SPEED, POWER AND ROUGHNESS: THE ECONOMICS OF OUTER BOTTOM MAINTENANCE

Abstract

Measurements of the hull roughness of ships of various ages have been carried out, over the past three years, by the Ship Performance Group. These surveys, conducted at yards throughout Europe, were made on a variety of ship types whose wetted surfaces had been coated with products from eleven coating manufacturers, and embraced a total of 147 surveys on 47 ships. The surveys and results are discussed in detail. The Authors then discuss the characteristics of an ideal hull-bottom surface, together with the possibilities of achieving it, under the headings:-1: The Ideal Hull Surface. 2: Paint Materials (Gravity--Rate of Drying--Polymer Choice). 3: Application Methods. 4: Anti-Fouling Mechanisms and Roughness Control. The costs of bottom maintenance are examined under the headings:--1: Docking. 2: Specification. 3: Paint System Costs. Selection of a bottom-maintenance policy for a ship or fleet is a very difficult task without the facilities for making a sound economic judgement of the alternatives, and two case studies are presented as examples of the use of rational-economic models for assisting in making decisions on the maintenance of a seven-year-old ship. The investment policy for bottom maintenance of new ships is similarly discussed. Among the concluding remarks, it is mentioned that the cases studied have shown that more money could profitably be invested in bottom maintenance. Continued research is necessary on the roughness/drag relationship, but enough is known to begin useful economic accounting. There is also a need to monitor the speed and power of ships in service, and simple shipboard systems with well-serviced torsionmeters, together with satellite navigators, can give useful results provided that the realities of data recording practices at sea are recognised.