What are your driver-settings, Anisotropic Filtering in particular?
Try to raise that one as high as possible (8x, or even 16x).
Reboot your PC, and start your game without touching any other program...this is to ensure the largest possible free RAM upon loading.
Now when you finally load and get in your command-room, wait a couple of minutes, before you hit outside view...this is to ensure all sounds and graphics in your uboat's area are pre-loaded correctly.
Still no bow-wake?
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