I presume a submarine
must gain speed in steep dive, just like an aircraft gains airspeed in this way.
Gravity is slightly reduced in water, but not by all that by much.
Is this modelled in SH3/4? I have never thought to really monitor My boats submerged speed while diving or accending.
Does the boat accellerate and still continue at a higher than normal speed after levelling off (having gained momentum), then gradually reduce speed down to whatever RPMs your electrics are driving?
IN SH3/4 I never noticed the effects of gravity or physics simulated in thii way, but then I was never looking for it.....
Then again, maybe my theroy is wrong?