46 U.S.C. § 7306

(a) In General .— The Secretary may issue a merchant mariner credential, to members of the deck department in the following classes: (1) Able Seaman-Unlimited. (2) Able Seaman-Limited. (3) Able Seaman-Special. (4) Able Seaman-Offshore Supply Vessels. (5) Able Seaman-Sail. (6) Able Seaman-Fishing Industry. (7) Ordinary Seaman. (b) Classification of Credentials .— The Secretary may classify the merchant mariner credential issued under subsection (a) based on— (1) the tonnage and means of propulsion of vessels; (2) the waters on which vessels are to be operated; or (3) other appropriate standards. (c) Qualifications .— To qualify for a credential under this section, an applicant shall provide satisfactory proof that the applicant— (1) is at least 18 years of age; (2) has the service required by the applicable section of this part; (3) is qualified professionally as demonstrated by an applicable examination or educational requirements; (4) is qualified as to sight, hearing, and physical condition to perform the seafarer’s duties; and (5) has satisfied any additional requirements established by the Secretary, including career patterns and service appropriate to the particular service, industry, or job functions the individual is engaged.