Dynamic characteristics of ship impressed current cathodic protection systems

Abstract

Physical scale modelling was employed to identify the characteristics of the closed loop control systems for ship impressed current cathodic protection (ICCP) for different hull and operational conditions with three ICCP configurations. A one-hundredth scale metal model hull, with intact and damaged paint coatings, and with a damaged plastic cladding, were protected by ICCP under static and flowing electrolyte conditions. The three types of ICCP system all showed at least second order control characteristics in response to switch-on in static conditions. The damping ratios and natural frequencies of the dominant mode depended upon the hull condition and the ICCP system configuration. Characteristics of two single zone systems changed when they were combined as a two-zone configuration. Maximum peak overshoots, and times to overshoot, were lower with an intact paint coating than with a damaged, whereas natural frequencies and damping ratios were higher. Less damping occurred with damage to cladding than to a paint coating. In response to simulated underway conditions, driving voltages were oscillatory. Damping ratios were much lower than in static electrolyte and natural frequencies were higher. Such studies provide further insight into the processes of ICCP.