I'm playing SH3 with GWX and MaGui.
- To control the RPM you could input a specific speed in knot, usually 2 kts is considered silent (IIRC <100 RPM), if you want to be extra silent command 1 knot speed.
- To run deck awash try setting your depth as close as possible but not equal nor greater than 8 meters. At exactley 8 meters, in my experience, the uboat is considered submerged.
- Finally, very important: to command an exact value in the dials don't click:
keep the left mouse button clicked down and you will be able to preview the final position of the needle in the dial, you can then micro-adjust the needle posiont
with small mouse movements and when the needle position is exactley where you want it to be,
release the left mouse button et voilą 