Hydrophone RPM: propeller or engine?
 

I am trying out Greyrider's en Raduz' hydrophone stuff.
Now I'm wondering, I read about listening on the hydrophone to propeller sounds, but I believe it's actually the engine you are hearing.

For example:
- A C2 has three prop blades. Yet you hear: Chug-chug-chug-chug.
- Shoot off the propeller with a torpedo or deck gun. The ship comes to a stop, but you still hear it on the hydrophone. Shoot up the engine compartment and it will silence.

:hmm: