Motion Dynamics of a Coupled Lighter and Sealift Ship in Seaways: A Parametric Study

Abstract

Abstract : The joint services are presently working together to develop inter-operable components that will perform effectively as an integrated cargo transfer system compatible with sealift operations conducted in heavy seas through sea state 3. Providing rough water components is not in itself a sufficient condition for guaranteeing sea state 3 performance, however. Even as major hardware systems with sea state 3 maturity are fielded, other critical ship and shore interface links remain sea-state limited. The Naval Facilities Engineering Service Center is exploring new technologies that will enable U.S. military watercraft to exchange cargo with sealift ships during heavy seas. In a typical operation of Joint Logistics Over the Shore (JLOTS), cargo is offloaded from a large container vessel onto a smaller watercraft, such as the Amphibious Cargo Beaching (ACB) lighter, using an auxiliary crane ship (T-ACS) to make the required lifts. For the docking model of an ACB lighter coupled directly to a T-ACS during sea state 3, this report presents analytical results for motions and forces. The method of analysis selected requires the application of two successive computer codes: a hydrodynamic model that determines such basic vessel characteristics as added mass, damping and wave excitation, and a motion response model that uses output from the hydrodynamic model to calculate absolute and relative motions, and coupling forces. The stated objective is to predict typical motion responses and coupling forces so that a baseline for design requirements can be developed in support of a concept being incubated by the Government.