SAC Calculations for "Multi-Level" Diving

In preparation for my "Advanced Nitrox / Deco" course, I'm reviewing concepts like SAC rate calculations.
I'm wondering if there are any decent algorithms for computing SAC for "multi-level" dives or is it just
SOP to use the deepest depth and "total time." One formula for a "single depth" calculation I've seen is:

SAC = (psi consumed / total bottom time{min} ) / ((depth{ft} + 33) / 33).


Now the example given assumes a depth of 60ft and a bottom time of 40min + 3 min safety stop at
20ft, so total time = 43 min, but doesn't take into account the change of depth from 60 to 20 ft,
or perhaps time at interim depths before reaching the safety stop. With 2500psi consumed, the SAC
by the above formula = 20.7 psi/min. Of course, this formula also doesn't take into account the tank
size/volume either so it would have to be recalculated for different tanks.

In any event, is there such a thing as a "multi-level" algorithm for SAC (using different times at different
depths), or better still, some existing software to compute multi-level SACs (that, perhaps, may also take
tank size into account)?

As an aside, I find it very concerning that when I Google SAC Rate on certain Scuba websites, I get
such responses as "Sacramento Mortgage Rates" and "Refinance Quotes" etc. etc.

Thanks.


____________________________________________
Regards,

Arnold


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"mag3" <zmpmag3-plongee@yahoo.com> wrote in message
news:5dtf139lacqvdm3b4pngnv8rkodroh5glh@4ax.com...

> In preparation for my "Advanced Nitrox / Deco" course, I'm reviewing
concepts like SAC rate calculations.
> I'm wondering if there are any decent algorithms for computing SAC for
"multi-level" dives or is it just
> SOP to use the deepest depth and "total time." One formula for a "single
depth" calculation I've seen is:
>
> SAC = (psi consumed / total bottom time{min} ) / ((depth{ft} + 33) / 33).
>
>
> Now the example given assumes a depth of 60ft and a bottom time of 40min +
3 min safety stop at
> 20ft, so total time = 43 min, but doesn't take into account the change of
depth from 60 to 20 ft,
> or perhaps time at interim depths before reaching the safety stop. With
2500psi consumed, the SAC
> by the above formula = 20.7 psi/min. Of course, this formula also doesn't
take into account the tank
> size/volume either so it would have to be recalculated for different
tanks.
>
> In any event, is there such a thing as a "multi-level" algorithm for SAC
(using different times at different
> depths), or better still, some existing software to compute multi-level
SACs (that, perhaps, may also take
> tank size into account)?
>
> As an aside, I find it very concerning that when I Google SAC Rate on
certain Scuba websites, I get
> such responses as "Sacramento Mortgage Rates" and "Refinance Quotes" etc.
etc.
>
> Thanks.
>
>
> ____________________________________________
> Regards,
>
> Arnold

30 seconds returned the following;

http://groups.google.com/groups?as_q...007& safe=off

http://tinyurl.com/2ywuzy

In article <5dtf139lacqvdm3b4pngnv8rkodroh5glh@4ax.com>, zmpmag3-
plongee@yahoo.com says...
> In preparation for my "Advanced Nitrox / Deco" course, I'm reviewing concepts like SAC rate calculations.
> I'm wondering if there are any decent algorithms for computing SAC for "multi-level" dives or is it just
> SOP to use the deepest depth and "total time." One formula for a "single depth" calculation I've seen is:
>
> SAC = (psi consumed / total bottom time{min} ) / ((depth{ft} + 33) / 33).


You determine your SAC at a single depth. You record the PSI and
starting time at the start of the test and then the PSI and time at the
end. You swim at a normal pace for the entire time of the test. It
doesn't have to be your whole dive. Your instructor will most likely
supervise this.

PSI/minute is specific to one size tank. In this class, you will be
using a sling tank of deco gas that is most likely smaller than the one
(s) on your back. What you need to determine and use for calculations is
cu ft or liters per minute. When you plan a multi-level dive, you use
your SAC * time * depth in ata * whatever fudge or safety factors you
are using to determine the gas requirement for each depth segment and
then add them up to get your total gas requirement for each gas you are
carrying.

The deco software I use lets you plug in your SAC for each segment and
calculates your gas requirements.

