Some months ago I ordered a linear actuator from aliexpress. I recently have been sailing using it, and it has the specifications:
speed: 170mm/s
force: 50N
range: 300mm
https://www.aliexpress.com/item/2255800497051447.html
This turns out to be a quite fast movement speed, and to compound matters, the distance from the attachment to the rudder is only 14 inches instead of the usual 18 or 24 inches. What this means, is it is too fast, as half-speed movement for 200 milliseconds already makes the boat react significantly. I would have done better with a lower speed! Anyway I will increase the distance (and leverage) at the reduction of speed. It can do full range of rudder movement in 1.5 seconds, as beyond 25 degrees or so the rudder stalls (useful for braking but pypilot doesnt know about that yet)
The motor did not seem to get warm at all in use. This is sailing speeds 8-10 knots.
To get acceptable steering I had to adjust the default gains to be much lower.
ap.pilot.basic.D = 0.0192
ap.pilot.basic.DD = 0.0088
ap.pilot.basic.FF = 0.4943
ap.pilot.basic.I = 0
ap.pilot.basic.P = 0.0017
ap.pilot.basic.PR = 0.0017
Compare these to the gains on your boat.