Give a guy who is an analysis nerd and a new diver some data and this is what happens.
On my first dive trip (earlier this year), my first-ever ocean dive was an 80ft wall dive...I surfaced with 400psi of air (I think the DM couldn't believe it when I told him I was at 1000psi) while nobody else in the group was below 1700psi. I had been breathing my normal way of breathing during endurance athletic exercise which is to belly breathe rather forcefully. It probably also doesn't help that according to some doctor, I have 99th percentile lung volume. Anyway, I spent the rest of the trip trying to make new breathing habits that would still satisfy all the safety requirements while maybe making me less of an air hog.
I recently went on my 2nd dive trip, this time with an air-integrated dive computer. Here's how my first dive went...SAC vs. time (this is in PSI/minute if you divide the numbers by 100...so, my average SAC was 21 PSI/minute on a standard AL80, or an RMV of 0.56 cf/min). It was a super easy dive...shallow and mellow.
I'd have been pretty happy with that except that my dive buddy surfaced with over 2200psi left while I surfaced with 1100psi. By the end of the trip I determined that my buddy probably was not human and was just burping some air from their tank in order to not make it too obvious that they are not an air-breathing being. BTW, I believe the spike at the end is me inflating my BC at the surface.
On the 2nd day of the trip, we dove a wreck which included a couple swimthroughs. This was my first-ever wreck dive. I'd done a short reef swimthrough at one point on my first trip but a wreck is kinda a different story. I spoke at length with the DM about my concerns, and we made the call once we got there. My buddy and I decided to do it. Can you tell where the swimthroughs were?
I think the initial spike in SAC is from adding air to the BC as I descend combined with cooling of the tank (although the water was 84 degrees, the tank had been sitting in the sun). I may also be breathing faster when I first descend...although it doesn't feel like it. This initial spike is characteristic of most of my dives (although strangely, not the first one).
The two obvious bumps to 35 PSI/minute are of course where the swimthroughs were. I found myself breathing faster in order to keep from floating up/down as I swam through. I think the next time I do something like that I'll be more confident that I can control buoyancy with slower breathing...of course, there was a little claustrophobic fear feeding that breathing too. I stayed very concentrated on the fins of the DM right in front of me...that seemed to help.
The most beautiful dive of the trip was a wall dive on the last day. It looked like this:
So, no real decrease in SAC through the trip...if anything, it went higher a bit (I'm not gonna post all 15 dives here, you'll have to trust me when I say I posted my most flattering "typical" dives here).
Since my dive buddy doesn't use air, I am always the one who determines when the dive ends. This doesn't feel great, but I'm coming to terms with it. Fortunately, my buddy doesn't care...their comment is that they are just happy that they got in the water at all.
This may be somewhat instructive to my fellow new divers...things I learned on these dives and by looking at this data:
1) You can get a lower SAC with a bit of attention to detail. I've slowed down my breathing from what my habit is when doing something physical and I think it's helped. Based on what I can find online, a SAC in the 20-25 PSI/min range isn't crazy high.
2) Don't believe people when they say you'll get better with experience. You might not. I'm a semi-serious endurance athlete with large lungs and I'm not tiny. There's probably nothing I can do to get my SAC down to the 12 PSI/min range my inhuman buddy uses.
3) If you're planning a dive where you're going to be doing something you haven't done before, expect your air usage to go up. A lot. Figure on double.
4) Don't be competitive. It is hard for me to get to the point of being OK with not having the best SAC on the boat. I'm a competitive person. I told myself from the beginning that diving could not be competitive or I'd kill myself doing it. Even with that initial approach, it is hard to not get grumpy about it. I did feel good on one dive to be the last one out of the water. It's a funny competition...who can be the most chilled out to use the least air? Yeah...don't compete.
4) You might spike your air usage on descent. I'm not sure I've figured out that initial spike in SAC. I don't add much air to my BC when descending. Except on that first dive, on this trip I wore a 2.5mm full wetsuit and 8-10 lbs of lead. I think I could have gone with 6, but I wanted to keep some weight in my trim pockets and the smallest weights they had were 2 lb. I have bought some 1 lb soft weights to take with me on my next trip. I don't think it'll make any difference to this spike though. Maybe that's just normal from tank cooling and buoyancy adjustment as you descend. Perhaps the fact that there's no wetsuit on me in the first dive explains why no initial spike...less buoyancy adjustment due to no suit to compress. Or maybe it's a new experience every time I descend and I'm just using air.
Anyway, nothing deeply meaningful here, but this is something I've been scouring the internet for information on (it's the next best thing to diving while I sit here at my desk). I haven't seen a lot of specific examples, so I figured I'd post mine in case someone else is nerding out in a similar way.
Oh, and I'm going to try some Atomic Splitfins on the next trip to see if fin efficiency is noticeably improved. I'm hoping it is, but won't be surprised if it isn't.
