Well, if I did the math right, with the sailor sitting on the windward hull the side force on the sail is roughly 43 Kg (421 N). Each foil will have to supply 10.75 Kg of side force and lift 37.5 Kg (367 N). So your ratio of vertical to side force is 37.5/10.75 or an angle of 74 degree. If you do all the math for alpha=11 degree (gamma of 3 degree), lift coefficient of 0.1 per degree, board aspect ratio of 10 and a speed of 5.1 m/sec you get a cord of 0.1 meter. The board will be one meter long and you would have four of them. Sounds believable...