(a) The minimum service required to qualify an applicant for an endorsement as master of Great Lakes and inland self-propelled vessels of less than 500 GRT is—

(1) Three years of total service on vessels. One year of the required service must have been as a master, mate, or equivalent position on vessels of 50 GRT or more while holding a license or MMC endorsement as master, mate, or OUPV.

(2) [Reserved]

(b) An applicant holding a license or MMC endorsement as master of ocean, near-coastal, or Great Lakes and inland towing vessels is eligible for this endorsement after 6 months of service as master of towing vessels and completion of a limited examination. This requires 3 1/2 years of service. Two years of this service must have been served while holding a license or MMC endorsement as master or mate (pilot) of towing vessels, or mate.