for control. Anyhow I envision a couple different modes of operation. The simplest is just "keep the boat pointed that way" and this should be built into a dumb controller that works by itself using just the compass and tiller position data. So the autopilot needs a microcontroller to do this.
A more advanced strategy would be to have a computer figure out corrected headings based on actual boat motion to compensate for current/leeway and allow the boat to track a course. Final goal is I should be able to punch in lat/long and boat simply goes there - using charts and radar to avoid traffic/obstacles.
While I distrust technology - I think a staged and distributed approach will be best with each system fully manual, dumb semi-automatic (state maintaining), and then smart central control to tell the dumb systems what their states should be. This way, if the main computer dies, I only have to babysit the systems from time to time. Ditto if a subsystem (steering, motor control, whatever) fails.
Sort of a smart home approach for boats. Commodity parts for ease of replacement will be favored wherever possible.