Analyzing and predicting underwater hull coating system wear.

Abstract

The coating system of an aircraft carrier's underwater hull consists of two layers, an anticorrosive under layer and an antifouling upper layer. The antifouling layer is a soft paint designed to ablate, continuously releasing toxins to inhibit marine growth. This feature causes the antifouling layer to wear over time and with hull cleaning. Sufficient antifouling paint needs to be applied so that the antifouling layer remains effective through a ship's operational cycle until the next dry-docking availability. The NSTM guidelines for how much antifouling paint should be applied are inadequate. NSTM fails to recognize that paint is not applied uniformly and that wear of the antifouling layer is also not uniform. Difficulties in implementing the guidelines are compounded by the fact that the antifouling layer cannot be measured directly. We propose a remedy for this situation. A simple method for estimating the distribution of the thickness of the antifouling layer is given, based on measurements of the coating system before and after the antifouling layer is applied. In addition, a model is fit based on data from five aircraft carriers collected over ten years that predicts the change of the total coating thickness as a function of the number of years at sea, number of hydro-washes and number of underwater hull cleanings.