((a)) ** .—** An agreement to establish a capital construction fund shall provide for the deposit in the fund of the amounts agreed to be appropriate to provide for qualified withdrawals under .

((b)) ** .—** Deposits in and withdrawals from the fund are subject to the requirements included in the agreement or prescribed by the Secretary by regulation. However, the Secretary may not require a person to deposit in the fund for a taxable year more than 50 percent of that portion of the person’s taxable income for that year (as determined under ) that is attributable to the operation of an agreement vessel.