An extended-Lewis form family of ship-sections and its applications to seakeeping calculations

Abstract

A three-parameter extended-Lewis form family is considered and investigated. The parameters used are the half beam to draft ratio λ, the area coefficient σ, and the $\overline{\mathit{K}\mathit{B}}$ to draft ratio κ, where $\overline{\mathit{K}\mathit{B}}$ is the vertical distance of the centroid of the section from the keel. The region of values λ, σ and κ corresponding to conventional, free of deficiencies, ship-like forms is investigated and determined.

Various applications of the extended-Lewis forms to ship hydrodynamics are discussed. It is demonstrated that the hydrodynamic characteristics (added mass and damping coefficients) of ship-like forms depend considerably on the κ parameter.

The effect of the longitudinal $\overline{\mathit{K}\mathit{B}}$ distribution of a destroyer-type hull on its seakindliness is also investigated. It is found that to reduce ah motion characteristics over a wide range of ship speeds and seaways, the forebody as well as the afterbody center of buoyancy should be taken as lower as possible (U-shaped sections). The apparent contradiction of this conclusion with previous results is explained.

To minimize mean added resistance in head waves the forebody center of buoyancy should be taken as lower as possible, while the afterbody center of buoyancy should be drawn as higher as possible.