Re: Now I need trimtab help
Let me give it a try (though without a diagram). You need to figure out where the imaginary line that continues your main rudder pintle pins is at the height of the tiller on the trim tab. A long straight-edge clamped alongside the rudder pintles should likely work OK (Make sure it is really straight when in position!). Measure the distance from the trim-tab shaft to this line from the straight edge along the trim-tab tiller. The linkage should attach 80% of that distance along the tiller from the trim-tab shaft.
If the forward edge of the rudder is straight and parallel to the pintles all the way to the position of the trim-tab tiller (as the drawing implies), you could just measure the offset of the pintle centers from that rudder edge and use that to figure out the needed distance.
In any case, the linkage attachment needs to be *behind* the axis of the rudder pintles to get the correct feedback.