For the purposes of this section, the tonnage of a ship shall be ascertained as follows: —
(a) if the ship is a Singapore ship, its tonnage shall be taken to be its registered tonnage increased, where a deduction has been made for engine room space in arriving at that tonnage, by the amount of that deduction;
(b) if the ship is not a ship as is mentioned in paragraph (a) and it is possible to ascertain what would be its registered tonnage if it were registered in Singapore, that paragraph shall apply (with the necessary modifications) as if the ship were so registered;
(c) if the ship is not a ship as is mentioned in paragraph (a) and it is not possible to ascertain its tonnage in accordance with paragraph (b), its tonnage shall be taken to be forty per cent of the weight (expressed in tons of two thousand two hundred and forty pounds) of oil which the ship is capable of carrying;
(d) if the tonnage of the ship cannot be ascertained in accordance with paragraphs (a), (b) and (c), the Director shall, if so directed by the Court, certify what, on the evidence specified in the direction, would in his opinion be the tonnage of the ship if ascertained in accordance with those paragraphs, and the tonnage stated in his certificate shall be taken to be the tonnage of the ship.