Weight of the air in the tank.

[saxman242]

I'm checklisting a lot of things that consume air.

- If I have too much weight and it's below my CoG, then I'm "swimming" nose up. This causes drag, and climb and wasted energy/air correcting and so on. So: a) reduce weight and b) move the weight up.

- I've come a long way in "calming down" in the water to conserve energy/air - always room for improvement especially on ...

- I'll be working on buoyancy on my next trip there. I was impressed with the instructor down there who was teaching others on the boat ("Advanced" course) and he gave me some buoyancy tips - I may take a buoyancy course from him while there to improve. It's likely my best potential for improvement.

- Most dives my mask is "just right" and doesn't need to be cleared. Some dives it seems to leak more so I flood it and clear it. Yep - lot's of air.

- My fins are large, plain fins that I've had forever. I could look at new ones, but I'm pretty sure 95% of the problem is me, not equipment.

- Body type: I'm tall and big with a pretty huge lung capacity. That can't be overcome easily - so I have to work the other details.

20 minutes? I'll settle for 10.

Profiles? One guy I'm comparing to was all over - often 10 - 20' or more deeper than the group. One of those guys who doesn't really seem to even need air.

Do you track your sac rate?

 

[tursiops]

Steve_C / turisops: The only place I recall water baths (about 2 or 3 inches of water flowing in a channel where the tanks were standing) was in Cuba as I walked by the fill line. I don't know about Roatan where I'll be going in March - but I will take a look this time.

I guess an option would be to have good air flow in the filling room.

All I see on the web (from this forum) is risk of water being blown into a tank from wet fill room equipment (esp. whips). If the cooling water is just in the bottom few inches it would seem low risk. Further, the technicians would presumably be very aware of that risk and would take care...

And what value do you think a few inches of water provides?
Air flow is almost irrelevant too; the heat transfer from the tank to air is minuscule.
The answer is, fill slowly.
If you Google enough, you'll find the info on how little a full water-bath helps....why risk water inside the tank for no useful gain?

 

[Alan Browne]

Do you track your sac rate?

My sac has been at a constant 2B since I was born, so that's steady at 0B/minute. It's also that at all depths though I don't actually look or feel. My intuition is that if I have 2B before the dive and 2B after the dive that I probably had 2B during the dive. Although I have learned to no longer be surprised when my assumptions are wrong.

Was that funny? I think so.

SAC rate, I'd have to check. I'll measure my lung capacity and then my resting surface rate and work out the numbers.

 

[Dan]

Watch those zeros!

I think it is more like 12,927 grams per 1,000 liters.

366.05 grams per cubic feet

Or something like that

My brain hurts now.

Ya, too many zeros on your number.
According to: Density of air - Wikipedia

Density of air at 15C is 1.225 kg/m3 or 1.225 g/L as 1kg = 1000g & 1m3 = 1000L so those 000 zeros on the numerator & denominator cancel each other

 

[Alan Browne]

And what value do you think a few inches of water provides?
Air flow is almost irrelevant too; the heat transfer from the tank to air is minuscule.
The answer is, fill slowly.
If you Google enough, you'll find the info on how little a full water-bath helps....why risk water inside the tank for no useful gain?

Just telling you what I saw. The rate of heat transfer would obviously depend on temperature differential, contact area, thermal resistance and the replacement rate of the water to keep the difference maximized. I see some mentions online of tanks immersed up to the shoulder of the tank. That would be more effective, obviously. If the operation has the right procedure, then getting water into the tank is eliminated. That would be an operator decision, obviously.

Time is gain if it's the long pole on the chart...

 

[Dan]

Air weighs around 800g per 1000 liters..
Converting that to cubic feet works out to around 22.7g a cubic foot

Michael

Not according to: Density of air - Wikipedia

1225g / 1000 liters at 15C.

It’ll get lighter when you heat it up (that’s how the hot-air balloon works). To get 800g / 1000 liters, you need to heat it up to 188C.

 

[Dan]

Because air actually weighs about 1293g/1000 liters.

@runsongas is right. It depends on temperature as density is a function of pressure & temperature.
Density of air - Wikipedia

Your number probably is based on the ambient air pressure at 0C, not at 15C.

 

[Dan]

You are right, I should, thanks.

0.807 lb/cuft · 453.592 g/lb ∙ 0.0353147 cuft /l ∙ 1,000 l/kl = 12,927 g/kl

Still getting the same answer.

Air density is 0.08 lb/cuft, not 0.8. You still have 10 times denser air

 

[saxman242]

My sac has been at a constant 2B since I was born, so that's steady at 0B/minute. It's also that at all depths though I don't actually look or feel. My intuition is that if I have 2B before the dive and 2B after the dive that I probably had 2B during the dive. Although I have learned to no longer be surprised when my assumptions are wrong.

Was that funny? I think so.

SAC rate, I'd have to check. I'll measure my lung capacity and then my resting surface rate and work out the numbers.

Sac rate, not sack rate. Ha!


I find it useful to track my sac rate over multiple dives so I can get a good idea of if my air consumption is improving, etc... Helps with dive planning to. I find if I go on a week long trip, I often have an elevated rated the first few dives and by the end of the trip, I may see a 20% drop, largely due to just getting comfortable and in the flow of things.

 

[Alan Browne]

I find it useful to track my sac rate over multiple dives so I can get a good idea of if my air consumption is improving, etc... Helps with dive planning to. I find if I go on a week long trip, I often have an elevated rated the first few dives and by the end of the trip, I may see a 20% drop, largely due to just getting comfortable and in the flow of things.

I've never done that for diving and wonder why I never even thought to do so. Don't recall an instructor or DM ever mentioning it.

Definitely my first 2 or 3 dives are more "nervous" than the remainder on a trip. I'm now at 49 dives and I know what to expect on a first dive of a weeklong, so you'd think I'd adapt quicker. Right? (Probably not).

I'll keep the SAC and sack rates separate next trip and see how I do. It's a very good tip. Thanks.