Yes, I know that method also, however, the stadimeter is broken so you can not find the distance. This is my problem, there are two ways to calculate speed. One requires knowing the ships length (which the game does not give you), the other is being able to mark its exact position on the map, and the range finder is broken.
You said on your original post that you weren't using any major mods, I assumed the standard game had ship markers on the map to make it more accessable to normal players. Thats why I suggested the 3.15 method. Also I seem to remember reading that the weapons officer gives you things like range etc if the realism settings are turned off.
The only way I know without identifying the target first is the 4 bearing method. You dont have to even surface your ship with this method. But, considering you dont want or can't identify a ship I doubt this method is for you.
Im confused with your posts really, I find it hard to see how base game can provide a identification book and not put ship length in it, but, I have never played any time on standard game I knew to stay away from it. It is completely littered with bugs and everything I have read suggests its unplayable with the tonnage bar bug.
Your main concern I have read is that the stadimeter is broke. I found this in the mods section >
https://www.subsim.com/radioroom/sho...d.php?t=171615
Hope this helps.