Section 15.403 - When credentials for ratings are required(a) Every seaman referred to in this section, when required, must produce a valid MMC or MMD with all applicable rating endorsements for the position sought, a valid TWIC unless the mariner is exempt under 46 CFR 10.203(b)(2) , and a valid medical certificate to the master of the vessel at the time of his or her employment before signing Articles of Agreement. Seamen who do not possess one of these credentials may be employed at a foreign port or place within the limitations specified in § 15.720 of this part.(b)(1) Every person below the grades of officer and staff officer employed on any U.S. flag merchant vessel of 100 GRT or more, except those navigating rivers exclusively and the smaller inland lakes, must possess a valid MMC or MMD, along with a valid medical certificate, with all appropriate endorsements for the positions served.(2) No endorsements are required of any person below the rank of officer employed on any barges except seagoing barges and barges to which 46 U.S.C. chapter 37 applies.(3) No endorsements are required of any person below the rank of officer employed on any sail vessel of less than 500 net tons while not carrying passengers for hire and while not operating outside the line dividing inland waters from the high seas. 33 U.S.C. 151 .(c) Each person serving as an able seafarer-deck, or a rating forming part of a navigational watch (RFPNW), on a seagoing vessel of 500 GT or more must hold an STCW endorsement certifying him or her as qualified to perform the navigational function at the support level, in accordance with the STCW Convention (incorporated by reference, see § 15.103 of this part).(d) Each person serving as an able seafarer-engine, or a rating forming part of an engineering watch (RFPEW), on a seagoing vessel driven by main propulsion machinery of 1,000 HP/750 kW propulsion power or more must hold an STCW endorsement certifying him or her as qualified to perform the marine-engineering function at the support level, in accordance with the STCW Convention.(e) Notwithstanding any other rule in this part, no person subject to this part serving on any of the following vessels needs an STCW endorsement:(1) Vessels exempted from the application of the STCW Convention, including- (i) Fishing vessels as defined in 46 U.S.C. 2101(11)(a) ;(ii) Fishing vessels used as fish-tender vessels as defined in 46 U.S.C. 2101(11)(c) ;(iii) Barges as defined in 46 U.S.C. 102 , including non-self-propelled mobile offshore-drilling units;(iv) Vessels operating exclusively on the Great Lakes; or(v) Pilot vessels engaged in pilotage duty.(2) Vessels not subject to any obligation under the STCW Convention due to their special operating conditions as small vessels engaged in domestic, near-coastal voyages, including- (i) Small passenger vessels subject to subchapter T or K of 46 CFR chapter I;(ii) Vessels of less than 200 GRT (other than passenger vessels subject to subchapter H of 46 CFR) chapter I; or(iii) Uninspected passenger vessels as defined in 46 U.S.C. 2101(42)(B) .