コンテナ船, Ro/Ro船の輸送性能分析

Abstract

Container- and Ro/Ro-vessels are featured especially by the reduction of terminal time as a result of containerized cargo handling of lift-on/lift-off and roll-on/roll-off method, respectively. This paper analyzes the transportation energy efficiency of both vessels built in Japan so far, with paying attention to the feature mentioned above. Firstly the hull resistance characteristics are analyzed. In the same as car ferry, both vessels have the property being able to separate the hull function into buoyant support and cargo vessel. This property permits the hull form to have less resistance than general cargo ships. The performance level of hull resistance is same for all container-and Ro/Ro-vessels except the large, high speed container vessels with the speed above 26 knots and the displacement above 50, 000 tons, of which hull form are different because of the Panamax limit, and result in inferior level by about 30%. It is pointed out, therefore, that the enlargement of hull size over the Panamax limit is excessive as for the container ship. Secondly the cargo performance, which is indicated by the payload-to-displacement ratio, is analyzed. The payload of container- and Ro/Ro-vessels can be regarded as the carrying number of containers. The above ratio of container vessel is mainly determined by two factors of deadweight-to-displacement ratio and container number on deck loading. The deadweight-to-displacement ratio raises undesirably with speed. While it cannot be improved by the increase of displacement. Therefore the high speed container ship above 26 knots cannot have necessarily good cargo performance in spite of the design for increase of container number on deck loading. The cargo performance of the Ro/Ro ship is worse by two times than the container ship due to the roll-on/roll-off cargo handling method. This demerit sets off inevitably the merit that the Ro/Ro ship can handle cargoes without the special equipment ashore.