Relation detween Dezincification Corrosion of Manganese Bronze Propeller and Zinc Plates for Cathodic Protection

Abstract

In the paper read before the autumn meeting in 1955 of the Kansai Society of Naval Architects under the title, Experimental Research on the Corrosion of Propeller Blade and Sleeeve, the author referred to that zinc plates would suppress the corrosion of copper alloys. In the present paper, the author mentions the results of experiments, by which he intended to verify the above statement. In the sea water, by making electrical circuit between manganese bronze and zinc plates, the former becomes anode and the latter cathode. By the chemical action, zinc ions are carried to the anodic manganese bronze and its surface is covered by a film of gilded zinc. In this case, dezincification of manganese bronze is suppressed and corrosion does not occur. Generally zinc plates are fitted for the purpose of protection against the corrosion of hull plate. Zinc plates are fixed on the hull plate by studs or other means, and propeller shaft, intermediate shafts and main shaft are supported by bearings through oil film. So that shafting and hull is electrically insulated. The author supposes that, if the ship hull and shafting are electrically connected, by electrolytic action between manganese bronze propeller and zinc plates, the propeller blades are covered by zinc film and dezincification of the propeller will be suppressed.