One simplified estimation method of ship waves generated by a small vessel requires the ships data of the tonnage, the horse power and the principal scale of a ship. The data of detailed ship hull geometry for the model test in the towing tank are not required. From this method, it is sufficient to know the wave height, the wave length and the wave period around the cusp line, and the maximum wave height and wave period can be calculated7) . However, we cannot obtain the wave profiles of ship waves from this method.
The maximum ship wave height are estimated as follow,
Ho means the maximum wave height at the parallel line100m apart from the ships route. s is the distance from the sailing line, V is the sea speed of full load (knots), Vk is the actual ship speed (knots) and L is the ship's length. EHPw is the maximum continuous horse power and can be obtained as follow,
where g is the acceleration of gravitv, To is the period of transverse waves and T is the period of divergent waves. θis 35° -16' and shows the theoretical wave direction of transverse waves obtained by Kelvin's ship wave theory.
(2) ESTIMATION METHOD(CAL-2)
The other estimation method of ship waves is based on the linear ship wave-making theory, and the use data for the estimation are the simplified hull geometry under the water plane and the principal scale of a ship. The wave elevation of the bow divergent waves at the arbitrarily position (R, θ) is defined as
where R is the distance from the origin fixed at the bow on the still water, θ is the angle from the sailing line as shown in Fig.2. and Ko＝g/Vk2 is a wave number.
Fig-2 Coordinate system of wave calculation
Calculating the equivalent singularity distributions from thesimplified hull geometry by the power series of non- dimensional coordinate x and z, the wave amplitude function SF(θ) is obtained. Successively, the exact expression of asyrnptotic expansion of the integral in eqn. (5) was applied. Though the time history of the ship-wave profile at theposition in arbitrary distance from the advancing ship can be obtained satisfactory by this method, it is usually difficult to know the more detailed information of ship waves due to the simplified estimation method,.
The calculated maximum wave periods of ship waves were obtained from the time history of wave profile.
