The 155k-m3 Sayaendo
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Mitsubishi Heavy Industries Technical Review Vol. 49 No. 1 (March 2012) 12 The 155k-m3 Sayaendo: A New Generation LNG Carrier with a Continuous Integrated Tank Cover SAI HIRAMATSU*1 KENJI TSUMURA*2 RYUSUKE TAKADA*3 TOSHINARI ISHIDA*2 KAZUYOSHI HIRAOKA*2 Mitsubishi Heavy Industries, Ltd. (MHI) has received an order for the newly developed 155k-m3 Sayaendo, a next-generation liquefied natural gas (LNG) carrier with a continuous tank cover integrated with the hull. Sayaendo retains the reliable configuration and sloshing resistance of spherical tanks, while integrating a continuous tank cover to improve the carrier’s overall structural efficiency, thus achieving a lightweight and compact design. Furthermore, adoption of a high-efficiency ultra steam turbine (UST) propulsion system enhances operating economy by significantly reducing fuel costs. This article describes the advantages of Sayaendo, including its improved maintainability, compatibility with LNG terminals, and environmental performance. |1. Introduction The name “Sayaendo,” which means peas in a pod in Japanese, comes from the vessel’s appearance, featuring spherical tanks (“endo” or “peas”) in a continuous cover (“saya” or “pod”). In conventional liquefied natural gas (LNG) carriers, the upper half of the spherical tanks above the ship’s deck is covered by a semispherical dome and the lower half under the deck is supported by a cylindrical skirt structure. In contrast, the Sayaendo employs a continuous cover, integrated with the ship’s hull, to house all tanks entirely, thus improving the overall structural strength and achieving weight reduction. For the main power plant, the Sayaendo uses the Mitsubishi Heavy Industries, Ltd. (MHI) ultra steam turbine plant (UST), a new turbine plant that achieves higher thermal efficiency through effective use of thermal energy by reheating steam. Together with the weight reduction and improvements in propulsion performance, the new ship achieves more than a 20% reduction in fuel consumption compared with conventional ships. Furthermore, in conventional LNGCs, piping, electric cables, and passages atop the tanks are supported by complex structures. The new design makes such complex supporting structures unnecessary, thus improving maintainability. The continuous cover also improves aerodynamics by substantially reducing longitudinal wind force, which serves as a drag on the ship’s propulsion, contributing to reduced fuel consumption during actual operations at sea. |2. Characteristics of the 155k-m3 Sayaendo LNG carrier 2.1 Development concept and key technologies The 155k-m3 Sayaendo has a new-generation hull form designed to achieve significant improvements in long-haul operating economy, operational flexibility and environmental performance, by combining the advantages of key technologies such as the continuous cover, stretched tanks, and UST propulsion plant. Characteristics of the Sayaendo are described in the following sections. 2.2 (1) Improved operating economy Light weight and compact design In conventional LNGCs, a hemispherical cover has little effect on the overall strength, which is maintained by other structures. The 155k-m3 Sayaendo employs a continuous cover to house four spherical tanks entirely, enabling the cover to be used as a hull-reinforcing element, *1 Group Manager, Ship & Ocean Engineering Division, Shipbuilding & Ocean Development *2 Engineering Manager, Ship & Ocean Engineering Division, Shipbuilding & Ocean Development *3 Ship & Ocean Engineering Division, Shipbuilding & Ocean Development

Mitsubishi Heavy Industries Technical Review Vol. 49 No. 1 (March 2012) 13 resulting in greater overall strength and a reduction in weight. The new design also reduces the depth of the ship (Figure 1). Size comparisons with a conventional 147k-m3 carrier are shown in Table 1. (2) Increased cargo capacity via stretched tanks The capacity to transport 8,000 m3 more LNG than a typical 147k-m3 carrier is achieved without increasing the beam by using vertically stretched spherical tanks that maintain the same tank diameter. Thus, the new design provides a higher cargo capacity while meeting the...

Mitsubishi Heavy Industries Technical Review Vol. 49 No. 1 (March 2012) 14 Sayaendo is capable of 0.080%/d, which is even lower than the 0.10%/d adopted recently as the low boil-off rate. (5) Lower maintenance costs In conventional hemispherical tank covers, piping, electric cables, and passages atop the tanks are supported by complex structures. The continuous tank cover makes such supporting structures unnecessary, thus significantly improving maintainability. 2.3 Enhanced terminal compatibility (1) Highly versatile cargo capacity A larger cargo capacity increases economic competitiveness...

Mitsubishi Heavy Industries Technical Review Vol. 49 No. 1 (March 2012) 15 Four cargo tanks are arranged entirely under a continuous cover, with the inside consisting of four hold areas designated for each tank. Loading/unloading manifolds are placed between the second and third holds where the cover is cut out. Piping and electric cables are located at the flat section on the top of the continuous tank cover, improving accessibility and maintainability. Furthermore, a portion of space between the third and fourth holds under the cover is designated as a cargo equipment room, thus freeing...

Mitsubishi Heavy Industries Technical Review Vol. 49 No. 1 (March 2012) 16 |4. Propulsion plant and performance 4.1 Improved propulsion performance By leveraging the advantages of a lightweight hull, combined with state-of-the-art computational fluid dynamics (CFD) technology, MHI developed an optimal hull form to achieve superior propulsion performance at a wide range of speeds, including low-speed operations. The carrier is also equipped with a Mitsubishi reaction fin to further enhance its high performance. Tests conducted in a wind tunnel with headwind confirmed that the wind resistance...