Forgot to mention, as long as you're modding might as well fix the "going deep" part - stock SH4 programming shows that the developers read the wrong books, the diving time is realistic only for a new boat with a new crew who hasn't done any drilling on fast dives yet. Actual time to periscope depth for even a big fleet boat was 30-35 seconds, not 2-3 minutes.
Find the ballast flood speeds in the sim files, make them about double then time standard "periscope depth" P key and "crash dive" C key from fully surfaced with the stopwatch, adjust as desired.