Talador wrote: “If the proa's rudders rotated 180˚ when shunted it would be trivial to set up NACA GOE611 airfoils angled so that the aft foil generated less lift than the forward foil.”

For a start, it’s not trivial to rotate a rudder through 180 degrees.  At least in the configuration I envisage.  This config sees the foils mounted on stub beams fairly close to the extreme ends of the craft in order to increase pitch stability.  The loads that these foils subject upon hull and stub beam are not trivial.  A finite element analysis demonstrates this.  If you need to rotate thru 180 degrees, the stub beam is longer, increasing the loads.  A symmetrical lifting foil has span.  If kickup is required then the kickup pivot must be angled outward so the foil will kickup outward and clear the hull.  I’m exploring doing all these things but it ain’t trivial.  (Note that you said “trivial to set up)

Talador wrote: “I thought I was very clear, A GOE611 foil with the leading foil angled upwards a couple of degrees and the trailing GOE611 angled downward a few degrees at the bottom of their respective rudder. Do you need the polars?”

Not clear.  No need for polars.  The clarity issue related to pitch stability, not angle through rotation – read what I said.  This depends upon foil config.  I must presume you are referring to T foils without active flap control – a conclusion that depends upon a missing premise in your argument (which is generally a sign that the argument suffers from confirmation bias).  Did you read the links I provided?  Your comments here are at odds with the pitch and heave stability achieved by C-Fly.  Further, although I don’t like the J foils for offshore wave profiling, they are pitch and heave stable (if the rudder angle can be adjusted and wave length is substantially shorter than the foil separation) through leeway modulation (if you don’t know what this is find out what Tom Speer has said on Boat Design forum and watch the Battle of the Bats video link I provided  few days ago).  The asymmetric configuration is not upon first inspection, particularly suited to rotating thru 180 degrees.

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Talador wrote: “The reason it is unstable is because without the hull dampening effect there is no altitude control and it will porpoise.” 

This statement fails to address the pitch and heave stability of surface piercing foils – again refer to C-Fly.  You cannot directly translate experiences from air planes to foil borne craft.  Foil borne sailing craft are operating at the boundary of two fluids of substantially different density.  Surface piercing foils take advantage of this change in density.

Talador wrote: “I have built airplanes with canards and they are designed to porpoise. That is how they prevent stalling.  The canard loses lift before the main wing can stall.” 

Again a certain degree of confirmation bias is present.  You are presuming that a canard foiled boat will exhibit the same characteristics – and that this porpoising is a problem.  If a surface piercing canard loses lift it will sink somewhat, decrease its angle of attack and increase its surface area. As the canard pushes through a wave it will lift the bow, correcting the angle of attack of the main foil (initially).  Having broken through the wave the canard reduces lift area and increases attack angle, potentially stalling and sinking before increased area and reducing attack angle, leading to recovery.  While the main foil remains behind the wave crest, the increased angle of attack may precipitate a stall.  So what!  The middle of the hull settles into the wave crest, reducing the angle of attack of the canard (and the likelihood of stall) as it reaches the trough.  Again your assumptions are incorrect in this environment.

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