John,
I'm pleased if some of this is useful. I have worked from the original blade from my Sinbad which is sitting patiently on a cradle in Woodbridge. I am in deepest Leicestershire and brought the tiller, stock and rudder blade home as the latter is corroded and bent.
The blade is 1210mm or 47 3/4"inches high and weighs 21kgs or 46lbs. Well mine does anyway! If you have tried to scale it up from the previous drawing it will come up around 50mm short. That will be corrected.
I took a photo of the blade, imported the pic into a CAD drawing and traced around it. Then I measured the stock and drew that too, with emphasis on the relationship between the pivot hole and large radius. When I overlayed the stock and blade they didn't fit! :-(
Not a problem, I just played around with the blade drawing until it did. To prove it I printed the top part of the blade drawing at 1:1 to make a template and cut it out of 3mm ply (an old draw base, every one has one in their garage don't they?). I drilled the pivot hole and it fits!
But the proof of the pudding and all that.... I could end up looking rather silly now if the laser cut item doesn't fit!
Still, I have plenty of time to think of excuses and a large hammer to adjust it.
I too thought about adding a bit to the leading edge but as the attached drawing shows, (if correct; maybe someone else could confirm?) there is already a little in front of the pivot line. The writer (page 13 of the manual) seems to intimate there is none as standard. I read in a Googled article that too much can have an adverse effect so as a novice, I'm bottling out of that one. The pivot detail on the drawing is not thorough; just indicative, but the dotted line is clear enough.
My goal is to get the boat sailing first with a few compromises between time and mods. I dream that one day I may even be experienced enough to tell the difference between a good and bad rudder!
Floyd