An Investigation of Head-Sea Parametric Rolling and Its Influence on Container Lashing Systems

TLDR

Extreme weather in October 1998 caused a post‑Panamax containership to suffer extensive deck‑container loss, illustrating that parametric rolling—an unstable, pitch‑coupled phenomenon that generates large roll angles and high loads on containers—is a critical issue for the many vessels scheduled for delivery in the coming years. The paper presents findings on how extreme head‑sea parametric rolling affects container securing system design and offers recommendations for further research into vessel design and operational factors influencing this propensity. The study used model tests and numerical analyses of the vessel’s motions during the storm to confirm its parametric rolling response in head seas. The investigations show that post‑Panamax containerships are prone to extreme head‑sea parametric rolling when unfavorable tuning, low roll damping, and large stability variations (due to wave characteristics and hull form) combine, producing significant motions and accelerations.

Abstract

In October 1998 a post-Panamax C11 class containership encountered extreme weather and sustained extensive loss and damage to deck stowed containers. The motions of the vessel during this storm event were investigated through a series of model tests and numerical analyses that confirmed the vessel's parametric rolling response in head seas at the time of the casualty. These studies provide insight into the conditions in which post-Panamax container ships are likely to experience head sea parametric rolling, and the magnitude of motions and accelerations that can occur. The findings from this investigation are presented in this paper, together with discussion of how such extreme motions impact the design and application of container securing systems. Also outlined in the paper are recommendations for additional research needed to better understand the influence of vessel design and operational considerations on the propensity of post-Panamax containerships towards parametric rolling. This investigation and other recent studies demonstrate that parametric roll in extreme head or near head seas can occur when unfavorable tuning is combined with low roll damping (reduced speed) and large stability variations (governed by wavelength, wave height, general hull form, bow flare, and stern shapes). Parametric rolling is an unstable phenomenon, which can quickly generate large roll angles that are coupled with significant pitch motions. The rolling occurs in phase with pitch, and on containerships introduces high loads into the containers and their securing systems. It appears that post-Panamax containerships may be particularly prone to this behavior. This is an important issue considering the large number of these vessels scheduled for delivery in the next few years.