Assessment of Maneuverability in Waves

Abstract

Maneuverability of ships is presently standardized (normed) by rules of classification societies, shipowner requirements, and International Maritime Organization (IMO) standards for ship maneuverability. The latter address turning, initial turning, yaw checking, course keeping, and emergency stopping abilities, evaluated in simple standard maneuvers in calm water, and have practically become an industry standard. However, these standards do not address ship maneuverability in adverse weather conditions; after the introduction of the energy efficiency design index (EEDI), the importance of this issue increased because of concerns that propulsion and steering abilities of ships may become insufficient if EEDI requirements are achieved by simply reducing the installed power. To provide a rational basis for the standardization of maneuverability of ships in adverse weather conditions, relevant criteria, measures, and standards need to be developed, as well as efficient ways to evaluate the criteria in practical design and approval, keeping in mind that, on the one hand, maneuvering in waves is a difficult hydrodynamic problem, presently tackled in research projects in few centers worldwide, and, on the other hand, simple practical regulations are urgently required to be routinely used in design and approval of all new-built ships as a part of EEDI requirements. Obviously, this contradiction requires significant simplifications. The aim of this study was to outline possible approaches to practical assessment, based on a sequence of pragmatic simplifications and leading to practical assessment procedures of various complexity (some of which are implemented in the presently acting 2013 Interim Guidelines for determining minimum propulsion power to maintain the maneuverability of ships in adverse conditions, and in other proposals), validate the proposed simplifications, and summarize remaining difficulties. 1. Introduction Maneuverability of ships is presently standardized (normed) by rules of classification societies, shipowner requirements, and nonmandatory (but gaining increasing acceptance by administrations and classification societies) IMO standards for ship maneuverability (IMO 2002), which address turning, initial turning, yaw checking, course keeping, and emergency stopping abilities, evaluated in simple standard maneuveres in calm water. These standards do not address ship maneuverability in adverse conditions, which requires, on the one hand, evaluation of ship-specific environmental forces and, on the other hand, assessment of the ability of the ship's steering and propulsion systems to overcome these forces.