Using RFB1.5, I've never had a problem with fuel..
My settings: (from Pearl via Midway)
- 100% reality
- ~10 knots on surface, 1-2 knots submerged
- I only start submerging during the day from west of ~140 east (I think it is).
- Arrive off Okinawa with 75% fuel, leave Japan when at 25% fuel.
- On station, I scan areas during the day submerged - monitoring sonar.
At night ~10 knots on the surface until dawn, submerge and scan again.
If I feel I'm in a 'good' area, I cruise around in circles at 1 knot on the surface at night.
- On day contacts, p-scope depth - If I'm in a good position Attack, else 'tag' it till sunset then chase it on the surface. If it's going to fast I just leave it.
This method I've found gives me plensh time on station.