optimum speed for Subs?

[steinbeck]

On my 1st patrol to Bashi Channel.

Installed mods:

1_TriggerMaru_Overhaul_2-5
RSRDC_TMO_V502
RSRDC_V5xx_Patch1
1.5_Optical Targeting Correction 031312 for RSRDCv502
1.5_OTC_Realistic Scopes for 16 to 9 RSRDCv502
Improved Ship Physics 2.6_TMO_RSRDC_OTC
OTC_ISP_Crew Mod
1.5_OTC_UIS Radar from Start for TMO
FJB Two Tone Navigation Map
Historical Prop Rotation
Midway Career
NSM4 Classic
TMO_Visuals_for_RSRDC
Traveller Enhabced Soundsv 1.0
Webster's Better Mouse Arrows for 1.4 and 1.5
Webster's No Crew Fatigue for 1.4 and 1.5

The problem is fuel?
So far I have travelled from Midway, 2.515.5nm.
To reach Bashi Channel: still to travel, 1.471.6 = total of 3.987.1nm

Fuel left in tanks 51% So for a 1/4 of a tank I've travelled 1.257.75

I cannot get on station, patrol for 72 hours and be able to return to Midway.

What is wrong ? I cannot see any of the mods causing this! Or do I get back with fumes in the tanks?