Hi h.sie,
I would not spend too much time on the CO2 stuff. IMHO, it's fine if there are only two states: work (whatever it is) and rest (triggered by silent running). Usually, you will not use silent running if there is no threat. In this case there is also no need to stay submerged for ages. So, it's more or less only important if there is a threat and then work is the main difference.
I also don't think that the 10 min. update interval is a problem (btw, it's the same with fatigue. Every 10 min. the fatigue is decreased). If someone wants to use it to cheat then let him cheat.
Concerning the two points I mentioned earlier: I think there must be a variable that contains the probability for being spotted. I guess the stealth meter shows its value. Would be great to identify this variable because it would allow to easily modify many aspects (thermal layers depending on depth value

, repair noise,...). In combination with a variable that would somehow indicate exploding depthcharges, deaf sensors should be easy to achieve
Anyway, thanks a lot for your continuous work! You are starting to become a legend
Cheers, LGN1