SAC Rate

[DA Aquamaster]

Here are some more based on different SAC and depths.
The SAC rate will be the first number. The following numbers will be the depth/time based upon an AL80 with 500 psi remaining:

.40 - 50/64, 60/57, 70/51, 80/47, 90/43, 100/40

.50 - 50/51, 60/45, 70/41, 80/37, 90/34, 100/32

.60 - 50/42, 60/38, 70/34, 80/31, 90/29, 100/26

At the risk of getting us back into "the deco on a single AL 80 argument", I do think it needs to be pointed out that:

.40 - 60/57, 70/51, 80/47, 90/43, 100/40

.50 - 70/41, 80/37, 90/34, 100/32

.60 - 80/31, 90/29, 100/26

are all schedules that would require decompression even on the first dive of the day. 100 ft for 40 minutes requires a 15 minute stop at 10 ft even with the very liberal US Navy tables. When you figure gas used in the ascent and at the 10 ft stop, you are going to be OOA or very close too it. (and doing intentional deco on a singlel tank is in fact just plain stupid as you have no redundant gas supply in case you experience a failure of your primary system.)

So I guess my point is, what exactly is the point of pushing your SAC to low extremes - bragging rights for most air remaining back on the boat?

The thing many divers do not consider is that the quest for low SAC rates often involves CO2 retention and problems stemming from that such as increased suceptibility to nitorogen narcosis and oxygen toxicity as well as really painful and persistent CO2 headaches. Plus you get so focused on lowering your SAC that you enjoy the dive a lot less.

In my opinion you need to work on developing excellent bouyancy skills, learn to move efficiently in the water with no flapping arms or extra leg, trunk or body movement, develop a cleaner and more streamlined gear configuration to reduce the power required to move at a given speed and develop an efficient breathing pattern consisting of breathing deeply and pausing slightly at the top of the inhale to maximize gas exchange.

Pushing it beyond that to try to get the lowest SAC on the boat by extending the pause or using an unnaturaly slow inhalation and exhalation is potentially dangerous and more than a little stupid.

 

[Charlie99]

.40 - 60/57, 70/51, 80/47, 90/43, 100/40

.50 - 70/41, 80/37, 90/34, 100/32

.60 - 80/31, 90/29, 100/26

are all schedules that would require decompression even on the first dive of the day. 100 ft for 40 minutes requires a 15 minute stop at 10 ft even with the very liberal US Navy tables.

So I guess my point is, what exactly is the point of pushing your SAC to low extremes - bragging rights for most air remaining back on the boat?

But the situation is quite different once you start looking at multilevel dives. Even at 0.4cfm SAC I can easily use up a tank while never going into deco per Buhlmann or DSAT model, which are more conservative than the USN/Workman model.

The thing many divers do not consider is that the quest for low SAC rates often involves CO2 retention and problems stemming from that such as increased suceptibility to nitorogen narcosis and oxygen toxicity as well as really painful and persistent CO2 headaches. Plus you get so focused on lowering your SAC that you enjoy the dive a lot less.

In my opinion you need to work on developing excellent bouyancy skills, learn to move efficiently in the water with no flapping arms or extra leg, trunk or body movement, develop a cleaner and more streamlined gear configuration to reduce the power required to move at a given speed and develop an efficient breathing pattern.

I strongly agree. To put it another way, a low SAC should be the naural result of how one dives, rather than a specific target or goal that one consciously tries to achieve.

 

[rockjock3]

At the risk of getting us back into "the deco on a single AL 80 argument", I do think it needs to be pointed out that:

.40 - 60/57, 70/51, 80/47, 90/43, 100/40

.50 - 70/41, 80/37, 90/34, 100/32

.60 - 80/31, 90/29, 100/26

are all schedules that would require decompression even on the first dive of the day. 100 ft for 40 minutes requires a 15 minute stop at 10 ft even with the very liberal US Navy tables. When you figure gas used in the ascent and at the 10 ft stop, you are going to be OOA or very close too it. (and doing intentional deco on a singlel tank is in fact just plain stupid as you have no redundant gas supply in case you experience a failure of your primary system.)

So I guess my point is, what exactly is the point of pushing your SAC to low extremes - bragging rights for most air remaining back on the boat?

The thing many divers do not consider is that the quest for low SAC rates often involves CO2 retention and problems stemming from that such as increased suceptibility to nitorogen narcosis and oxygen toxicity as well as really painful and persistent CO2 headaches. Plus you get so focused on lowering your SAC that you enjoy the dive a lot less.

In my opinion you need to work on developing excellent bouyancy skills, learn to move efficiently in the water with no flapping arms or extra leg, trunk or body movement, develop a cleaner and more streamlined gear configuration to reduce the power required to move at a given speed and develop an efficient breathing pattern consisting of breathing deeply and pausing slightly at the top of the inhale to maximize gas exchange.

Pushing it beyond that to try to get the lowest SAC on the boat by extending the pause or using an unnaturaly slow inhalation and exhalation is potentially dangerous and more than a little stupid.

