Modeling and Analysis of Ship Repairing Time

Ship repairing (hereinafter referred to as repairing) time, duration of stay of a ship in a shipyard (also a slipway or a floating dock), is a part of the routine maintenance schedule of a ship, mainly required by the classification societies and the flag states. With an interval of approximately 24-30 months, the regulations of both the flag state and the classification society call for a ship to carry out docking survey, intermediate survey, or special survey (once in 5 years), depending on the age of the ship, in a shipyard/floating dock/slipway (hereinafter referred to as a yard). It is mandatory to fulfill the requirements and comply with the rules and regulations for maintaining statutory certification. Owners and yards always try to reduce the repairing time to reduce the loss of income (for an owner) and maximize the annual turnover through handling more ships (for a shipyard). Repairing time and related information for 600 cargo ships were collected from a single shipyard. A multiple linear regression model was developed and analyzed using these basic data. Ship repairing time was then expressed as a function of a ship's age, deadweight, repairing works of mainly hull coating, piping, structural steel, and tank coating. "Method of least squares" was applied to estimate the regression coefficients. In this article, the authors have made an attempt to identify the number of those independent variables that influence repairing time (the dependent variable) and their interrelationship. A mathematical model has been developed and proposed, as a guiding tool, for the decision-maker to estimate a more realistic ship repairing time for the fleet maintenance.