The sail is patented (No 2255541), and it controls an asymmetric underwater hydrofoil, to counteract the side force.
Bob died in 2004 - any enquiries to Gen Quinton These clips are from a video made by Genevieve Quinton. Any enquiries to: Genevieve Quinton, Boatek, Abbey Farm, Gulpher Road, Felixstowe, Suffolk, IP11 9DN, UK. Telephone (+44)394 670302
See also the still photos elsewhere on this site
See their web page on http://www.boatek.club24.co.uk