What are some of your favorite methods for determining your SAC rates?
Printable View
What are some of your favorite methods for determining your SAC rates?
Breathe off a tank at the surface and time it from one pressure to the next or time it over say 10 minutes and figure it out that way. Or buy an air integrated computer that just tells you as you go. Never use it for hard calculations on air as it fluctuates depending on what your doing and how much your working.
Matt
Lately I've been assuming an RMV of 1.0 just to be conservative.
To determine my SAC rate I first determine the Tank Factor (TF) of the cylinders I am using. Because I am diving doubles, I then multiply that by 2 (doubles....it works). I multiply the TF by the total gas pressure used, in the portion of the dive I am calculating, giving me the Gas Consumed (measured as: cu.ft.) Divide this by the dive time( in minutes), giving us a gas consumed per minute. Divide the Gas consumption by the depth of the dive in ATA's (atmospheres). All this equals SAC rate. Now for practical example:
The word problem: A dive is undertaken to 115 feet (figure a square profile) for a time of 35 minutes. The "hearty diver" is diving with 2 aluminum eighties. and consumes a grand total of 1755 psi.
The math: Aluminum 80's TF=.027 x 2 =.054
.054 x 1755(psi. Gas consumed) = 94.77( cu.ft.)
94.77 (cu.ft. gas used ) / 35 min. (dive time) = 2.7077.....(2.71 cu.ft. (gas used per min)
2.71 (cu ft per/min) / 4.48 ATA = .6049 (.61) SAC rate
Our diver is a figment....but he/she enjoyed the dive immensley!
The math may be a bit intimidating, but it is fairly easily mastered with some practice.
Note: some Tank Factors Al 80 =.027 Al 100 = .030 LP 95's = .036 LP 104's = .039
I hope this will obscure the elementary with all this jiberish.
I have a whizzo spreadsheet I created to calculate a) actual SAC and b) a planner to confirm I have enough gas for a future dive.
If anyone would like a copy then PM me your email.
Unfortunately, I use ltrs/mtrs/bar, and I think most of you use cu ft/ft/psi?
The spreadsheet was created for me and my diving so it is basically for square profile diving (wrecks) and up to 2 gas mixes. If only using one mix then leave mix two at zero and ..............
Each diver needs to know the speed at which his breathing gas consumed. This information is important to choose an appropriate point of view, as well as the size of cylinder diving with others, with different rates, and to be able to predict how much gas is needed to dive deep into the most famous of the period known time.