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The surface area of the trim tab will be 20% of the effective surface area of the rudder; both the upper and the lower sections of the trim tab will do work. Based on my research, this ratio is traditional and conservative.
The trim tab's action is pretty similar to what the servopendulum achieves - it's a sort of power steering system that deflects the flow, using the motion of the boat to turn the rudder. It will make it possible for the wimpy Simrad (no insult intended; it's a wonderful device, just not that powerful) to drive this boat in quartering seas (which currently require yours truly to man the helm for hours on end, sometimes to the point of utter exhaustion).
As far as the pintle/gudgeon business, I am thinking of eliminating them with a set of interlaced tabs between the back of the rudder blade and the front of the lower section of the trim tab, run through with stainless steel tube and nylon bushings, and staked together with stainless steel rod. That's how the whole rudder is hung on this boat. Built like a tank, I tell you! The rudder even has a swim step built as part of it.
The guy I bought this boat from said: "Most of the steering on Hogfish is done with the feet." At the time, I thought he was being funny; not any more. I've spent too many hours tucked into the cockpit, with both feet on the tiller. This boat NEEDS power steering, which is what I hope to get out of the trim tab, in addition to all the other advantages (more steerage when maneuvering, wind vane, ability to use autohelm more of the time).
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