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<p>Hi Rick,<br>
</p>
Am 06.01.2017 um 03:24 schrieb Rick Walsh:<br>
<blockquote
cite="mid:CAF+v9Jut8qbH9MfRgSL+CXs1xiCZHOytmR+mJAWuQc9AzLGBfA@mail.gmail.com"
type="cite">
<div dir="ltr">Hi Stefan,<br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On 4 January 2017 at 05:38, Stefan
Fuchs <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:sfuchs@gmx.de" target="_blank">sfuchs@gmx.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
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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_<wbr>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>
</div>
</blockquote>
<div>Do you feel like implementing the rock bottom gas
feature and sending a patch?<br>
</div>
</div>
</div>
</div>
</blockquote>
I have to start with the unhappy part of my answer: I would like to
send a patch but unfortunately I won't be able to. I already failed
multiple times during my life to teach myself even basic application
programming skills. To explain in other words: I'm an electronics hw
engineer. ;-)<br>
<br>
So I have to hope for s.o. like you, Robert, Dirk,... starting to
like my idea and writing a patch :-)<br>
<br>
<blockquote
cite="mid:CAF+v9Jut8qbH9MfRgSL+CXs1xiCZHOytmR+mJAWuQc9AzLGBfA@mail.gmail.com"
type="cite">
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<div class="gmail_extra">
<div class="gmail_quote">
<div>While it's not hard to do the calculation, or a simpler
approximation of it, in your head, I think this is worth
looking at after the 4.6 release. Of course the argument
against doing so is that it introduces yet more planner
preferences, or someone else will propose a different
method (e.g. I don't think anybody feels like implementing
automated contingency planning). But what you've proposed
should be simple and flexible enough for basic use.<br>
<br>
</div>
<div>FWIW, for an ocean dive I'll typically consider 3x gas
for ascent as minimum (equivalent to SAC_factor =1.5 in
your equation, but ignoring problem solving time), but
will also check a separate contingency for lost deco gas
(which almost always governs).<br>
</div>
</div>
</div>
</div>
</blockquote>
I have the feeling that any kind of rock bottom/minimum case
calculation will always require a few additional user inputs/planner
preferences. I even was very happy when I recognized that only two
additional things ("problem solving time" and "SAC_rate") would be
needed and all the other info is already available in the planner. <br>
I also hope that my proposal would be ok for most of the people. As
you are already mentioning, everybody may have his own strategy for
minimum gas calculation and this should be accepted. With my
proposal one can e.g. set "problem solving time" also to very low
value or even 0min and SAC_rate to a low value like in your example.
<br>
<br>
Your comment about lost deco gas is correct. I also consider lost
deco gas when planning a dive. But I do this differently compared to
the rock bottom/minimum gas calculation for the bottom gas. For lost
deco gas I do not plan for sharing air from one divers deco gas
cylinder but I plan for doing the deco with the remaining bottom
plus deco gas of the individual diver. I handle this at the moment
by "switching off" deco gas in the planner by entering "99m" in the
"Deco switch at" field of the gas. Then I can check the result (will
I be able to do my deco?) and can save the backup plan as a copy.
This is clearly also a workaround but its ok for me.<br>
Automatically generating plans for lost deco gas (do you mean this
with "automated contingency planning"?) from my point of view
currently does not fit together well with the overall concept of the
Subsurface planner. Therefore I wouldn't ask for this at the moment
unless anyone else has a good idea how to do it.<br>
<br>
<blockquote
cite="mid:CAF+v9Jut8qbH9MfRgSL+CXs1xiCZHOytmR+mJAWuQc9AzLGBfA@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div>Currently, a warning is printed if end pressure is less
than ascent gas (i.e. not enough gas to share on ascent,
assuming sac factor of 1), or if end pressure is less than
10bar. Your proposal should be in place of these
warnings.<br>
</div>
</div>
</div>
</div>
</blockquote>
So I would consider my rock bottom/minimum gas proposal only for the
bottom gas cylinder (last used). For the deco gas cylinders one
could keep whatever is there already.<br>
<br>
<br>
<br>
Best regards<br>
Stefan<br>
<br>
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<p>Stefan Fuchs<br>
Banzhaldenstr. 66<br>
70469 Stuttgart<br>
<br>
E-Mail: <a href="mailto:sfuchs@gmx.de">sfuchs@gmx.de</a></p>
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