12.—(1) Subject to regulation 16 below, no vessel to which this regulation applies shall proceed or attempt to proceed to sea unless the appropriate certificate is in force in respect of the vessel.
(2) Before any such vessel proceeds to sea, the master of the vessel shall produce the appropriate certificate to the officer of Customs from whom a clearance for the vessel is demanded; and a clearance shall not be granted, and the vessel may be detained until the appropriate certificate is so produced.