Long-Term Prediction of Speed Reduction Due to Waves and Fuel Consumption of a Ship at Actual Seas

The improvement of ship motion and propulsive performance becomes vital in various ocean engineering applications. As the notion of energy saving and environmental protection gradually finds its way deep into people’s heart, the issue of energy efficient design and operation of the vessels has attracted more and more attentions. How to make the vessels maintain service speed while consuming less fuel has quickly become the main concern of the naval architects. In this paper, we present a new procedure to predict speed reduction and fuel consumption of a ship at actual seas. The prediction takes into account the added resistance due to waves since it is recognized to be the predominant component, while wind resistance, fouling effect and other resistance components are relatively small and temporarily ignored. The calculation of the added resistance is based on a three-dimensional frequency-domain panel method for regular waves and spectral approach is applied to obtain the mean value. Then speed prediction is performed based on a simplified model assuming the balanced working point among the ship, propeller and the engine under the assumption of linear relationship between the engine torque and its rotation. Fuel consumption prediction is carried out through calculating the engine power, the effective fuel consumption rate and the time for sailing. Long-term prediction is made through combining the short-term result with the long-term ocean wave statistics from the Database of Winds and Waves which is newly developed in Shanghai Jiao Tong University (SJTU). A long-term probability model which takes into account the ship’s actual navigation conditions is applied, and the expected ship speed and fuel consumption along her actual sea route are predicted accordingly. For the purposed of practical use, a VLCC ship type is adopted for the prediction as an example. Finally, it has been concluded that the propulsive performance, i.e. speed and fuel consumption, of the vessel at actual seas can be improved through design considerations such as hull form optimization, engine selection and weather routing.