Real time SAC? How? (Ridiculous SAC)

[estresao]

In answer to the OPs question at the end of the post yes the perdix and Teric can show you real time SAC when you use them as AI. I have used the SAC display to help me improve air consumption.

Thanks! I guess that could help me in monitorig and correlate "moments" to SAcs.

I know my SAC rate heavily depends on how relaxed I am in the water. With any kind of task load or worries it can easily go up significantly. Looking at SAC rates from a number of divers, everybody's minimal SAC rate (totally relaxed dive and diver, at least for experienced divers) is to good approximation proportional to your body mass as it is mostly determined by your basic metabolism. So, if you are a somewhat big bloke you will never achieve the SAC rate of your tiny female buddy.

If you use a dive computer with pressure sensor, Subsurface will also color your cylinder pressure line according to your momentary SAC (but that is somewhat hard to determine, given that there are only a few samples per minute and that cylinder pressure sensors are somewhat crude). But often enough, you can see that the line turns red the moment your task load went up.

I used to have a SAC of 13-16 for first dives, and that rised up, some times near 40 l/m, after swapping to hogartian configuration.. Now I can do, sometimes, 20 l/m, but us far from the initial rates. Last week I made 14 l/m, soooooo happy, just want to keep finding out what's going on. I see I can do better, just need to tell what to fix.

 

[estresao]

What did you input your cylinder size as? How many liters?

When single I use 15L at 200 bars, when doubles I used my 12L x 2 at 200 bars.

What is your height and weight?

height: 185 cm
weight 94 Kg

 

[estresao]

The dive I made 14 liters/minute was after thinking about the problem, during weeks of "dry vacations", where I've concluded the cause could be the way I breath to manage my buoyancy, and the fear I some time have of get off to the surface in a sudden. I like I feel safer when my buoyancy is a little negative because I can control it breathing deeper and this way it less likely I get off the water uncontrolled.

So when these 14 liters/minute I was more aware of that and, diving in a controlled site, no more that 7m, I "played" making my buoyancy more neutral rather than negative. And it seems it could be the (or a) cause.

I've realizaed it could be the way I breath when reading some stuff about Lung volumes: Lung volumes - Wikipedia Based on that, let's say that I think I'm breathing from the bottom of tidal volume to almost the top of the inpiratory reserve capacity, when I should stick to the tidal volume range only.

 

[Edward3c]

When single I use 15L at 200 bars, when doubles I used my 12L x 2 at 200 bars.

But which did you dive for the profile you have posted. Because the 2,900Lt displayed doesn’t relate to either option.

 

[BlueTrin]

OP is your equipment the same ?

If you switched for example from wetsuit to drysuit, you’ll probably use more air ?

More importantly are you throwing a party and buying beers for your 100th dive ?

 

[wnissen]

I wouldn't put too much emphasis on SAC unless you have it in context. Keep in mind that the SAC survey here is almost certainly not representative of the typical diver. Previous surveys have found that most divers wear a backplate / wing (BPW) and half of all divers have completed divemaster (DM) training. Obviously, the typical Scubaboard poster is far more accomplished than the typical diver in the water. Personally, I am low-moderately aerobic conditioned, about 10cm shorter and 10kg heavier than you, and I use 16 L/min in warm, easy diving, and 20L in cold, more challenging diving. So take that for what it's worth.

 

[CptTightPants21]

14-15L would be a great SAC rate even for an experienced diver--that's basically .5cuft/per min. I would expect the average experienced normal sized male diver to have a SAC rate somewhere around 16-19L per min. That said, you should look at your SPG and gauge your air usage in 5 min intervals--see what tasks or aspects of the dive are increasing or decreasing your usage. Doubles, drysuit, they can all add to increased breathing rate. Another factor is that your GUE training has greatly increased your overall awareness. Before GUE, you would do a dive and you were mostly unaware of your buoyancy--go up a little bit, go down -- as long as you weren't crashing into anything you thought you were good and relaxed. Now that you have GUE training you see what real buoyancy is and you notice even a 1ft/.3 meter depth change. You can use a lot more air maintaining a correct depth - I know that my SAC rate during deco when I am hanging on a line or sitting on a ledge is .4-.5 cuft/min (12-14L), but if I deco in the open ocean off a line my sac rate will be .6 because I am breathing more to stay right at 20ft and swimming to stay near the anchor line.

