To msumpsi, you're quite right in thinking there are issues with manual targeting with the game. The developers had intended to make an American Campaign of Submarine warfare in the Pacific (much like its successful namesakes of the Silent Hunter series from Strategic Simulations)
but, they based SH4 on a game engine designed for the U-Boat game. Silent Hunter 4's American Campaign is the bastard child of the developers, who had
from the release date, designs to bring the U-Boats into the Pacific. The underlining files are riddled with Silent Hunter III leftovers.
To this end, the simplest tasks of measuring a yard for a yard were ignored, making manual targeting (which relies heavily on optical observation) to be only somewhat feasible. The Stadimeter is only as accurate as the measurement point it uses, and how well you place the mark with the mouse. The lens Telemeter divisions won't give accurate measurements as long as the world view is not sized correctly. The stock radar is only providing eye candy, there is no way of measuring a "blip" on the screen. The only accurate tool to manual targeting is the sonar, but you'll pay for it after a ping is made with an enemy warship near. Having the Map Contacts enabled
is like cheating. You can get all the necessary information for manual targeting right off the map. Speed, Range, AoB, Relative Target Bearing all can be gotten from the map.
So, what's the solution. First make sure you simply enable the option for "No Map Contacts Update". No matter what the mod may do with the contacts, having them turned off will prevent you from getting a clear picture of what's on the horizon. You'll still be able to plot a targets position on the map, you'll just have to do it yourself. Figuring relative bearing, AoB, target tract, target speed are still possible from map plotting. The difference is YOU make the plot, not the computer. It's on
your shoulders to make an estimate on what you see for a firing solution. To me, this brings the simulation to life when it's your skill that makes an accurate firing solution.
Second, get a mod like
Optical Targeting Correction that provides accurate measurements when using the periscope or TBT/UZO. Since the game renders different world views through these optical devices depending on which resolution/aspect ratio you play the game with, you'll need to correct the view with the mod addition that's specific for it. You'll get a Range Dial for inputting estimated range to the TDC, plus an authentic tool called an Range Omnimeter for calculating distance from the telemeter divisions found on the scope lens. You'll also get a working Radar that will provide a reasonably accurate range estimate. Which can be used to input range to the TDC. The mod also has the "SCAF like" measurements for providing as accurate a stadimeter process as possible. The errors in an unsuccessful manual firing solution should be from
your lack of skill, not the fault of the tools you use.