Lewis form

A Lewis form is a ship cross-section generated by a two-parameter conformal mapping of a unit circle, introduced by F.M. Lewis in 1929. The two free parameters are fixed by the section beam-to-draft ratio and the section area coefficient, so any real station is approximated by the closest Lewis section. The value is that the added mass and damping of the mapped section in heave and sway have closed-form or tabulated solutions, which makes Lewis forms the standard building block of strip-theory seakeeping, where the hull is sliced into 2D sections and the sectional hydrodynamic coefficients are summed. Extended three-parameter and multi-parameter mappings improve the fit of bulbous or hard-chine sections.