Towards A Rational Intact Stability Criteria For Naval Ships

Abstract

ABSTRACT Defining rational criteria and methodology for assessing ship intact stability poses a difficult problem. The survival of a ship in extreme sea and wind conditions is a dynamic and nonlinear phenomena with many potential capsize scenarios. Naval ship criteria in use today do not attempt to represent actual capsize behavior in waves. Current criteria are based on the static righting arm curve, are largely empirical using WW II data, and do not explicitly consider many variables which can have a significant impact on dynamic intact stability. However, the current criteria are well accepted by the naval architecture community, and within the bounds of conventional hull forms, have proven to be a reliable, generally conservative, ordinal measure of intact stability. The US Navy and other navies continue to rely on these simple criteria until more sophisticated methods are developed and validated. This paper proposes an improved intact stability “weather” criteria which attempts to bridge the gap between the current empirical approach and future analytical methods. In order to maximize commonality with commercial specifications, the proposed criteria is modeled after the current IMO “weather” criteria, with refinements and modifications adapting it for naval ships. It considers the righting arm curve and other ship characteristics influencing roll motion. It also includes the effect of sea state and provides a more rational approach to wind effects including gusts. The proposed criteria is compared to model test results, US Navy criteria and IMO criteria as applied to four US Navy ships.