On the Horizontal Slow Oscillation and the Dynamic Stability of Ships Moored to Single Point Moorings

Abstract

In the single point mooring (SPM) probrem of a tanker, it is wellknown that slow oscillations have a large influence on the mooring load. About the slow oscillation, theoretical and experimental studies have been actively practiced in order to estimate allowable enviromental conditions and the design criteria of mooring equipments for the design of SPM system. However, SPM has been used mainly for mooring tankers, therefore, the relation between ship form and the slow oscillation does not seem to have been taken account. In this paper, authors examined the effect of ship form on the slow oscillation by two kinds of theoretical approaches, that is, time domain analysis and dynamic stability analysis, and showed that ships with large B/d are more stable for the slow oscillation. And fins like fish gills fitted on the bow part of a tanker are also confirmed to have much effect to reduce the oscillation. These fins can be considered to be a practical way to reduce the oscillation when a tanker is used as a storage tank. As for the external forces in SPM probrem of a tanker, it has been said that current force is most effective to the slow oscillation comparing with wind and wave drift forces. therefore, only current is considered in this paper.