It is not that hard to find ships in the coastal waters.
But I have never edited the hydrophones on the U-boat before, only on ships, so I cannot be sure on how well it will work.
I made an attempt many months ago, it gives the hydrophone 100 km of listen distance (Only for the AI operator) so you should get the lines pointing to them at 100 km.
As I said before, I cannot guarantee the effectiveness.
http://www.mediafire.com/download/va...ot_Sensors.sim
This link should contain the download.