History of International Tonnage Certificate

In 1694 the Thames Tonnage Measurement was used. In 1849 a royal commission originated the basic concept that assessment of dues should be based on a vessel’s potential earning capacity. It was known as the Moorsom System after the secretary of the commission, George Moorsom. This came into force in 1854. In 1873 an international tonnage commission was held at Constantinople. Its findings were not followed, except by the authorities of the newly opened Suez Canal. In 1930 the League of Nations tried to obtain universal agreement but it was not followed by either the British or Americans, though it was adopted by most other countries.  In 1967 the Merchant Shipping (Tonnage) Regulations were passed.  In 1969 the UN agency IMO (International Maritime Organisation) held the International Convention on Tonnage Measurement of Ships. This convention at long last brought in a universally accepted system of gross and net tonnage on 18 July 1982. Note that as these tonnages are independent of the nationality of the ship they no longer need to be linked to the registration of the ship, so their official title is gross tonnage (GT) instead of gross registered tonnage (GRT). Likewise, since 1982 net tonnage is abbreviated to NT instead of NRT. When initially measured, ships are issued with an International Tonnage Certificate (1969).