Thus, max width at that section is 1.2 inches. The rudder blade is a pretty good design and fabrication project - similar to building a hull shape as it is continually changing from top to bottom, fore to aft, and presumably maintaining NACA 0012 shape for most of the blade. I haven't checked other sections to see how well the mold was made, nor have I checked side to side symmetry. Can't find my profile match gauge since the fire.You may have to compromise at the trailing edge, like Roger apparently did, to keep it thick enough to hold together.
Anyway, I'm not an aeronautical or marine engineer, nor am I a naval architect. But, I did get thrown out of a holiday inn last night. The body of knowledge on rudder design appears to be extensive, and the little bit I've reviewed shows a lot of variation from one source to the next regarding shape, size, foil/flat, mounting position, canted/vertical, single vs twin, etc.
One source stated that rudder size should be 1-2% of sail plan area. Based on a 241 sf sail plan (I didn't verify this number) and wetted area of both rudders of about 4.2 sf, the M has about 1.7% rudders (not accounting for heeling). So, it looks like Roger didn't wander too far off the path on the rudder area decision, anyway.
The wetted height/width aspect ratio of approx 3, is on the high side of at least one source's recommendation. This source says 2 is upper limit unless you're building high performance, which might get up to 3-4 range. Higher aspect ratios are reportedly prone to stalling at lower attack angles compared to lower aspect ratio rudders. This might be an area where some improvement could be made. Anybody got one of those exercise pools with a 5 knot current in it? All we'd need is a scale hull model and a selection of rudder shapes, and we could take a crack at figuring out what a better rudder might look like. My guess is, Roger didn't do a lot of tank testing on rudder design - due to the expense of it. We did some model testing on some of the labs we worked on and I was always amazed at the expense of it. If you feel that stock rudders are a problem, you could build a couple of different shapes and sizes and try them out. You wouldn't need to even put a finish on them as long as they are faired. That is one area most sources agree on - fairing is important.
Again, I'm not posing as a marine engineer, just relating what I found during my enjoyment of this thread.
