(3) If it is not possible to install the mast light or ring white light on the centerline of the ship's head and tail, the mast light or ring white light of a motor boat of less than 12m in length may be displayed off the centerline, provided that its side lights are combined into one and shall be installed on the centerline of the ship's head and tail, or as close as possible to the centerline of the mast light or ring white light.