S.A.C. and How to not suck so bad :/

[tschmitt]

So one of the things I've realized as a new diver is that I suck - Air that is and a lot of it. I'm 6'4" 180 lbs, so I'm big but pretty lean. I'm in good shape and do yoga. My buddy (girlfriend) is 5'2 and 100 lbs. Guess who's OOA first ??

My question - I purchased a Suunto Cobra and in the downloaded dive information it calculates your SAC (Surface Air Consumption) rates. My average SAC rate for 14 dives is 0.65 SCFM. First of all, what is SCFM - Standard Cubic Feet / Min ?? Is this number good based on my experience level? If I understand it correctly, a lower SAC rate is better right? What is a reasonable goal for my size? Any tips or tricks besides the obvious (relax, streamline, buoyancy, be in shape, etc..)?

Also, looking at the dive profiles it appears that my SCFM goes DOWN at deeper depths, shouldn't it go UP? For example my SAC is around 0.40 SCFM at 95 ft, but 1.0 SCFM during my safety stop. This seems backwards to me.

 

[ucfdiver]

The best way to lower it is to stop worrying about it. With comfort in the water, your SAC rate will improve. You're getting to view a world that 99% of the people you'll meet will never get to see, ENJOY IT, and if that means getting bigger tanks so you don't care about your sac rate then do so!

If you're in good shape, I think time will fix this for you.

Go have FUN and don't let having to surface 5 minutes earlier worry you!

 

[Blackwood]

My guess is that SCFM stands for surface cubic feet per minute (which is redundant in a discussion of SAC rate).

.65 is respectable, and it will likely get better with time. Perfecting buoyancy and maintaining good trim will contribute.

On sucking down more during a safety stop... my suspicion is that your buoyancy control needs work, particularly in mid-water where you don't have a big depth reference (such as the sea floor). You're probably working harder to maintain your depth than you are to just monkey during the dive.

 

[Teamcasa]

That's the main reason I use a HP100 and my wife uses a HP80. It works out very good for us.

 

[Anti-Hero]

Like others mentioned, the three biggest things that improved my SAC rate are: Weight, Trim, and comfort. Comfort being the most general of terms, for me it was a combination of correct exposure protection for the dive, gaining more experience, and a good high-quality regulator.

My first regulator AL Titan LX is a good middle of the road workhorse but it breaths noticeably harder than my MK25/S600. The relaxed breathing of the MK25 has had a noticeable impact on my air consumption.

Also, forget about trying to match the SAC rate of your girlfriend, the physiological differences will almost certainly make that an impossible goal. I had a woman DM once that used a single AL80 tank for two dives deeper than 60ft. I think she was showing off!

 

[roakey]

Search->advanced search, type in "consumption" for the keyword, limit the search to titles only and you'll find over 70 discussions from other folks that didn't use the search function either.

Roak

 

[TSandM]

.65 for a guy your size really isn't bad at all.

All of us who love to be underwater search constantly for how to get more bottom time. For newer divers, the first obvious hurdle is gas consumption. They usually start by thinking about their breathing, but that's rarely the problem. High gas consumption is almost always directly associated with inefficient diving. Not being neutral, not being horizontal, not being relaxed, swimming with the hands, and hurrying through the dive are big gas burners. Overusing one's breath for buoyancy control burns through gas, as well (and may be the reason for your higher consumption on safety stops!)

For a given level of exertion, each of us has a bottom line SAC rate below which we really won't be able to go safely. If you've plateaued out on improvement and still find gas limiting your dives before deco or temperature, the next step is a bigger tank.

 

[tomboyy]

Search->advanced search, type in "consumption" for the keyword, limit the search to titles only and you'll find over 70 discussions from other folks that didn't use the search function either.
Roak

good advice until you had to get that dig in at the end

Tom

 

[ucfdiver]

good advice until you had to get that dig in at the end

Tom

I think he may just be letting the OP know that posting without searching dilutes the search results. It's certainly something to be careful of.

Hopefully he didn't mean it rudely. Sometimes emotions are hard to understand online.

 

[ScubaSteve]

I am going to give you a little something from my personal experience. I am a bigger guy (6'2" and 280lb) and when I started diving I was sucking through air and very concerned about it. I too have a cobra and log all my dives so that I can track this. I was wearing a silly 42 pounds weight and going through air at a silly .65 to .85 (on average). Now I am down to 26 pounds wearing the same everything (still a lot of weight but it is coming off) and my average dive is around an SAC of about .50. This is only buy taking weight off, my buoyancy and trim are excellent now AND I am very comfortable underwater (after about 300 dives). I have a ways to go still but I really am living proof you get better when you do not worry about it.

All I have really done is worked hard on my buoyancy which makes a huge difference....comfortably using my breath to control my ups and downs. This and diving a lot....I was never really uncomfortable underwater HOWEVER I am now a whole lot more comforatable. No matter how comfortable you think you are....you can always be more comfortable. And it all helps. Time and experience heal this "air consuming" wound.