8000 meters is the default distance at which a ship will send out a contact report w. TDW's mod. In game, a ship may spot you on the surface from a lot farther off on a clear day. When I do a run around on the surface, I stay completely out of sight of the convoy or at most, at the very edge of visibility.
The problem with the marks disappearing from the maps upon a reload is hardcoded. It's been there in every SH game.
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