11. Without prejudice to any conditions attached to an approval by the Queen’s Harbour Master under paragraph 10 above but subject to the provisions of article 22 any specified work or operation shall be so constructed or carried out as to ensure that traffic in the harbour is not interfered with more than is reasonably necessary and that at all times an unobstructed main navigation channel for the safe passage of vessels is maintained and kept dredged by the undertaker to such depth as the Queen’s Harbour Master may reasonably require and to a width of not less than 120 metres.