Are you referring to the SubName.sim file Niume, under the "unit_submarine" nodes, the front_ and rear_diveplane with the "drag=0.02" and "prop_fact=0.0" or maybe 0.05? I am not certain, but if I remember correctly, the "drag" was how much using the diveplanes being used slowed your depth change and speed, and the prop_fact is for how much the speed of the prop spin (hence the speed of the boat) affected dive and rise times. The rear planes on a some subs are right there with the rudder behind the props, and would utilize the prop wash more "efficiently" to help change depth. This is from memory of an ETR3(SS) note on one of his sub mods... brain matter here deemed unreliable at data recovery...
- notice though that the numbers are using hundredths... but of what? for what? a multiplier? dunno