1) I don't think i've ever been on anything bigger than the Woolwich Ferry
Must fix that one day and book myself a cruise on a big liner.
2) The different sound files of the tankers compared to merchants may be partly due to them being wider than the cargo's and merchants then, therefore displacing water at a wider angle - flow noise. And possibly different prop sizes/numbers.
By the same token a 10,000 ton ship should create a different flow noise to a 5,000 ton ship due to the width and length of hull , number/size of props etc.
3) which would result in benefits to the game players in building up experience at the sonar station to differentiate between the different hydro sounds, IF there were more subtle variations in the sounds.
4) If the reports stayed the same, see 3) above

.
Saves the game doing the work for you. If you don't wanna waste your time chasing useless contacts, get on the sonar yourself.
Yes PT, i'd be happy to.
Had a look on your "version 3.2" thread and noticed the comment for V4 says " New multiple hydrophone engine sounds". Seems you're on the case already. Thanks dude
Couldn't find the download of V4 on your filefront page tho.