(1) Where a qualifying ship is operated by two or more companies by way of joint interest in the ship or by way of an agreement for the use of the ship and their respective shares are definite and ascertainable, the tonnage income of each such company shall be an amount equal to a share of income proportionate to its share of that interest.
(2) Subject to the provisions of sub-section (1), where two or more companies are operators of a qualifying ship, the tonnage income of each company shall be computed as if each had been the only operator.