not sure but i think it is a glitch in the fuel consumption rate for those types of boats... i have seen a number of people take issue with it.
When i have used the IX boats i have always dashed over to the US. East coast or to South Africa at Ahead Standard - stopping at milk cows or supply ships on the waythere and back and topping off. when you get to the target area you must have fuel for a contingency plan should you have to chase down a high value target or something.
If supply ships are not available (WELL - REALLY EVEN IF THEY ARE AVAILABLE) i recommend the following.
1. Make maximum use of your batteries. Submerge and wait until they are about 75% drained and then surface. this will maximize diesel range.
2. Unless a valuable target appears right in front of your boat at 1200 meters dont waste fuel chasing targets or contact reports until you are close to your patrol zone. if heading to the US Coast i usually draw a line from the eastern tip of Cuba, to the northeastern tip of Newfoundland and i dont attack anything unless i am West of that line. If heading to south africa use a point of reference like the equator... dont chase "ghosts" until you get south of a point of your choosing.
3. Use the milk cows - it will nullify your patrol zone and you will have to remember where you were going but extending your range is their business.
4. Run at ahead slow any time you are on the surface. If air patrols are a threat and you are in fairly calm seas just run with decks awash (7 meters or so - but make sure watch crew stays on bridge) and this will cut down on dive time if you get into a pinch. keep in mind though that decks awash increases fuel consumption. so only do it in areas of heavy air patrol if you NEED to do it.
5. If youre using GWX... rough seas will nearly cut your fuel range in half - i dont care what the navigator estimates. its best to ride out storms submerged and save the fuel.
good luck and...
SINK THEM ALL MY FRIEND!!!
