On 25/01/2018 11:16, Rick Walsh wrote:
On 25 Jan. 2018 8:07 pm, "Willem Ferguson"
<[email protected]
<mailto:[email protected]>> wrote:
I am working on the user manual. Because of UI changes, this
includes replacing all the images in the section dealing with the
dive planner. I am trying to get the recreational planner to work
and I have a problem. See attached image.
If the initial cylinder pressure is not set, then the planner
provides a dive at the specified depth and duration is determined
by the NDL, limited by the present cylinder size and initial air
pressure. So I select a 12 litre 232 bar cylinder and do not set
the initial cylinder pressure.
1) The ceiling and profile do not approach the NDL limits based on
dive tables, even with GF=90/90.
Hi Willem,
In the example you provide, the air NDL at 30m is 13min with gf 35/75.
This looks about right to me. From memory the Buhlmann NDL (gf
100/100) is ~17min, and the PADI and navy tables are 2-3 minutes
longer. Reducing the gf to 35/75 would reduce the NDL.
I suspect this is not the complete explanation. The NAUI, NOAA and US
Navy tables all give the NDL with air at 30m between 22 and 25 min. With
gf=100/100, Subsurface gives 16 min. In addition, the profile does not
get close to the ceiling at NDL. I suspect that, with initial cyl
pressure not specified, the whole calculation just does not work.
Forcing the bottom time to 26 min (gf=100/100) brings the ceiling close
to the profile which is more or less acceptable. So that part of the
planner works. But if the bottom time is specified as much shorter than
26 min, the NDL also is much shorter. There is a problem or bug there.
Then there is the question of the use of GF with recreational mode,
since the Bühlmann option has been *de-selected*. Does this mean that
VPM conservatism can also affect the profile? I thing there is a need
for me to document the way thing work because the current text is
clearly not sufficient. I have a feeling the only difference between a
conventional ZH dive plan and a recreational dive plan is the latter's
ability to automatically provide a NDL profile, which in this case does
not work anyway.
2) Even more important, at the bottom it says that the dive
requires 1245 litres of gas, more than is in the cylinder. But
this is wrong because the 12 litre 232 bar cylinder takes 2784 litres.
That looks like a bug. I'm guessing the calculation here assumes the
starting pressure was zero. If you don't enter a starting pressure,
the planner should assume cylinder working pressure.
I would agree. The gas volume calculation is accurate. The cylinder
volume/pressure is lost somewhere.
Kind regards,
willem
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