Cathodic protection of ship propellers - using an automatically adjustable resistor between the propeller shaft and the ship hull

摘要

Adjusting cathodic protection of ship propellers uses a slip ring and contact brush system. A resistor placed between the propeller shaft (6) and the ship hull (1) is automatically adjusted at set instants with the use of control variables consisting of the cross-over voltage V1 between the shaft and the hull and the voltage V2 which is the potential of the cathodically protected ship hull, and is established via a measuring electrode (5). The resistor is adjusted so that the electrochemical potential of the bronze propeller is reduced by 200 mV in comparison with its free corrosion potential. The appts. incorporates a control unit (12) and an additional brush (9) between the propeller shaft (6) and the hull (1) for measurement of the cross-over voltage V1 by means of a voltmeter (10). USE/ADVANTAGE - The invention takes into account the fact that the electrochemical protection potential of the propeller bronze is about 0.3 V more positive than that of the steel ship hull. As a result, better corrosion protection becomes possible, with savings in the current consumption.