Do you use your SAC for anything? POLL

[bowlofpetunias]

This is something that I hear a lot. I'd like to give an alternate perspective, as an air hog. When people talk about their worst instabuddy dives, many of them involve their buddy going through a tank in an insanely short time, forcing them to cut short their expensive dive. This makes those of us with high SAC rates really focus on our SAC rates as a measure of our worth as a diver. As much as people say that it is what it is, my SAC determines the group's dive time. I did two dives today with a guy who was on his 11th dive, swam with his hands, ridiculously fast, yet used significantly less air than I did. When the standard answer to "how to lower SAC" is "get comfortable in the water", a lot of people start thinking that a high SAC indicates a bad diver.

There's a lot of times when getting a bigger tank is not feasible, not cost effective or means that your buddy wants a bigger tank too (leaving you in a similar position)

Yes I know what you are talking about! Nobody wants to feel like they are shortening everybody's dive!

I have seen people go on about SAC rates like they are an indicator of the diver's skills and comfort in the water! IMHO that is rubbish! It may improve slightly with comfort level, trim and so on but some people just have a higher SAC rate...period!

My SAC rate was low from the beginning no credit to me.. just was. I was uncomfortable in the water, trim wasn't great and all the problems normal in new divers. I dived with people who were very competent divers who had much worse SAC rates and were certainly more fit than I! Not fair but it is what it is. You can do little things to help a little but some people just use more air!

I know bigger tanks are expensive and so on but I would rather suggest bigger tanks than go on about, comfort in the water, trim, and all the nit picky things we do during the dive... I am sure there will be a lot of people happy to point those things out! We normally use smaller tanks so our dive time fits with our dive buddies. Diving is not and should not be a competitive sport! Anybody who gets into My tank has to be as big as or bigger than yours isn't someone I want to have in my list of buddies:shocked2:

I'd rather have a buddy who is an air hog than one with a bad attitude, interferes with the creatures, ignores safe buddy procedures or is selfish and inconsiderate! BTW... how is your navigation? mine sucks I'll take a good navigator over a low SAC rate any day

 

[Eric Sedletzky]

How do you know if your SAC is still the same as the SAC you planned on when you were on the surface (it could have changed due to unpredicted/expected increase in exertion level U/W during the dive)?

I can get a rough idea of an increase. For instance I may spear a fish and have a battle or get into a current or rip, then my SAC will increase so I allow for this by decreasing my dive time by a few minutes.
On the other side, if the conditions are stellar with no stress and the whole dive is a wonderful stroll through a garden then I might increase my time by a few minutes.
Then there's the fact that I have a reserve lever to pull which gives me 400 PSI of remaining air.
I also plan my time with an upper end SAC rate as a measure of safety. I also try to stay in shape and pay attention to factors such as how I feel. I'm not going to start smoking two packs a day and putting on fifty pounds anytime soon so I know my SAC will stay fairly constant.

The other factor is that with my vintage gear the air doesn't just run out instantly where I'm left with nothing to breathe with no warning. The air slowly begins to draw harder and harder. It takes several minutes before it really draws hard so there is plenty of warning.

But this is somewhat moot because diving vintage or minimalist, air supply, dive time, depth, turn around time, etc. has all been accounted for and payed attention to.
There never would be a time that I would be stuck out at 60 feet deep with no air because I forgot to look at my time and depth and didn't have a plan.

This is all part of the training.

 

[Puffer Fish]

As my current computer keeps track of it, I can actually see how much it varies.

The computer, however, is just keeping track of how much air is used, so puttng air in a Wing (BC) or inflating an SMB would also be in the calculation.

My normal, relaxed dive, in warm water, with just some relaxed swimming is .45 for the first dive, and .41 for the second dive and any dive there after for the day.

Why I always use more air on the first dive is a mystery to me...

How much does it vary? +/- .3. And some of that is due to the suit and depth I am wearing (best dive has been .38, and was not wearing any neoprene, so did not have to use air to compensate.

A swimming dive - add just .15

Cold water - add .12

Note: Sliding scale on the cold water, more neoprene and then switching to a dry suit use up some of this, as does getting cold for the neoprene, but I tend to fiddle more with the air when using a dry suit.

My last dive was .62 (cold water, with lots of neoprene), and I was swimming a lot to stay warm.

That is it, all the variation there is for me.

