46 CFR § 12.403 - Service or training requirements for able seaman (A/B) endorsements.
(a) The minimum service required to qualify for the various categories of endorsement as able seaman is as follows:
(2) Able seaman - limited. Eighteen months of service on deck on vessels of 100 GRT or more which operate in a service not exclusively confined to the rivers and smaller inland lakes of the United States.
(5) Able seaman - sail. Six months of service on deck on sailing school vessels, oceanographic research vessels powered primarily by sail, or equivalent sailing vessels operating on oceans or on the navigable waters of the United States, including the Great Lakes.
(b) Approved training programs may be substituted for the required periods of service on deck as follows:
(1) A graduate of a school ship may be qualified for a rating endorsement as A/B, without further service, upon satisfactory completion of the program of instruction. For this purpose, “school ship” is interpreted to mean an institution that offers a complete approved program of instruction, including a period of at-sea training, in the skills appropriate to the rating of A/B.
(2) Training programs, other than those classified as a school ship, may be substituted for up to one-third of the required service on deck. The Coast Guard will determine the service/training ratio for each program and may allow a maximum of 3 days of deck service credit for each day of instruction.