The propulsion performance of actual ship at sea tends to deteriorate mainly due to the fouling of hull and propeller. It is important, therefore, to monitor the present situation of ship propulsion performance in order to make an optimum operation and maintenance planning for cost saving. The monitoring method of propulsion performance by the use of Logbook data has been to analyze the consumption and/or ship velocity, which is just variation of overall propulsion performance. This paper proposes a new analyzing method of Logbook data, which could make it possible to investigate the surface fouling effects on hull resistance and propeller performance individually. At first, the surface roughness effects on propeller performance are calculated using the numerical estimation method developed by the authors in the previews paper, and the validity of estimate are conformed by the experimental results of model and actual propellers. Next the behaviors of propeller torque and thrust coefficient change due to surface fouling is investigated, and it is revealed that is a certain relation between the changes of torque and thrust coefficient ΔK
Q and ΔK
T. The paper suggests that is possible to predict simply ΔK
T from ΔK
Q by the use of relation instead of carrying out the numerical calculation. Finally, based on the above results, the paper indicates the possibility of a new useful monitoring method of ship propulsion performance at sea, which can analyze the recitation of hull resistance and propeller performance individually.
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