46 CFR §11.406

1. (a)The minimum service required to qualify an applicant for an endorsement as Second Mate of ocean or near-coastal self-propelled vessels of unlimited tonnage is—
   1. (1)One year of service as Officer in Charge of a Navigational Watch (OICNW) on ocean self-propelled vessels while holding an endorsement as Third Mate; or
   2. (2)While holding an MMC endorsement as Third Mate of ocean self-propelled vessels of unlimited tonnage, 12 months of service on deck as follows:
      1. (i)A minimum of 6 months service as officer in charge of a deck watch on ocean self-propelled vessels.
      2. (ii)Service on ocean self-propelled vessels as Boatswain, Able Seafarer, or quartermaster while holding a certificate or MMC endorsement as Able Seafarer, which may be accepted on a two-for-one basis to a maximum allowable substitution of six months (12 months of experience equals 6 months of creditable service).
2. (b)Service towards an oceans, near-coastal or STCW endorsement will be credited as follows:
   1. (1)Service on the Great Lakes will be credited on a day-for-day basis up to 100 percent of the total required service.
   2. (2)Service on inland waters, other than Great Lakes, that are navigable waters of the United States, will be credited on a day-for-day basis for up to 50 percent of the total required service.
   3. (3)Service on vessels to which STCW applies, whether inland or coastwise, will be credited on a day-for-day basis.
3. (c)If an individual holds an endorsement as Master of Great Lakes and inland self-propelled vessels of unlimited tonnage or Master of inland self-propelled vessels of unlimited tonnage, they may obtain an endorsement as Second Mate of ocean or near-coastal self-propelled vessels of unlimited tonnage by completing the prescribed examination in subpart I of this part.
4. (d)A person holding this endorsement may qualify for an STCW endorsement, according to § 11.309 of this part.