If i'm impatient and crossing the high seas - 2000-ish or 4000-ish TC's the first 50% of the trip, when approaching the patrol zone or enemy coast i get down to 1024 first then 512, and when really close to coasts, patrol areas or just get that stomach-feeling that something is out there - maximum TC is 128.
Why the hurry? Well, i am a pretty impatient guy and i couldn't bother with sailing at slower than 1024 when close to germany or a fair bit out from occupied coasts i frequently pass, simply because it eats up too much time... Call me gamey or stressful but everyone has their own methods.
On the collision-note i have had similar experiences a handful of times, always related to cruising at too high TC in unfamiliar or coastal areas or those darned minefields before i realized i actually had a map where they are located...
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But night-time surface hunting in calm waters outside the british coast or between scotland and the hebrides is great fun at max 32 TC, always a chance of encountering that lone fishing-boat or motor vessel to feed some lead with the AA-gun to save up those oh-so-limited deckgun shells
