VPM-B oddity

Rick Walsh rickmwalsh at gmail.com
Thu Sep 10 11:41:06 PDT 2015


On 11 Sep 2015 04:29, "Robert Helling" <helling at lmu.de> wrote:
>
> Rick,
>
>> On 10 Sep 2015, at 20:26, Rick Walsh <rickmwalsh at gmail.com> wrote:
>>
>> The model assumes that deco starts at the last input point.  This is ok
for a square profile dive.  But for a multi-level dive, especially with a
deep bouncing, it doesn't make much sense.  I think a better assumption
would be that the Boyle's ceiling be taken is the deepest ceiling at any
point in the dive.  This gives very nearly the same result for a square
profile dive, but in a multilevel dive such as your example, the
decompression time would increase with the deep bounce, as one might expect.
>
>
> I thought you had already sent a patch for this.

No patch from me for this.  I used the deepest ceiling assumption when
playing around with a VPM-B ceiling for a real dive.  But that was never
submitted because I didn't sort out the CVA calculation on a real dive.  I
planned to look at it after v4.5.

The deepest ceiling calculation is a little bit harder in the planner
because it won't occur at a waypoint in your example. Or any planned bottom
time that includes a long ascent.

I could probably out how to do it this weekend.  It then raises the
question of whether we want to do something that we believe is more logical
than the published model.  Certainly if I were planning such a dive I would
want it addressed.

> BTW, the thread that I got the idea from to look at this was about
MultiDeco which (due to a bug apparently) gets the bounce dive really wrong.

That's reassuring.... unless you want to dive the calculated plan.

Rick
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