Published on Australian Maritime Safety Authority (https://www.amsa.gov.au)
A ship which is more than 24 metres in tonnage length and intending to go on an overseas voyage must have an International Tonnage Certificate (ITC). Tonnage measurements can be arranged through one of the following recognised Classification Societies:
An International Tonnage Certificate issued by, or on behalf of another flag State, remains valid for up to three months after the transfer of flag and may be used for ship registration purposes.
An Australian-issued International Tonnage Certificate should be issued to the ship within three months of the ship transferring flag and a copy provided to the Shipping Registration Office.