I just can't stop playing with it. Here is another version
http://roger.questions.cz/other/sim3.zip
It has bank autopilot (B key) which tries to hold sail up.
It also has pitch angle and depth autopilot, just set desired depth or angle (both has shortcuts too, check the readme). Any manual input to controls will switch of corresponding autopilot (planes to angle or depth, rudder to course, bank to bank).
All autopilots reacts based on speed, they use larger elevations at slow speed. It's harder to loose control with them, but not impossible. All autopilots are very simple now.
Note that all autopilots now work only around 'normal' conditions, and only with forward movement. Anyway if you find some really strange behavior, let me know.