Well, I tried to measure time to recharge... after 3 hours submerged, I had to be surfaced at least 1 hour 15 minutes to recharge...few times even longer almost 1 hour 45 minutes... that was in bad weather... but when weather suddenly calmed it took only 35 minutes
... so what to do... dive and wait for better weather? Or surface, order flank speed, and pray not to be caught by radar for hour and a half period of time?