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  Topic Review (Newest First)
09-22-2009 12:40 PM
Servo-rudder with tiller autopilot - a good idea?

My Southern Cross 31 has an Autohelm 2000 tiller autopilot. As is often the case, this autopilot does not have the power or throw to handle the boat in confused seas while running. Nigel Calder in his book describes a modification he made to his boat to deal with this problem: he fitted a servo (or trim) rudder to the trailing edge of the boat's rudder. He inserted a pipe into his tiller arm perpendicular to the arm, and he mounted a tiller autopilot to the pipe. So the tiller, pipe, and autopilot swing as one unit. The autopilot's arm is connected to a series of bellcranks that actuate the servo rudder. He says that the autopilot needs to generate only about one pound of force to handle his much-bigger boat in challenging conditions. Do you have experience with such a rig?

As background, the Southern Cross 31 is a nearly full-keel, 14,000-pound, double-ender. The rudder is entirely external to the hull, it is driven by a tiller, and its trailing edge forms a line that, when extended upwards, just clears the rudder stock. The Autohelm unit has separate actuator, control head, and flux gate subunits. Installing Calder's rig would seem to be a relatively straightforward job on this boat. Relative to a windvane, this setup would seem to have a lot of advantages, and the only big disadvantage I can think of is (thereby reduced) power consumption. Yet I don't recall ever seeing a boat so equipped. Am I missing some show-stopping drawback?

Lastly, can you think of someone in mid-coast Maine who would do a good job of making this modification?

Thanks for considering these questions.

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