I own three sizes of tanks, and can easily get AL80's...so diving with someone else, we can match up tanks sizes to each of our SAC rates. I also use it to decide which tanks to bring for a specific dive.

I guess if I dove one size of tank, and just used a tank down to 500 psi at the end of the dive, didn't ever plan any dive, it would be useless information.

I'm with you...I remember at one point I was inquiring with an LDS about a Solo Cert and the divemaster asked me what my SAC rate was; I remember thinking "are you kidding me, that's gotta be like the most meaningless thing anyone could know". Like you said, SO MANY things are going to affect your breathing rate: temp, vis, surge, how you're feeling, if you run into trouble, if you see a lot of cool stuff, get a cramp, remember that you left the iron on, etc. Plus if I'm measuring my SAC (I'll refrain from making a joke here) my SAC rate will be different than it is when I'm simply breathing on the surface and not testing myself. I dunno, I suppose in some instances (or at least for some people) there are meaningful applications, but it's not something I find useful in the slightest.

 

[Eric Sedletzky]

Yes I know what you are talking about! Nobody wants to feel like they are shortening everybody's dive!

I have seen people go on about SAC rates like they are an indicator of the diver's skills and comfort in the water! IMHO that is rubbish! It may improve slightly with comfort level, trim and so on but some people just have a higher SAC rate...period!

My SAC rate was low from the beginning no credit to me.. just was. I was uncomfortable in the water, trim wasn't great and all the problems normal in new divers. I dived with people who were very competent divers who had much worse SAC rates and were certainly more fit than I! Not fair but it is what it is. You can do little things to help a little but some people just use more air!

I know bigger tanks are expensive and so on but I would rather suggest bigger tanks than go on about, comfort in the water, trim, and all the nit picky things we do during the dive... I am sure there will be a lot of people happy to point those things out! We normally use smaller tanks so our dive time fits with our dive buddies. Diving is not and should not be a competitive sport! Anybody who gets into My tank has to be as big as or bigger than yours isn't someone I want to have in my list of buddies:shocked2:

I'd rather have a buddy who is an air hog than one with a bad attitude, interferes with the creatures, ignores safe buddy procedures or is selfish and inconsiderate! BTW... how is your navigation? mine sucks I'll take a good navigator over a low SAC rate any day

I should also mention that I am in the upper half with air hoggedness.
I attribute some of this to diving wet in cold water and the fact I'm not a small person.
I just use bigger tanks than everyone else to compensate.

SAC rates, once comfort and competence are acquired; they are what they are.
I agree, SAC rates have nothing to do with how good of a diver you are, there are many factors beyond skill that determine your SAC rate.

 

[Insta-Gator]

We gave up on boat dives years ago (will do more in the future, but not as a standard) so we like to plan our dives very simply...know the terrain, know the depths, know the currents, know the direction to/from entry point, know everyone's gas volume, enter, descend to max depth, head up current until first person reaches 1500 psi, ascend to second (more shallow) depth, reverse course, ascend when at initial descend point, swim back. SAC doesn't really matter.

Perhaps such questions should be asked within a specific frame of reference; ie. tech diving, deep diving, vacation diving, etc.

 

[aquaregia]

BTW... how is your navigation? mine sucks I'll take a good navigator over a low SAC rate any day

My nav's passable Let's go diving!

 

[bowlofpetunias]

Sure if you put down the knife!

 

[aquaregia]

I usually only use that to convince people to share air with me in order to extend my dive

Actually mostly it lives in my kitchen to terrify my housemates' friends.

 

[billmas]

I can't answer the OP's question, but I know I do like to monitor my SAC rate on each dive, so much so that I have cobbled together some software of my own that reads the dive logs of my Atom 2 and gives me SAC rate during the dive, not just an average for the whole dive.

I think it is useful - from this I learnt early on that your mental workload can be as important as your physical workload in increasing the SAC rate. It is also useful to see how different parts of the dive (ie activity at the time) affect the rate.

Using my numbers, I know that a 3L pony (with me stressed or not) *will* get me up from 30metres Surely that alone is worth doing the maths for!

Not allowed to post links/images yet, but have a look at....

i241.photobucket.com/albums/ff25/billmas/KyarraSAC3.jpg

Hth
Bill

 

[BoltSnap]

billmas,

If I am reading your chart right (the picture is very small on my screen), your "instantaneous" SAC readings are not following the conventional expectation that air consumption would increase with dept.