tchil01 once bubbled...
OK, this is a pretty simple question, but I am having a brain cramp today
I have an Oceanic Datmax Pro Plus. Oceanics download program Oceanlog is pretty anemic, to say the least. One of the things it does not do is calculate SAC for a dive. It does give me a readout of my depth every 30 seconds as well as my beginning and ending PSI. Is calculating average depth of a dive as simple as taking the average of those logged readings?
Also, does anyone have a better program that will interface with the Oceanic computers?
Thanks
Ty
If what you want is to compute your "surface air
consumption rate", you have enough data to do it.
However, in general it's not as easy dividing
your total air consumption by your average average
depth and total dive time.
Please allow me a bit of calculus:
Your average air consumption rate for a dive , R,
in psi/min, is given by the integral
R = (1/T) INT(0,T) {[33/(33+z(t))] [dp(t)/dt] dt}
where T = duration of the dive
"INT(0,T) denotes the integral from the
beginning of the dive (t=0) to the end
(t=T)
t = time in minutes
z(t) = dive depth (in feet) at time t
p(t) = tank presure at time t
"d" denotes the derivative
Unfortunately, to obtain R it is NOT, in general, a simple calculation of dividing total air consumption by average depth and total time. However, in the special case where one spends one's entire dive at a constant depth Z for a period of time T and consumes P psi from one's tank, then and only then does R=[33/(33+Z)]P/T
With your 30 second data, you can approximate the
integral with:
R = (1/0.5N) SUMi(i=1,N) {[33/(33+zi)] [pi-pi-1)}
where SUMi(i=1,N){...} = sum of N sets of values
{...}
zi = depth (in feet) at the ith 30 second
interval
pi-pi-1 = change in pressure at the end of
the ith 30 second interval
My apologies for the mathematics, but it's important:
(1)to be able to accurately compute average air consumption rate, R, and to realize that R is simply computed with the equation R=[33/(33+Z)]P/T ONLY when one's depth is constant throughout the entire dive, and
(2) to realize that you can accurately approximate R with 30 second data regardless of your dive profile.