http://www.formula16.net/content/view/13/36/lang,en/

1.6.4 (Added by vote, August 2007) For the avoidance of doubt, daggerboards/centerboards will conform to the following :
a) Curved/’Banana’ boards will not be allowed.
b) Assymetrical cross-section profile boards will be allowed.
c) Fore/aft movement of the boards when in the down position will not be allowed.
d) End fences/horizontal appendages below the waterline will not be allowed. The board shall be capable of removal, without tools, via the upper opening of the case.
e) There will be no limitation on the daggerboard/centerboard length