Maybe you're right Webster, but I doubt it would change anything and I didn't think about that 6 months ago anyway
Now I thought a lot about this while "playing", especially the navigation part.
As I said in the OP, in SH3 (and worse in SH4) navigation is just plain boring. Set points, crank up TC, wait contact. In the Pacific even at 4096TC you can wait over 15 minutes to get anything to do!
Now, imagine a system with no GPS waypoints and no sub icon (at 100% realism).
You have two options, either full manual navigation or assisted by the AI (just like targetting in SH3).
You start from port so you know where you are, you go the map, and place a "waypoint" on the map, but there's no "wire" between the points and your boat.
In full manual, you set course and you calculate the time/speed/distance to get to that point, set your speed, set the amount of time, and when you're ready you don't use time compression but rather a "warp" key like in most combat flight simulators.
In automatic, just place the point and hit "warp".
If there's no contact on the way, the warp stops when you reach your waypoint. At this point, since there's no sub icon or anything, you have to make a navigation fix. In automatic the navigator just places the point on the map, his accuracy depending on the conditions (cloudy? time of the day to make the fix?) and on his experience.
In manual you do it yourself like in the realnav mod for SH3/4, only better integrated. The world doesn't to be round, if the referencials are adapted to a cylindrical world.
So basically you do have things to do during patrol other than sink stuff and avoid aircrafts. You calculate your position and your course to your next waypoint. The warp time is as fast as computer and game programming allow. Once you're out of warp, you can perform trim dive to improve or maintain the boat handling over the course of the patrol. Then make your sun/star fix, plot your next waypoint, and warp again.
When your warp is interrupted by a contact, you can use "direct navigation" to shadow a convoy or the like, and use "classic" time compression if you want/need to shadow until the night or whatnot.
Once the attack is finished and contact is lost, you have to make a position fix and then resume patrol.