One interesting feature of this linkage is that it makes it possible to switch between wheel steering and tillerpilot steering at the pedestal. The wheel can be disconnected from the steering linkage simply by pulling back on it, causing the pinion gear splined to its shaft to disconnect from the rack which it drives. This is useful, because it lessens the inertial load on the tillerpilot from the angular momentum of the wheel. My preferred tillerpilot (Simrad TP32) can generate up to 100 lbs of force, but with considerable power drain and wear. With the wheel disconnected, the force required from it will be low, because the linkage is of lightweight aluminum and the rudders are balanced.
Referring to the schematic diagram below, the green vertical plane on the left is the transom. The two rudder shafts are mounted to the outside of it, using brackets. Each rudder shaft is joined to a tiller through a horizontal pivot (axes of the pivot points are shown in blue) and each tiller is joined to one end of a tie-rod using vertical pivots. At its center the tie-rod is joined to the aft whip-stalk using a two-axis pivot (left/right and fore/aft). Steering action is indicated using red and green arrows (red for starboard, green for port).
The forward whipstalk is connected directly to the steering shaft inside the pedestal. At the top of the forward whipstalk is a rack, which is moved left/right by a pinion gear splined to the wheel shaft. The forward whip-stalk also holds a pin (not shown) for mounting a tillerpilot. Before engaging the tillerpilot, the tip of its telescoping arm is snapped onto the pin, and the wheel is pulled back on its shaft, disengaging the pinion from the rack in order to reduce the load on the tillerpilot.
Magenta arrows indicate the action of the brake lever. When actuated, it introduces a bend into the aft whipstalk, making it shorter. In turn, this causes the two tillers to pivot down. Because of the angle of the rudder posts, this has the effect of towing in the rudder blades by a few degrees.