Abstract
Recent measurements on a ship at sea indicated that there was a significant galvanic corrosion current between the bronze propellers and holidays in the painted steel hull on a ship equipped with shaft grounding when the cathodic protection system was shut off. In an effort to determine the effects of the distance between a holiday and the propeller on the penetration rate at that holiday, a large bronze rod was electrically connected to several small steel specimens at different distances away from it in a large tank of seawater. The resulting galvanic current for each specimen was monitored using a zero resistance ammeter. The experiment was repeated several times with minor variations. The measurements did not yield consistent results with respect to the effects of distance, but did suggest that there were no practical differences between penetration rates as a function of distance. The value of conducting multiple experiments was demonstrated, as individual experiments could have led to inappropriate conclusions. The results showed that a ship with a well-painted hull and cleaned propellers would suffer a higher penetration rate than a ship with many holidays and propellers coated with protective films.
