Don't know the stats on the Type XXIII, right off the top of My head... but... with Type II-D, I extended the fuel by running submerged for as long as I could.. then would do a check of the are by sonar, then periscope.. once determined all clear, I'd surface.
After that, would run the diesels to do a recharge of batteries until daylight...
& rinse and repeat...
Dunno if that'll help with the XXIII... but.. is something to consider... that & avoid going all out balls to the wall surfaced... only thing I can think of as a suggestion...
M. M.
