Chapter I : Blockade in time of war - Art. 16.
Art. 16. If a vessel approaching a blockaded port has no knowledge, actual or presumptive, of the blockade, the notification must be made to the vessel itself by an officer of one of the ships of the blockading force. This notification should be entered in the vessel's logbook, and must state the day and hour, and the geographical position of the vessel at the time.
If through the negligence of the officer commanding the blockading force no declaration of blockade has been notified to the local authorities, or, if in the declaration, as notified, no period has been mentioned within which neutral vessels may come out, a neutral vessel coming out of the blockaded port must be allowed to pass free.