I'm not much of a boatsman and/or sim guy either man, so don't worry...it's definitely worth it even if you don't want to do the whole immersion shabang thing where you have to do pretty much everything manually.
There is range of paramaters you can switch on or off depending on your taste, which will determine your "realism" percentage. The realism is standard at 29% in career mode.
You want to know how insane you can get wrt realism? Normally speaking, your watchman provides you with accurate info on the distance, type, speed, angle, etc of a ship in your view. But you can turn that off. What you need to do then is...
-get ship on visual (periscope, deck)
-pull out ship recognition manual
-basing yourself on its silhouet and size, you make an assumption as to which type you're dealing with. You call the ship type out to the crew.
-you measure distance, by checking its top mast length (provided in manual, IF you made the correct assumption on the ship type) against the waterline. The shorter, the further, etc. Obviously.
-you measure speed, usually by setting your stop watch between two set points. Harder than it sounds at sea (no landmarks) and heavily dependent on your skill to assess distance first.
-you measure angle using all of the above. (ship type, distance, speed)
-you fire your torpedos, subtracting the time the torpedos need to cross the distance to the ship from the ship's speed and ETA at a given point.

I don't think I need to say that this is HARD when you're over a 1000m away, on a stormy sea, with little or no visibility.
But in normal game mode, your watcher will estimate all that shit for your, you can 'lock on' to a target and your torpedoman will make his best effort to hit the target smack in the middle. The most important things you need to do as a captain is plotting the course and calculating interception points. And avoiding detection by warships. And calling the shots in combat situations (when attacking convoys etc.). And managing your crew. etc

There's still a whole lot to do without resorting to extreme realisme. So if you're interested and can pick up SH3 for a few quid, I'd encourage it.
(Silent Hunter IV is good too but that's in the pacific with American subs. Fuck that shit, U-boot is where it's at!)