(1) A Cargo Ship Safety Construction Certificate issued under section 277 shall remain in force for five years or such shorter period as may be specified in it, subject to the power of the Director-General to cancel the certificate and an exemption certificate issued under this Part shall remain in force for the same period as the corresponding qualifying certificate.

(2) The Director-General may extend the period for which a certificate under subsection (1) is issued for a period not exceeding three months.

(3) Notwithstanding the power of extension conferred under subsection (1), where a certificate under this section is in force in respect of a ship and the certificate was issued for a shorter period than is allowed under this section, the Director-General or any person authorized by the Director-General for the purpose may, if satisfied on receipt of declarations of survey in respect of the ship that it is proper to do so, grant an extension of the certificate for a period not exceeding one year and in any event not exceeding in total the period of five years specified in subsection (1).