On my first dive trip (earlier this year), my first-ever ocean dive was an 80ft wall dive...I surfaced with 400psi of air (I think the DM couldn't believe it when I told him I was at 1000psi) while nobody else in the group was below 1700psi. I had been breathing my normal way of breathing during endurance athletic exercise which is to belly breathe rather forcefully. It probably also doesn't help that according to some doctor, I have 99th percentile lung volume. Anyway, I spent the rest of the trip trying to make new breathing habits that would still satisfy all the safety requirements while maybe making me less of an air hog.
I recently went on my 2nd dive trip, this time with an air-integrated dive computer. Here's how my first dive went...SAC vs. time (this is in PSI/minute if you divide the numbers by 100...so, my average SAC was 21 PSI/minute on a standard AL80, or an RMV of 0.56 cf/min). It was a super easy dive...shallow and mellow.
I'd have been pretty happy with that except that my dive buddy surfaced with over 2200psi left while I surfaced with 1100psi. By the end of the trip I determined that my buddy probably was not human and was just burping some air from their tank in order to not make it too obvious that they are not an air-breathing being. BTW, I believe the spike at the end is me inflating my BC at the surface.
On the 2nd day of the trip, we dove a wreck which included a couple swimthroughs. This was my first-ever wreck dive. I'd done a short reef swimthrough at one point on my first trip but a wreck is kinda a different story. I spoke at length with the DM about my concerns, and we made the call once we got there. My buddy and I decided to do it. Can you tell where the swimthroughs were?
I think the initial spike in SAC is from adding air to the BC as I descend combined with cooling of the tank (although the water was 84 degrees, the tank had been sitting in the sun). I may also be breathing faster when I first descend...although it doesn't feel like it. This initial spike is characteristic of most of my dives (although strangely, not the first one).
The two obvious bumps to 35 PSI/minute are of course where the swimthroughs were. I found myself breathing faster in order to keep from floating up/down as I swam through. I think the next time I do something like that I'll be more confident that I can control buoyancy with slower breathing...of course, there was a little claustrophobic fear feeding that breathing too. I stayed very concentrated on the fins of the DM right in front of me...that seemed to help.
The most beautiful dive of the trip was a wall dive on the last day. It looked like this:
So, no real decrease in SAC through the trip...if anything, it went higher a bit (I'm not gonna post all 15 dives here, you'll have to trust me when I say I posted my most flattering "typical" dives here).
Since my dive buddy doesn't use air, I am always the one who determines when the dive ends. This doesn't feel great, but I'm coming to terms with it. Fortunately, my buddy doesn't care...their comment is that they are just happy that they got in the water at all.
This may be somewhat instructive to my fellow new divers...things I learned on these dives and by looking at this data:
1) You can get a lower SAC with a bit of attention to detail. I've slowed down my breathing from what my habit is when doing something physical and I think it's helped. Based on what I can find online, a SAC in the 20-25 PSI/min range isn't crazy high.
2) Don't believe people when they say you'll get better with experience. You might not. I'm a semi-serious endurance athlete with large lungs and I'm not tiny. There's probably nothing I can do to get my SAC down to the 12 PSI/min range my inhuman buddy uses.
3) If you're planning a dive where you're going to be doing something you haven't done before, expect your air usage to go up. A lot. Figure on double.
4) Don't be competitive. It is hard for me to get to the point of being OK with not having the best SAC on the boat. I'm a competitive person. I told myself from the beginning that diving could not be competitive or I'd kill myself doing it. Even with that initial approach, it is hard to not get grumpy about it. I did feel good on one dive to be the last one out of the water. It's a funny competition...who can be the most chilled out to use the least air? Yeah...don't compete.
4) You might spike your air usage on descent. I'm not sure I've figured out that initial spike in SAC. I don't add much air to my BC when descending. Except on that first dive, on this trip I wore a 2.5mm full wetsuit and 8-10 lbs of lead. I think I could have gone with 6, but I wanted to keep some weight in my trim pockets and the smallest weights they had were 2 lb. I have bought some 1 lb soft weights to take with me on my next trip. I don't think it'll make any difference to this spike though. Maybe that's just normal from tank cooling and buoyancy adjustment as you descend. Perhaps the fact that there's no wetsuit on me in the first dive explains why no initial spike...less buoyancy adjustment due to no suit to compress. Or maybe it's a new experience every time I descend and I'm just using air.
Anyway, nothing deeply meaningful here, but this is something I've been scouring the internet for information on (it's the next best thing to diving while I sit here at my desk). I haven't seen a lot of specific examples, so I figured I'd post mine in case someone else is nerding out in a similar way.
Oh, and I'm going to try some Atomic Splitfins on the next trip to see if fin efficiency is noticeably improved. I'm hoping it is, but won't be surprised if it isn't.
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