What kind of dives are you doing? Are they new dives in new places or dives you have done many times before. Sometimes there is additional stress on our breathing rate even though we don't actually "feel stressed at all". I know that a SAC rate is usually higher if you are leading a group of divers vs just following a long in a pack. I once took a class where my SAC rate was 25-40% higher than avg. I found it very strange. I didn't feel stressed, but first day after class I was doing the SAME exact type of dives I was doing in class and my SAC rate had returned to normal.

I don't use AI and I don't particularly trust computer SAC calculations. I always take notes of time, depth, starting and ending pressure and do the calculations myself so that I know I can trust the results.

 

[outofofficebrb]

Thanks! I guess that could help me in monitorig and correlate "moments" to SAcs.

@loosenit2

I do exactly that. I keep my tank pressure visible on the bottom row along with my real-time consumption rate. I am able to connect task load and actions with resulting air consumption and it is really interesting to see how it affects it, or it reminds me to slow down on my breathing given what I am trying to do or accomplish while keeping in mind the conditions. It is very insightful. I have everything going through MacDive and I pick tank size there. It is fun to see the data graphs on my air consumption rate steadily lower over the last few hundred dives. Using MacDive, I can also use keywords or tags and then use those to search and only show what it is in warm water vs cold, or for a certain country or region I was diving, etc, or conditions (by tagging it with "current" or "drift", etc. ).

 

[GJC]

The primary trigger for increased breathing is an increase in the CO2 your body is producing. If you are working harder to swim, are cold, or nervous, you are producing more CO2 and need to breath more. If you are relaxed, warm and not moving your muscles a lot, your SAC will drop.

Using your lungs to maintain your buoyancy can affect how well your lungs get rid of CO2. Taking slow deep breaths, fully inhaling and fully exhaling is the best way to get rid of CO2.

If you are overweighted and compensating for it using your lungs, you will not be exhaling as much as you should be (keeping a good amount of air in your lungs to maintain buoyancy) and not getting rid of CO2 efficiently. This causes you to breath faster to get rid of CO2 and your SAC goes up.

If you are underweighted and compensating for it using your lungs, you will not be inhaling as much as you should (keeping your lungs partially deflated). CO2 is not efficiently removed and you need to breath faster (but shallower) and your SAC goes up.

So your best bet to reduce SAC is to get your weight right for neutral buoyancy, relax, stay warm and don't work hard.

 

[BlueTrin]

The primary trigger for increased breathing is an increase in the CO2 your body is producing. If you are working harder to swim, are cold, or nervous, you are producing more CO2 and need to breath more. If you are relaxed, warm and not moving your muscles a lot, your SAC will drop.

Using your lungs to maintain your buoyancy can affect how well your lungs get rid of CO2. Taking slow deep breaths, fully inhaling and fully exhaling is the best way to get rid of CO2.

If you are overweighted and compensating for it using your lungs, you will not be exhaling as much as you should be (keeping a good amount of air in your lungs to maintain buoyancy) and not getting rid of CO2 efficiently. This causes you to breath faster to get rid of CO2 and your SAC goes up.

If you are underweighted and compensating for it using your lungs, you will not be inhaling as much as you should (keeping your lungs partially deflated). CO2 is not efficiently removed and you need to breath faster (but shallower) and your SAC goes up.

So your best bet to reduce SAC is to get your weight right for neutral buoyancy, relax, stay warm and don't work hard.

I mostly agree with you but the effect of being overweighted is that you’ll have more air in your BCD when neutral so you’ll swing more when you change depth. You don’t become negative because you are overweighted: you just put more air in your BCD so you’ll have to handle a bigger volume of gas.

Unless you are so overweighted that you cannot compensate with your BCD, but then I think you have bigger problems