Section 11.446 - Requirements for master of Great Lakes and inland self-propelled vessels of less than 500 GRT(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.(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 31/2 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.