SAC rate & RMV

[nereas]

Once again nereas demonstrates his inability to read. All Australian waters are not tropical.

Tortuga lives in Melbourne, Australia, it's temperate water diving. Heck, Saspotato recently posted about her drysuit for local Melbourne dives. Hobart water's even colder. Don't let reality get in the way of your preconceptions.

www.diveoz.com.au - Average Underwater Temperature Map

But only an Auzzie from the warm part would apparently seem so confused about the mammalian reflex.

As once again shoredivr demonstrates his own inability with logic, which is apparently not taught in Canadia. Don't let the ice and snow up there get in the way of blood to your brain.

 

[Blackwood]

For the ignorant among us: what is RMV?

An annoyingly different name for the same thing.

Personally, I only use the term SAC rate, since most people understand what it means (and AC rate sounds stupid).

I often write the units (such as 0.5 CFM/ATM) to prevent any confusion.

 

[nereas]

Thanks, Blackwood, for changing the subject back to the topic and away from the troll rant.

 

[lowviz]

What would the secondary reason be? Global warming??

2) Complemental air

3) Global warming.

 

[CoralSeaMan]

I see no reason that SAC rates cannot be used to approximate gas consumption for planning purposes. If I have a SAC rate of .5cuft and an aluminum 80cuft tank, I can estimate 160 minutes at the surface and 80 minutes at 33 ft. What am I missing?

 

[lowviz]

I see no reason that SAC rates cannot be used to approximate gas consumption for planning purposes. If I have a SAC rate of .5cuft and an aluminum 80cuft tank, I can estimate 160 minutes at the surface and 80 minutes at 33 ft. What am I missing?

Nothing.


RMV is your consumption in volume/time this is the roughly the same at any depth.

SAC is what your volume/time consumption does to your cylinder's psi, SAC is reported in psi/min or bar/min.

Two different ways to report the same thing.

 

[Peter Guy]

SAC is what your volume/time consumption does to your cylinder's psi, SAC is reported in psi/min or bar/min.

I honestly don't know if this statement is accurate or not, but, to me, it isn't particularly useful -- nor is the question regarding "RMV vs. SAC" -- which to use.

I admit I use the term "SAC Rate" to mean volume of gas breathed per minute at the surface, NOT PSI (what the heck is "BAR" anyway?) because PSI doesn't do me any good since I dive AL 80's (singles and doubles); LP 72's (singles and doubles); HP 130's; HP 100's (doubles) and others if that is what is provided. PSI is a meaningless number FOR PLANNING PURPOSES.

As someone once told me, you breathe VOLUME, not PSI. So what I want to know, FOR PLANNING PURPOSES, is what is my normal (average, standard, take your pick) estimate of how much gas I will breathe per minute at the surface. From there it is easy to guestimate how much gas I'll need to do X minutes at Y depth.

Of course, once I'm down there, I get to see how much gas, in PSI, I'm actually breathing per minute which will then allow me to guestimate how much time I'll actually be able to dive.

 

[MXGratefulDiver]

I honestly don't know if this statement is accurate or not, but, to me, it isn't particularly useful -- nor is the question regarding "RMV vs. SAC" -- which to use.

I admit I use the term "SAC Rate" to mean volume of gas breathed per minute at the surface, NOT PSI (what the heck is "BAR" anyway?) because PSI doesn't do me any good since I dive AL 80's (singles and doubles); LP 72's (singles and doubles); HP 130's; HP 100's (doubles) and others if that is what is provided. PSI is a meaningless number FOR PLANNING PURPOSES.

As someone once told me, you breathe VOLUME, not PSI. So what I want to know, FOR PLANNING PURPOSES, is what is my normal (average, standard, take your pick) estimate of how much gas I will breathe per minute at the surface. From there it is easy to guestimate how much gas I'll need to do X minutes at Y depth.

Of course, once I'm down there, I get to see how much gas, in PSI, I'm actually breathing per minute which will then allow me to guestimate how much time I'll actually be able to dive.

You just answered your own question, Peter.

RMV (or whatever you choose to call it) is useful for dive planning.

SAC (or whatever you choose to call it) helps you track your consumption during the dive. And since all you have to gauge actual consumption is the SPG, it also gives you the information you need to calculate actual consumption useage, which you then convert to volume using cylinder baselines (cylinder volume divided by cylinder working pressure).

... Bob (Grateful Diver)

 

[CoralSeaMan]

It seems I am using the term "SAC "incorrectly as well. My various dive log programs calculate my air consumption in cubic feet per minute and call it "SAC." There appears to be a correlation between that number and my effective bottom time in rough terms (of course I do not generally dive square profiles). I mostly use the same type of tanks with the same type and pressure (AL 80s with 3000psi). I presume that makes it less necessary for me to do conversions. So it appears to me that "SAC" is an adequate planning tool for recreational diving when access to the surface is not limited by extreme depth, overhead environments, or decompression needs.

 

[lowviz]

... So what I want to know, FOR PLANNING PURPOSES, is what is my normal (average, standard, take your pick) estimate of how much gas I will breathe per minute at the surface. From there it is easy to guestimate how much gas I'll need to do X minutes at Y depth. ...

Call it whatever you like, you are getting the right answer.

-You may want to calculate cubic feet/ 100 psi for each of your tanks and write it on the tank somewhere. This 'tank factor' will allow for quick conversions between pressure and volume (volume measured at the surface).