"hydrophones" can, yes. U-boat hydrophones can't. A DD has its hydrophones on the keel, that's why it can't hear crap on the surface level. German hydrophones can technically hear things while the boat is surface, but unless the engines are stopped and the sea is mirror like, all you would hear is yourself and the waves, so the fact that you can hear as clearly on the surface + diesel engines as you do submerged + electric engine is a bug. And if you happen to have a KDB, it's located on the deck, so yes hearing propeller noise with it while on the surface is definitely a bug.
Man do I hate it when people brag about "physic class" and the like when it's just about research and reading. Besides dozens of people of NYGM, GWX, WAC and others have been researching exacty that for about 4 years, I guess they all missed physic class as well
