The foils on the surf boards are basically air-chair foils. The work I did on them was in an effort to raise the effective foiling transverse metacentre (because the guys were having trouble keeping the foil under them) and then moving the tail fin further aft to increase longitudinal stability. The boat builder who manufactured the first prototype cut some corners (and a whole lot of fibres) and it broke during its first testing section. The guy who was meant to be paying me (the son of a friend) decided he couldn't be bothered developing "better" foils and went off to learn to use what they had. I never pursued the issue because we're not talking about a lot of money and I'd really taken the job on as an intellectual challenge.