Hydrophone surface range

[Inajira]

I read it on these boards recently that the hydrophones have a very short range while the boat is surfaced. I was under the impression that they did not function at all while surfaced. I tried testing this during night attacks in the fog and rain (one cannot rely on much else), and found I could not pick up ships even under 1NM distance. So is there a range while surfaced or not?