46 U.S.C. § 12303: Exemption from numbering requirements

(a) When the Secretary is the authority issuing a number under this chapter, the Secretary may exempt a vessel or class of vessels from the numbering requirements of this chapter under conditions the Secretary may prescribe. (b) When a State is the issuing authority, it may exempt from the numbering requirements of this chapter a vessel or class of vessels exempted under subsection (a) of this section or otherwise as permitted by the Secretary.