Theoretical Analysis of the Rolling of a Ship with Negative-GM

Abstract

Assuniing the stability curve of third degree, the author investigates the rolling of a ship with negative-GM. At first, he studies the free rolling, giving some modifications to Prof. Scribanti's formula and some approximate formulae. Next he analyses the rolling among waves without wind and then accompanied by wind. Therefrom the following conclusions are deduced : 1. The rolling of an ordinary ship with negative-GM among usual waves is quite safe, as there occurs no possibility of synchronism when accompanied by wind, the rolling increases considerably, but is not very dangerous, if sufficient cares are taken on her free-board, and he gives the approximate formula for the maximum rolling angle in that case, which may afford some means to determine the free-board of such a ship.2. A ship, especially under medium size, with the usually adopted value of positive-GM is very liable to get into a dangerously heavy rolling, which corresponds to synchronism in simple harmonic rolling, but takes place on the waves with shorter period.Consequently, he recommends the adoptation of small or negative GM, provided with sufficient free-board, for comparatively small-sized full cargo ships, as is generaly believed.