18. The following ships shall be exempted from the payment of light-dues under this Act, namely:- (a) any ship belonging to Government or to a foreign Prince or State and not carrying cargo or passengers for freight of fares; and (b) any ship of a tonnage of less than fifty tons; and the Government may, by notification in the official Gazette, exempt any other ships, or classes of ships, or ships performing specified voyages from such payment, either wholly or to such extent only as may be specified in the notification.