46 CFR §11.457

1. (a)An applicant for an endorsement as Master of inland self-propelled vessels of less than 100 GRT must provide 1 year of service on any waters. In order to raise the tonnage limitation to more than 100 GRT, the examination topics indicated in subpart I of this part must be completed in addition to satisfying the experience requirements of § 11.452(a).
2. (b)To obtain an endorsement for sail or auxiliary sail vessels, the applicant must submit evidence of 6 months of service on sail or auxiliary sail vessels. The required 6 months of service may have been obtained prior to issuance of the MMC endorsement.
3. (c)All endorsements issued for Master or Mate of vessels of less than 100 GRT are issued in tonnage increments based on the applicant's qualifying experience in accordance with the provisions of § 11.422.