Surveys are made in accordance with the harmonised survey system for ships, to harmonize intervals between surveys of all legitimate certificates issued to all marine vessels.
The harmonized system is presumed to facilitate all the troubles of periods between surveys so that any ship would not have to worry about going into the process of a survey schedule required by one convention right after having gone through the same thing concerned in connection with another instrument.
The harmonized system provides for:
- A one-year standard interval between surveys, based on initial, annual, intermediate, periodical and renewal surveys as appropriate;
- A scheme for providing the necessary flexibility for the execution of each survey with the provision that the renewal survey may be completed within three months before the expiry date of the existing certificate with no loss of its period of validity;
- A maximum period of validity of five years for all certificates for cargo ships;
- A maximum period of validity of 12 months for the Passenger Ship Safety Certificate;
- A system for the extension of certificates limited to three months to enable a ship to complete its voyage (or one month for ships engaged on short voyages);
- When an extension has been granted, the period of validity of the new certificate is to start from the expiry date of the existing certificate before its extension.