I have to believe the set screw idea is working for you guys but it sounds risky.

That said I have no idea what's holding the control arm for auto onto my rudder stock. It could just be all that rust?

I'm always a little worried about what happens should my autopilot installation fail. What if the rudder reference fails or slips out of position? What if the control arm spins on the rudder stock? Does the autopilot ram shove the rudder over too far and damage the rudder and boat? Do we start to sink? Does someone in the cockpit get crushed by the tiller?

I worked up a PID controller for an autopilot design on my model boat. In the process I did a fair amount of research trying to understand full sized autopilots which is hard because nobody in the marine industry wants customers to understand how systems work.

I'm not a hydraulic guy so can't speak with authority but it seems to me that the hydraulic rams in use aren't very safe and safety could be built into the system by having limits on the pressure in the system. You can also get hydraulic cylinders with built in position indicators which would remove the super expensive rudder reference and associated delicate linkages.

If/when my real autopilot fails I plan to pull the whole system and take it home to reverse engineer it. I believe autopilots can be much better and safer if not cheaper. If it were up to me I'd have a pressure monitor and if it went higher than is reasonable the system would shut down.

Has anybody ever had a failure of this kind? It seems like it must happen pretty frequently.