46 C.F.R. § 143.215 – Existing vessels built to class.

(a) An existing towing vessel classed by a recognized classification society, as appropriate for the intended service and routes, is considered in compliance with the machinery and electrical standards of this subpart.
(b) An existing vessel built and equipped to conform to a recognized classification society's rules, appropriate for the intended service and routes, but not currently classed, may be deemed by the Officer in Charge, Marine Inspection (OCMI), or third-party organization (TPO), to be in compliance with this part, provided that the towing vessel conforms to the class rules.
(c) Existing vessels meeting either paragraph (a) or (b) of this section must also meet the requirements of §§ 143.245 and 143.450.