The a-class rule about foils is that the maximum angle of the boards is so far angled that when the bottom of the centerboard is full inside the hull ( bottom hull is bottom board) the measured width on the top of the board is not more then 2,3 meter. This means that boat is never more than 2,3 mtr's in width. This means that you never get the extreme foils like the Icarus.
Hans
I assume curved foils are banned ?
