As for coastal vessels, a lot of those are not heard on sonar, which is a "game" thing. We have moved some of the smaller Japanese vessels into Type=108, which was renamed to "Motorized Coastal Vessel", but left some as Type=104, which are "silent" to sonar, simulating vessels without motors... yet you'll find Sampans in convoys in the Stock game doing 9 knots, and silent as a ghost...
- anyway, I don't think we've messed with the Allied traffic much yet, but that is a plan for the future.
As for the course discrepancies, I assume that they intended to model in some ocean sea current drift, and a tired helmsman's drift, etc., but it does happen all of the time. Even if you set a course, you will usually find that the helmsman is off by a couple of degrees, and if you order him to return to course, you'll hear "Returning to course - yes sir", and then notice, as you mentioned, that the error becomes larger...
- what to do? Court-martial? Keel-haul??
- while you don't have to watch your crew as much as you did in SH3, you do still have to keep an eye on them. If you want to micro-manage the crew, go through their qualifications, and move them around if desired. You might find someone who could steer closer to the assigned course... then again, it might be worse...
For the "real navigation", the key part of what you said is "based on reality". They attempted to simulate the night skies and celestial movements, but there are some things that just get out of whack with each other. If you discuss this with Rockin Robbins, he will unequivocally tell you that the game is messed-up in this regard, but he is an amateur astronomer, and knows his stuff. If you watch a sunrise of sunset in the game, you might notice some "distortion" in the distance traveled versus the elevation, so there are certain times when the celestial world is distorted. But if you do things the same time everyday, then you'll be consistent...
