BobinNC
Registered
What is the best formula for figuring SAC rates?
SAC Rates
- Thread starter BobinNC
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
The Kraken
He Who Glows in the Dark Waters (ADVISOR)
ScubaBoard Supporter
Scuba Instructor
Divemaster
Bob,
If you have Excel, I'll send you a spread sheet that does lots of stuff, if not:
(((Pb-Pe)/Pb)x((Pb/Pw)xV)/T)/((D/33)+1)
Where:
Pb = Beginning Pressure
Pe = Ending Pressure
Pw = Working Pressure of Tank
V = Volume ot Tank
T = Time of Dive in Minutes
D = Average Depth of Dive if Feet
the K
If you have Excel, I'll send you a spread sheet that does lots of stuff, if not:
(((Pb-Pe)/Pb)x((Pb/Pw)xV)/T)/((D/33)+1)
Where:
Pb = Beginning Pressure
Pe = Ending Pressure
Pw = Working Pressure of Tank
V = Volume ot Tank
T = Time of Dive in Minutes
D = Average Depth of Dive if Feet
the K
The Kraken
He Who Glows in the Dark Waters (ADVISOR)
ScubaBoard Supporter
Scuba Instructor
Divemaster
Bob,
Update, sent you the Excel spreadsheet.
the K
Update, sent you the Excel spreadsheet.
the K
gene02
Guest
Can I get a copy? Please
the formulas do not include water temperature? why not? the diff between 40 degree water and 80 should be significant no?
Most people work harder in colder water and that will result in a higher SAC but it is not a variable to calculate.
Can I have a copy of the excel sheet?
- Messages
- 7,660
- Reaction score
- 4,717
- # of dives
- 200 - 499
Along this line, your SAC is not a single value. -resting, easy swimming, hard swimming, warm water, cold water all make a big difference. If your SAC rate was a precise number, by now someone would have mentioned that you use 33 for saltwater and 34 for freshwater in the calculations. Calculate a SAC for various effort levels and conditions and you will have a way to make something better than a wild a**ed guess about how much gas you will need for a particular dive. Expect your SAC to drop as skills increase.
Why include water temp? As far as I can tell, the temp, in and of itself, should have virtually no difference on one's SAC rate -- NOTE, I'm saying the temp "in and of itself" has no (or almost no) influence on the volume one breathes at any given depth.
OTOH, your SAC rate is almost always greater in cold water than in warm water due to any number of factors that are a result of the temp differences -- more exposure protection, more weight, lower viz, etc. But as far as the calculations are concerned, temp is pretty much irrelevant as far as I can tell.
OK -- IF you don't have a computer that provides you with your average depth for the dive, what do the SB gurus suggest is the best way to determine SAC? Should you try to estimate your "time weighted average depth" (that is, X minutes at Y depth + M minutes at N depth +.... to arrive at the "time weighted average depth") or just do the test -- record starting pressure, swim for 10 minutes at a constant depth, record ending pressure and just use the snapshot. What say ya'll?
Similar threads
