Kan. Stat. § 32-1110
Every undocumented, mechanically propelled vessel or sailing vessel using the waters of this state, as its state of principal use, shall be numbered, except those exempted by K.S.A. 32-1113, and amendments thereto. No person shall operate or give permission for the operation of any motorboat or vessel propelled by sail on such waters unless such vessel is numbered in accordance with this act, applicable federal law or a federally approved numbering system of another state, and unless (1) the certificate of number awarded to such vessel is in full force and effect and (2) the identifying number set forth in the certificate of number is displayed on each side of the bow of such vessel, unless otherwise provided by rules and regulations of the secretary.
K.S.A. 32-1110