: Chris, I always look forward to your advise in what I am trying to do since
: this is your area of expertise and experience.

John,

You are always welcome to ask any question you like. I really like what you are doing with your problem solving actions as you develop your own boat to this end.

: Going to an 0012 now wouldn't be good for me now since I have my glued up oak
: boards planned to the 15/16 inch thickness already for the 0009, and this
: thickness just fits my aluminum rudder housing already made. If I glued on
: another three inches to the back end of the rudder and used the 0009 foil
: shape, would that cause problems or would it kinda of work. To be honest I
: would like to have more wetted surface that a rudder 12 inches wide would
: give me with out going any deeper to get more wetted surface. If necessary
: I could glue thin slats where the thickest area of the rudder would be for
: 0012 foil. I'm not sure what that size would be right now. Probably just
: over 1 inch plus.

Then, by all means, leave it the way it is for now and get out on the water for testing when spring comes back to us in this hemisphere. If you experience a detached flow from a stalled rudder, you'll know it as there won't be any tiller response and the boat will go where it may on its own. The issue will be most pronounced at slow speed, if it is present, but you have a decent amount of chord in thae described blade to negate a good deal of that problem.

: If I do, I would make it near Balogh's 38 sq. feet batwing, which has a
: luff of 11 feet and a foot at 4 feet 3 inches. He warns that this is too
: much sail for most. Do you think it is?

The batwing aspect ratio and sail area evolved due to several design needs.

One: The ability to store the sail, comfortably, within the boat hull.
Where does one put a rig with a much longer foot inside the boat? He doesn't.

Two: How much drive can the typical kayak absorb, especially on downwind angles when the sail force vector is driving over the boat at a forward oriented angle of about 45 degrees? Not much, is the answer here as kayaks are not known for having very much forward buoyancy when confronted with the large power that can come from a sail rig. A 50 sq. ft. sail (keeping the numbers simple for reference)can generate 1 hp. Compare that to the power of a fit human with a paddle at one fourth of that potential. And, the sail rig just keeps generating that kind of power as long as the wind is blowing, where a human will see a loss of power as time wears on.

A human will not be able to drive the bow of the typical sea kayak down on flat water, leading to a pitchpole capsize. A sail rig is capable of that kind of power, especially when one considers the lever arm of the mast length, multiplying the forces present.

Three: this is a small craft in any measure of the word and sudden, upward wind strength changes can create huge problems for a boat that is flying too big of a sail that cannot be reduced in size with some quickness. The bigger the sail, the longer it takes to get it down and under control. Reefing is a significant capability when you are offshore farther than you want to (or can) swim.

So, the answer is to not over-power the boat in those conditions and this is where a practical limit in sail area originates. I tend to keep the sail area on a kayak in the 38-50 sq. ft. range, depending on ama size and position, reefing ability and prevalent conditions for an area. The higher the normal wind, the smaller the standard sail.

Properly rigged, you'll get an nice sailing machine that can surprise you with the distances it can cover in a short period of time. It can also be paddled by simply putting your rig away. All that and it car tops easily and can be handled by one person. Not many boats can do that with any grace.