I didn't notice anybody suggesting to dive these profiles. They were only given as an illustrative point. Pretty much everybody that I have read from so far on this thread has suggested proper methods of lowering your sac by improving your skills. I don't have sac in the .4s because I hold my breath or do anything else unsafe. I simply don't fin like crazy, have very good buoyancy, have my weight to within 1 lb of perfectly neutral and relax under water. Any new divers that come into the group of divers that I dive with the first thing I work on them with, if they are new to diving, is getting them to relax and helping them get weighted properly. Without exception this has greatly increased all of their sac rate within just 2-3 dives. The rest comes with time.

 

[ScubyDoo]

SAC rates vary alot depending on the mechanics of a particular dive. Its pretty typical for new divers to have SAC rates in 60's...I know I was in the 60's when I first started diving. This is due in large part to a larger amount of stress on new divers. The more stress...the higher the SAC rate. All divers doing their open water cert dives are under stress for obvious reasons. As time goes on, and more dives and dive experiences are under ones belt, the more comfortable one is with diving. As you get more comfortable, the more controlled your breathing becomes. The more controlled and relaxed your breathing...the better your SAC rate.

I wouldnt worry about it as a new diver.. Just dive. Concentrate on relaxing...not on SAC rates. One takes care of the other. I dont know what my average SAC rate is today...but know its in the low 40's. Just take long slow in breaths...and long slow outbreaths.. Its all gravy after that.

 

[ItsBruce]

I'll let someone else do the math, but here is my thought: There is probably some SAC rate that gives you bottom time that is roughly equal to your NDL time (at least for the first dive of the day). Looking back at my log book, I'm thinking it is probably around .6. Can anyone work it out? If so, wouldn't that be a good SAC to shoot for (absent Nitrox)?

 

[The Kraken]

DA,
You make a good point. However I was responding in a purely mathematical answer to a question that contained no caveats regarding decompression or mixtures of gasses.

The question was about volume, SAC rates and time.

Simple question, simple answer.

However, if one were diving EAN36, there would be only 2 deco dives, the 90' and 100' dives at the .40 SAC rate.

And if the diver elected to dive EAN39, he COULD make that 100' dive for 32 minutes.

the K-alculator

 

[dbg40]

UGH..... Were off track here. The original post was about SAC, and wondering what others were. Innocent question, and an inquery only to have a number to base on. Then the question of DECO rears its ugly head. James is absolutely correct in saying that planned deco should NOT be done on an AL 80. Also correct is "conjuring" up a low SAC is not healthy. I see posts with "tricks" to lower rates and think it's bad practice to do any of them. A low SAC rate GENERALLY is a mark of being comfortable in the water, and your environment, wich comes from experience. Not training, experience, the more you do somthing, the more comfortable you become in it's practice. James is also correct in seeing bragging rights for low SAC's as wrong. It gives a false reality to new divers that do what ever it takes to reach these numbers. Like breath holding, skip breathing, or shallow breathing. All of these "methods will lead to poor skills, as any experienced diver with low SAC rates will tell you that they breath slowly, and deeply, and are simply comfortable where they are. Any other practice WILL raise "bad gas" levels, and the likelyhood of a DCS incident. On a single HP 100, I am back on the boat with around 15-1700 lbs of gas still in the tank. The limiting factor being NDL's not SAC's. So even with a higher SAC rate, there is little benefit other than having a little more emergency gas if needed. In normal diving, the real benefit is being on a shallow reef where saturation is not a problem. Then it's nice to have the extra down time. The real answer is to go diving, alot! and just have fun. The lower rates will follow as a natural evolution of skills and comfort.

 

[cummings66]

So I guess my point is, what exactly is the point of pushing your SAC to low extremes - bragging rights for most air remaining back on the boat?

As I see it, the biggest benefit to a low SAC is air for your buddy in an OOA situation. Many divers do not factor that into their air usage and think that hitting the surface with 500 psi is good, so why should they improve their SAC rates when they can do that? The answer of course is to extend their dive time and have a reserve of air for the buddy just in case. Of course if your buddy has a high SAC rate then your low one will result in bragging rights on the boat...

Once you can hit the NDL by SAC rates, then no further improvement is really needed as long as you have enough air for an OOA. Unless you intend to start diving Nitrox when lower SAC rates also benefit you.

As many have said, don't use tricks to get there.

 

[The Kraken]

I think many divers misunderstand the SAC rate.
The SAC rate is not fixed for any diver. The SAC rate varies with numerous conditions, the gear one is wearing, the type of dive, the temperature, the work load, the stress load, so forth and so on.

What a diver can do is track his/her SAC rate over a period of time and develop a general planning tool based upon the dive to be made.

the K

 

[shoupart]

Nice discussions here, especially the training tips.
Has anybody ever tried a tool that functions to make resistance when you breathe? I seem to recall it looks kind of like a kazoo and makes breathing more of an effort, supposedly giving us a bit of a workout so we learn to breathe slower and more efficiently. Or something.