You can always ask your navigator to give you your maximum range at your current speed. However, you need to be aware that the weather has an affect on this i.e. in calm weather the given range will be further than if the sea is rough. In a type VII your most fuel efficient speed is around 8 knots in ideal conditions.
Nemo
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"I'm afraid there is no disguising the fact that King's obsession with the Pacific and the Battle of Washington cost us dear in the Battle of the Atlantic".
Sir John Slessor GCB, DSO, MC, DL
AOC-in-C Coastal Command RAF
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