A Dockmaster is a person in charge of a dock used for freight, logistics, and repair or maintenance of ships (a shipyard or drydock). This title is distinct from Harbourmaster, which is a higher rank than dockmaster. A dockmaster is assisted by a deputy dockmaster and an assistant dockmaster. For example, in the Port of London in the United Kingdom, shipping movements in dock complexes, and within a short distance of the outer lock gates (i.e. in the tidal river) are under the jurisdiction of a Dockmaster and his staff. Each Assistant Dockmaster has a marine staff of about 70 men. In all, each dock complex employed about 360 marine staff. The Port of London consists of all the tidal portion of the River Thames from Margate on the south coast, Clacton-on-Sea on the north, through to Teddington- a total of around 95 miles (150 km). Up until the 1980s the Port of London Authority Dockmaster was responsible for five large enclosed dock systems and miles of quayside isolated from the tides by locks. These systems were London and St Catherine's Docks, Surrey Commercial Docks, India and Millwall Docks, Royal Docks, and Tilbury Docks. of which only the lower two systems are presently operational. Eventually Tilbury Docks were privatized and became The Port of Tilbury, with their Dockmaster upgraded to Harbourmaster.