The effect of water flow on leaching rates of antifouling paints : Consideration of mechanism and preliminary results of laboratory tests

The rate of loss of copper from many antifouling paints has been found to be 2–4 times greater from ships while steaming than from raft panels. For paints having relatively high cuprous oxide and low rosin contents, evidence is presented that the effect is due not to erosion, but to accelerated solution made possible by substantial removal of diffusion layers by the turbulent flow conditions over a ship's hull. A apparatus designed to enable leaching rates to be measured at low and high water speeds (1 and 20 knots) is described. Preliminary results show that the usual criteria for turbulent flow and its effect on diffusion to or from a surface do not apply in the case of a paint, the surface layers of which develop into a skeleton of insoluble constituents. With additional turbulence stimulation, an acceleration factor of about 3 is obtained at first, but later the value falls to about 2. It is concluded that further study of turbulence-development is required.