When I 'interrogated'

my nav officer for fuel endurance (distance in km) at different speeds in every new uboot type, it gave ranges for speed that look like a bell curve ( __-^-__ ). As I left Willemshaven, in calm waves and wind, 8 knots being the economy-speed top at about 34000km for a type7b (one way trip). Even if you go rather slow (1-4knots) , the diesel you have won't get you very far. Just like going fast.
The following thread might have some more information:
http://www.subsim.com/radioroom/show...864#post835864
EDIT: p.s. my data is from GWX 2.1