@Werewolf
Set submerge range to 150000.

150000! Yes i know but 150000 seems to work. I tried 5000, 8000 ranges where it failed in the battery/Air/CO2 running out very quick in a matter of seconds with time compression up. Took a look at the Le Terrible files and notice submerged range is 150000. Input the Narwhal to 150000 submerge range and made a trip submerged from Midway to Tokyo having to surface couple of times cause of CO2 depletion but battery/Air was OK, just the CO2 would slowly deplete can't figure out how to stop that.
Also are you using any mods that change the sub files? Disable them first then make changes to the sub files in that mod (not in the main SH4 data files) This could be why your still getting 70-80nm after the changes - the mods overrighting your changes everytime you load the game up.