Approximately every 3 or 4 years, vessels have to be drydocked, either in accordance with specific rule requirements or to gain an overall view of the vessel’s condition. These drydockings can incur considerable expense because they involve the inspection, overhaul, and, where necessary, the modification of existing equipment. It is imperative for ship managers and operators to monitor and control drydockings because lower drydocking costs do not just affect sound financial performance, but are also a requirement for it. This article proposes a method for forecasting the actual cost and the cost at completion of vessel drydockings based on the Gray system theory. Results show that the accuracy of the GM (1,1) forecasting model is highly efficient.