Overweighted at beginning of dive but underweighted at end in shallows

[rsingler]

Yeah, it is a little over the top with detail.
Fortunately, the Quik Results tab gets you "an answer" if you have no interest in the theory.

 

[scubadada]

...But @scubadada is also correct. During a dive the best way to reduce your SAC and improve dive duration is to optimize elimination of CO2. And the way to do that is to 1) consciously slow your rate of breathing; 2) make a full inhalation; and 3) pause  briefly at end inhalation to allow CO2 exchange in your lungs before...4) a full exhalation to dump that CO2, and a small partial inhalation to resting lung volume...

,,,So...it's complicated. Just takes practice.

Hi @rsingler

Thanks very much for the detailed reply, just what I was expecting. I believe I picked up this breathing pattern from being a competitive swimmer from a young age. It has been the way I've breathed on scuba since I began in 1970, and I have always had very good gas consumption. It wasn't until much later that I paid enough attention to realize how I was breathing.

I do not take overly large breaths, though larger than tidal volume, and breathe slowly, with my pause after inhalation. I must be weighted appropriately for the average buoyancy I get from my breathing pattern. I have plenty of remaining breath volume control to get an additional amount of negative or positive buoyancy. Though the explanation may sound complex, I do not pay any attention to by breathing while diving, it is natural to me and I am grateful for the result.

 

[ibj40]

6 pounds is entirely reasonable as well. Being weighted within 5 pounds is the goal. Most everyone should be able to deal with that.

I resemble that remark! The divers in the springs and caves I frequent often marvel that I only wear a t-shirt and swim trunks. If you're built like a manatee, you get to dive like one. Don't worry about it until the Save the Manatee peeps keep pushing you back in the water saying things like: "You can make it, big fella!".

That, and throwing you heads of lettuce?

 

[ibj40]

I dive a BARE Velocity 5mm and always request two 4s and four 3s from the dive crew. Slightly overweight but nail the safety stop.

I'd also like to add that where you add the weight may be just as important as adding the weight itself.

In my configuration, I have two of the 3s in trim pockets on my tank strap, and the two 4s and the other two 3s in a pouch-style weight belt.

I have found this to give me a nice horizontal, slightly head up posture while diving.

 

[The Chairman]

I'd also like to add that where you add the weight may be just as important as adding the weight itself.

Trim is hella important. If you're not flat, you'll be inflating and deflating the whole dive through.

 

[The Chairman]

I have found this to give me a nice horizontal, slightly head up posture while diving.

Wha??? You don't dive in the Buddha position? Do the agencies know about this??? Too late! I've taken screen shots and have forwarded them to the proper authorities!!!

 

[BRT]

Yes, I'm starting to try doing this but will take some time. I'm not a mouth breather and underwater my natural tendency is definitely to pause after inhale rather than exhale so some things I need to continue work on. I think there is a silly subconscious thing where if I can't draw breath from my regulator I want to have full lungs to figure something out rather than empty lungs. A weird phobia of needing air and it not being there for whatever reason. It's dumb and just something to work on.

Thanks for the note.

Keep in mind that if you want to get the most O2 out of the air and get rid of the most CO2 with your exhale then you will pause after the inhale not the exhale.

 

[BRT]

Since the weight needed to be added is to compensate for the approximately 2.4% density increase from fresh to salt water, and one is compensating for total displacement of water when submerged, then 2-4 pounds corresponds to a total body weight of 83 to 166 pounds, which is probably a bit low. 4-7 pounds added probably covers more people; this is typically 4-5 pounds for women, 6-7 pounds for men. In my experience, and as calculated.

I think your numbers are good but don't forget that it is total weight, not just body weight. Weight of BCD, weight of weights, weight of fins, etc.

 

[tursiops]

I think your numbers are good but don't forget that it is total weight, not just body weight. Weight of BCD, weight of weights, weight of fins, etc.

I was sloppy. Thanks, I just edited my post to take out "body."

 

[The Chairman]

Keep in mind that if you want to get the most O2 out of the air and get rid of the most CO2 with your exhale then you will pause after the inhale not the exhale.

The gas exchange happens in a very small space inside individual alveoli. Turbulence helps, but is also dampened by those alveoli. I would suggest that for the average diver, learning to stop moving so much would do more to alleviate CO₂ buildup. They'll do that by learning how to adjust their depth with only their breathing rather than kicking. The less you move, the less CO₂ you produce. The less CO₂ you produce, the less you need to transpire that CO₂, so the less you'll need to breathe.

Look at your respiration while you're sitting in a chair. Your chest moves so little because you're producing very little CO₂. Walk and your respiration will probably increase in frequency, rather than volume. Running will produce a rather large increase in both frequency and tidal volume. Just try to pause that breathing to maximise efficiency after a good run, wink, wink. Normally, it doesn't take much to fill and empty those tiny alveoli, even though there are hundreds of millions of them. So, keep your activity down. Don't scull. Adjust your depth with your breathing. Avoid currents like the plague. Relax and let the ocean do your work for you whenever possible. Be a Zen diver, but avoid that silly buddha pose!