american u-boat 1944: speed vs. duration

Formular y = 2.402133918·10^-6 x^6 - 2.480632527·10^-4 x^5 + 1.022176849·10^-2 x^4 - 2.159633693·10-1 x^3 + 2.53236561 x^2 - 18.08338354 x + 115.6332116
Battery capacity of type vii C maybe found in commanders handbook
some other info here
http://www.uboat.net/technical/batteries.htm
and her3
http://sourceforge.net/apps/trac/der...i/VIIbatteries
NYGM or GWX3 (SH3) have totally different calculations.
Ex. With ordered submerged speed 6 kts the battery lasts longer than 23 hours but the speed droppes off sharply etc.