Okay, I'm still hung up on a paddle-wheel submersible.
If the vanes swivel, assume clockwise motion while moving left to right. Vanes at 9 and 3, / + \; vanes at 12 and 6:
_
+
I
with small adjustments to maintain trim, making one half rotation per 'clock'.
Insane?
Still say it'd make a great surface excursion boat!
Doug