Subsurface mobile general question

Paul-Erik Törrönen poltsi at
Wed Nov 17 02:47:29 PST 2021

On 2021-11-16 20:43, Robert Helling wrote:
> thanks a lot for those files. My model only involved the total O2 and
> diluent use, so I don’t need those pressures as a function of time.

A ok.

> Here is what I found:
> The data scatters quite a bit over the dives and that does not get
> better using the correction. Plus there is a clear trend in this plot
> vs depth: Dives deeper than 60m have an almost constant but pretty
> much twice as high O2 consumption. Does that in any way correlate with
> the workload?

I'd say it correlates more with the excitement. Many of the deeper dives 
are done with a scooter, so there should be less physical exertion.

I have only had my heart rate monitor on a couple of dives (shallower 
than 60m), where the rate was high in the beginning, but as the dive 
progressed, it went lower and lower (already at bottom time) towards the 
end of the dive which is where you anyway also have the deco-stops and 
periods of inactivity.

Other than that there should not be really any workload, I tried to pick 
dives which I recall being quite effortless, but this is obviously a 
subjective view.

One thing to keep in mind is that when you ascend from deeper dives, 
your unit is in pretty much constant lower-than-setpoint-state, which 
means that it pushes continuously O2 to the loop all the while you're 
also purging that gas. It is only when you ascend to a deco stop that 
the unit actually may get the loop gas to the setpoint. The deepest 
stops are usually 1-5min before you get to the 12-6m range where they 
become longer.

I looked at a couple of the dives and plotted the in-dive O2 
cylinder-pressure vs. depth and to me it looks like the only way to 
really distinguish at any level what is the true consumption from 
O2-loss from ascend purging would be to compare bottom time consumption. 
Which means that it can only be applied to \___/-shaped dives.

Maybe this is an exercise in futility and the only practical thing to do 
is to replace OC SAC with the O2-usage (l/min) for CCR-dives when that 
data is available? Ie. there is the in-dive O2-pressure data, and 
cylinder-volume available.


More information about the subsurface mailing list