[CaptainHaplo]

SH4 does the same as SH3 in many ways - this included (to a point).

Your speed does contribute - but only to a certain extent. The vast majority of up and down speed comes from displacement calculations. To change the rate of rise and sink - you actually modify the displacement, ballast tanks and tank fill rate.

By tweaking these values, you can make speed become more of a factor. However, its a balancing act. Too big a ballast tank makes for a yoyo effect - too small makes things too slow. Same effect with the flooding time. You have to balance them both to get a nearly neutral effect - along with vessel displacement. Once you start there - you also start affecting other things like fuel consumption, etc. Its a complex problem that CAN be worked on.