How long should my air last?

[sdorn]

My soon-to-be wife and I recently got certified and went on our first dives this weekend post-certification. We went to a quarry in Pelham, AL which had a great setup. The weather was freezing, but the water was a reasonable 68 or 69 degrees. The tanks we rented were low pressure steel 77s (according to the man behind the counter, I didn't think to actually check the side of the tank itself). He explained that they actually held more air than an AL80 at a lower pressure. My SPG read at just over 2600 psi when we started the dive. I was down to right at 500psi at the end of the dive, after our safety stop, with total bottom time of just 31 minutes. The max depth on the dive was 49' and the average depth was probably around 37' or so.

My fiance still had 1000psi left in her tank when we finished the dive. So was I breathing way too much or something?

The dive shop asked us to let a third diver join us on this particular dive as he didn't have a buddy, and I was the one "navigating" the dive for the most part. This meant that I was constantly looking around to make sure I knew where my fiance was and where the other guy was, so I was very likely working much harder than they were. Would that account for it?

How do people get 45 minutes or more at deeper depths without running out of air?

 

[don hughes]

its quite normal for women to use less air then men sorry j
ust the way it is there lungs are smaller

 

[*dave*]

How do people get 45 minutes or more at deeper depths without running out of air?

They breathe less and use less gas in controlling their buoyancy.

There's lots of threads that go into detail on this topic, but to summarize:

Get your weighting squared away. Over weighting results in the need for a higher volume of gas to counter the negativity. New divers are typically adding/dumping gas from the BCD much more than experienced divers and the issue is magnified when a diver is over weighted.

Master neutral buoyancy. If you are negative or positive, you will have to kick to maintain depth. Kicking burns gas.

Stay warm. Cold causes your body to work in order to generate heat. Work burns gas.

Relax. Stress has a huge impact on breathing.

Slow down. Propulsion requires energy and producing energy burns gas.

 

[Papa_Bear]

Until the end of your dive if you planned well! Really you can do a search here and find many threads on the subject! It is a personal thing depending on many factors...... You will find regardless it will get better with experience! Think of locking yourself in a closet, how long will your air last? How panicked are you how much activity? Do a search and you will find tons of info! Good advice and spirited conversations on the subject!

BTW Dave I like you quoting me, but put a link to the entire statement, you sound like MSNBC just a little out of context!

 

[RJP]

How do people get 45 minutes or more at deeper depths without running out of air?

Gas utlization is a function of your respiration rate, which is a function of...

• Are you properly weighted? Extra lead = extra work = more burned gas
  
• Is your trim horizontal? Swimming at a 45deg angle all the time is woefully inefficient!
  
• Are you streamlined? Stuff hanging all over, flapping in the breeze, requires more work to push through the water.
  
• How's your propulsion technique? Bicycle kicking like mad or nice slow, efficient kick cycles? Try a frog kick to really lower your air consumption!
  
• What are you doing with your arms and hands? Most people burn tons of gas with unnecessary arm flailing.
  
• Are you comfortable and relaxed in the water? This is a biggie! If you're huffing and puffing on the verge of panic all the time you're gonna burn through air mighty fast. This one comes with time and experience.
  
• Lastly, the #1 thing you can do to improve your air consumption: SLOW DOWN! Slow EVERYTHING down. Then slow down some MORE. Then, if you think you're going slow...you're STILL going too fast!

If you REALLY want to improve your gas consumption try these things.

 

[dkktsunami]

Two things going on here: You are a new diver and you are comparing your air consumption rate to that of a woman. Your rate will improve with experience, but so will hers. Best advice is to not compete with females in the category of air consumption - you ain't gonna win. However keep trying to improve. I have a really good sac rate for a guy but my wife is better. I dive a lot more. I work at it. But she is still better.

 

[Road Guy]

echo what others have said..

My wife & I equal out pretty close on shallow dives (less than 50') but on deeper dives she will return with much more air than I pretty much every time, even using 100's.

Its gotten better with each additional dive, but there is always going to be a "gap"

 

[Gombessa]

I was down to right at 500psi at the end of the dive, after our safety stop, with total bottom time of just 31 minutes. The max depth on the dive was 49' and the average depth was probably around 37' or so.

My fiance still had 1000psi left in her tank when we finished the dive. So was I breathing way too much or something?

How do people get 45 minutes or more at deeper depths without running out of air?

To directly answer your question, half an hour is a completely reasonable bottom time for a new diver with ~80cf of air. Your breathing rate (and your wife's) will improve as you dive more and become more comfortable in the water.

My suggestion is to not actively try to conserve gas by limiting your breathing, just take deep, steady breaths, as naturally as you can manage through the reg, and enjoy the dive. Once you have 50-100 dives under your belt, you'll notice that you're just naturally using less air than before.

 

[sdorn]

That is good to know. I knew there are many things I can do to reduce the amount of air I consume, and will focus on those things as I get more experience diving. I just wanted to make sure the bottom time I got was in the range of what was to be expected. It doesn't seem like anyone is saying that something was wrong, just that I need to work on it which is to be expected.

 

[mike_s]

The tanks we rented were low pressure steel 77s (according to the man behind the counter, I didn't think to actually check the side of the tank itself). He explained that they actually held more air than an AL80 at a lower pressure. My SPG read at just over 2600 psi when we started the dive. .

ABWA started using Steel 77's in their rental fleet a few years ago.

It's 77cubic feet. which is the same as an AL80 (which is 77cf also).


The LP77 is rated for 2400psi and if "+" rated, you can overfill it by 10%, which brings it up to 2640psi.

the rated volume, 77cf, is based on the "plus" rating and a pressure of 2640psi.

so they really don't hold more than an AL80, unless you over fill them past 2640psi.


Many like these tanks better for several reasons.
* some people over fill them past 2640psi, upwards to 2800psi or 3000psi, giving it a lot more volume.
* they are more negative, which means you don't have to wear as much weight.
* they are about 3" shorter than an AL80. which is better for shorter people.
* since they are lower rated, it's less demanding on compressor/bank/fill systems.