Practical assessment of manoeuvrability in adverse conditions

Abstract

The introduction of EEDI raised the need for norming (standardising) of ship's manoeuvrability under adverse conditions. Besides the necessary criteria, measures and standards, developed in several research projects and described elsewhere, also procedures and methods for the practical evaluation of the proposed criteria in design and regulatory approval are required, which are addressed in this paper. The idea is to develop a flexible assessment framework, ranging from advanced assessment procedures, necessary in cases with large uncertainties and near the acceptance boundary, to simple procedures, which are sufficient for the majority of conventional vessels. The paper outlines the background of three levels of assessment procedures and describes in detail possible approaches towards level 2 and level 1 assessment procedures for propulsion and steering criteria. The proposed assessment procedures require definition of multiple input components: time-average wave-induced forces and moments, wind forces, calm-water reactions, rudder-induced forces and propeller characteristics. The paper discusses the availability of different methods (experimental, numerical or empirical) for these components and, besides, proposes and validates several simple empirical formulae developed specifically for the simplified assessment to further reduce its complexity.