Invader 22
My main site home allsorts *** *** The Rudder

Once you have the template - the easiet way to go is to epoxy fair an exact profile narrow band, top and bottom of the rudder. Then fair between the two with a straight edge. The trailing edge is not so important - and if made simply from timber this trailing edge would be too thin, strength wise. If you are epoxy fairing timber, then the edge could be solid epoxy
A Sad Looking Rudder - but a nice piece of wood !

Well - this is the rudder as it is. Not too pretty a sight. The actual gudgeons and pintles are fine - heavy cast bronze - and the stainless continuous bar fitment is sound, though would be better fixed than just with split pins - maybe just a small through bolt at the top to avoid any possibility of the bar dropping.
The upper fitment would be better, imho, sitting on top of the upper transom fitting.
Not the original - I presume. The kick forward is strange and the feathering aft starts way below waterline. But it 's a sound mahogany plank.
Courtesy of the Snapdragon Owners Ass - and a scale diagram of a 670 - essentially identical to the Invader - I have an outline of the original rudder section - I've outlined it below.

This make much more sence - it's a constant line aft and generally slopes aft, although is a parallel shape.

I'm considering modifying this board - essentially by planting in 4 x 40mm reversed strips of mahog straight down through the middle, where the max thickness is. Then I can reprofile the leading and trailing edges easier - probably with epoxy fairing. I can also tuck the rudder in somewhat more to the transome.

There is an exellent profile freeware program - search 'Nacagen'. The program opens in a dos window - but gives you all the thicknessing measurments. I'm a bit foggy with dos, ie. I'm not sure how to print a dos window - if you can ?. However, the 'print screen' button trick works - simply press 'print screen' - open an image editing program such as photoshop, open a blank file, then 'edit/paste'. Left is an example - based on the NACA 0012 profile - which trial an error gave results for my present thickness of 35mm on a chord ( width) of 13.5 inches.

Once you have pasted it into photoshop - you can invert it, as it is here ( it pastes as a black dos window with white text ) - then I placed it into an A3 Illustrator doc so I could print it out on two A4 sheets full size to use as a template. You could of course draw it up from the info - but it's all in 100ths inch !

The leading edge is the important bit - apparently and the position of the thickest section.
Yet another little project to fight with around the weather !