Knowing your SAC rate is essential to gas planning. The thing I’m most certain about my SAC rate is that it sucks. However, it’s still important to know what it is.
I’ve started logging and tracking my SAC on actual dives more often this year in hopes of getting a better idea of how it varies with my dive profiles, gear setups, and environmental circumstances. It’s a little more guesswork nowadays with computers allowing so much multi-level diving, but, here are the estimates I’ve come up with so far based on about 50 dives:
1) Warm water drift diving with 1 mil wetsuit and minimal gear: 0.5-0.6 cu ft/min
2) Cold water (50deg f) diving in a 7mil wetsuit, double tanks, lights, reels and modest activity (finning, running lines, deploying lift bags, etc.): 0.70-0.80 cu ft/min
3) Case 2 but heavier activity (mainly swimming against current): 0.9-1.0 cu ft/min
I’m curious how this stacks up to what others have measured for themselves, and what a reasonable improvement goal might be for a 6 ft, 200lb, 52 year old guy like me.
Also, are there any computers on the market that attempt to track your SAC, or at least provide you with a time average depth for your dive?
How Does Your SAC Track?
Started by
BubbleBoy
, Aug 25 2007 11:53 AM
49 replies to this topic
#1
BubbleBoy
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Posted 25 August 2007 - 11:53 AM
BB
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#2
finGrabber
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Posted 25 August 2007 - 12:12 PM
the Vyper I have can be downloaded to my PC using their SDM software...inside that is an area where you tell it what size tank you used, the beginning PSI and the ending PSI...it can then give you a SAC rate for that dive
computing your SAC rate at rest, under minimal activity and under max activity can indeed tell you how much gas you need for a given dive. And knowing how much gas you use at depth is invaluable as well. I know I burn alot more when I get below 100' vs 90 or above
computing your SAC rate at rest, under minimal activity and under max activity can indeed tell you how much gas you need for a given dive. And knowing how much gas you use at depth is invaluable as well. I know I burn alot more when I get below 100' vs 90 or above
#3
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Posted 25 August 2007 - 02:24 PM
Bubbleboy - your numbers look close to what I measured in my deco class this spring, but then in July I had a really tough swim against the currents down to the mooring in 70' trying to catch up with my daughter on the downline (that I missed)
700# from a tank rated at 3500 = 20%
5 minutes - 4% per minute
130 * .04 = 5.2 fpm
Converting to sea level is left as an exercise for the reader. I started at the surface and went down quickly, and then about 3 minutes at depth.
Profile attached.
700# from a tank rated at 3500 = 20%
5 minutes - 4% per minute
130 * .04 = 5.2 fpm
Converting to sea level is left as an exercise for the reader. I started at the surface and went down quickly, and then about 3 minutes at depth.
Profile attached.
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#4
BubbleBoy
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Posted 25 August 2007 - 04:30 PM
Bubbleboy - your numbers look close to what I measured in my deco class this spring, but then in July I had a really tough swim against the currents down to the mooring in 70' trying to catch up with my daughter on the downline (that I missed)
700# from a tank rated at 3500 = 20%
5 minutes - 4% per minute
130 * .04 = 5.2 fpm
Converting to sea level is left as an exercise for the reader. I started at the surface and went down quickly, and then about 3 minutes at depth.
Profile attached.
OK, I'll do the math. At 70ft that translates to a SAC of 1.67 cf/min. Yea, I think I would be at least that level under these circumstances too. (either that or unconcious with a SAC of zero
). It's one of the reasons I've started using higher estimates of my SAC when planning redundant and reserve gas. I assume that the circumstances surrounding a need to actually use these backup quantities would likely involve a higher than normal SAC Rate.
BB
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#5
Basslet
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Posted 25 August 2007 - 05:36 PM
I have an Aladin Prime (Uwatec) and it's supposed to be air integrated but I have never figured out how to calculate my SAC.
#6
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Posted 25 August 2007 - 06:18 PM
On the Grenada trip I burned through 2800 PSI on an AL80 and 2700 PSI on an AL30 in about 15 minutes total dive time on the Bianca C. Not a typical dive.
My last Grenada dive was 1 hour 3 minutes at 60 feet on an AL 80. Only used 2500 PSI for that one.
My last Grenada dive was 1 hour 3 minutes at 60 feet on an AL 80. Only used 2500 PSI for that one.
Remember, email is an inefficient communications forum. You may not read things the way it was intended. Give people the benefit of the doubt before firing back... Especially if it is ME...! 
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#7
swfladiver
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Posted 25 August 2007 - 06:32 PM
damn now I have something else to do. I was very happy this last weekend to push an aluminum 80 for 25 min to 90 feet with a saftey stop of course. I was excited cause the dive was against current and we were spearfishing. Just an added insintive that I made the right choice to stop smoking 2 months ago
#8
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Posted 25 August 2007 - 06:34 PM
Well my SAC has been improving all summer even with having a nagging cough that wont go away. Its been in the .3-.6 Ft3 min range down from the 1.0 ft3 min during my advanced nitrox class.
