Scubamedicjoe
Contributor
alum 80 3000 psi
Calculating air consumption SAC / SCR / RMV
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if that is 58~70 psi/minute with an AL80 it is quite high....
but if you really meant that your SAC is usually .58 ~ .70 cf/minute then that is a different story....
I suspect that you just forgot the decimal point in your first post.
For gas management we figure our working SAC at .6 and resting SAC at .5
It will usually be lower but this gives us a s.f.
but if you really meant that your SAC is usually .58 ~ .70 cf/minute then that is a different story....
I suspect that you just forgot the decimal point in your first post.
For gas management we figure our working SAC at .6 and resting SAC at .5
It will usually be lower but this gives us a s.f.
Scubamedicjoe
Contributor
yes its .70 and i did forget the decimal point .
there are several reasons to keep track of your SAC but the most imortant one is so that you can plan your gas needs for a dive.
Note what you were doing on your last dive. If it was strenuous activity then the next dive that you plan to do strenous activity you would want to figure your gas needs at a .7 SAC
The object isn't to see who can get the lowest SAC... the object is to know how much gas you can expect to use on a certain kind of dive.
Note what you were doing on your last dive. If it was strenuous activity then the next dive that you plan to do strenous activity you would want to figure your gas needs at a .7 SAC
The object isn't to see who can get the lowest SAC... the object is to know how much gas you can expect to use on a certain kind of dive.
Scubamedicjoe
Contributor
.7 sac well it was a wreck dive but it was cold and heck of a current and was rough ride out to the site might be it.
I hope, seems higher than my average before
I hope, seems higher than my average before
Spectre
Contributor
Precisely. When one has themselves a 'bad' dive, in that they were overly worked or overly stressed due to problems [navigation, equipment, whatever] those are the key ones to make sure you record.
If you plan dives based on your normal relaxed SAC rates [both your relaxed rest and your relaxed working] you may find yourself in trouble when you get yourself into trouble. One should always plan their gas management based on SAC rates that are high compared to your normal diving profiles.
e.g. if you generally run with a SAC rate of .7 working, and .5 resting. You definately don't use .6 for your planning. You shouldn't use .7 for your working part and .5 for your resting part either.
You could get away with planning .6 for resting and .8 for working, but you're better off planning based on a 'stressed' environment your whole dive. e.g. if you or your buddy have a problem, that 'resting' ascent won't be very restful.
I know my average SAC rates run between .5 and .75. I plan with .8. I had a really bad dive that averaged out to .97, but by having the .8 planned for my 'resting' ascent, I had my turn pressure calculated and while my dive was shorter than planned [and shallower than planned], I had plenty of gas for my stressed ascent... and plenty to hang extra long to reflect on the problems that occurred.
Like Uncle Pug said, it's not a contest. Your SAC rate it what it is, and it will improve as skills and confidence improve. You have no reason to rush improvement, as that can only lead to trouble when things go wrong...
I average about 13-14 litres per min in a dry suit. That about <fx clicking sounds> 0.5 cf/m the way the others have been expressing it. In the tropics I average about 0.35 cf/m.
With that as a starting point, I'd say that 25litres per min (+/- 0.88cf/m) is on the high side but it's probably a safe starting point for planning.
R..
I read about every thread I could find on these terms (well. except for LMNO...) and the first two seem to be used interchangably. Examples:
I found SCR expressed as PSI per minute and cylinder dependent, as well as expressed as a volume measurement.
I found SAC expressed as Cu Ft per minute and not cylinder dependent...
RMV...what the heck is this?
In my SSI AOV, I received the dive planning slate and assorted hoopla that goes along with it (EAD/MOD Calc, Tables, etc.) and there is this device with dials, windows and pointers used to calculate SCR, and its expressed in "P.S.I. / MIN" Several threads I read express SCR in volume, not pressure. I've been using the device to track the SCR of my dives.
As you know, I am attempting to reduce my absolute computer dependance (my OMS SPG will be in tomorrow...) and regenerate some of my rotted brain.
