Section 6(b), with paragraph (2) thereof, requires the employer to pay to an employee, “if such employee is employed as a seaman on an American vessel, not less than the rate which will provide to the employee, for the period covered by the wage payment, wages equal to compensation at the hourly rate prescribed by paragraph (1) of this subsection for all hours during such period when he was actually on duty (including periods aboard ship when the employee was on watch or was, at the direction of a superior officer, performing work or standing by, but not including off-duty periods which are provided pursuant to the employment agreement).” The “hourly rate prescribed by” paragraph (1) of the subsection is the minimum wage rate applicable according to the schedule shown in § 783.23.