[UKönig]

At least in vanilla SH3, I've noticed the visual ranges are usually:
Clear = to the horizon
Light fog = approx. out to 5-7 km
medium fog = " out to 2 km
heavy fog = " out to 300-350m
But at 300 meters, you're both close enough to trade spit.
And the early war torpedoes (T1-T2) had to travel 400 meters to arm. Which makes you lose visual contact. I *hate* engagements in heavy fog.
And yes, It did happen to U99 once where the fog was so thick, we made physical contact before we made visual contact, and the bad news, it was a C2 class merchant we hit. Port, forecastle. Captain Koenig wasn't very happy with the crew that day...