Sonar contact lines disappear when you get visual contact. Your sonarman won't even "report on nearest contact" when it is within visual range (visible on map). A way around this is manually aiming the hydrophones in the sonar-station like Tomoose described, and then giving the order. Try diving to periscope depth or a little deeper and make sure both scopes are down. It will still take your guy some time to confirm the contact, so be patient, or listen and confirm mannually.
Hope it helps.
