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AUTHORS' REPLY

The authors would first like to thank Mr. Johnsson for his valuable comments. Mr. Johnsson did point out some key points in this paper. Mr. Johnsson may be right about the effect of the hydrophone position. The authors will continue to investigate if the hydrophone extruded outside the ship having any influence on the pressure fluctuations.

Regarding the difference between the computations results presented in the paper and carried out by Breslin and Andersen [D1], the authors have carefully investigated the results and conclude that this difference can be explained.

First, we know that the ship effective mean wake is 0.29, and the model nominal mean wake is 0.436. The model effective mean wake calculated is 0.35 by the present paper, and 0.254 by [2]. Therefore, the result calculated by the present paper is more reasonable since the model effective mean wake should be higher than the ship effective mean wake. When authors use the effective wake distribution calculated by [2], the magnitudes of pressure fluctuations calculated decrease as expected. However, they are still higher than those calculated by [2] (as in Figure 1). This is apparently because the ship hull is modeled differently by two methods. Anyhow, we have to point out that the computations of the effective wake distributions in the present paper are rough due to the simplicity of the model.

Because the pressure fluctuations measured in SSPA cavitation tunnel were clearly smaller than those of the full scale, SSPA took the average of the max 5% as the measured values to have a better correlation with the full scale. This however may suggest that the experimental data are too low. On the other hand, as described in the paper, the computational results are supposed to be larger since it is according to the model effective wake distribution instead of the full scale effective wake distribution. This is also supported by the investigation of Blake et al. [1], in which they found that the surface forces calculated or measured by the model wake distribution were larger than those at the full-scale condition. The experimental results in HYKAT by Friesch, et. Al., [R1] (Fig.15) also showed the same tendency.

The figure Mr. Johnsson presented about the influence of the height and shape of the stern wave is very interesting. The authors will include a free-surface calculation to consider these effects in the future.

REFERENCE

[R1] J.Friesch, C.Johannsen, and H.G.Payer. Correlation studies on propeller cavitation making use of a large cavitation tunnel. Trans. SNAME, 100: pp. 65–92, 1992.

Figure 1: Calculated pressure fluctuations by the present method and by Breslin et al. at the blade frequency. Both methods use the same effective wake distribution.



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