Sea Spectra Revisited

Abstract

The paper demonstrates that the sea spectra recommended by ITTC, based on the Bretschneider formulation, can be reduced to a nondimensional spectrum, the same for all the spectra, with unit area. In other words – these well-known spectra have geometrical affinity. This fact has been unknown in literature. Any ITTC sea spectrum, described by two parameters A and B, can be generated using the nondimensional spectrum. The same also applies to JONSWAP spectra. The latter requires in addition a third parameter, termed as the peak-shape parameter. The paper explores this possibility. The fact that all the sea spectra used by naval architects can be reduced to a common dimensionless spectrum of unit area opens up the possibility of approximating them by probability density functions of certain types. Such spectra, contrary to ITTC ones, are narrow-banded, with the bandwidth parameter less than 1, and have moments of any order.