21. If any vessel enters the area of works after the date specified in a notice under article 20 (removal of vessels from area of works) during the period of temporary closure the harbour master may direct the master of the vessel immediately to remove the vessel from the area of works, and if the master of that vessel does not immediately comply with such directions, the provisions of paragraphs (3) and (4) of article 20 shall apply to and in respect of that vessel as if the vessel had been within the area of works before the date specified in the notice.