Counting the rotations ???
 

I remember reading in a few books, both u-boat and fleet boats, the hydro guys were able to get pretty accurate speed readings by counting the rotations of the screws/rpm's

Many times the sound guy would give an estimate of the sound and after the captain/firing team checked, it was always pretty accurate.


Can it be done in this game?

No it only has two speeds slow for merchants and fast for warships.