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Autopilot drive mounting question
(I'm cross posting this from another site; I'm the author; trying ot get more input).
The orthodoxy of below-decks autopilots is that the linear drive be connected to a separate tiller arm that is attached to the rudder post, and not to the existing radial drive.
For those of you not familiar with this setup, I am referring to boat that have vertical rudder posts that are steered with Edson wheel steering, using a circular, cable-driven fixture called a radial drive - like a quadrant that simply goes all 360 degrees.
Edson's recommended bronze tiller arm is a whopping $417! That's the direct price, and for the C-36 unit with 2.860" bore for rudder post, there is no machining charge.
Edson warns against attaching to the radial drive, but gives no compelling reason.
"In no case should the autopilot be attached directly to the quadrant or radial drive wheel!"
I think it's just because they want to sell tiller arms! One purported reason for the tiller arm is that in the event of a steering system failure, the autopilot provides a backup. But, with the linear drive on the radial drive, which is directly connected to the rudder post, there seems to be nothing in the path to break except the radial drive itself, which seems quite robust.
I can only imagine that the radial drive is strong enough to be driven by the linear drive, especially since Edson puts a rudder stop right on the top outside edge of the drive, which can presumably absorb the rudder force in that condition.
As a matter of fact, that rudder stop might be a good place to attach the linear drive, and then make an alternate rudder stop solution.
So, my question is, what are your thoughts on just connecting to the radial drive, and skipping the separate tiller arm?