Mitsubishi Heavy Industries, Ltd. (MHI) delivered the cargo-passenger ship Tachibana-Maru to Tokai Kisen Co. The vessel is a “super eco-ship” with a high-efficiency propulsion system that achieves energy savings, environmental load reduction, and enhanced passenger comfort and safety.
The ship employs a tandem-hybrid contra-rotating propeller (CRP) propulsion system developed by MHI. The system comprises single-shaft propulsion propellers driven by low-speed marine diesel engine and electric-drive azimuth propulsion propellers that enable the direction of propulsion power to be changed freely.
In comparison to conventional twin-shaft propulsion systems, the new system enables less appendages for propulsion systems such as skegs, shaft brackets and rudders and reduces water resistance, and improves energy-saving efficiency by allowing the use of only fuel-efficient low-speed diesel power in bays and channels where slower navigation speeds are required.
The new propulsion system enables the Tachibana-Maru to achieve 15.6% higher fuel efficiency than the Salvia-Maru, a cargo-passenger ship built by MHI and currently in service at Tokai Kisen. In addition, the use of an electronically controlled fuel injection system enables the main low-speed marine diesel engine to achieve higher combustion efficiency, thereby ensuring that the Tachibana-Maru emits less CO2 and NOx. The ship is also equipped with a system that utilizes exhaust gas thermal energy more efficiently.
The propulsion system’s ability to deliver required power using only a single-shaft configuration, with the load shared between a single diesel engine and an electric drive system, ensures higher passenger comfort by reducing both noise and vibration. In addition, the electric-drive azimuth propulsion system can be used as a stern thruster in combination with the bow thruster to enhance safety and swiftness when approaching or departing the pier.
The cargo-passenger ship measures 118.0 meters (m) in length overall (LOA), 17.0m in width, and 8.95m in height (5.40m in draft). The 5,681 gross tonnage vessel has a service speed of 19.0 knots per hour (about 35.2 km/h). MHI began construction of the ship in March 2013 and launched it in November of the same year. The ship will be put into service on the route between Tokyo and the Izu Islands on 27 June 2014.