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<p>Hi All,</p>
<p>don't know if this was ever discussed here:<br>
Today I installed and tested the 4.6 beta 2 a little bit and
planned some dives to see how long I can stay at 60m with and w/o
bottom stage :-)</p>
<p>At this moment it became clear to me in which way subsurface
already today supports you to do rock bottom gas calculation and
how this could be improved.</p>
<p>What we already have today:<br>
We have "Bottom SAC" GUI user input, cylinder size of last
cylinder used in "dive planner points" and we already have tank
pressure consumption from this cylinder in planned ascent
including all calculated deco stops until we reach first deco gas
switch. That's a good starting point.</p>
<p>What we would need for the rock bottom calculation:<br>
- Problem_solving_time (including some margin) as GUI input,
integer number of minutes, default e.g. 4min<br>
This is the worst case time the buddy team will stay at max.
depth after OOG situation happened.<br>
- SAC_factor<br>
This is the increase factor for bottom SAC rate in OOG
situation. I would multiply bottom SAC by 2 already hard coded and
then again multiply by this factor.</p>
<p>Rock bottom cylinder pressure would then calculate as:<br>
(Problem_solving_time * Bottom_SAC * 2 * SAC_factor *
ambient_pressure_end_of_bottom_time / cylinder_size) +
(tank_pressure_consumption_ in_planned_ascent * 2 * SAC_factor)</p>
<p>Example1 (60m, D12, ~25bar for ascent (deco below 21m!),
18barl/min SAC):<br>
(4min * 18barl/min * 2 * 2 * 7 / 24) + (25bar * 2 * 2) = 184bar <br>
</p>
Example2 (40m, D12, ~6bar for ascent (direct ascent to 21m),
18barl/min SAC):<br>
(4min * 18barl/min * 2 * 2 * 5 / 24) + (6bar * 2 * 2) = 84bar <br>
<br>
The result could be simply printed to the dive plan details together
with the info about the corresponding cylinder (for cross check
only!). <br>
One could also compare cylinder pressure at end of bottom time with
calculated value and give a warning but this IMHO is optional.<br>
<br>
Maybe too late for V4.6 but for a later version? :-)<br>
<br>
<br>
Best regards<br>
Stefan<br>
<br>
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<p>Stefan Fuchs<br>
Banzhaldenstr. 66<br>
70469 Stuttgart<br>
Tel.:
0711/4116289<br>
Mobil: 0172/8922025<br>
E-Mail: <a href="mailto:sfuchs@gmx.de">sfuchs@gmx.de</a></p>
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