Operational Seakeeping Considerations in LCU Deployment

Abstract

The current class of Landing Craft Utility (LCU) has been in service in the U.S. Navy since the 1960s. Primarily used to land heavy vehicles, equipment, personnel, and cargo ashore in an amphibious assault, its basic design has served well over the last half century of use. However, certain loading combinations impacted by weight creep of particular cargoes have recently come to challenge established operational stability limits. The stability criteria currently employed came from traditional open ocean stability studies and therefore may not be optimal for the typical coastal transits of these specialized vessels. This study examines the intact transverse static and dynamic stability of the LCU in order to determine more appropriate criteria for short-range transits close to shore. The analysis mainly uses the Program of Ship Salvage Engineering (POSSE) software and the standard Ship Motion Program (SMP) to model a stochastic sea state, simulate the LCU's loading conditions, and predict the craft's dynamic response in various sea state conditions. The LCU's static transverse stability is derived by the POSSE software in terms of righting arm diagrams for different loading conditions, while the SMP software determines the dynamic transverse stability. The SMP analysis is based on seakeeping theory, using sea spectra model techniques to determine the LCU's roll angle dynamic responses. Based upon these simulation results, the study evaluates the current stability criteria and arrives at several dynamic stability recommendations and operational limits for loading conditions of interest.