This paper discusses the wharf operation ratio in a port by use of wave data obtained by Nationwide Wave information network for Ports and HAabourS (NOWPHAS). The observed interval of wave data was twenty minuets of every two hours due to the limitation of data transformation during about thirty years after starting the wave observation in 1970. In recent years, continuous wave data have been observed in the remarkable progress of information processing and communication technology. However, the effect on the wharf operation ratio depending on the difference of wave observation interval was not discussed. This paper thus examines the differences of wharf operation ratio estimated when discontinuous or continuous data were applied, respectively.