How to reduce a monstrous SAC

[GramsciBeat]

I've got about 150 dives under my belt and I am comfortable in the water. I dive on a 15l steel in a 5mm wetsuit, so at the beginning of the dive I am very slightly negatively bouyant in order to be properly neutral at the end of the dive for the safety stop - but in that context my bouyancy control is good. I am 41 years, 1.88m (6.2ft)tall and 110kg (240 pounds). I am fit and do competitive open water swimming. During a dive my heart rate rarely exceeds 70 bpm and generally averages at just under 65 bpm.

My SAC rate is 21 litres per minute (about 0.74 cu feet per minute, I think). I would really appreciate some advice on how to reduce my SAC to a more manageable level.

Thanks

 

[g1138]

Try using your BC more and your lungs less when controlling your buoyancy.
Some people just have larger resting SAC's. They have larger lungs and take up more air than others on a normal breath.

Other than the usual recommendations for lowering your SAC that's the only other thing I can think of that might help.
Usual recommendations are to
- swim less during your dive
- calm down and basically zen your entire dive
- get better buoyancy and trim control
- (& my personal favorite) suck less

Just remember to breath normally at all times though.

 

[elan]

Well it depends on the environment. It is not unusual for me to have a 0.7 in a cold water - about 40f. If you actively swim during the dive it increases the sac. If you are cold it increases rthe sac.

 

[cascas]

Stopping to worry about it might drop your sac rate... if you need 21l/min, you need 21l/min...

 

[Quero]

It's hard to say without seeing you dive. Here's why:

First of all, you sound like a very fit person who doesn't tire easily, and it also sounds like you have a lot of muscle mass to fuel. Say for example that you are diving out of trim, which by definition means that you are finning ineffectively, and because of your fitness level you are able to make forward progress without feeling at all tired or making your heart rate increase much. Nevertheless, all of that effort put forth in finning ineffectively takes oxygen to fuel that large muscle mass you've got and which you are not using to good purpose. That oxygen comes from the air in your tank, so you have to breathe it down rather quicker than you'd prefer.

Now I can't say for certain that you are swimming out of trim, since I've never seen you dive, but even a slight leg-down posture can make a fairly big difference over the course of a dive in terms of the effort your muscles are making to propel you forward. Therefore, this is just an example of one possible factor in your air consumption, not a critique of your actual diving technique.

Get somebody to videotape you for five or ten minutes when you are not paying any special attention to your technique, and then compare what you look like to what your instructor or another role-model diver looks like. Evaluate:
1) Are you consistently in trim?
2) Are you swimming frequently with your arms or using your hands for stability or maneuvering? (This has a big impact on air consumption.)
3) Are you finning effectively? What is your typical finning style? Do you kick and glide or kick continuously (another big drain on gas)?
4) What is your breathing pattern like? How many breaths a minute can you count (watch the frequency of exhales)?

When you identify areas for improvement, get some coaching. It may take a while for any changes to become ingrained, but when they become habitual, your air consumption should drop accordingly.

 

[Kevrumbo]

Not bad . . .my cold water SCR (Surface Consumption Rate) is 22L/min here in the temperate waters of Southern California (currently 12 to 15deg C at depth); my tropical warm water SCR is typically 30% better at around 15-17L/min, my personal best being 11L/min diving with the drift currents in Palau. . .I'm 49yo, 170cm tall and 70kg weight, using double 11L AL80 tanks here in Calif (for a Pressure SCR of 1 bar/min --which is why I'm seemingly the only US diver on this Board who prefers using the Metric System). . .

 

[GramsciBeat]

Thanks for the input - I am not aware of breathing anyway but normally (other than when using breath control to control bouyancy), & while I do not flap my arms around, I think my trim may definitely be an issue & I will ask a buddy to video me. The other suggested action that caught my eye is around actual breathing rates, which I'll assess and look to improve.

The other assumption I made is that comfortable = relaxed, which is not necessarily the case. I also need to accept I have big lungs and that my SAC rate will reflect that.

 

[GramsciBeat]

My measured SCR was taken in currentless 22 degree water. However, in line with what Quero said about my fitness levels meaning I do not realise my workload, it does not really change when I get into colder water or environments with surge & high current.

 

[Bubbletrubble]

In addition to what others have recommended...

Try not to move around so much. Conduct an entire dive where you remain in one small area. Check out the macro life on the reef/rocks. Relax. Watch an octopus hunt. See where the nudibranchs go. Search for camouflaged blennies in a rock wall. It's incredible how much stuff divers miss by whizzing through an area that's chock full of underwater life.

Commit yourself to being neutrally buoyant 99% of the time. Hover more to hoover less.

Hope this helps...

 

[dumpsterDiver]

A 240 lb athlete has more muscle and a higher (resting) metabolic demand than a 132 lb women with a fat butt and chubby cheeks. Sorry to break it to you.....

My advice: Don't worry about it it too much. Try to make a SMALL change in your breathing pattern and concentrate on a slightly more complete exhalation than feels natural for the exertion level. This is a more efficient way to remove CO2. And of course try to not exert yourself.

A competitive swimmer has a huge capacity to blow through air. That is what makes you competitive in an aerobic sport. 0.75 cu-ft/min is not that huge of a rate.

Go diving, breath slow and deep, carry a big tank, have fun, stay warm and move slowly if you want the tank to last.