What it does?
Makes the harbors pitch black during night.
Installation
Either via JSGME or by manually copying the data folder in to your Silent Hunter 5 folder.
*gasp* There's no screenshots! Nah, won't download it. 
Go into a room with no windows, shut off the lights. There.
Linky:
http://www.filefront.com/15866397/Darkened_Harbors.rar/
If you think this is a bit too radical, then I suggest you try the Az's great "Window lights redone" mod found here:
http://www.subsim.com/radioroom/showthread.php?t=165348