NYK Line, Namura Shipbuilding Co., Ltd., and Sasebo Heavy Industries Co., Ltd. are collaborating to replace the main propulsion on steam turbine–driven* Moss-type LNG carriers. In October 2023, NYK was granted Approval in Principle (AiP) from the Japanese classification society Class NK for converting the steam turbine of an LNG carrier to a dual-fuel diesel engine. This is the first AiP granted by Class NK for main engine conversion on LNG carriers. The three companies will proceed with a detailed design of steam turbine conversion, aiming to improve environmental performance, make efficient use of existing vessels, and contribute to stable LNG transportation.

LNG is promising as an essential transition energy for realizing a decarbonized society, and LNG transportation demand is expected to grow steadily. On the other hand, the shortage of LNG carriers is a concern due to the limited number of new LNG carriers that can be ordered and the retirement of steam turbine–driven LNG carriers due to their inferior fuel economic performance compared to diesel engine LNG carriers.

To solve this problem, the three companies will replace the main propulsion of steam turbine–driven LNG carriers with dual-fuel, low-speed diesel engines** called X-DF engines. The Moss-type LNG tanks*** installed on steam turbine–driven LNG carriers are durable and can withstand long-term use. Therefore, in addition to improving fuel economic performance, the engine replacement contributes to an efficient use of the ship's resources.

The three companies will support stable LNG transport by converting main engines and contribute to the efficient use of ship resources with the technical capabilities of Japan’s maritime cluster.


* Steam turbine engine
An external combustion engine is used to heat fuel in a boiler, and the resulting high-temperature, high-pressure steam is injected into the blades to produce rotational energy. This type was widely used in early LNG carriers because of its high reliability and suitability for larger vessels.


** Dual-fuel diesel engine
An internal combustion engine that directly combusts fuel to generate rotational energy. It has higher thermal efficiency than steam turbines. Technology development has led to larger diesel engines, which have recently been used on many LNG carriers. Two types of fuel — i.e., heavy fuel oil and LNG fuel — can be switched for use.


*** Moss-type LNG tank
A spherical LNG tank with a thick and sturdy structure that was used in many Japanese-built LNG carriers

Company Name: NYK Line
President: Takaya Soga
Head Office: Tokyo

Company Name: Namura Shipbuilding Co., Ltd.
President: Kensuke Namura
Head Office: Osaka

Company Name: Sasebo Heavy Industries Co., Ltd.
President: Kensuke Namura
Head Office: Nagasaki