY the same -18 buoyancy as with the AL80s!
Further, it is idiotic to argue that you can do a ditch, either in whole or part, at depth to compensate for this. Why? Because as soon as you start up that suit buoyancy will return! Unfortunately, you have now dropped your ballast on the sea floor, so you are now inescapably positive - with nothing you can do about it. That's an absolutely fabulous recipe for an embolism or a SERIOUS DCS hit.
The correct soution to carrying too much weight in GAS, and/or too much exposure protection buoyancy shift due to depth, is to have a redundant means of lift to protect against your primary means becoming compromised.
This means either some sort of lift device that you can use to make it possible to swim up against your negative buoyancy, OR an inherently-usable secondary lift device (e.g. a drysuit)
If you have a bag, for example, you could clip it off on your left shoulder D-ring. Put some gas in it - not a lot - just enough so you can swim up against it. You now have +5 or +10 worth of lift. You can now swim up the kit. As you rise, and your suit buoyancy returns, you dump the bag to avoid a runaway ascent.
If you have a drysuit, then you can use it for emergency lift in the same fashion. Just crank down the exhaust and add air.....
The error in GI3s argument is in thinking that the problem is due to the tank material and that compensating for it by ditching things (like a canister) is an acceptable alternative at depth. It most certainly is not an acceptable alternative, because it leaves you unable to stop the ascent you initiate once you perform the ditch.
The problem is, in fact, that the shift in buoyancy that you are taking with you is too large to permit you to swim against it. This is a combination of the gas you have on your back and the exposure protection you are wearing.
The container the gas is in has zero bearing on either the problem or its solution!
Why GI3 and the DIR folks continue to spout this nonsense in the face of the inarguable facts of the matter is beyond me.
SPEEDSTER
Guest
While I agree with you that you should not ditch your weight to the bottom the ocean, as it WILL lead to an uncontrolled ascent, I do believe I would rather take my chances with a buoyant ascent rather than plummeting to the depths and eventually drowning.
is that GI3s mantra on this point is DANGEROUS.
The correct solution is not to go diving with a kit you cannot swim up. This means that if you have too much gas and suit shift buoyancy then you need a means to "cover" the possibility of losing your primary lift device.
That need, however, has nothing to do with the cylinder material. It has everything - and only - to do with the TOTAL buoyancy shift during your dive.
The crux of this is that you need to determine how much negative buoyancy YOU can swim up (which will depend on your physical condition, fin type, etc.) If that figure is 15 lbs, then for any configuration that results in you being more than -15 at depth you must carry some form of redundant lift - whether that is a drysuit, a bag you can quickly get to, or some other means of providing emergency lift.
Anything else is foolhardy, and asserting that the problem is the material the tank is made out of is beyond foolhardy and into Darwin candidate territory.
The correct solution is not to go diving with a kit you cannot swim up. This means that if you have too much gas and suit shift buoyancy then you need a means to "cover" the possibility of losing your primary lift device.
That need, however, has nothing to do with the cylinder material. It has everything - and only - to do with the TOTAL buoyancy shift during your dive.
The crux of this is that you need to determine how much negative buoyancy YOU can swim up (which will depend on your physical condition, fin type, etc.) If that figure is 15 lbs, then for any configuration that results in you being more than -15 at depth you must carry some form of redundant lift - whether that is a drysuit, a bag you can quickly get to, or some other means of providing emergency lift.
Anything else is foolhardy, and asserting that the problem is the material the tank is made out of is beyond foolhardy and into Darwin candidate territory.
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