I've been toying around with that as well, lol
what I did come up with so far is this:
your average destroyer is round about 100 meters long. 195/time it needs to cross your view = speed (roughly)
this comes out reasonably accurate, launch fast eel x degrees ahead or slow eel 2x degrees ahead has scored me several hits so far
i suck at math tho, completely unable to come up with a definitive solution for the value
