Many thanks, Kpt. Lehmann for your reply... and to everyone else for their input / suggestions. Got my hard-earned KptLt rank back.
Quantifying this renown-generated rank advancement (or reduction) will make me think twice before spending another 9,000 on a shiny, new U-boat (and leaving moths in my BdU bank account). On the flip-side, saving it will give me something to shoot for promotion-wise. Maybe someone should mod a renown "overdraft protection" system... because getting demoted (even temporarily) positively blows prop-mangled tuna chunks.
Happy 4th of July Weekend to all (if you are celebrating it)!
Cheers,
Easy_Eight65