[PATCH]Re: Deco calculation for repetitive dive - strange effect

Thu Feb 9 12:50:24 PST 2017

Hi All,

Am 08.02.2017 um 00:09 schrieb Rick Walsh:
>  
>
>
>     There is probably no point in arguing about the original model
>     since that IIIRC does not consider repetitive dives but I have to
>     check the docs again.
>
>
> Eric Baker's Fortran VPM-B program, which I assume you mean by the
> "original model", does indeed consider repetitive dives and surface
> intervals.  Input is in the form of a text file containing details of
> the dive/s to be planned.  I compiled it on my laptop at home, but I'm
> at work now and won't have a chance for a few days to test the
> effect.  Given what's written in the article I linked above, I suspect
> the crushing radius is not reset in between dives.
>
> I tested similar profiles to Stefan's test case with GUE Deco Planner
> 3.1.4 (funnily enough, I couldn't work out how to set the final ascent
> rate to 1m/s, even though this is GUE standard practice).  First dive
> (18/45 to 60m) had leaving 6m (last) stop at 83min (same as
> Subsurface).  Second dive (air to 40m) had leaving 3m stop at 52min
> for either 47:30 surface interval, or 1hr surface interval.  Doing the
> 40m air dive without a previous dive, the 3m stop ends at 51min (same
> as Subsurface), so a slight penalty is paid for doing it as a
> repetitive dive.  Note that Deco Planner treats surface intervals
> unconventionally: it assumes the surface interval is performed at 1m
> depth, so tissues never fully de-saturate.  I am not aware of any
> other planning software doing this.
>
I also did some more investigations based on more or less the same setup
with two dives like the one I posted initially. There are some findings
which are not encouraging. I meanwhile understand why Robert and Linus
are not really happy with VPM-B and it's various implementations. The
tests were done with VPlanner configured to VPM-B (not B/E, etc.) and in
a similar way as Subsurface.

1. VPlanner in some way also gives you a bonus (shorter deco) when doing
the second dive as a repetitive dive but in a different way. You get a
bonus of up to 4min for a surface time below 3h. The shorter the surface
time, the higher the bonus. Starting from 3h surface time or longer the
results are the same as if you start with clean tissues. So this is
again different to results from a) Subsurface before reset fix b)
Subsurface after fix and c) GUE Deco Planner based on what Rick wrote.

2. For the first dive I was impressed to see that VPlanner and
Subsurface results are really the same. Plus GUE Deco Planner results
from Rick are also the same.

Subsurface Tauchplan
Runtime: 92min

Tiefe

Dauer

Laufzeit

Gas

➘

15m

1min

1min

(18/45)

➙

15m

9min

10min

➘

60m

4min

14min

➙

60m

14min

28min

➙

60m

6min

34min

-

33m

4min

38min

-

30m

2min

40min

-

27m

2min

42min

-

24m

2min

44min

-

21m

6min

50min

(50/15)

-

15m

3min

53min

-

12m

5min

58min

-

9m

7min

65min

-

6m

21min

86min

Sauerstoff

➚

0m

6min

92min

CND: 79%
OTU: 122

Deco model: VPM-B at +2 conservatism, effektive GF=55/45
ATM pressure: 1013mbar (0m)

3. Then for the second, much simpler dive I am surprised that the
results are different! I planned this very simple dive then "standalone"
in both tools -> still the same difference. VPlanner gives you shorter
deco and I really have doubts if I did s.th. wrong but I can't figure
out what.

Subsurface Tauchplan
Runtime: 55min

Tiefe

Dauer

Laufzeit

Gas

➘

40m

4min

4min

Luft

➙

40m

16min

20min

-

15m

6min

26min

-

12m

3min

29min

-

9m

4min

33min

-

6m

7min

40min

-

3m

12min

52min

➚

0m

3min

55min

CND: 9%
OTU: 24

Deco model: VPM-B at +2 conservatism, effektive GF=27/66
ATM pressure: 1013mbar (0m)

	V-Planner 3,98 by Ross Hemingway,
VPM Code by Erik C. Baker.

Dekompressionsmodell:  VPM - B

TAUCHPLAN
Oberflächenpause = 5 Tag(e) 0 hr 0 min.
Höhe über N. N. = 0m
Konservatismus = + 2

Abst.    40m        (4)    Air    10m/min Abstieg
Tiefe    40m     16:00    (20)    Air    1,02  ppO2,  40m ead
Aufst.    18m        (22)    Air    -10m/min Aufstieg
Stop    18m      0:48    (23)    Air    0,58  ppO2,  18m ead
Stop    15m      2:00    (25)    Air    0,51  ppO2,  15m ead
Stop    12m      3:00    (28)    Air    0,45  ppO2,  12m ead
Stop    9m      3:00    (31)    Air    0,39  ppO2,  9m ead
Stop    6m      7:00    (38)    Air    0,33  ppO2,  6m ead
Stop    3m     10:00    (48)    Air    0,27  ppO2,  3m ead
Oberfl.            (51)    Air    -1m/min Aufstieg

Ausgasung beginnt bei  27,4m

OTU's Tauchgang: 21
CNS Total: 7,4%

Finally I decided not to worry too much :-)
- I prefer to see a penalty for any repetitive dive I plan so I like the
fix you did now
- Subsurface at least in this examples gives similar or slightly more
conservative results -> also ok for me
- My buddies and me will continue to compare different results before we
go diving
- I don't do repetitive dives so often because actually I'm too lazy to
get in and out of my dry suit more than once a day + plus I'm so hungry
and thirsty after each dive that this also stops me from doing a second
one afterwards ;-)

Best regards
Stefan

-- 

Stefan Fuchs
E-Mail: sfuchs at gmx.de <mailto:sfuchs at gmx.de>

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