(8)For the purposes of these rules—
(a)A ship's tonnage shall be reckoned as under the Merchant Shipping Act, 1894, for dues payable on a ship's tonnage, with the addition required in section eighty-five of that Act with respect to deck cargo, or in the case of an unregistered vessel in accordance with the Thames measurement adopted by Lloyd's Register.
(b)A year shall be reckoned from the day of the month on which this Act commences.