Effect of different speed reduction strategies on ship fuel consumption in realistic weather conditions

In this paper, the estimation of ship fuel consumption is computed for different weather conditions along the ship route. The propeller is first optimized for calm water conditions using a previous developed optimization model coupling NavCad software and a nonlinear optimizer integrated in Matlab. Then, the propeller performance and ship speed reduction are computed based on the added resistance corresponding to weather conditions expectable along the route. The Aertssen method is used to compute the ship added resistance based on significant wave height and wave period. Three ship speed reduction strategies are proposed in this study when the ship speed exceeds the engine limits, therefore the ship speed is corrected at: (1) 90%, (2) 70% and (3) 50% of the engine rated power. Then, a weighted average fuel consumption along the ship route with different weather conditions is computed for each case. It has been found that the expectable reduction in fuel consumption is of 2.6% and 1.7% in cases (2) and (3) respectively, when compared to the first case.