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 in which the vessel is principally used; 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 in which the vessel is principally used.