A proposed standard of stability for passenger ships

Abstract

The authors have developed a standard of stability for passenger ships engaged in Ocean-going and Coasting Services. This standard was worked out in a similar manner to that for Smooth Water Area and Small Craft by the Ministry of Transportation with the cooperation of Tokyo and Kyushu Universities, Nippon Kaiji Kyokai, etc.

In preparing this standard, investigations have been made on the various external forces affecting stability such as wind, waves, shipping of sea water, shift of weights on board, steering, as well as metacentric height, dynamical stability, maximum righting arm, etc.: Whereupon the method of judging the stability has been developed as follows:

1. Dynamical stability as criterion.

Amongst external forces, the effects of wind and waves have been considered. Let us assume that, a ship is listed under the statical transverse heeling moment due to steady wind, and the ship is subjected dynamically to a gust when the ship is at he maximum angle of roll to windward due to waves. In order that the ship has sufficient dynamical stability:

work ratio $\mathit{C}\mathrm{>}1$

2. Maximum righting arm as criterion.

The external forces, due to shipping of sea water, shift of heavy weights on board, steering, etc. have been considered $\mathit{G}{\mathit{Z}}_{\mathit{m}}$ must satisfy either of the following formulae:

$\mathit{G}{\mathit{Z}}_{\mathit{m}}\geqq 0.0215\mathit{B}$ or $\mathit{G}{\mathit{Z}}_{\mathit{m}}\geqq 0.275\mathrm{(}\mathit{m}\mathrm{)}$

3. Metacentric height as criterion.

The $\mathit{G}\mathit{M}$ criterion is the same as that for ships engaged in Smooth Water Area when wind pressure and shift of passengers have been taken into consideration:

$\mathit{G}\mathit{M}\geqq \mathrm{(}1.1\mathit{A}\mathit{h}+\sum \mathit{k}\mathit{n}\overline{\mathit{B}}\mathrm{)}\mathit{B}\mathrm{/}100\mathit{f}\mathrm{\Delta }$ , $\mathit{f}\leqq \mathit{B}\mathrm{/}5.5$