Welcome to the forum, capnandrew, glad to have you aboard. Forgive me if I don't answer your question correctly but I will offer some ideas based on what I interpret as your issue.
With the PPI surface radar, if you operate the radar yourself, you will always detect a "blip" on the screen before the AI crewman does. I guess this is in order to simulate superior experience on the part of the sub skipper, or something. Anyway, what is happening is that you are detecting a contact before it is actually in range (to a degree that the radar can detect accurately). Eventually, it will show up on the map screen and you'll be able to begin your course plot. If I detect a radar contact in such a way, I often begin switching between the radar screen and the TBT/periscope, scanning the area where I believe the contact lies. Sometimes (during clear daylight), I get a visual and lock on the target. This places an icon, for a few seconds, on the map screen from which I begin drawing my plot line, making adjustments as necessary.
There is a mod available (don't have the link off-hand) that allows you to send radar contacts to the TDC. I'm sure one of the members can post a link for you soon.
Hope this helps some.
