46 CFR §11.405

1. (a)The minimum service required to qualify an applicant for an endorsement as Chief Mate of ocean or near-coastal self-propelled vessels of unlimited tonnage is 1 year of service as Officer in Charge of a Navigational Watch (OICNW) on ocean self-propelled vessels while holding an MMC endorsement as Second Mate.
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.
   2. (2)Service on inland waters, other than Great Lakes, that are navigable waters of the United States, may be substituted 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)A person holding this endorsement may qualify for an STCW endorsement, according to § 11.307 of this part.