My past couple of dives i have gotten my sac down to almost .2 while on saftey stop as my last two dives have been over 95 minutes with average depths in the 30' range, at one point in my dive my computer said i had about 79 minutes remaining at 34 feet and i have been down for 30 minutes at that point, i thought that was pretty good
last two dives have been 97 and 105 minutes respectively with max depths of 60 feet and average depths of of around 30'
Dan
My past couple of dives i have gotten my sac down to almost .2 while on saftey stop as my last two dives have been over 95 minutes with average depths in the 30' range, at one point in my dive my computer said i had about 79 minutes remaining at 34 feet and i have been down for 30 minutes at that point, i thought that was pretty good
last two dives have been 97 and 105 minutes respectively with max depths of 60 feet and average depths of of around 30'
Dan
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#9
secretsea18
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Posted 25 August 2007 - 07:22 PM
I don't know what my SAC is, but my Vytec air integrated model will calculate what your remaining AIR time is given continued depth and breathing rate. This is particularly good for us photographers, to minimize task loading while trying to shoot pictures.
Didn't get the hoseless transmitter for this purpose, but I sure do love this feature.
OH yeah, it will also do the download thing on the computer that they Vyper commented earlier will do in the software.
Robin
Didn't get the hoseless transmitter for this purpose, but I sure do love this feature.
OH yeah, it will also do the download thing on the computer that they Vyper commented earlier will do in the software.
Robin
#10
Scubatooth
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Posted 25 August 2007 - 07:57 PM
i dont know where this comes from about wireless transmitters in dive computers and strobes in that it must be a design flaw or bad engineering that i dont have a problem with my cochran gemini (new and old versions) as i dont loose communication with my wrist unit when my strobes go off.
also the transmitter box on mine displays the psi per minute im breathing(along with the other data i need for my dive ). i do the psi to ft calc in my head all the time so i can keep a eye on it at any point as it plugs into the first stage.
tooth
also the transmitter box on mine displays the psi per minute im breathing(along with the other data i need for my dive ). i do the psi to ft calc in my head all the time so i can keep a eye on it at any point as it plugs into the first stage.
tooth
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#11
secretsea18
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Posted 25 August 2007 - 08:23 PM
i dont know where this comes from about wireless transmitters in dive computers and strobes in that it must be a design flaw or bad engineering that i dont have a problem with my cochran gemini (new and old versions) as i dont loose communication with my wrist unit when my strobes go off.
also the transmitter box on mine displays the psi per minute im breathing(along with the other data i need for my dive ). i do the psi to ft calc in my head all the time so i can keep a eye on it at any point as it plugs into the first stage.
tooth
Tooth,
I didn't say that I lose my hoseless connection when I shoot. I have no problems with the transmitter nor with my strobes (that is computer related anyway) interacting. I said that my Vytec tells me how many minutes I can keep doing what I am at that depth and breathing rate, because it is air integrated and it has software in it to tell me this.
Robin
#12
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Posted 25 August 2007 - 08:29 PM
oh ok i miss understood then, sorry.
back to your normally scheduled thread
back to your normally scheduled thread
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#13
ScubaDadMiami
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Posted 25 August 2007 - 08:35 PM
Having a low RMV (Respiratory Minute Volume) is good to a certain point. Beyond this, this can be a tip off that the diver may be a carbon dioxide retainer, which is not so good.
On CCR, the great thing is that it does not really matter how quickly the diver breathes because gas recirculates until oxygen is metabolized. The metabolic rate is not dependent upon respiration rate nor depth, which is really cool because this can allow the diver to remain underwater, independent of depth, for many hours on teeny tanks! How cool is that?!
On the other hand, the CCR diver still needs to keep track of RMV in case the diver has to bail out to open circuit in the (unlikely but possible) event of a CCR failure. (I can't wait for the day when I can finally stop dragging those open circuit bottles around!
) For our cave dive in the Bahamas, we each had to bring two 80s plus a 40 along though we dropped the 40s right near the beginning of the dive.
On CCR, the great thing is that it does not really matter how quickly the diver breathes because gas recirculates until oxygen is metabolized. The metabolic rate is not dependent upon respiration rate nor depth, which is really cool because this can allow the diver to remain underwater, independent of depth, for many hours on teeny tanks! How cool is that?!
On the other hand, the CCR diver still needs to keep track of RMV in case the diver has to bail out to open circuit in the (unlikely but possible) event of a CCR failure. (I can't wait for the day when I can finally stop dragging those open circuit bottles around!
) For our cave dive in the Bahamas, we each had to bring two 80s plus a 40 along though we dropped the 40s right near the beginning of the dive.
"The most important thing is not to stop questioning." Albert Einstein
"For the diligent diver, closed circuit rebreathers are actually safer than open circuit scuba." Tom Mount
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#14
BubbleBoy
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Posted 25 August 2007 - 10:32 PM
Well my SAC has been improving all summer even with having a nagging cough that wont go away. Its been in the .3-.6 Ft3 min range down from the 1.0 ft3 min during my advanced nitrox class.
Dan
That's great. I'm curious about the specifics that you believe contributed to the improvement? Do you feel more comfortable and relaxed since you are diving more frequently? Have you been exercising more? Are your dive profiles and environmental conditions less strenuous? Have you changed gear (different fins, thermal protection, etc.) Have you changed the way you manage buoyancy and trim? Have you changed the way you behave, think and act underwater?
I'm looking for specific improvement practices that I can try to put into play (without giving up my weekend cigars of course
) .
Edited by BubbleBoy, 26 August 2007 - 07:18 AM.
BB
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When you make fish laugh, they can't bite you.
#15
secretsea18
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Posted 25 August 2007 - 10:48 PM
oh ok i miss understood then, sorry.
back to your normally scheduled thread
No worries. Have fun finishing up your PR stint!
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