WIDE HEADFOILS – RIG FACTOR

Extra wide headfoils are considered to be a way to gain ‘free’ un-measured sail area, and are therefore covered by IRC rule 21.2.2 (red highlight added): 

21.2.2   RF may be increased for: fractional, racing and lightweight rigs, high aspect ratio and efficient plan forms, wing and double luff sails, specialised sail stiffening, exotic sailcloth materials, large headboards/cranes, permanently bent or highly controllable spars, hi-tech rigging, exotic rig materials, advanced winch and deck gear arrangements, flush/efficient deck design, and any other feature which increases sailing efficiency that is not already rated through the rated dimensions. 

 
An example is a boat fitted with a partially fabric foil with a luff groove on the trailing edge, measuring a total of 75mm compared to a sistership’s standard 40mm foil. 
 
The IRC Technical Committee has agreed the following: 

Measurers and owners shall report the maximum dimension in millimetres of any luff groove device that is greater than 1 mm per 0.0033 x LH*. The maximum dimension is measured at right angles to its longitudinal axis.  *As a simple and practical first check only this approximately equates to 1 mm per 1 ft LH. 

IRC Technical Committee  20 April 2020