Model Test Evaluation of High Speed Trimaran (HST) Sea Train Concept

Abstract

Sea Train is a longitudinal assembly of essentially similar size transportation units that increase the overall length resulting in a performance benefit to the system. Different types of mechanical connector hydrodynamic loads in a sea state have been the Achilles heel of platform assemblies operating on the sea surface. For example, Mobile Offshore Base project was discontinued in the early 1990s, partly because of the risk associated with extremely high connector loads. The paper describes the Sea Train concept that eliminates the need for a mechanical link type of connector between units, thus allowing for rapid automatic assembly/disassembly into Sea Train formation. All of the previously explored seatrain concepts resulted in a very long assembly of units, and the concepts with no yaw articulation between units were expected to have very large turning diameters. Therefore a bulbous above water cylindrical nose and socket were designed to allow yaw articulation. The proposed connectorless approach to Seatrain assembly with ball and open socket coupling will also allow for lateral articulation between units to enhance turning. Sea Train is a new concept for Military Sealift as well as for a broad spectrum of potential commercial marine transportation applications. The main advantages for Sealift are high speed and austere port access. A commercial application includes an America’s Marine Highway (AMH) Concept. A seatrain carrier for rolling stock envisioned along with the possibility of continuous coastal service that has units dropping off and other units joining up to deliver cargo. Recently, selected model tests and operational demonstration, were performed by NSWCCD at their indoor tow tank and their outdoor maneuvering facility at Tridelphia Reservoir. A combination of individual unit tow arrangements, control algorithms for propulsion and steering, and remote control operation were examined. In conjunction with the operational demonstration, towing tank tests were done to measure a number of hydrodynamic factors. The primary objective was to determine the magnitude of resistance. These test results have confirmed basic Sea Train expectations and are presented in the paper.