The ornamental design for a crowneddeckingboard, as shown and described.
FIG. 1 is a perspective view of a crowned decking board in accordance with the present design with the board shown in broken lines indicating an indeterminate length.
FIG. 2 is a front view thereof, with the rear view being the same.
FIG. 3 is a right side elevation view thereof, with the left side being the same.