DukeAMO
Contributor
Tatiana's thread got me thinking...
Instead of theory, I'd like to base this on my own data...
On a recent dive in the Atlantic ocean, we used AL 80s. The maximum depth was about 100 fsw.
We started our ascent from the line at about 90 fsw.
We're still pretty new divers, so our SAC rates are reasonable, but not great. I don't have exact numbers because our computers can't give us an average depth. :-( I may yet pay $80 for the stupid data cable so I can figure that out.
It took us each about 300 PSI to ascend at a leisurely rate (around .5 feet/second) to the hang bar at 15 fsw.
The 3-minute safety stop used another 100 PSI apiece. The boat was bucking, so we were not especially relaxed there.
Swimming to the tag line and getting back on the boat (hard exercise in current and 3 foot waves) used another 100 PSI apiece.
So that means each of us needed 500 PSI to ascend and get back on the boat safely.
If we were stressed and breathing hard, we might need double on the ascent portion, so that would be 300 + 300 + 100 apiece, or 700 PSI, to get to the surface.
A safety stop is mandatory if you've been at those depths.
You have to assume you can't use the last 200 PSI, but you don't have to use the regulator on the surface (although it sure does help).
700 + 700 + 200 = 1600
So... would 1600 PSI be a good point to start our ascent on the next deep dive of that type?
Our DM in Hawaii advised us to head up from a similar dive at 1500 PSI, but I think they were basing that on the pool-like conditions we had there.
Maybe we'll use AL 100s next time, so then we'd have to do some more fancy math to figure that out, but it's not too difficult to convert to cubic feet.
Also a good data point for learning: on the dive in Hawaii we had to use air, and we really had to watch our NDLs closely. One guy got down to 1 minute remaining mid-dive; I think I had 3 minutes remaining at that point. Then we moved 10 feet up to the upper deck. On the Atlantic dive we used Nitrox 30, and had plenty of time remaining before the NDL (closer to 9 minutes remaining at 100 fsw before we moved up to the deck). Hooray Nitrox.
Instead of theory, I'd like to base this on my own data...
On a recent dive in the Atlantic ocean, we used AL 80s. The maximum depth was about 100 fsw.
We started our ascent from the line at about 90 fsw.
We're still pretty new divers, so our SAC rates are reasonable, but not great. I don't have exact numbers because our computers can't give us an average depth. :-( I may yet pay $80 for the stupid data cable so I can figure that out.
It took us each about 300 PSI to ascend at a leisurely rate (around .5 feet/second) to the hang bar at 15 fsw.
The 3-minute safety stop used another 100 PSI apiece. The boat was bucking, so we were not especially relaxed there.
Swimming to the tag line and getting back on the boat (hard exercise in current and 3 foot waves) used another 100 PSI apiece.
So that means each of us needed 500 PSI to ascend and get back on the boat safely.
If we were stressed and breathing hard, we might need double on the ascent portion, so that would be 300 + 300 + 100 apiece, or 700 PSI, to get to the surface.
A safety stop is mandatory if you've been at those depths.
You have to assume you can't use the last 200 PSI, but you don't have to use the regulator on the surface (although it sure does help).
700 + 700 + 200 = 1600
So... would 1600 PSI be a good point to start our ascent on the next deep dive of that type?
Our DM in Hawaii advised us to head up from a similar dive at 1500 PSI, but I think they were basing that on the pool-like conditions we had there.
Maybe we'll use AL 100s next time, so then we'd have to do some more fancy math to figure that out, but it's not too difficult to convert to cubic feet.
Also a good data point for learning: on the dive in Hawaii we had to use air, and we really had to watch our NDLs closely. One guy got down to 1 minute remaining mid-dive; I think I had 3 minutes remaining at that point. Then we moved 10 feet up to the upper deck. On the Atlantic dive we used Nitrox 30, and had plenty of time remaining before the NDL (closer to 9 minutes remaining at 100 fsw before we moved up to the deck). Hooray Nitrox.