Outboard Motor Auto Pilot

I would like to make an auto pilot for my boat. This is a wide shot of the stern to get a general overall feeling for the space involved.

BCC_W Stern view.

This is a detail of the interface of the steering control arm and the Mercury 85hp motor.

OAP_Detail

Detail view of the stern. Note where the control arm meets the meets the control horn on the motor.

 

 

 

 

 

Question: What might I use for the actuator. I’d like to stay away from hydraulics on this small of a project.

 

OAP_horn_Detail OAP_Engine_Mount_Detail

Notice the bolt (left picture) at the center that connects the motor to the steering control arm. Here is a detail showing there is enough room to perhaps get another thingie of some sort attached. Plenty of room to change bolts (right picture) to allow some bracket to hold the house for the thingie!

So what might we use for a thingie? Worm drive? Mega stepper? Help!