Abstract
This paper discusses the results of a test program designed at a meeting of interested parties*, held at the Sea Horse Institute,** Harbor Island, N. C. on June 8, 1950. The principal object of the investigation was to determine whether cathodic protection can be applied to operating ships without inactivating anti-fouling paints in the manner frequently observed when certain anti-fouling paints are associated with areas of bare steel or zinc. Secondary objectives concerned the effects of variations in the composition of the paints used and in variations in the dried film thicknesses of the anti-corrosive paints used in the paint systems.
Several variations of two basically different types of ship bottom paint systems were studied for in-activation of the anti-fouling point by cathodic protection. In general, it was found that ship bottom paint systems which can be expected to inactivate, and hence foul without cathodic protection, are the same paints that will be inactivated in a relatively short time by protective currents. The importance of the anti-corrosive undercoats in preventing inacti-vation is stressed for it was found that both cases of inactivation observed in this test were substantially eliminated by a better "barrier" coating between the anti-fouling paint and the steel plate. Paints of low permeability and good alkali resistance materially reduced the current requirements for protection.
The most important observation made in this test program was that the current density should be controlled by limiting the potential to the minimum necessary for the protection of the steel. This was not done in this preliminary investigation and hence almost all the coatings were severely damaged by the effects of the unnecessarily high currents.
