Thanks for your reply Rick.  This is what I want - a constructive and critical dialogue.  I won't focus here on the specifics of my boat other than that it's a finite element engineered structure designed for foiling, 3 tonne stripped down displacement, capacity for over 5 tonne.  Bruce number of 2 and planned high L/D from a wing rig and foils.

When it comes to foiling, the foils must support the weight of the boat, so angle of attack is required. Secondly, if these foils are steering V foils situated at the bow and stern then they must cope with a wide range of attack angles.  They then should be set up to principally operate within the most efficient attack range.  The V foil does this by reaching equilibrium between required lift, lifting surface area and angle of attack (lift coefficient).  The fully immersed T foil is only more efficient within a narrow speed range - a T foil set at low attack at high speed will, it is generally argued, be less efficient than a V foil set at the optimal angle of attack (best L/D).  It is possible to get the foils efficient at a slightly lower angle of attack - thinner, less camber - but this reduces the attack angle range at which they will operate.  C-fly are using super-ventilating wedge bow foils (at a high attack angle) for the reason that the bow foil is subject to wide attack angles.

V-foils damp pitching and heave, due to the reserve surface area.  Tom Speer and others have discussed the importance of pitch stability and that it is obtained by more heavily loading the forward foil.  This is a straightforward concept where the main foil is under the centre of mass and is achieved by making the rudder foil larger than would be the case for even loading, thereby enabling it to be set at a lower angle of attack.  But it happens naturally with foils at each end of the craft - due to the pitching force generated by the rig.

What you're saying is more likely to apply to the rear foil which is more lightly loaded.  Even pitch will require a reduced angle of attack at the rear foil.  I have not yet established how much attack should be applied to maximise pitch stability.

Will heavily loaded foils hum?  Rudders spend most of their time near centred (relatively light loading) where Xfoil shows the asymmetric Speer foil to be less effective (the symmetric proa foil has a pronounced drag bucket (low drag) centred between +-1 degree).  I'll discuss the drag bucket more when I post my rudder results.  I don't know the answer to this question.  More research required.  Maybe a 3d CFD analysis - considering aeroelastic behaviour may well yield some answers, but analysing the effects at the water surface may prove to be both difficult and highly speculative.  A V diamond shape will generate additional rigidity.

Rotating a  T foil through 180 degrees and enabling kickup is problematic.  I've already discussed the weight problems associated with providing hull clearance.  I haven't ruled out a ladder T - but lean toward V.  I'm not interested in setting up wands and trying to rotate thru 180 degrees.  If I use a ladder it may well be along the lines used in P28 Gonnet et Cie or Monitor.  These could entail two rudders either side of the hull with a central pivot, the foil being pivoted over these rudders and retracted when not foiling.  A release and tether mechanism in the event of a collision.

Your observations re asymmetric rudders are instructive as I've been musing on these matters as well.

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