There is a SAC calculator here: http://cisatlantic.com/trimix/tools.htm
under "Other Applications".

mag3 <zmpmag3-plongee@yahoo.com> wrote:
>In preparation for my "Advanced Nitrox / Deco" course, I'm reviewing concepts like SAC rate calculations.
>I'm wondering if there are any decent algorithms for computing SAC for "multi-level" dives or is it just
>SOP to use the deepest depth and "total time."

The easy way is to have or borrow a computer that will do the
work for you. The Suunto Cobra (and probably many other
air-integrated models) records your starting pressure, your
ending pressure, and it computes your average depth for the dive.
If you download it to a PC and use their divelog software, you
simply tell it your tank's capacity and rated pressure, and the
SAC is computed for you.
I get a SAC figure for each dive. It shows me how well I'm
doing and how strenuous each dive was.
Since the SAC doesn't significantly change with depth, your
alternative would be to make a single-level calculation and just
use that figure. Decide which level you want to work with and
just note the starting pressure and time and the ending pressure
and time before leaving that depth.

--
Ron
(user ron
in domain spamblocked.com)

On Sat, 07 Apr 2007 21:08:02 -0400, Ron <r....@see.below> wrote:

> Since the SAC doesn't significantly change with depth, your
>alternative would be to make a single-level calculation and just
>use that figure. Decide which level you want to work with and
>just note the starting pressure and time and the ending pressure
>and time before leaving that depth.

Which may as well then be the deepest depth as that would invlove the greatest
consumption of gas per time interval, all other things being equal.

Either that, or I can average several readings at several depths. I just have to
record PSI levels manually as that seems the only thing my computer doesn't
record (and it is air-integrated).

The SAC calculator Al recommened is pretty good actually.

____________________________________________
Regards,

Arnold

On Sat, 07 Apr 2007 21:54:13 GMT, Al Wells <a.....lls@gmail.com> wrote:

>The deco software I use lets you plug in your SAC for each segment and
>calculates your gas requirements.
>
>There is a SAC calculator here: http://cisatlantic.com/trimix/tools.htm
>under "Other Applications".

That's a nice site in general. I'm sure it will come in handy later.

Thanks. The SAC calculator is pretty good.

____________________________________________
Regards,

Arnold

mag3 wrote:
> In preparation for my "Advanced Nitrox / Deco" course, I'm reviewing concepts like SAC rate calculations.
> I'm wondering if there are any decent algorithms for computing SAC for "multi-level" dives or is it just
> SOP to use the deepest depth and "total time." One formula for a "single depth" calculation I've seen is:
>
<snuip>

Best answer: http://www.hhssoftware.com/v-planner/ (or something similar).

Next best answer: Just plan all the levels separately and add them together.

John Eells

In article <enrg131c16pc049vjltjt0li5iisvbsdv5@4ax.com>, zmpmag3-
plongee@yahoo.com says...
> On Sat, 07 Apr 2007 21:54:13 GMT, Al Wells <a.....lls@gmail.com> wrote:
>
> >There is a SAC calculator here: http://cisatlantic.com/trimix/tools.htm
> >under "Other Applications".
>
> That's a nice site in general. I'm sure it will come in handy later.

The site hasn't been updated for several years, but it has a lot of good
information and entertainment. It was born during the tech diving feuds
of the mid to late 90's and early 2000's. The owner is Jim Cobb in
Virginia Beach. Much of what you read there may not agree with what your
TDI instructor tells you.

On Sun, 08 Apr 2007 11:17:35 GMT, Al Wells <a.....ls@gmail.com> wrote:

>In article <enrg131c16pc049vjltjt0li5iisvbsdv5@4ax.com>, zmpmag3-
>plongee@yahoo.com says...

>> That's a nice site in general. I'm sure it will come in handy later.
>
>The site hasn't been updated for several years, but it has a lot of good
>information and entertainment. It was born during the tech diving feuds
>of the mid to late 90's and early 2000's. The owner is Jim Cobb in
>Virginia Beach. Much of what you read there may not agree with what your
>TDI instructor tells you.

Well, as is said here time and time again, it's the "instructor" that counts. But it's
still a pretty decent reference point. It's good to learn things like this now as it
may influence future decisions like equipment purchases etc. (computers that
actually *do* some of this stuff etc. - or at least capture the data so you can
do it).

____________________________________________
Regards,

Arnold

"Al Wells" wrote

> I will be happy to show you my neat, elegantly simple gear setup this
> spring and point out a few walking CF's

Careful Al, someone will come along and call you a "cultist". <grin>

Curtis