If you read the
Submarine Sonar Operators' Manual you'll find all the little details that are sadly missing from Silent Hunter 4. And you'll be confronted with the game devs' obvious problem of rendering a horrendously intricate system in a way that allows us to gain the benefits but avoid the pitfalls of our computers going up in smoke trying to reproduce it all!
But the manual makes it clear that in real life, upon surfacing the sonar operator remained at his post, listening to the supersonic sonar sets under the keel, which were quite effective and expected to make or clarify targets in the surfaced condition. Looking through after the war reports of every contact developed during the entire war doesn't find a single contact ever discovered on the surface with sonar. But that doesn't mean that it was useless. We don't know how many targets were tracked after they were discovered by other means. The manual makes it clear that the sonar was considered very effective when surfaced, that the sonar operator was expected to develop contacts and he was to remain at his listening post until relieved by the Captain.