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www.sea-technology.com November 2015 / st 45 When the ship shaft power is too large, the engine speed should be re- duced to improve energy effciency. However, too much reduction of ship speed means the ship cannot reach port on time. The fuzzy logic model uses real-time acquisition of ship speed and shaft power data to deter- mine the best engine speed for optimal ship energy effciency. Decision-Making Model The ship's shaft power and navigation speed data are the input variables, and the main engine speed is the output vari- able. The fuzzy sets of the model were determined based on fuzzy statistical theory, thus obtaining the corresponding membership functions of the variables. The ship's shaft power was blurred into seven fuzzy sets, as was the ship's navigation speed. To achieve higher precision, the output variable was blurred into nine fuzzy sets. For different shaft powers and navigation speeds, a cor- responding fuzzy rule can be established. For example, if the shaft power of the ship is (NB) and the navigation speed is (NB), then the optimum engine speed should be (PB). So, a total of 49 fuzzy rules can be established. The fuzzy rules are based on the following principles: when the ship shaft power is too high, then the lower en- T he International Maritime Organization (IMO) has con- tinuously improved the standards for ship energy-saving and emissions reduction. For example, the 62nd session of the Marine Environment Protection Committee unani- mously passed mandatory greenhouse gas emission reduc- tion measures, representing the world's frst mandatory in- dustry regulation on greenhouse gas emissions. With the increasingly stringent requirements of energy saving and emissions reduction in the shipping industry, exploring effective ways to enhance ship energy effciency has become more and more important. Eff- ciency is affected by storms, waves, currents and other environmen- tal factors during sailing. Due to the high randomness of these factors, the engine speed for op- timal ship energy effciency is ambiguous and uncertain. Ship navigation speed has an important effect on energy effciency and the ship's overall economy. Systematic research on the infuence of the navigational en- vironment on ship energy effciency is scanty. The development of relevant the- oretical research, such as in fuzzy mathematics, provides a new way to solve this problem. Energy effciency is affected by random environmental factors, so it is diffcult to establish an exact mathematical model for optimal ship speed. Fuzzy logic can evade needing a complex mechanism analysis by establishing an engine speed decision-making model under different random parameters. Therefore, we propose that the best engine speed deci- sion-making method for optimal energy effciency be based on fuzzy logic. This method requires acquiring real-time data on the ship's shaft power and navigation speed. Our experi- mental results validate this model, resulting in reduced fuel consumption per unit distance and improved ship energy ef- fciency. The effect of environmental factors on the ship resistance will eventually be refected in changes of ship shaft power. Fuzzy Logic Method For Ship Energy Effciency Decision-Making Model to Determine Optimal Engine Speed By Kai Wang • Dr. Xinping Yan • Dr. Yupeng Yuan (Top) The optimal ship speed decision-making mod- el. (Bottom) A depiction of the fuzzy rules being applied.