Whenever I start from Kiel in a type IIA, I always go at 5 knts through the Keil canal and stay at that speed until im past Heligoland. I then set my speed to 6-7 Knts, submerging for about 10 hrs. This way I can get to Scapa Flow and back with just enough fuel left.
Failing that, you could just head back to Heligoland, and start you next patrol from there.
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