; and (ii) operates with more than 16 individuals on board; or (B) in the case of a fish tender vessel, engages in the Aleutian trade. (2) The term auxiliary craft means a vessel that is carried onboard a fishing vessel and is normally used to support fishing operations. (3) (A) The term built means, with respect to a vessel, that the vessel’s construction has reached any of the following stages: (i) The vessel’s keel is laid. (ii) Construction identifiable with the vessel has begun and assembly of that vessel has commenced comprising of at least 50 metric tons or one percent of the estimated mass of all structural material, whichever is less. (B) In the case of a vessel greater than 79 feet in overall length, for purposes of subparagraph (A)(i), a keel is deemed to be laid when a marine surveyor affirms that a structure adequate for serving as a keel for such vessel is in place and identified for use in the construction of such vessel. (4) The term subject vessel means a vessel to which this chapter applies that— (A) operates beyond 3 nautical miles from the baseline from which the territorial sea of the United States is measured or beyond 3 nautical miles from the coastline of the Great Lakes; (B) operates with more than 16 individuals on board; or (C) in the case of a fish tender vessel, engages in the Aleutian trade. (5) The term substitute-eligible vessel means a fishing vessel or fish tender vessel that is— (A) a subject vessel; (B) at least 50 feet overall in length, and not more than 180 feet overall in length as listed on the vessel’s certificate of documentation or certificate of number; and (C) built after February 8, 2016. 4503. Safety standards (a) In general The Secretary shall prescribe regulations that require that each vessel to which this chapter applies shall be equipped with— (1) readily accessible fire extinguishers capable of promptly and effectively extinguishing a flammable or combustible liquid fuel fire