The Office of Merchant Mariner Credentialing has published CG-MMC Policy Letter 03-21 titled: Issuance of Endorsements for Master of Self-Propelled Vessels of Less Than 100 GRT to Mariners Holding Endorsements as Mate of Self-Propelled Vessels of 200 GRT or More.
As is specified in 46 CFR 15.901(a), an individual holding a merchant mariner credential (MMC) endorsed as mate or pilot of inspected self-propelled vessels of 200 gross registered tons (GRT) or more is authorized to serve as master on inspected self-propelled vessels of less than 100 GRT within any restrictions on the MMC, without further endorsement.
This policy letter provides that a mariner holding an endorsement that authorizes service as Mate on an inspected vessel of 200 gross register tons (GRT) or more may be issued an endorsement for Master of Self-Propelled Vessels of Less Than 100 GRT. Mariners must specifically apply for the endorsement to have it added to their MMC.
This policy is available here.