Section 173.15 - Vessel number required(a) Except as provided in § 173.17 , no person may use a vessel to which this part applies unless:(1) It has a number issued on a certificate of number by the issuing authority in the State of principal operation; and(2) The number is displayed as described in § 173.27 .(b) This section does not apply to a vessel for which a valid temporary certificate has been issued to its owner by the issuing authority in the State of principal operation.CGD 72-54R, 37 FR 21399, Oct. 7, 1972, as amended by USCG-2003-14963, 77 FR 18699, Mar. 28, 2012