Analysis of Hull Coating Renewal in Ship Repairing

Abstract

Hull coating (external blasting and painting) renewal (repair) is a part of routine ship maintenance. It is carried out only when the ship is in a dock (graving dock, floating dock, or slipway). For a regular maintenance schedule, the scope of hull coating repairing works dictates the duration of stay of a ship in the dock. It is very vital therefore to estimate the scope of work for hull coating before docking. As soon as the ship is docked, a joint hull inspection by representatives of the owner, dry-dock, and coatings supplier accurately determines the hull coatings scope of work. Most of the time, the inspection result does not match with the preplanned dock operation schedule. Hence, the overall dock operation schedule gets affected due to delay or early undocking of a ship. Hull coating repair and related information for 149 cargo ships were collected from a single shipyard. It was analyzed and presented in both tabular and graphical forms to show the relationship between the scope of work and the age, size, and type of ships. The physical size of a ship has a great influence on the hull blasting and painting repairing works irrespective of design parameters and types of the ship. Using ship dimensions, actual surface area, and other factors, a method of estimating the hull coating scope is proposed. In this article, the authors have made an attempt to identify the independent variables that influence the scope of work (dependent variable), and suggested the possible interrelationships between the dependent and independent variables, which appeared to be linear. 1. Introduction For a newly built ship, the external hull is coated with two types of painting system, namely, anticorrosive painting system and antifouling painting system. Anticorrosive painting system is to protect the steel from corrosion caused by oxidation, and antifouling painting system is to protect the underwater surface from marine growth. After proper surface preparation, multiple coats of anticorrosive paint are applied to the entire hull (underwater and above water) as per painting schemes followed by multiple coats of antifouling paints to the underwater area.