BAC Award impressed current cathodic protection (ICCP) systems from BAC Corrosion Control of Telford have been selected to provide long term corrosion protection for the first large gas turbine propelled vehicle-passenger vessel to be built outside Europe. Austal Auto Express 86, constructed by Austal Ships, Western Australia is destined for service in the Baltic Sea.
BAC’s systems are installed in the water jet tunnel, void space and bow thruster tunnel. The sea chests and hull are also being monitored. Drive shafts are fitted with BAC shaft earthing and monitoring systems to prevent erosion. An impressed current system uses inert (non-galvanic) anodes with an external source of low voltage DC power to impress a current from anode to cathode(hull). Reference electrodes, installed adjacent to the anodes, are electrically connected into the system to provide a remote monitoring facility that continuously presents information, both visual and in printed log form, on the bridge.
Although the aluminium used for the hull produces its own natural passivating oxide layer which resists seawater corrosion, practical experience has shown that additional protection is needed to prevent galvanic corrosion in the waterjets themselves, due to the presence of stainless steel and copper alloys. The same applies in the thruster tunnels and the sea chests where materials other than just aluminium are used.
Traditional sacrificial anodes are not ideal for such applications due to their short life and capacity and therefore inadequate protection. Hence the BAC Award ICCP systems to protect components that are subject to high velocity water flow and greater than usual corrosion.
The void space anode assembly -- Award VS -- comprises a mixed metal oxide coated titanium wire anode mounted into a header cable and enclosed in a perforated plastic housing which also incorporates a reference electrode. The anode is wound around the external surface of the stainless steel water jet impeller cone housing and electrical connections are taken through a glanded void space inspection hatch.
The 86 metre gas turbine powered aluminium hulled catamaran will be chartered to the Danish Government and operated by Bornholms Trafikken in the Baltic Sea between Ronne on the Danish island of Bornholm and Ystad in south eastern Sweden. With a maximum speed in excess of 50 knots, it will be one of the fastest vehicle-passenger ferries in the world with the capability to carry 186 cars and over 1000 passengers. It will operate at a service speed of around 40 knots to comfortably achieve the scheduled crossing time of 65 minutes.