Well it is simulated in some way... like in real life, you learn a lot by experience. After having some patrols on the log, you can identify ships without going to the book, and you start to have some rough idea of the distance - at least in close quarters like 500 to 2000m - as well by looking in the scope or the UZO.

Eyeballin'
 

Yes, I agree there is a sim factor here we can count on but of course that wouldn't compare to being up there on the conning tower as your ship races across the ocean towards a merchant. There you can take in and integrate all the factors you are experiencing: sight, sound, angles, the breeze against your face, the actual movement of the ship and distance as it nears its prey, speed, etc. Like you said it's probably not simmable...at least not in the near future.

I've done a bit of sailing. The experience on a sailboat isn't comparable at all to say Virtual Sailor...not in the least. IRL you're taking in your environment through your senses and using that information to do what is needed. Here we're staring at a two-dimensional screen.

Now if SH only went 3-D with pitch and roll motion chairs we could sit in, along with a little squirt bottle that sprayed sea water on your face and an implosion band you fit around your skull that would constrict as your little uboat plummeted towards the ocean floor because Bernard had left the tube doors open to the sea.... :)