Can't use hydrophone?

[UKönig]

Originally Posted by Marcello

In real life GHG receivers were located around the forward diving plane, so they would be underwater even when the submarine was surfaced.
Thus they might still hear something albeit nowhere near as good as at depth.

I put those on the 125 scale model of the U99 that I did. The original hull did not include those, but I knew they were there.
You're likely correct too, the GHG probably would work from time to time while you were on the surface, but, you couldn't be going very fast, or else the water rushing over your own receivers would deafen them. It's worth to consider when searching for ships...