In recent years, electrically controlled variable pitch propeller mechanism has been widely used as a way to improve fuel economy and help protect the environment.

In the field of hydroelectric power generation, the Kaplan turbine has the same structure as variable pitch propellers for ships, and in 1994, the world’s first hydraulic power plant incorporating synchronous differential transmission mechanism-based electric variable pitch propellers began operationsed. Subsequently in 2007, a 10,500kW Kaplan turbine using the electric variable-pitch propeller mechanism　started operations at the Shin-Chuubetsu Power Station in Hokkaido Electric Power Company. This paper describes the development process and characteristics of the synchronous differential transmission mechanism developed at that time. The mechanism enables the use of electric variable pitch propellers with power capacity up to 22,000kW, and it can also be applied to large vessels. This paper also explains the structure, main characteristics, of the mechanism and its scope of application.

Gas turbine combined systems using natural gas as fuel can be used as ship propulsion systems, given their low NOx and zero SOx emission characteristics. In this paper, the authors examined their adaptability to ships by comparing them with diesel engines that meet both NOx and SOx emission requirements, from the viewpoints of their sizes and initial costs. Up until now, gas turbine combined systems have rarely been used for ships, and NOx and SOx reduction systems for diesel engines have not been widely utilized. For these reasons, every available information about these systems has been used to examine the case. The results found that gas turbine combined systems using natural gas as fuel required much less space than the diesel engines and that the initial cost of the gas turbine combined systems per unit power was somewhere between that of a diesel engine with NOx and SOx reduction systems and that of a diesel engine with a NOx reduction system using low sulfur fuel.

Tugboats are rarely required to produce great propulsion power even while they are “On Service’. In this paper, the authors compared SFC (specific fuel consumption) for a hybrid propulsion system with that for a conventional propulsion system while they are on service. SFC was calculated by using a method developed by the authors. The fuel consumption characteristics of the hybrid propulsion system were measured against those of the conventional propulsion system that included the main engine and the diesel generator. The results showed that the hybrid propulsion system has higher SFC than the conventional one, highlighting the possibility that the former can, lead to increased fuel consumption. This indicated how diesel generators being forced to operate at low loads have an impact on fuel consumption. Furthermore, this also indicated the importance of designing ratings of motor generators appropriately in hybrid propulsion system.