We have two separate autopilot computers and two separate autopilot drives.
Each computer output goes to a rotary switch so you can select if you wish to use the Raytheon T-300 autopilot computer or if you wish to use the B&G AC42 computer.
The output from that switch then goes into an identical rotary switch so you can select if you wish to use the Raymarine rotary drive or the Raymarine linear drive.
Because of the two rotary switches, you can use the B&G autopilot with either the rotary or the linear drive, and you can use the Raytheon autopilot with the rotary or the linear drive as well.
Key to having two separate systems is that each system has its own sensors. Otherwise, if both systems use the same sensors and they go down... then both computers will be disabled. So the B&G is on a NMEA 2000 network and has access to the boat's NMEA 2000 heading sensor, wind sensor, GPS, autopilot controls and displays, and its own rudder position sensor. The Raytheon has access to the NMEA 2000 network data, but in its absence, it can perfectly steer to a magnetic target because it has its own dedicated gyro, compass, rudder sensor, and its own keypad and display, as well as a Raymarine SmartController wireless remote control. When the NMEA 2000 net is disabled, the Raytheon in our configuration loses the ability to autopilot to a wind angle because we discarded the boat's factory original Raymarine wind sensor.
In the aft quadrant the Amel factory already had the Raymarine rudder sensor occupying one side of the quadrant. The B&G rudder sensor was installed upside down (reversed) on the other side of the quadrant, and fortunately there is a setting in the software for exactly this situation.
SM2K Nr. 350 (2002)
At anchor, La Maddalena, Sardinia