of its super slender twin hull (SSTH) vessel, technically, the recently built ferries are positioned somewhere between conventional ferries and the SSTH in performance. Their design was developed on the basis of the builder's accumulated know-how regarding both types.
The main targets for developmental efforts were:
(1)Iteration between optimization of fine hull form and stability;
(2)Reduction of wave-making resistance with an improved bow shape;
(3)Enhancement of propulsive efficiency with an improved stem shape;
(4)Increase of main engine power, and
(5)Improvement of the performance of high-power controllable pitch propellers.
The company's CAE/CAD system was used in developing the hull form for the new fast ferries, and the overall performance was evaluated by smooth water resistance and propulsion tests, maneuverability tests, tests on motion and resistance increase against waves, tests on propellers' independent performance and cavitation tests in the hull form test basin.
To suppress vibration, which would otherwise be increased by the greater engine power, the engine bed vibrations are reduced by elastic support. Although the vibromotive force of the main engines is less than in conventional car ferries, the fluctuating propeller pressure is made greater by the higher engine output than in usual ferries. Therefore, the vibration of the stem structure was analyzed by FEM while comparing the analytical results with the measurements of hull vibration in conventional ferries attributable to the propeller's vibromotive force. The structural arrangement is planned to adequately prevent resonance of the natural frequency with the blade frequency and to sufficiently reduce the vibration response to the fluctuating propeller pressure. Furthermore, various structural parts of the hull were put to vibration analysis by FEM to design a resonance-free structure.
These research and development efforts have borne fruit in the service speed of 29.4 knots at the 37,330 kW economy output of two DU-SEMT-Pielstick 1 8PC4 main diesel engines. The maximum trial speed was 31.4 knots. The maneuverability and oscillation performance of the ferries were also confirmed to be satisfactory.
The two ferries are now operated by Shin Nihonkai Ferry on the Tsuruga (Fukui Prefecture)/Otaru (Hokkaido) route, which they cover in about 21 hours, as opposed tothe 28 hours taken by conventional ferries.
