Keeping submarine still without any human intervention since the start of the round.

What the subject says. Note: manually enabling autopilot counts as human intervention.

I tried: enabling autopilot in nav terminal in sub editor, but it seems like autopilot settings don't get saved so the sub starts with autopilot off.
Also tried setting ballast pump targetlevel to neutral ballast level, it kinda works but it only keeps sub from accelerating upwards after it fills, it doesn't stop the speed it gained while it was still empty, the sub just drifts upwards that way instead of stopping in place. Also neutral level shows only to the 1% precision, you usually get target level a part of percent off of real neutral level so the sub starts to slowly sink or continues to move upwards after it mostly stops.

Any other ideas?