Study on Economical Ship Speeds

Abstract

This paper presents a method for theoretically predicting the quantity of fuel oil consumed by a ship going through irregular waves, and a method of deciding optimum ship speeds which minimize the quantity of fuel oil consumed by a ship crossing over an ocean. The author designates the optimum ship speeds as the economical ship speeds. Theoretical calculations are carried out in order to evaluate the quantity of fuel saving which is achieved by navigation under economical ship speeds. Two ships are chosen for the calculation. One is a 140,000 DWT bulk carrier on a Japan∼Australia route and the other is a 86,000 DWT bulk carrier on a Japan∼North America route. The effect of navigation on fuel consumption is clarified by using the following three kinds of navigation methods for the calculation: (1) navigation under economical ship speeds (2) navigation under constant engine power (3) navigation under uneconomical ship speeds The results of the calculations verify that the navigation under economical ship speed is the most effective method for fuel saving, and that the fuel oil consumed by the navigation under economical ship speeds is 2% lower in the case of the 140,000 DWT bulk carrier than that of navigation under constant engine power, and 6% lower in the case of the 86,000 DWT bulk carrier.