Up to this time, the model test to estimate the calmness in a barbour has been carried out by using the regular waves. But problems were encountered in the reproducibility because of the regular waves, and it was found that they would often vastly exaggerate resonance effects and regular reflection patterns, although similar effects were found in the real harbours. Then, we carried out wave disturbance tests with regular and irregular waves to compare each result, and concluded that irregular wave models may provide reasonably reliable results in the wave disturbance tests. So, we described concretely a procedure of a model test, following the example of Tajiri Port.
　It is fairly difficult to estimate quantitatively the degree of the calmness in a harbour and there have been few attempts to do so. Here, as an index of a calmness in a harbour, we tried to use a probability that wave heights in a harbour exceed any value. In order to presume the wave heights of sea waves in a harbour, we used a hydraulic model test, a computation of the diffraction coefficients by a digial computer and solution by a diagram.