Subsurface mobile general question

Willem Ferguson willemferguson at
Sun Nov 14 23:18:33 PST 2021

On 2021/11/15 00:07, Robert Helling via subsurface wrote:
> Hi Poltsi,
>> On 14. Nov 2021, at 22:44, Paul-Erik Törrönen via subsurface 
>> <subsurface at 
>> <mailto:subsurface at>> wrote:
>> When CCR, you're mainly interested in the consumption of O2 as noted 
>> previously. The diluent is not really telling since it is mainly a 
>> function of your profile as you use diluent to equalize the pressure 
>> in the loop. A serrated profile (lot's of ups and down) == large 
>> volume of diluent used because of addition to loop when going down, 
>> then dumping it when ascending.
> I can see that the amount of O2 used divided by total dive time could 
> be of interest. But it’s definitely something else than SAC and thus 
> should not be mixed with it. For example, in any statistics when you 
> have both CCR and OC dives, it would make zero sense to combine the 
> two. So even if we computed this number, it should not be displayed as 
> SAC or stored as such. Let alone the number with an ambient pressure 
> correction like the SAC makes zero sense for a CCR.
>> Of course this also happens to O2 also, but what would be interesting 
>> to see is how/when your consumption of O2 changes due to increased work.
> I meant more the other way around: If you diluent also contains O2, 
> you underestimate the O2 consumption if you only use the pressure drop 
> in the O2 cylinder.

The O2 consumption under CCR is not a dive characteristic because the 
diver can bail out to OC. So O2-consumption would be a cylinder-level 
characteristic, associated with cylinder 0 ?? (i.e. the diluent cylinder 
because as far as I can remember the O2 cylinder does not explicitly 
exist in the Subsurface CCR dive log). In pSCR bailout is often part of 
the normal dive procedure during deco.

> So here is a question I have: For a typical CCR dive, what is the 
> ratio between used O2 and used diluent? I understand this depends on 
> how often descend and how often you flush but what is a ballpark type 
> figure?
As a ball park approximation, many CCR dives (up to 65m) are done using 
air as a diluent, supplemented with oxygen from the O2 cylinder to make 
up for oxygen consumed as well as for higher O2 levels during shallower 

Kind regards,


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