Centerboard Fairing

What are the rules for "fairing? the centerboard? I've read through the measurers reports and there is a good section on not fairing the trailing edge (not specific) and grandfathered boards but --- what are the actual rules for fairing the board? (filling mold seams ??) I don't want to fair a board and have it declared illegal at some NAC's later down the road. Thanks, Bruce Cattanach #3817 Monmouth Boat Club Red Bank NJ