In the early war, I tend to go two hours surfaced, two hours submerged, as there's a better hydrophone range that eyeball. If I'm on the surface, I'll keep a WO up there.
In later war, radar and nastily competent RN types make it a pain to be around, so I tend to stay submerged as long as possible, and only surface when I need to and only at night.
Cheers
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