((a)) ** .—** A charter under this chapter shall provide that if, at the end of a calendar year subsequent to the execution of the charter, the cumulative net voyage profit (after payment of the charter hire reserved in the charter and payment of the charterer’s fair and reasonable overhead expenses applicable to operation of the chartered vessel) exceeds 10 percent a year of the charterer’s capital necessarily employed in the business of the chartered vessel, the charterer shall pay to the Secretary of Transportation, as additional charter hire, half the cumulative net voyage profit in excess of 10 percent a year. However, any cumulative net voyage profit accounted for under this subsection is not to be included in the calculation of cumulative net voyage profit in any subsequent year.

((b)) ** .—** The Secretary shall define the terms “net voyage profit”, “fair and reasonable overhead expenses”, and “capital necessarily employed” for this section. Each advertisement for bids and each charter shall contain these definitions, stating the formula for determining each of these three amounts.