With 60+ meticulously logged dives, I want to establish a baseline of gas comsumption so I can better plan my dives. I think diving in ignorance and racing to the chain with XXX gas is just lame, as I always emerge with way too much. Not that I want to plan so I surface with my last breath, but theres a lot to see, and I'm missing it because I keep emerging with 1200, 1300, 1000, etc. I understand some of this is buddy dependent, etc. But you see me working. My plan should be based on my consumption, not on a clock on my computer. Baseball, not football.
I've been using the SSI device, and I've seen a dramatic improvement/reduction in my SCR. Since I've been using the same cylinder for almost all of my dives, I can only conclude that as I've been diving more, I'm diving smarter and using less gas.
That said, I need to know more about this alphabet soup.
Is there a generally accepted preference - volume or pressure? How is that correctly expressed (SCR, SAC...which is which?) Is there a preference for reaching my objectives? Are my objectives realistic? I can't imagine not knowing my consumption. It just seems ignorant and unsafe not to know, you know?
Can my objective (baseline gas consumption under various conditions) be achieved using one of these two formulas?
As there is nobody in my diving circle that would aspire to something so bold as to one day pocket their computer, I'm pretty much without mentor or guide in this endeavor. Any assistance would be appreciated as I plow through this alone. Use small words.
Its late - my brain hurt.
Thanks -
Ken
I found SCR expressed as PSI per minute and cylinder dependent, as well as expressed as a volume measurement.
I found SAC expressed as Cu Ft per minute and not cylinder dependent...
RMV...what the heck is this?
In my SSI AOV, I received the dive planning slate and assorted hoopla that goes along with it (EAD/MOD Calc, Tables, etc.) and there is this device with dials, windows and pointers used to calculate SCR, and its expressed in "P.S.I. / MIN" Several threads I read express SCR in volume, not pressure. I've been using the device to track the SCR of my dives.
As you know, I am attempting to reduce my absolute computer dependance (my OMS SPG will be in tomorrow...) and regenerate some of my rotted brain.
With 60+ meticulously logged dives, I want to establish a baseline of gas comsumption so I can better plan my dives. I think diving in ignorance and racing to the chain with XXX gas is just lame, as I always emerge with way too much. Not that I want to plan so I surface with my last breath, but theres a lot to see, and I'm missing it because I keep emerging with 1200, 1300, 1000, etc. I understand some of this is buddy dependent, etc. But you see me working. My plan should be based on my consumption, not on a clock on my computer. Baseball, not football.
I've been using the SSI device, and I've seen a dramatic improvement/reduction in my SCR. Since I've been using the same cylinder for almost all of my dives, I can only conclude that as I've been diving more, I'm diving smarter and using less gas.
That said, I need to know more about this alphabet soup.
Is there a generally accepted preference - volume or pressure? How is that correctly expressed (SCR, SAC...which is which?) Is there a preference for reaching my objectives? Are my objectives realistic? I can't imagine not knowing my consumption. It just seems ignorant and unsafe not to know, you know?
Can my objective (baseline gas consumption under various conditions) be achieved using one of these two formulas?
As there is nobody in my diving circle that would aspire to something so bold as to one day pocket their computer, I'm pretty much without mentor or guide in this endeavor. Any assistance would be appreciated as I plow through this alone. Use small words.
Its late - my brain hurt.
Thanks -
Ken
Hel lo Ken. My name is Mech Diver. How are you?
Okay, for ME:
SAC is psi/min at surface and is cylinder dependant.
RMV is cu3/ft per min at surface and is NOT cylinder dependant. And is therefore, for me, a much more useful term. I was told in another thread that that is not the correct use of the term RMV, but it is what all my IANTD classes have taught, and it works for me.
As long as YOU know what the term means to you, use it accordingly. The most useful term, IMO, is surface consumption in cubic feet per minute. Whatever you decide to call it is not that critical.
MD
Ken,
There are only two measures that really matter.
SAC
This is measure of air consumption in pressure per min (the pressure could be bar or psi) and is cylinder dependent.
RMV
RMV means Respiratory Mean Volume and is a measure of air consumption in volume per min independent of cylinder size (could be litres per min, cf per min).
Generally speaking people don't distinguish between the two. Obviously RMV is the more useful measure for planning gas requirements.
R..
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