Not this again. Sonar contacts on the surface were reality. If it drives you crazy you have a reality crisis.
We can debate all day over whether the sonar works too well on the surface. Sonar conditions are variable anyway, but a quick reading of the fleet boat sonar manual will reveal that the sonar station was explicitly directed to be manned while the sub was surfaced. Sonar operators were trained in surface operations. Contacts were expected to be developed in that configuration.
Swdw in Real Fleet Boat has come up with a great solution to any problems. The sonar begins working at a depth of 20' to 25', decks awash. At this depth you are on the surface but are unable to go faster than 10 knots. At this speed the sonar would clearly work. American boats had supersonic sonar heads under the hull.
The U-Boats might have some kind of crossover with Fleet Boat sonar functionality. If you're talking about them, you'll have to find a GWXer. They're the experts on U-Boat sonar.
Edit and new findings: Here's
the link to the no surface sonar on U-Boat mod. I think kapitan_zur_see is a GWXer, so you may be onto something with the U-Boat. It also appears that his mod only works on the U-Boat and not on the Fleet Boat. That's evidence of good game design! I may be loading up this mod myself!