The autopilot drive unit in Sol Purpose is an old Smith Industries unit that dates back to 1993. As the boat was built in 1994 I have to assume that the unit is the original unit that came with the boat. It is built like a tank and so was never replaced when we overhauled the electronics back in 2013. When installed, they cut a section out of the upper rudder bearing support structure to allow the drive unit piston access to the quadrant. The autopilot mount was then attached to this structure. This wooden frame that is more implied than shown in the diagram below.
Over the years, the constant action of the autopilot has flexed the support structure enough times that the motion is greater than I am comfortable with and so I decided to attach a secondary mount to the hull outboard of the current support. This was made easier by the fact that the bracket that supports the drive unit is much longer than needed and almost reaches to the hull already.
I fabricated a mount out of marine ply and covered it with three layers of woven and chopped strand mat. I then removed all the bilge coat from the location on the hull that I intended to place the mount and glassed the mount onto the hull so as to sit beneath the support bracket.
With the dry fit of the support bracket checked, I then gave it several coats of bilge paint and reattached the support bracket, drive unit and assembled all wiring.
Once completed, the admiral ran the unit through its paces and I verified that there was no longer any flexing of the structure. We might even find that the autopilot tracks more accurately as the lack of flex should give better feedback from the heading sensor to the course computer. Only time will tell…