Why the Prejudice about DIR or GUE

[Soggy]

I don't ascend from dives very often with headaches, but on these dives? Nope. Have I made an ascent from dives with headaches? You bet. I've researched the problem and contributed it to C02 retention, which I'm sure that's what are thinking correct?

Yup...Exactly. Maybe you are just a freak of nature...I can't explain it. You do need to calculate from AVERAGE depth, though, not deepest depth. Deepest depth will lower the number you get.

 

[TSandM]

I'm nowhere near that good . . . I average about .4, and strangely enough, that doesn't seem to change whether it's warm or cold water.

 

[amascuba]

Yup...Exactly. Maybe you are just a freak of nature...I can't explain it. You do need to calculate from AVERAGE depth, though, not deepest depth. Deepest depth will lower the number you get.

I don't think I'm a freak of nature. What others think is a different story . My SAC being that low only happens when I'm very relaxed, as in I could fall asleep if somebody would let me relaxed. My average SAC has been between .45 - .53cf lately. That's in 62 degree water, doubles, and drysuit. I don't get nearly as relaxed on these dives because I'm still learning the equipment and working more on skills and situation awareness. Also, I'm pushing more mass through the water.

 

[SparticleBrane]

Yes, average depth is required for calculating SAC. My girlfriend's SAC was really good until I noticed she was calculating it using max depth instead of average.

If you use max depth, that's literally assuming that you started the dive at the depth you provided, stayed there the entire time, and then that's it. Thus if your max depth were 100fsw and your average depth 58fsw, but you use 100fsw for calculating, that's assuming that you were at 100fsw for your entire dive and didn't move--producing an incredible SAC rate.
Obviously this isn't how it happens. You have to get your average depth from a dive computer or bottom timer, or calculate it using the dive profile provided by your computer/bottom timer.

 

[jeckyll]

I just realized recently that I've been calculating my SAC's wrong... I've been using AL80's and using 80 cf as the volume. Of course it's on 77 so now I need to go back and recalculate all my dives ... nawww

I get in the low 0.5's in a drysuit in cold, dark water, which makes me fairly happy. Perhaps high 0.4's if using 77 cf for some dives. I figure for at 6'1" and 195 that's not too bad with less than a year of diving...

How's this realted to DIR again though??

 

[amascuba]

Here is my last dive in doubles, drysuit, and 62 degree water (9/16/06). It was a night dive.

Tank: Double AL80's (154.8cf, or 77.4x2))
Max Depth: 69ffw
Average Depth: 39ffw
Bottom Time: 59min.
Tank Rated Pressure: 3000psi
Start Pressure: 2100psi
End Pressure: 1100psi

1. 154.8cf/3000psi = .052cf/psi
2. 2100psi - 1100psi = 1000psi used
3. 1000 x .052cf/psi = 52cf used
4. 52cf / 59min. = .88cf/min. used
5. 39/34 + 1 = 2.15ATA
6. .88cf/min./2.15ATA = .41cf

I got the average depth from my computer (aladin tec wrist), which was being dove in gauge mode.

 

[SparticleBrane]

0.4? Not bad.

 

[Peter Guy]

Since you asked:

According to my Cobra's calculation (so NON-DIR!), in warm water (like last week), SAC is in mid-high 40's -- in cold water (drysuit) high 50's/low 60's.

The interesting thing (to me) is that my SAC rate goes down about 10-15% on night dives -- I wonder if I just don't move as much.

 

[amascuba]

Since you asked:

According to my Cobra's calculation (so NON-DIR!), in warm water (like last week), SAC is in mid-high 40's -- in cold water (drysuit) high 50's/low 60's.

The interesting thing (to me) is that my SAC rate goes down about 10-15% on night dives -- I wonder if I just don't move as much.

My SAC is typically lower on night dives as well. I'm usually more relaxed on night dives. I think part of it is that I only am focusing on whats in the presence of my light and situation awareness is easier at night since my buddies light is typically in my peripheral vision.

 

[MXGratefulDiver]

The interesting thing (to me) is that my SAC rate goes down about 10-15% on night dives -- I wonder if I just don't move as much.

That will change radically when a six-gill swims into the cone of your light out of the darkness ... or in a couple of months when (a now 250-lb but still playful) Junior comes back to spend the winter harassing divers in Cove 2 ...

... Bob (Grateful Diver)