There's been some discussion concerning the difficulty of setting up foils on a proa.  Shunting, mass distribution and complexity create unique challenges.  Yet on two critical grounds the proa qualifies at the front of the pack: Bruce number and L/D ratios.  Without smothering the craft in ladder foils, foiling requires high power to weight in order to fly, and high L/D in order to go fast enough to fly.  The rest is engineering innovation – and without the right Bruce number and L/D, engineering isn’t going to get you very far.

I’m not going to go into any great detail concerning what may or may not work, other than observing that only one windward foil is required.  The only goal of this foil is to provide lift to a relatively short windward hull, which has no pretensions toward providing pitch stability, and which presumably is close to flying anyway.  The other foils would need to provide lift, pitch and yaw control.  The beauty of the proa is that foils can be placed a long way apart on the long leeward hull in order to control pitch.  This can be contrasted against a conventionally placed rudder with main foil near the CLR of the rig which necessarily places large pitching loads upon relatively closely spaced foils.  This fails to take advantage of waterline length.  In my opinion, this configuration is the result of two factors.  Firstly, it doesn’t involve a radical departure from the conventional rudder-daggerboard configuration, so can provide similar handling characteristics.  The concept works well when seeking extreme performance – but only on fairly protected waters. C-Fly and Trifoiler are exceptions to this foil placement convention.

The two foil proa has already departed from convention because one foil is always significantly in front of the centre of effort – i.e. canard configuration.  Canard boats have been described as being particularly difficult to tack: the rudder is pulling the bow toward the windward side whereas a conventional rudder allows the stern to slip to leeward, assisted by weather helm.  Of course the proa doesn’t tack so canards are more feasible and given that both foils steer the tacking problem vanishes.  Interestingly, C-Fly foils with canards, but they use conventional rudders in displacement mode.  Consequently, at least on the grounds I've outlined, the proa offers a platform potentially more suited to toying with canards and other foil configurations.

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