air consumption

[Willar]

OK, if I want 500 psi when I surface from a 66fsw dive (please, no comments, it's just an example). 2700psi starting point -500 = 2200. So 2200/2700= 86% of tank to use. So 60 minutes X .86 = 52 minutes.

Of course, all these calculations are nice as a guide, but there's no substitute for looking at my SPG!

 

[jonnythan]

You're sort of missing the point. At 52 minutes you'd have 500 psi left, and you're still at 66 fsw. The 500 psi is totally arbitrary anyway. Is 500 psi enough gas to get you and your buddy up should there be an OOA?

How much is enough? How much is too much? The right answer is a concept called Rock Bottom.. do a search on it. There's a lot of reading to be done.

 

[Willar]

I'm not missing the point. I wanted to check my math and I realize that I have not adjusted for ascent, safety stop, OOA, etc. Since SAC rate varies on each dive, it's a guideline and not a precise measurement anyway. Thanks for the help.

 

[jonnythan]

http://jonnythan.com/rockbottom.html

It has to vary with depth. 25% (750 psi) is not nearly enough for an 80 foot dive, but it can be too much for a 30 foot dive. Even 1000 psi is much more than you'll need for a 40 foot dive, but not enough for that 90 foot one. This is a very useful safety tool.

 

[HPT3]

I'm still fairly new, with about 40 dives or so. But I can say this, I dive off of NJ, it is dark, cold, mysterious. I dove in the blue waters of Mexico, which is very clear. I have found that I was more relaxed when diving in clearer waters and my air lasted me a very look time. I seem to be more tense when diving off NJ. For one, I'm jumping into waters that are rougher at the surface and I'm getting pounded around a bit. Then I'm descending into the darkness of the unknown. Don't get me wrong, I enjoy the thrill and excitement and thats what makes my heart race and my breaths quicken. In Mexico, it was very enjoyable and I felt at peace. Very relaxed. So relaxed, that it was dream like. I could have stayed down for an hour, I'm sure. So, to some things up, I've learned the secret. It's being comfortable with your surroundings. I know, in time, the more I dive the dark 2 to 60 visiblity off the Jersey coast, the sooner I will be more comfortable in the surrounding. Until then, I think I may buy doubles.

 

[knotical]

are there other ways of getting my breathing better

CO2 is what makes us want to breathe. Exhaling more deeply reduces our dead air space and eliminates more CO2. That’s the quickest way I know to get better at air consumption. For newer divers: if the thought of running out of air just after you’ve exhaled deeply is worrisome, try it first on dry land. Exhale deeply and don’t inhale (never do this underwater, remember – breathe continuously). It’s several seconds before you are in real distress. Of course, always monitor your SPG and that shouldn’t be a problem.

 

[Natascha]

Well, I think it would also be helpful to know if you are comfortable with your gear. I mean, your buoyancy may be perfect, but if you are fighting with your fins, you’re still going to hoover up all of your air - or you might be 'comfortable' with your gear because you are used to it, but there might still be something more suiting for you out there.
And for HPT3 – I don’t know if you’ve ever done night diving, but it helps a lot of people that dive in colder/darker water. ‘Cause you expect it to be dark so you kind of relax more – that is at least how it was for a lot of my friends. Also, it can help if you have a light with you (daytime diving in cold water) – most people concentrate so much on the things they see in the light beam, that they forget to be nervous.

 

[rubbachicken]

Well, I think it would also be helpful to know if you are comfortable with your gear. I mean, your buoyancy may be perfect, but if you are fighting with your fins, you’re still going to hoover up all of your air - or you might be 'comfortable' with your gear because you are used to it, but there might still be something more suiting for you out there.
And for HPT3 – I don’t know if you’ve ever done night diving, but it helps a lot of people that dive in colder/darker water. ‘Cause you expect it to be dark so you kind of relax more – that is at least how it was for a lot of my friends. Also, it can help if you have a light with you (daytime diving in cold water) – most people concentrate so much on the things they see in the light beam, that they forget to be nervous.

i think i'm pretty comfortable with my gear, and my fins, i tried looking into the calculations but my mind blows steam, it's like using big words
night diving,, i LOVE night diving if i get lucky enough to dive on a full moon and we are on a site i know reasonably well then the torches get very littly use, i find it far more enjoyable watching by moon light rather than torch light, we see the ilumesant plangton where other don't, also the fish don't get dazzled, in the new year after work has settled down, i'm hoping to get to dive every weekend in the cold, once i'm happy and used to my drysuit i hope to be ready to start my dive master course so i think lots of regular diving will help me make my air last longer


thanks for all your input people, keep it coming

 

[kidspot]

http://www.spearfishing.org/bruces_tips/java/sac.html has some good tools for calculating SAC and other figures. . . I guess it's cheating, but it is quick.

Tim

 

[Mako Mark]

get a bigger tank..