It is perfectly realistic to receive sound contacts on the surface. If you'll use your external camera, you can travel under your boat to see the two sonar heads below the forward torpedo room, which always protrude at least 15' below the surface of the water, even when the submarine is on the surface.
Yes, the diesel engines were noisy, making use more difficult on the surface, but they were still useful. The sonar operator had a full set of attenuation filters to filter out frequencies of on-board sounds and amplify sounds coming from outside the boat, where our game sonar is much too simplified to appreciate the sophistication they enjoyed. Using sonar on the surface was done, and contacts were found in that configuration during the war.
However, the cries of the wrong have been so loud that even Ducimus has removed surface contacts from sonar in Trigger Maru, because nothing is louder and more indignant than the voice of the ignorant.
The problem is most of us (including myself) aren't old enough to be able to merely lower the volume on our hearing aids to ignore their prattle.:rotfl: